This PDF file contains the front matter associated with SPIE Proceedings Volume 10682, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The power transmission technology to the equipment is remained behind in contrast to the progress of wireless communication. The existence of wiring and its connections greatly restrict the location of use, installation, maintenance, and configuration of the equipment. Solutions of wireless power transmission may lead to major changes in society, such as new services and new industries as well as convenience. Wireless power transmission such as electromagnetic induction is beginning to be put into practical use in smartphone, etc., however there are issues in extremely short transmission distance, large size, heavy, and so on. Optical wireless power transmission will be an important technology for expanding the field of wirelessly usable equipment due to features such as small size, short, mid and long distance transmission. On the other hand, there are some problems to be solved such as efficiency and safety. In this presentation, I would like to discuss the possibility and challenges of optical wireless power transmission using VCSEL as a high output and high efficiency light source.

For short-haul optical interconnects, state-of-the-art technology are vertical-cavity surface-emitting lasers (VCSELs). To transmit data, direct current modulation is used. The corresponding intensity modulation resonance frequency is determined by design and material parameters of the laser and therefore practically limited to a few tens of GHz. To overcome this limitation, an alternative approach is the utilization of spin-VCSELs. In this case, the information carrier is no longer represented by the intensity, but instead by the polarization. The polarization can be controlled by the carrier spin. The birefringence in the cavity has the strongest impact on the polarization modulation resonance frequency. This can be explained by the generation of resonant polarization oscillations in the circular polarization degree in a spin-VCSEL. The circular polarization is composed of the two orthogonal linearly polarized cavity modes. The electromagnetic fields emitted from the two modes are coupled in phase by birefringence and in amplitude by dichroism. However, dependent on the birefringence in the cavity, their frequencies may differ. Spin pumping, i.e., circularly polarized optical pumping pulses, causes the fact that both modes become active. This results in an oscillation of the circular polarization degree of the emitted light, representing the polarization dynamics resonance frequency of the spin-VCSEL device. We demonstrate that the birefringence can be manipulated in actual VCSEL devices over a broad tuning range. Employing this parameter tuning, we demonstrate a polarization dynamics resonance frequency of 89 GHz, which is much faster than currently obtained intensity dynamics resonance frequencies. Not only the maximum frequency, but also the amplitude of the polarization effects should be optimized. An important factor for the amplitude damping is the dichroism, which represents the difference in the gain of the two orthogonal modes. We investigate the influence of birefringence on dichroism and the polarization oscillation amplitude.

Direct modulation lasers are attractive for short-to-mid range fiber communication system. Transistor lasers (TLs), which are hetero-bipolar transistor with an active layer in the base, have a potential to overcome modulation bandwidth limitation of conventional laser diodes (LDs). One of the reasons of the modulation bandwidth limitation of the conventional LDs is delay of carrier diffusion to quantum wells (QWs). With proper design of TLs with some current gain, this delay can be reduced and TLs can have wider modulation bandwidth under the emitter current modulation configuration. In the first part of the presentation, these theoretical analyses will be discussed. By theoretical analysis of TLs with rate equations taking account of carrier diffusion lifetime, 50 GHz modulation bandwidth can be expected with a current gain of ~1.7. Also, by applying voltage bias between the base and collector under the common-base configuration, which causes Frantz-Keldysh effect at the interface layer (GaInAsP in our case), internal loss can be controlled if the bandgap of layers at the interface is appropriately wider than the energy corresponding to the lasing wavelength. This is a kind of “built-in” electro absorption modulator. Therefore, voltage modulation, which corresponds to “loss” modulation, can be configured and has wider modulation bandwidth. The reason why loss modulation has wider modulation bandwidth is that the slope of decay curve of small signal modulation over a relaxation oscillation frequency is slow compared with that of conventional current modulation. In the second part, buried-hetero (BH) regrowth techniques of AlGaInAs QWs will be discussed. AlGaInAs TLs with lasing wavelength of 1.3 µm is very important for fiber communication system. By adopting proper annealing conditions in an organo-metallic vapor-phase-epitaxy (OMVPE) reactor, non-radiative recombination at the AlGaInAs/InP regrowth interface can be significantly reduced even after exposing in the air. Annealing gas, temperature, and the time are important parameters to find optimum annealing conditions. We found using PH3, instead of AsH3, as the annealing gas is effective to remove oxidation at the interface under 650°C, 45-min. annealing. Using this annealing condition, 1.3-µm AlGaInAs BH-LD was realized with a low threshold current density of 140A/cm2/well. Finally, the fabrication process and characteristics of 1.3-µm AlGaInAs TLs will be discussed. Several regrowth steps by MOVPE were required including above mentioned BH regrowth. CW operation up to the temperature of 40°C was demonstrated with both 2 and 3-terminal configurations. For 2-terminal configuration (this means the collector was floating), the threshold current of 33 mA was achieved with the cavity length of 1000 µm and stripe width of 1.7 µm. For 3-terminal configuration, the device shows optical characteristics (I-L) and transistor (collector current) characteristics, simultaneously, under common-emitter and common-base configuration. For the common-emitter configuration, threshold “base” current was reduced by applying voltage between the emitter and collector, On the other side, for the common-base configuration, we observed threshold “emitter” current increase by applying voltage between the base and collector due to Frantz-Keldysh effect. From transistor characteristics, we found Early effect also had an important role for TL characteristics.

How short time scales substitute for cryogenic cooling: Quantum Coherent Effect in Room Temperature QD Amplifiers Gadi Eisenstein1 and Johann Peter Reithmaier2 1Electrical Engineering Dept. and Russell Berrie Nanotechnology Institute Technion – Israel Institute of Technology, Haifa 32000 Israel 2Technological Physics, Institute of Nanostructure Technologies and Analytics, CINSaT, University of Kassel, 34132 Kassel, Germany Abstract Semiconductor quantum dots (QDs) serve often as a two-level system for studying quantum coherent phenomena. Observation of quantum coherent effects requires observation times that are shorter than the coherence time. In room temperature semiconductor QDs, those times are of the order of 350 fs and therefore it is common to cool the QDs to cryogenic temperatures. A few years ago, we have introduced an alternative approach by which the cooling is substituted for by operation with ultra-short pulses having durations of 100-200 fs. The platform we employ is a 1.5 mm long InAs/InP QD optical amplifier. Measurements use the cross frequency resolved gating (X-FROG) technique and the experiments are accompanied by a comprehensive model that treats the QD amplifier as a cascade of two level system and also considers the QD gain inhomogeneity as well as non-resonant interactions such as two photon absorption and an accompanying Kerr-like effect. Several quantum coherent effects have been demonstrated including Rabi oscillations and self- induced transparency as well as coherent control of the Rabi oscillations achieved by shaping the pulses spectral phase. A modification of the experimental set up by which two pulses in a pump probe configuration are used with each pulse being separately measured using the X-FROG technique enables to demonstrate the optical analog of Ramsey-Resonances. Setting a nominal delay between the input pulses and changing the delay in 1 fs steps, we observe clear Ramsey fringes in the probe amplitude, instantaneous frequency and surprisingly also the separation between the two output pulses. The latter stems from the coupling between the real and imaginary parts of the susceptibility. It is unique to our system as it a cumulative effect that requires a reasonably long propagation distanced and can therefore only be seen in a waveguide configuration and never in a single QD which was used in all previous Ramsey experiments. The last effect is photon echo which was only studied numerically up to now. The talk will survey the various experimental results and will highlight the essence of operating with short pulses to induce and observe quantum coherent effects in room temperature QD amplifiers.

Quantum dot lasers have proven to be extremely interesting in terms of nonlinear dynamics. One of the key benefits is their highly damped relaxation oscillations. In this work we take advantage of this stability in a master slave configuration. We find a novel, dual state excitable dynamic resulting in antiphase operation between two lasing states in the device. We interpret the behaviour as a non-Adler but still Type I excitability. Phase measurements bolster our interpretation.

Passively mode-locked semiconductor lasers are inexpensive sources of short optical pulses with high repetition rates. They find applications in high-precision metrology and high-capacity optical interconnects, where pulse trains with low amplitude and timing jitter are required. Hybrid mode-locking [1] and dual-cavity optical feedback [2] allow for the reduction of the timing jitter, but add further electronics and optics and thereby also additional costs. New concepts of monolithic mode-locked semiconductor laser geometries for improved pulse stability has therefore become of major interest. Quantum dot (QD) based mode-locked lasers receive quite some attention as they exhibit reduced spontaneous emission [3]. However, the internal QD carrier dynamics act as a filter on the pulse generation, which can lead to strong pulse asymmetries with trailing edge plateaus or pulses [4]. This effect becomes more pronounced at greater optical gain and thereby makes the generation of stable, high power pulses challenging. In this work, we characterize the performance of a monolithic multi-section QD mode-locked laser with tapered geometry at the pulse emission facet. The laser output is analyzed using optical and radio-frequency spectra, auto-correlation traces and optical power measurements, from which the pulse peak power, pulse width, amplitude jitter and pulse-to-pulse timing jitter are calculated. For different laser biasing conditions, we report ultra short, high power pulses with outstanding stability. Combining a traveling-wave model for the electric field propagation with microscopically based quantum-dot (QD) charge-carrier rate equations, we investigate the performance and dynamics of the laser for different biasing conditions. To allow for numerical efficiency, the traveling-wave equation is transformed by an integration along its characteristic curve to a set of coupled delay-equations [5]. The excitonic charge-carrier dynamics are described by microscopic scattering processes that consider Pauli-blocking and a detailed balance condition. The light-matter interaction includes a charge-carrier dependent amplitude-phase coupling and uses a time-domain filter function to describe the gain spectrum of the QD ensemble. Pulse characteristics and statistics are extracted from time-series obtained by direct integration of the delay-differential equations. Our simulations nicely reproduce experimental results. We map dynamic regimes and pulse train characteristics for varying absorber lengths, absorber placements and taper angles and show, that trailing edge pulses can be suppressed for suitable configurations, leading to excellent pulse train stabilities at high output power. We report an optimum taper angle, where the range of injection currents, that yield stable fundamental mode-locking, is maximized. [1] T. Habruseva, et al., Appl. Phys. Lett. 104, 1–4 (2014). [2] L. C. Jaurigue, et al., Phys. Rev. E 93, 022205 (2016). [3] E. U. Rafailov, et al., Nature Photon. 1, 7, 395 (2007). [4] M. Radziunas, et al., IEEE J. Quantum Electron. 47, 7, 935 (2011). [5] J. Javaloyes, and S. Balle, Opt. Express 20, 8496 (2012).

Significant interest in compact InAs/InGaAs quantum dot (QD) lasers emitting near 1.3 mkm is caused by the diversity of their applications including non-invasive medicine and ultra-fast data transmission. In such lasers, lasing typically starts at the ground-state (GS) optical transitions of QDs. A further increase in injection may result in the appearance of an additional, short-wavelength spectral line associated with the excited-state (ES) optical transitions of QDs – a simultaneous lasing via QD GS and ES, i.e. multi-state lasing, takes place. The appearance of the ES-line may sufficiently affect the useful GS component. As injection current exceeds the multi-state lasing threshold, a decrease and even a complete quenching of GS-lasing may take place. As it was shown in [V.V. Korenev et. al, Appl. Phys. Lett. 102, 112101 (2013)], the usage of modulation p-doping has a positive influence on the hole concentration in QDs making GS-lasing quenching less pronounced. However, the influence of the concentration of p-dopant on multi-state lasing in general – and on the GS-lasing quenching in particular – has not been yet studied. To clarify this question experimentally, a series of InAs/InGaAs QD laser wafers was grown by molecular beam epitaxy. The active region of each sample was comprised of 10 layers of InAs/InGaAs QDs separated by 35 nm-thick GaAs spacers. Each spacer was p-doped into its central part of 10 nm using carbon atoms. Dependent on the sample, the carbon concentration was equal to 0, 3·10^17 cm^(-3), or 5·10^17 cm^(-3). A series of light-current curves corresponding to the GS component of output power was studied both theoretically and experimentally for “short” (0.5-mm-long) and for “long” (1.0-mm-long) samples. The experiment shows that in case of the short samples, the increase in p-doping level from 0 to 5·10^17 cm^(-3) results in the increase in maximum output power corresponding to the GS of QDs (WGS) from 0.8 to 2.2W, while in case of the longer samples the situation is opposite and WGS decreases from 4.5 to 3.7W correspondingly [V.V. Korenev et. al, Appl. Phys. Lett. 111, 132103 (2017)]. Qualitatively, such a discrepancy can be explained as follows. In case of the short samples, the higher p-doping level results in the faster hole capture into QDs mitigating the competition for the common holes between GS and ES optical transitions, which is an important reason for the GS-lasing quenching. In longer samples, optical loss is small and GS gain is far from its saturated value. Consequently, the ES energy level is weakly occupied and p-doping is not necessary to apply. However, even a small increment in the internal loss due to the p-dopant may lead to a noticeable decrease in laser`s differential efficiency. As a result, the higher p-doping level does not necessarily lead to the higher GS power as it was previously expected. However, if the sample is sufficiently short, the usage of modulation p-doping increases GS power. For a given cavity length, there is a certain p-doping level improving GS lasing characteristics.

Optical Frequency Combs (OFC) generated by semiconductor lasers at optical communication wavelengths are promising laser sources for high capacity optical interconnects exploiting WDM techniques; very often they are integrated with Silicon Photonic integrated circuits to realize compact and low-cost transmitters. Quantum Dot (QD) or Quantum Dash (QDash) single section Fabry-Perot lasers have turned to be a good candidate for this application because they can generate a comb of self-locked optical lines using just one laser diode operating in CW and no saturable absorber section. In this talk we review the state-of-art of these devices and their applications, evidencing also the analogies with single section Quantum Cascade Lasers, that, as for QD and QDash lasers, generates optical combs in the mid-IR or THz range. We will focus on the understanding of the physical effects that can explain the self-locking of the lasing lines and we will compare the self-locking mechanism in Quantum Dot and Quantum Well lasers. We will then present the numerical simulation tool we have developed to simulate the self-locking in Quantum Dot Fabry-Perot lasers. Our model is based on a Time-Domain Traveling-Wave (TDTW) approach that properly accounts for coherent radiation-matter interaction in the semiconductor active medium and includes the carrier grating generated by the optical standing wave pattern in the laser cavity. We show that the latter is the fundamental physical effect at the origin of the multi-wavelength spectrum appearing just above the laser threshold, but it is not enough for forcing the self-locking of the optical lines. The self-mode-locking regime associated with the emission of OFC is achieved for higher bias currents and it ascribed to nonlinear phase sensitive effects as Four Wave Mixing (FWM). To quantify the locking of the lines we have calculated some indicators that are obtained by the post processing of the calculated optical electric field of the laser output. These indicators are the RF spectrum at the beat note, the optical linewidth of the lasing lines and the Relative Intensity Noise (RIN) spectrum for both the total power and the power of each line. Varying the CW injected current above threshold we have observed three different regimes: in the first one, at low current, the laser is dominated by multi-wavelength emission with rather wide RF beat note and high low frequency RIN, this regime corresponds to an unlocked regime. In the optical spectrum we observe an optical line and side bands due to FWM components. In the second regime, at much higher current, the RF beat note is extremely narrow and the low frequency RIN of each line reduces significantly; in the optical spectrum the lines narrow and the side-bands disappear. This is a self-locked regime. In an intermediate current range, we have a transition regime where the state (locked or unlocked) depends on the initial conditions. Our results explain in detail the behavior observed experimentally by different research groups and in different QD and Quantum Dash (QDash) devices.

It is shown that dynamics of delay-coupled quantum cascade lasers can be described in good approximation by the simpler set of rate equations for conventional interband diode lasers. A comparison of the steady-state solutions for locking shows excellent agreement with results obtained by time integrations of the full rate equations. The delay introduces an effective coupling phase equal to the product of operation frequency and delay time and the detuning width of the locking range is shown to periodically change when the delay time changes over an interval equal to half of the operation oscillation period.

An important issue in the technology of QCLs is the capability to extract heat out of the laser active area in order to reduce the increase of the temperature. High temperature not only reduces most performance metrics but also decreases device lifetime and impairs its reliability, leading to degradation of laser mirrors and destruction of the device. In this paper, we report on the investigation of the temperature of QCLs based on different designs. QCLs are complex, multilayer structures, which require high current and voltage to polarize the structure in order to obtain level alignment. This results in high heat generation. Thermal limitations in case of QCL are the most critical factor decreasing the performance of a device. High electrical power combined with relatively low wall-plug efficiency results in high-temperature increase in the active core. Efficient heat dissipation is difficult due to hundreds of layers impeding thermal conductivity of the structure. Moreover, the materials composing the gain region are ternaries with a composition of roughly 50%, what results in thermal conductivity lower by a factor of 10 than in case of bulk InP. Knowledge of the temperature is gained through unique temperature measurement technique – CCD thermoreflectance (CCD TR). This method allows for rapid thermal characterization of QCLs, as the registration of high-resolution map of the whole facet of the device lasts only several seconds. CCD-TR allows accurate evaluation of the thermal characteristics of quantum cascade lasers. Here, we report on the influence of design on thermal properties of QCLs. The design of waveguides and optical confinement in QCLs is essential. The increase of the optical confinement was frequently achieved by placing the active core between two InGaAs layers. However, low thermal conductivity of InGaAs layers results in inefficient dissipation of heat from the active core. By removing or significant reduction of the layers’ thickness, observed temperatures of the active core are significantly lower. The modifications include Experimental investigation proves that performance improvements can be gained by introducing modifications into the design of the structure. Based on experimental data, methods to further improve the performance of QCLs are discussed.

Quantum cascade lasers are coherent light sources that rely on intrersubband transition in periodic semiconductor quantum well structures. They operate at frequencies from mid-infrared to terahertz. In cases of long wavelength and typical low thermal conductivity of the active region, temperature rise in the active region during operation is a major concern. Thermal conductivity of QCL epi-layers differ significantly from the values of bulk semiconductors and measurement of the thermal conductivity of epi-layers is critical for design. It is well known that Fabry-Perot spectra of QCL cavities exhibit fine amplitude oscillations with frequency and can be used for real time in-situ temperature measurement. Phase of the modulation depends on the group refractive index of the cavity, which depends on the cavity temperature. We fabricated QCL devices with from 12, to 24 um mesa widths and 2mm cavity length and measured high resolution, high speed time resolved spectra using a FTIR spectrometer in step scan mode in a liquid nitrogen cooled, temperature controlled dewar. We used the time resolved spectra of QCLs to measure average temperature of the active region of the laser as a function of time. We examined the effect of pulse width and duty cycle on laser heating. We measured the temperature derivative of group refractive index of the cavity. Building a numerical model, we estimated the thermal conductivity of active region and calculated the heating of the QCL active region in pulsed mode for various waveguide widths.

Vertical External Cavity Surface Emitting Lasers (VECSELs) have been used for mode-locked operation by using a Semiconductor Saturable-Absorber Mirror (SESAM), usually in the external cavity [1] but also integrated in the gain-chip [2]. Impressive progress has been achieved since the first demonstration of an SESAM mode-locked VECSEL in terms of pulse duration, average optical power, and peak power. While the shortest pulses have been achieved with optically pumped active layers, electrically pumped structures are promising for a number of applications. Α versatile and accurate, if fairly complex, delay-differential theoretical model for mode-locking in electrically pumping VECSELs based on the physical description of gain and SESAM chips has been presented [3], however only the linear cavity geometry has been studied. A somewhat different approach was taken in [4][5] where an experiment-informed model representing the laser somewhat artificially as a sequence of gain, absorber, and dispersion elements in a unidirectional ring cavity (reminiscent of the classic Haus theory) was developed, and successfully reproduced the measured laser parameters in both pico-and femtosecond regimes. In the current work, we present a somewhat simplified model based on the physical laser design as in [3], which however can accommodate realistic geometry, both linear and folded-cavity. The model is applied to study different regimes of laser operation, including the possibility of colliding pulse mode locking at harmonics of the fundamental roundtrip frequency. As in [3], we base the derivation on the analysis of amplitudes of waves incident onto, and reflected from, elements of the laser cavity, using the amplitude of the field reflected from the “bulk” of the cavity as the dynamic variables for the description of light. Standard rate equations are used for carrier densities. In the case of a linear cavity the model is thus somewhat similar to that used in [3] though somewhat simplified. No matrices of the type used in [3] are needed to recalculate the dynamic variables in our simplified model. The use of phenomenological gain-carrier density dependences and linewidth enhancement factors, while less rigorous than the simplified microscopic model of [3], enables relatively easy inclusion of polarization dependences, allowing double-polarisation frequency comb generation to be simulated. In the case of a folded (Z-type) cavity either the gain chip or the SESAM chip can be positioned “inside” the cavity. The dynamic variables in the case of the gain chip in the middle are the fields reflected from the bulk of the gain chip in the directions of the output mirror and the absorber chip, and from the bulk of the SESAM back to the gain chip . In the case of the gain chip in the middle position, the difference in the dynamics of the saturation of the gain chip changes the pulse parameters and stability limits compared with the linear cavity, but there is no qualitative difference. In the case of the absorber section in the intracavity position, colliding pulse dynamics was simulated with a rational relation between the delay times. Further results will be presented at the conference. References [1] U. Keller, A. C. Tropper, Phys. Reports, 429, 67 (2006) [2] D.J.H.C. Maas et al., Appl Phys B, 88, 493 (2007) [3] J. Mulet and S. Balle, IEEE J. Quantum Electron., 41, 1148 (2005) [4] M. Hoffmann et al., Opt. Express 18, 10143 (2010) [5] O.Sieber et al., Appl.Phys.B., 113, 133-145 (2013)

In this paper, we present a mode-locked laser photonic integrated chip developed within a multi-project wafer run at an InP-based generic foundry. The 1.66-mm-long Fabry-Perot cavity is formed with two on-chip multimode interence reflectors in which four gain sections and three saturable absorbers equally divide the cavity in four. The fourth harmonic colliding pulse configuration supports pulse train generation of 100 GHz, corresponding to 0.8-nm mode spacing. Autocorrelation traces exhibit the ultrafast pulse widths as short as 0.5 ps. Terahertz dual-mode spectra are presented as well.

We present a ring semiconductor amplifier system which is seeded by ultrashort pulses for additive amplification. An external cavity diode laser configuration is built to generate the ultrashort pulses based on a hybrid modelocking scheme. A monolithic multi-segment diode laser is utilized as a light source in the operating oscillator. It has the advantage that the gain and absorber are integrated on one chip. The oscillator operates at a fundamental repetition-rate of 206MHz and can be driven on various harmonics of this frequency. The generated pulses are injected into a tapered amplifier (TA) which consists of a ridge waveguide section (RWS) for coupling and a tapered section (TS) for amplification. The amplified pulses are coupled back after amplification towards the TAs RWS forming a ring resonator setup. By matching the cavity lengths of the oscillator and ring resonator, we can obtain additively amplified pulses. The emission spectrum of the chosen TA is centered around 850nm which is in the wavelength range of the oscillator. The spectrum of the additively amplified pulses is observed for different pumping parameters of the TA using an optical spectrum analyzer. Additionally, we characterized the system for the best seeding parameters by monitoring the output signal with an autocorrelator. We figured out that the best performance is achieved when the amplifier is seeded by pulses at the second harmonic of 412 MHz. When blocking the seeding pulses the amplifier operates in continuous wave (CW) regime. By comparing the obtained spectra for CW and additively amplified pulses, we conclude that the system operates with a CW background also in pulsed operation. However, from the comparison of the spectra, we estimate that the amplified pulsed power is about 120mW for a seed power of 1:1mW. Thus, the ring amplifier provides a significantly higher amplification than a single pass amplifier. In future work the CW background has to be suppressed, e.g. by synchronous modulation of the current into the amplifiers ridge waveguide section.

Lasing was observed from ZnO nanorods prepared by a simple method of chemical bath deposition (CBD) on ITOcoated glass substrates. The X-ray diffraction pattern showed a dominant peak for (002) plane typical for good crystalline quality of ZnO grown in the z-direction with a wurtzite structure. Continuous-wave photoluminescence (PL) spectra revealed a peak centered at 380 nm corresponding to the band gap of ZnO. Under pulsed optical pumping, lasing was observed above the nominal PL peak, initially for one mode at 384 nm. Two additional modes at 386 nm and 390 nm was observed when the pumping power is further increased. Threshold was achieved at 0.7 μJ which was 10 times smaller than that reported for powder-based random lasers. In addition, gain pinning was also observed for the dominant mode and the additional two modes appeared upon onset of this gain pining behavior.

Two coupled-cavity systems, or « photonic dimers », are efficient test-beds for nonlinear dynamics in nanophotonics. I will focus on two evanescently coupled photonic crystal nanolasers, which can be engineered to experimentally access interesting bifurcation points. I will discuss our recent results on two emblematic bifurcations: spatial symmetry breaking (pitchfork) and asymmetric mode switching (Hopf). Importantly, the underlying nanophotonic structure enables a high degree of control, for instance in terms of intercavity coupling parameters. A second important aspect to be discussed is the role of noise in these relatively large spontaneous emission factor (β) lasers. The interplay between determinism and noise at bifurcation points results in a very rich photon statistics which, in the case of mode switching instabilities, leads to strong dips in the cross-correlation of mode fluctuations. These results open up interesting prospects in the study of few photon bifurcations in semiconductor laser devices.

The laser's threshold properties gradually evolve from the macroscopic to the nanoscopic scale through the mesoscale, whose best examples are the Vertical Cavity Surface Emitting Lasers (VCSELs). We show how the latter contribute to the understanding of the evolution of laser physics as the cavity volume is reduced thanks to favourable conditions: sufficient photon flux for a complete characterization with current instrumentation, coupled to physical characteristics which already approach those of nanodevices. A further reduction in cavity volume is nowadays possible in VCSELs, bringing within reach the nanoscale on the basis of mature technology. This will speed up both the fundamental investigations on the physics of nanolasers and open up the field for shorter-term applications in terms of nanosources- e.g., for optical chips- thanks to the possibility of coupling the VCSEL output into waveguides. Finally, we present an overview of results we have obtained on the physical characterization of the lasing transition in currently available, electrically-pumped VCSEL devices.

Traditionally, the active material in a laser is modelled as independent emitters, but in recent years it has become increasingly clear that radiative coupling between emitters can significantly change the characteristics of small lasers. Collective effects in free space such as superradiance have been studied extensively [1,2], but the effects of inter-emitter correlation in micro- and nano-cavities need further examination to be put on firm theoretical ground. Several studies of collective effects in nano-cavities have been made [3-6], but the theoretical models employed are intricate, and numerical methods are needed both to generate the dynamic equations and to solve them. We propose a model where the complexity is strongly reduced, allowing analytical solutions [7]. We consider a collection of identical two-level emitters interacting with a single cavity mode. We start from Maxwell-Bloch equations, but instead of making the typical adiabatic elimination of the polarization, we allow the polarization decay rate to be of the same magnitude or smaller than other decay rates. Hence, the traditional laser rate equations for the photon number and the population inversion must be supplemented by equations for the emitter-field correlation and the emitter-emitter correlation. This gives us four generalized laser rate equations, which we solve analytically in steady state. Comparing with the steady state results obtained from the traditional laser rate equations we see that inclusion of collective effects leads to a reduction of the photon number for small pump rates, similarly to what is found in [4]. From the generalized laser rate equations, we derive a measure of the strength of collective effects in terms of laser parameters: This describes the difference between results with and without inter-emitter correlations, and it goes smoothly to zero as we approach parameter values where the traditional laser rate equations become valid. To gain insight into the photon statistics of the laser, we construct dynamic equations for higher order correlations of operators. We derive an analytical expression for the zero-delay photon auto-correlation function, and for low pump rates we find that the interaction of emitters results in super-thermal values of the auto-correlation. This feature is observed in experiments and numerical models [4-5], and with our analytical expressions, we are able to pinpoint the parameter combinations for which the collective effects have the largest impact. Considering the same model in terms of the Fourier components of the operators, we find results for the photon number that agree well with the previous approach, while allowing computation of the linewidth. Thus, we can examine how emitter-emitter correlation affects the line broadening of the laser.

As sources of short, high-amplitude light pulses, self-pulsing lasers are key elements in many applications, including telecommunications and optical processing of information. We consider here a semiconductor micropillar laser subject to delayed optical feedback. Without feedback, the laser is excitable, and, as such, displays an all-or-none response to external perturbations. Recent experiments demonstrated that, in the presence of feedback, a single external optical perturbation can trigger a train of optical pulses, whose repetition rate is determined by the delay time. These pulse trains can be controlled reliably through external optical perturbations. In particular, several pulse trains can be switched on and sustained simultaneously in the external cavity with different interpulse timing; moreover, they can be switched off or retimed, depending on the timing of the external perturbation. Such pulse trains are also referred to as localised structures or temporal dissipative solitons in the literature. We focus on the theoretical investigation of such pulsing dynamics. It has been verified experimentally and theoretically that, as long as the pulses are short compared to the delay time, the phase of the electric field is not relevant. Therefore, the Yamada model with feedback - a system of three delay differential equations for the gain G, absorption Q and intensity I - is a suitable mathematical model. We show that its temporal integration produces a wealth of pulsing dynamics in very good agreement with the experiment. The model allows us to explain the control and interaction of pulses by the interplay of the dynamics of the gain G and that of the net gain G-Q-1. We perform a bifurcation analysis of the Yamada model to unveil its complex dynamics. In particular, we show that several periodic solutions coexist and are stable. Each stable periodic solution corresponds to a pulsing regime with a given repetition rate, close to a submultiple of the delay time. These correspond to equidistant pulses in the external cavity. Importantly, no stable periodic solution with non-equidistant pulses are found. Although coexisting pulse trains may seem independent from each other on the timescale of the experiment, we demonstrate that they rather correspond to extremely long transients toward one of the available stable periodic solutions. Hence, the different pulses in the external cavity become equidistant in the long term. The rate of convergence toward the stable regime depends on the number of pulses in the external cavity, and can be determined theoretically. The maximum number of pulse trains that can be sustained simultaneously corresponds to the number of coexisting stable pulsing periodic solutions, and it strongly depends on the delay time and strength of the feedback. By providing a better understanding of pulsing dynamics in excitable lasers with feedback, these results constitute a step toward an all-optical control of pulse train duration, which may have applications in photonics. Because the mechanism for self-pulsations described here is typical and relies only on excitability and delayed feedback, our results might be of interest beyond the specific device considered here, for example for cell dynamics.

In this paper we describe our work on heterogeneously integrated laser diodes on a silicon photonics platform. Different types of laser diodes are presented, different both in terms of wavelength / material platform (850 nm, 1550nm, 2000nm, 2300nm) as well as laser geometry. The integration of the III-V semiconductor materials on the silicon photonic integrated circuits is realized through adhesive die-to-wafer bonding. We will report on the realization of hybrid 850 nm VCSELs and high-speed directly and externally modulated lasers, mode-locked lasers and tunable lasers in the C-band. We also discuss our work on single wavelength laser arrays and tunable lasers in the 2um wavelength range. These integrated laser sources complete the toolkit for silicon photonics enabling highly integrated solutions for optical communication and sensing applications.

Hybrid integration of GaInAsP laser diode on silicon platform by epitaxial growth using direct bonded InP/Si substrate is presented. InP/Si substrate was prepared by hydrophilic direct bonding with 1μm thickness of InP layer and silicon substrate annealed at 400°C. GaInAsP/InP double heterostructure was grown by low pressure MOVPE system on the InP/Si substrate. Lasing characteristics were obtained at room temperature by injecting the current through the bonding interface between InP and Si. The threshold current density was comparable to the same laser structure grown on the InP substrate.

A combination of high operation temperatures and small sizes of diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this work, we report on electrically-pumped III-V microdisk lasers monolithically grown on Si substrates with active regions of two kinds: either an InGaAs/GaAs quantum well (QW) or InAs/InGaAs/GaAs quantum dots (QDs). Microdisk resonators were defined using photolithography and plasma chemical etching. The active region diameter was varied from 11 to 31 µm. Microlasers were tested without external cooling at room and elevated temperatures. The QW laser structure was epitaxially grown by MOCVD on silicon (100) with an intermediate MBE-grown Ge buffer. Under pulsed injection (0.5-µs-long injection pulses with 150 Hz repetition rate), lasing is achieved in QW microlasers with diameters of 23-31 µm with a minimal threshold current density of 28 kA/cm^2. Quasi-single mode lasing (SMSR is up to 20 dB) is observed with emission wavelength around 988 nm. To the best of our knowledge, this is the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. Quantum wells are typically characterized by high optical gain and high direct modulation bandwidth, which can be important in view of further miniaturization of microlasers and their future application. The sidewall passivation can be helpful to reduce the threshold current. As compared to QWs, quantum dots demonstrate reduced sensitivity to threading dislocations and other crystalline defects as well as to sidewall recombination owing to a suppressed lateral transport of charge carriers which prevents their diffusion towards non-radiate recombination centers. The QD laser structure was directly grown by MBE on Si (001) substrate with 4° offcut to the [011] plane. QD microlasers were tested at room temperature in CW regime with a DC current varied from 0 to 50 mA and at elevated temperatures under CW and pulsed excitation (0.5-µs-long injection pulses with 10 kHz repetition rate). The InAs/InGaAs QDs active region provides the wavelengths in the 1.32–1.35 µm spectral interval. At room temperature, lasing is achieved in microlasers with diameters of 14-30 µm with a minimal threshold current density of 600 A/cm2 (compare with that of 427 A/cm2 in edge-emitting laser). The threshold current density and specific thermal resistance of 0.004 °C×cm^2/mW are comparable to those of high-quality QD microdisk lasers on GaAs substrates. Lasing wavelength demonstrates low sensitivity to current-induced self-heating. Lasing is single mode (SMSR 20 dB) with a dominant mode linewidth as narrow as 30 pm. Under CW excitation lasing sustains up to 60 °C in microlasers with diameter of 30 µm. Because of self-heating, an actual temperature of the active region is close to 100°C. Under pulsed excitation, the maximal lasing temperature is 110°C. To our best knowledge, these are the smallest microlasers on silicon operating at such elevated temperatures ever reported. Up to 90°C lasing proceeds on the ground state optical transition of QDs with wavelength about 1.35 µm. At higher temperatures, lasing wavelength jumps to the excited state transition.

The Silicon (Si) CMOS technology has long been the backbone of electronic devices. In these components, data communication is currently limited by the metal interconnects. An alternative solution based on optical transmission demands an additional light source due to the intrinsic indirect gap of Si, which prevents it from efficiently emitting light. The requirement of a monolithic, Si-compatible light source has made another column IV semiconductor – Germanium (Ge) - a potential candidate. Ge has, as Si, an indirect gap, but with a smaller separation between Γ and L energy levels. A direct gap Ge-based material can be obtained by alloying it with Tin (Sn) – a column IV semi-metal. Recent studies have demonstrated lasing in optical cavities made with Ge1-xSnx alloy: So far, lasing in Fabry-Perot cavity [1, 2] and in micro-disk cavity [3, 4] were reported. In this article, we study lasing in Ge1-xSnx - based photonic crystals, with 16% Sn concentration. Studies were conducted on Hn defect cavities (with n denoting the number of hexagonal ring of air holes removed from the center), and slow mode membranes – which are photonic crystals with low group velocity optical mode appeared in the photonic band structure, thus enhancing the interaction between emitted light and the gain medium. A step-graded epitaxy technique was used to fabricate the samples. It consists in inserting a thick buffer with discrete Sn content increases between the Ge virtual substrate underneath and the main Ge0.84Sn0.16 layer on top. With this method, misfit dislocations are distributed more evenly in the grading (instead of propagating towards the surface), which preserves the crystalline quality of the partly relaxed Ge0.84Sn0.16 optical layer. Both Hn cavities and slow mode membranes were under-etched to make the active layer fully relaxed. The photonic crystals are slightly curved due to strong relaxation of the active layer. The structures were optically pumped with a 1064 nm pulsed laser. Fourier transform infrared (FTIR) spectroscopy was used to study the photoluminescence of these samples. We demonstrate lasing on the H4 cavities and the slow mode membranes. The dimensions of both structures were calculated to pin the resonance mode (or slow mode under the light cone) around the emitted wavelength of relaxed Ge0.84Sn0.16. Based on the spectra and the Lin-Lout curve, we estimate the current lowest lasing threshold around 180 kW/cm2 for slow mode membrane at low temperature (15K), with emitted wavelength of 2880 nm. The lasing threshold obtained here is of the same order of magnitude of those reported for micro-disk and Fabry-Perot cavities [1, 2, 3, 4], suggesting that the intrinsic properties of Ge1-xSnx are the main limit factor to the performance. Surface passivation and carrier confinement with SiGeSn alloys and/or multi quantum well structures should be used to enhance the Ge1-xSnx radiative recombination efficiency. [1] S. Wirths, R. Geiger, N. von den Driesch, G. Mussler, T. Stoica, S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J. M. Hartmann et al, Nature Photonics 9,88 (2015) [2] S. Al-Kabi, S. A. Ghetmiri, J. Margetis, T. Pham, Y. Zhou, W. Dou, B. Collier, R. Quinde, W. Du, A. Mosleh et al, Appl. Phys. Lett. 109, 171105 (2016) [3] D. Stange, S. Wirths, R. Geiger, C. Schulte-Braucks, B. Marzban, N. von den Driesch, G. Mussler, T. Zabel, T. Stoica, J-M Hartmann et al, ACS Photonics 3, 1279 (2016) [4] V. Reboud, A. Gassenq, N. Pauc, J. Aubin, L. Milord, Q.M. Thai, M. Bertrand, K. Guilloy, D. Rouchon, J.Rothman et al, Appl. Phys. Lett. 111, 092101 (2017)

Photon-photon resonance (PPR) has been researched to achieve high modulation frequency bandwidth in direct modulation laser diode (LD). The phenomena of PPR, which has the potential of having a resonance peak at a higher frequency rather than carrier-photon resonance (CPR, namely, regular resonance), is based on different internal oscillation in a laser chip, therefore, it is essential to involve plural different internal optical paths in a laser diode chip. One biggest issue is to achieve flat frequency response as the frequency response normally deteriorate at a higher frequency region than CPR. To mitigate this issue, we have demonstrated multiple PPR by using active-MMI configuration, and have proved more than 40 GHz band-width so far successfully.

In this paper, we discuss about the recent progress of the active-MMI laser diode which enables to realize this multiple PPR phenomena, and the recent results. We hope and believe that this approach will contribute to realize over Tbps direct modulation laser diode, which will be integrated in the high-speed interconnection on board in the future.

The optical feedback dynamics of two multimode InAs/GaAs quantum dot lasers emitting exclusively on sole ground or excited lasing states is investigated under the short delay configuration. Although the two lasers are made from the same active medium, their responses to the external perturbation are found not much alike. By varying the feedback parameters, various periodic and chaotic oscillatory states are unveiled. The ground state laser is found to be much more resistant to optical feedback, benefitting from its strong relaxation oscillation damping. In contrast, the excited state laser can easily be driven into very complex dynamics. While the ground state laser is of importance for the development of isolator-free transmitters, the excited one is essential for applications taking advantages of chaos such as chaos lidar, chaos radar, and random number generation.

In this paper the injection locking properties of two laterally-coupled semiconductor lasers (LCSLs) are studied numerically. We consider external injection into either one (single external-injection scheme) or both (simultaneous external-injection scheme) of the LCSLs. We present stability maps for both schemes in the plane of the frequency detuning and the injection strength, where attention is centered on the influence of the waveguiding structures, the laser separation, the pump rate, and the frequency offset between the two coupled lasers. Our results contribute to a better understanding of LCSLs under external injection.

We report on a bifurcation scenario from which emerges oscillations at a frequency higher than the relaxationoscillation frequency in an edge-emitting laser diode subjected to polarized optical feedback; these oscillations appear in the square-wave regime. The study has been performed experimentally and numerically based on Lang-Kobayashi model. We unveil bifurcation diagrams showing a clear bifurcation point that marks the transition between sustained and damped oscillations on the plateaus of square-waves. We extend this first bifurcation study by providing additional analytical insight to characterize the main parametric dependence of the frequency of these undamped oscillations.

The stabilization of a relatively simple optoelectronic oscillator tunable across the X-band based on a laser subjected to optical feedback is achieved. Specifically, a resonance effect based on locking the two inherent frequencies of the system, as well as, self-modulation were utilized to achieve a sub-ps phase jitter.

Quantum cascade laser (QCL) is a semiconductor based laser in a superlattice structure based on intersubband transitions. Although QCLs have been achieved with high performance such as Watt-level emission, it is always highly desired to further improve the device performance with multiple functions , for example, achieving high beam collimation, arbitrary polarization control, and high speed modulation. It is also desired that those performance could be achieved through an integrated approach for miniaturalization, easy alignment and reducing cost. In this presentation, we will use Terahertz (THz) QCL as a demonstration example to obtain high collimated THz QCLs through plasmonic collimation designs with a record beam divergence, electrically tunable THz polarizations by designing integrated THz metasurfaces on a hybrid dielectric-plasmonic waveguides, and broadband graphene-based integrated THz modulators with a fast modulating speed.

Semiconductor disk lasers, also called vertical external-cavity surface-emitting lasers (VECSELs) have advantageous properties such as high output power, wavelength flexibility due to bandgap engineering and near-diffraction limited beam quality. The possibility to insert intra-cavity elements – filters, frequency doubling crystals or semiconductor saturable absorber mirrors (SESAMs) – enables wavelength tuning, second harmonic generation or mode locking with ultra-short pulses. A major challenge for these laser sources is the removal of heat which is introduced by optical pumping. The thermal management can improved by placing only the active region directly between two heat spreaders. This membrane external-cavity surface-emitting laser (MECSEL) allows emission in an even larger wavelength range, since the growth is not restricted by a distributed Bragg reflector. We present the fabrication, processing and characterization of MECSELs using different material systems for laser emission at various wavelengths in the visible and in the infrared spectral range. Our semiconductor structures are grown by metal-organic vapor-phase epitaxy and contain quantum wells (QWs) or quantum dots (QDs) in the active regions. We discuss our latest results of the membrane laser concept with investigations of strain effects on the photoluminescence and the laser emission and different pumping schemes. In particular, we show results of a MECSEL placed into a linear cavity and pumped by a 532 nm laser. The system was operated at a heat sink temperature of 10°C and achieved nearly 600 mW at 3.7 W pump power. The slope efficiency achieved here was 22.3 % with a threshold pump power of 1 W. This slope efficiency exceeds any slope efficiency published before with green pumped conventional VECSEL in this emission range at these elevated heatsink temperatures. Including a birefringent filter into the laser cavity allows for a tuning of the emission laser wavelength. The group could demonstrate a tuning range of 24 nm (650 nm – 674 nm), which is the highest value achieved in this spectral range by semiconductor lasers to date. All these achievements come with the expected Gaussian TEM00 mode with a beam quality factor of M2< 1.06[Optica 3(12), 1506-1512 (2016)]. To demonstrate the flexibility and usability of the MECSEL approach, we have created an optically pumped laser with a GaInAsP membrane for emission around 1000 nm, together with a group in Dundee. The set-up of the laser was similar to that of the red spectral range but instead of diamond, SiC was used as heat spreader material. Nevertheless, the achieved output powers could exceed 10 W with a slope efficiency of 27.5% and this with the heat spreader on only one side. This work was as well recently published in Electronic Letters 2017 [DOI:10.1049/el.2017.2689]. Actually, we realized a running membrane laser at a wavelength of 608 nm, a wavelength not accessible so far. The characterization measurements are now ongoing, first results will be presented at the conference.

We present a design and output characteristics of an optically quantum-well-pumped semiconductor laser for single- and dual-wavelength emission which has a resonant disk structure for two wavelengths that lie 36.7nm apart. The smaller resonance wavelength is intended for the pump wavelength of 940 nm. Laser emission, however, can either take place at the short and/or at the long resonance wavelength. A switch between the emission wavelengths is performed by moving the gain peak towards the desired wavelength. For instance, while the heat-sink of the laser is kept at -15°C the laser will only emit a wavelength of 957.0 nm, a change of the heat-sink temperature to 50°C does result in an emission at the other resonance wavelength located at 997.5 nm. In both cases slope efficiencies above 50% and output powers beyond 10W are possible. Limiting factor is the available pump power. A simultaneous emission at 960.8 and 997.5nm is observed for heat-sink temperatures between 21.3 and 27.1°C. The intra-cavity performed sum-frequency generation (SFG) of the dual-wavelength laser leads to an emission at 489.7 nm.

Most of the environmental gases like H2S, C2H2, CH4, CO(2), N2O and H2O have strong absorption lines within 2-3 µm wavelength range. Detection of these gases requires a spectrally broad, compact, efficient, cost-effective, and high output power light source. Such choice of parameters can be offered by high brightness and broadband superluminescent diodes (SLD). Here we report the development of GaSb-based high power broadband superluminescent diodes (SLDs) emitting around 2.55 μm. The active region consists of two GaInAsSb/GaSb quantum wells. To enable high gain and high output power we adopted a long ridge waveguide (RWG) geometry, i.e. 2.5 mm. The width (5µm) and etching depth (1800 nm) of waveguide was chosen to operate device in single transverse mode. Lasing inside the cavity was suppressed by tilting the waveguide 8° with respect to cavity facets. Recently developed cavity suppression element [1] was employed to further suppress the spectral modulations and smoothen out the spectrum. For operation at long wavelengths, we employed a pulsed driving scheme with sub-µs pulse injection to address temperature dependent non-radiative Auger recombination. Devices have demonstrated an average output power of more than 3 mW and peak power over 15 mW at room temperature (RT). The maximum full-width at half-maximum (FWHM) of spectrum was ~124 nm, corresponding to 1200 mA drive current. This is the highest power reported to date for 2.55 µm SLDs. For comparison, SLD at 1.90µm emitted a continuous wave (CW) output power up to 60 mW and FWHM of ~ 60 nm [1]. Integration of this high brightness, broadband light sources with SOI-waveguides enables realization of a compact multiple gas sensor in this wavelength range [2]. [1] N. Zia, J. Viheriälä, R. Koskinen, A. Aho, S. Suomalainen, and M. Guina, “High power (60 mW) GaSb-based 1.9 μm superluminescent diode with cavity suppression element,” Appl. Phys. Lett., vol. 109, no. 23, p. 231102, 2016. [2] P. Karioja, T. Alajoki et al, “Multi-wavelength mid-IR light source for gas sensing”, Proc. SPIE 10110, 2017.

We have devised an oxide- and regrowth-free approach for current confinement in vertical-cavity surface-emitting lasers (VCSELs) which uses the photons in the cavity to optically define a current path through the device. For this purpose, an optical switch, implemented as a phototransistor (PT), is epitaxially integrated into the cavity. The PT layers become locally conductive where the highest photon density is reached in the resonator and establish the current aperture. By introducing additional photons with an external laser beam into the resonator, we show here that this current aperture can be manipulated. We demonstrate the possibility of redefining the location of the current aperture and discuss the consequences on the light-current characteristics of the devices.

Polarization dynamics in vertical-cavity surface-emitting lasers (VCSELs) are much faster than their intensity-driven counterparts and can be a potential approach to overcome the bandwidth limitation in short-distance data transmission. The birefringence splitting B as the frequency difference between the two fundamental polarization modes is an important factor determining the polarization dynamics in spin-VCSELs. Although B can be strongly influenced by mechanical bending, for later applications an on-chip solution for birefringence tuning is favored. With an electrically driven asymmetric heating device we have demonstrated a thermally induced tuning range of ΔB = 45GHz. The maximum achievable birefringence tuning was not limited by the laser but by material parameters and the fabrication process. In this paper we present an optimized design for thermally induced birefringence tuning and additional possibilities to increase the efficiency of the mechanism.

Dilute bismide is a novel class of III-V semiconductor compound possessing a number of attractive physical properties such as a large band-gap bowing effect, a large spin-orbit split band and a less temperature sensitive band-gap etc. In this talk, I will present electrically pumped near infrared GaAsBi quantum well (QW) laser diodes (LDs) grown by molecular beam epitaxy with room-temperature lasing up to 1.14 m. Epitaxial growth is carefully optimized to ensure high bismuth incorporation and high optical quality at the same time. The LDs reveal an output power over 120 mW under pulsed excitation at 300 K and can operate under CW excitation up to 273 K. They also show high performance with an internal quantum efficiency of 86% and an internal optical loss of 10 cm-1. The characteristic temperature is 79 K in the temperature range of 225-350 K and the temperature coefficient of the lasing wavelength is 0.26 nm/K at 77-350 K, much smaller than 0.35-0.40 nm/K for InGaAs and InGaAsP QW LDs. These results suggest that GaAsBi LDs are attractive candidates for uncooled near infrared lasers on GaAs.

A theoretical analysis of optical frequency combs associated with the main and suppressed linear polarization modes of a gain-switched long-wavelength VCSEL is performed. We have studied the VCSEL polarization-resolved dynamics by using an extension of the spin-flip model to include nonlinear carrier recombination. Our results show that two orthogonally polarized combs are generated that combine to produce a wider overall optical comb. The dependence of combs on the VCSEL parameters and on the amplitude and frequency of the modulation is analyzed. Bistability between the two orthogonally polarized combs is found.

The realization of mode-locked lasers capable of generating short optical pulses in the near-infrared is a key enabler for various applications including high data rate optical interconnects. The related technology mostly consists of bulky and stand-alone devices, which tends to hinder their widespread use. In addition, the integration of such devices onto chip-based platforms could bring advantages in terms of robustness and stability, while offering some prospects for the realization of advanced hybrid photonic-electronic architectures. There has been recently some progress regarding the miniaturization of fast pulsed lasers [1], but the underlying cavity typically remains longer than a few millimetres and their integration on a chip is still a challenge [2]. Here, we aim at realizing a compact integrated pulsed micro-laser using an innovative photonic crystal (PhC) cavity based on low dispersion slow light modes. Most of the characteristics of mode-locked lasers are tightly linked to the product of the cavity length L and the group index ng of the modes traveling in the cavity. While miniaturization thus tends to degrade the quality of the generated optical pulses, we counterbalance this effect through exploiting slow light (high ng) modes in PhC structures. Dispersion engineering techniques have been successfully developed in passive Si/air suspended PhC cavities for decreasing the otherwise typically high dispersion of these modes [3]. We adapted these techniques to our asymmetric InP/silica structures so as to provide a frequency-equidistant comb of modes - a pre-requisite to laser mode-locking. While our geometry well improves laser heat dissipation with respect to PhC cavities suspended in air, it poses additional constraints and could increase the cavity mode optical losses. Using 3D FDTD simulations, we demonstrated the validity of this approach and designed, as an example, a 30 μm long, linear dispersion PhC cavity, with a group index of 29, providing at least 9 equally-spaced modes over an 11.5 nm bandwidth, which can afford the generation of sub-picosecond optical pulses. Despite the structure asymmetry, quality factors were all above 10,000, i.e. sufficient for reaching laser operation. Compared with a standard strip-waveguide-based laser cavity, this design provides a length reduction factor of almost one order of magnitude, as given by the ratio of the group index of each structure. Various designs enabled us to achieve a range of low dispersion bands with different group index (15-40), offering a relevant trade-off between device miniaturization and short pulse duration. Based on these designs, PhC active structures including InAsP/ InP quantum wells or InAs/InP quantum dashes were fabricated using molecular beam epitaxy, III-V/silica bonding, e-beam lithography and reactive ion etching. Near-field optical microscopy was used to identify both the spectral and spatial signatures of the cavity modes, which were in good agreement with the simulations. We also probed our cavities by microphotoluminescence. These cavities provide a first step towards the realization of miniaturized integrated mode-locked lasers. Their robust hybrid InP/silica geometry offers the potential for integration with silicon photonic devices, while enabling the integration of a saturable absorber, such as graphene, for achieving mode-locked laser operation. References [1] Joshi, S. et al. (2014). Quantum dash based single section mode locked lasers for photonic integrated circuits. Optics Express, 22(9), 11254. [2] Latkowski, S., et al. (2015). Monolithically integrated 25 GHz extended cavity mode-locked ring laser with intracavity phase modulators. Optics Letters, 40(1), 77 [3] Li, J. et al. (2008). Systematic design of flat band slow light in photonic crystal waveguides. Optics Express, 16(9), 6227–6232.

We illustrate the study of extreme events in the spatial transverse section of the electric field emitted by a broadarea semiconductor laser with saturable absorber. Spatiotemporal maxima of the field intensity in the threedimensional space (x, y, t) are identified as events for the statistical analysis. We clearly determine the regions of the parameter space where extreme events are most likely to occur. Furthermore the connection between extreme events and stationary and self-pulsing cavity solitons, occurring in the same system, is investigated.

We explore both experimentally and numerically the dynamics of semiconductor lasers subject to delayed optical feedback and show that the external cavity repetition rate can be resonant with the relaxation oscillations leading to a discretisation of the relaxation oscillation frequency which evolves in a series of discrete steps, remaining almost constant along each step. Numerically, the steps are found to result from different Hopf bifurcation branches.

This article describes a study of an 8 W optical output power single emitter laser diode. The used device is the WSLX808008-H-T-PD, manufactured by Wavespectrum, with 808 nm emitted wavelength, and with build in NTC (thermistor), photodiode and Peltier cell. First part of the study explains how the Pspice model of the optical output power is proposed and how parameters are obtained, especially considering temperature variations. A short review of related laser diode theory is done including necessary parameters for the model proposal. It is explained the used method to measure the diode's optical output power avoiding temperature drifts (cold measure) and how the method has been implemented in an automatic characterization system using a data acquisition card controlled with LabVIEW, to be applied at different temperatures using a climatic chamber, and to obtain the necessary model parameters values as required by theory. It is also confirmed that the measured parameters are effectively following the expected theoretical behaviour with the temperature variation. With obtained results, model is proposed and programmed in Pspice, and simulation results are compared with measured real results for model validation. In a second part, it has been studied the usage of laser's wavelength drift as a temperature measurement method, and also as a validation of the cold measurement method as it allows the temperature drift supervision during it. Advantages and disadvantages of this method compared with NTC usage are commented. Results using two different spectrometers, comparison with laser diode manufacturer's information and necessary temperature references for the method are commented. In a third part a proposal of an optical output power measurement setup and it use with diode's characterisation system is proposed. System measurements comparison in DC mode with a thermal power meter and related calibration are performed and applied to the automatic characterization system.

The external differential quantum efficiency, defined as the ratio of number of photons emitted per unit time to number of carriers passing the laser diode junction, is known to be sensitive to laser diode’s operating temperature. In this paper, high-resolution spectral emissions of a commercially available GaN-based blue laser diode are measured and utilized to study the effect of temperature on the external differential quantum efficiency and over the operating temperature range of 270 – 330 °K. Upon studying the L-I curves and over the full range of laser diode’s operating current and temperature, three distinct temperature regimes of the quantum efficiency were identified with the regime of temperature range 285 -301 °K yielding the highest temperature stability. In addition to experimentally determining the characteristic temperature of the laser diode, the effect of non-radiative recombination and free carrier absorption processes on external differential quantum efficiency will be discussed.

We discuss the design and the dynamics of a semiconductor laser integrated with a long on-chip optical feedback (see also [Verschaffelt et al., Chaos: An Interdisciplinary Journal of Nonlinear Science, vol. 27, pp. 114310, 2017]1). Such lasers with optical feedback are interesting for several applications that make use of their rich dynamical behavior. Moreover, they are ideal test-beds to experimentally study delay induced dynamics, because the system's parameters (such as the laser injection current and the optical feedback strength) can be easily accessed and accurately controlled. The system discussed here uses only standard building blocks of the generic Jeppix platform for photonic integrated lasers. The design is based on a DBR-laser with a spiral delay waveguide. We have included several control pads with which we can tune the fabricated laser's emission wavelength, the feedback strength and phase in order to compensate for fabrication tolerances. We have been able to integrate a 10 cm feedback length on a footprint of 5.5 mm². We illustrate that this delay is sufficiently long to drive the laser into a chaotic regime, and we analyze the chaotic dynamics based on the spectrum, autocorrelation and permutation entropy. We show - using the NIST statistical test suite for random number generators - that the observed delay dynamics is sufficiently complex for random number generation at a rate of 500 Mbits/s.

In this paper, we investigate the presence of time delay (TD) signature in the chaotic emission of semiconductor metalclad nanolasers subject to different types of optical feedbacks (OFs). We first examine the TD signatures in the cases when all-optical feedback via either conventional mirror, phase conjugate mirror, or grating mirror is employed. Second, we propose a mixed all-optical / electrooptic feedback scheme for concurrent suppression of TD feature in chaotic output emission. The mathematical model for proposed scheme is presented to integrate both the optical and electrooptic time delays. The concealment of TD signature is then investigated by means of the autocorrelation function. The results reveal that the chaotic output signal in each case has well eliminated TD signature at particular operational regions within which the system is more appropriate for applications related to secure communications and ultra-fast physical random number generators.

Vertical-cavity surface-emitting lasers (VCSELs) have emerged as a pioneering solution for many high-speed data communication challenges. Compared to large-signal analyses, the small-signal modulation response of a VCSEL can be isolated from the entire system, thus providing accurate information on the intrinsic laser dynamics. An alternative approach to that of using the rate equations is to transform theses rate equations to an equivalent circuit model. The dynamic operation characteristics including the device-circuit interaction can then be modeled and optimized using a circuit simulation software. Until now, it was assumed that the dynamic behavior of oxide-confined multi-mode VCSELs can be modeled using the single-mode rate equations developed for edge-emitters, even though the deviation between the single-mode based model and the measured data is substantially large. Furthermore, equivalent electrical circuit modeling of the VCSELs’ intrinsic dynamics was only done by modeling derived from the single-mode rate equations. Therefore, a new electrical circuit model, that can accurately describe the dynamic behavior of these VCSELs, is needed. In this work, electrical circuit modeling of the dynamic performance of multi-mode VCSELs, for the case where lasing modes do not share a common carrier reservoir, is presented. The electrical circuit model is derived from innovative advanced multi-mode rate equations that take into account the effect of spatial hole burning, gain compression, and inhomogeneity in the carrier distribution. The validity of the model is affirmed through experimental data fittings and plots of their modulation response are presented.

Catastrophic optical mirror damage (COMD) is a key issue in semiconductor lasers and it is initiated by facet heating because of optical absorption. To reduce optical absorption, the most promising method is to form non-absorbing mirror structures at the facets by obtaining larger bandgap through impurity-free vacancy disordering (IFVD). To apply an IFVD process while fabricating high-power laser diodes, intermixing window and intermixing suppression regions are needed. Increasing the bandgap difference (ΔE) between these regions improves the laser lifetime. In this report, SrF₂ (versus Si_xO₂/SrF₂ bilayer) and SiO₂ dielectric films are used to suppress and enhance the intermixing, respectively. However, defects are formed during the annealing process of single layer SrF₂ causing detrimental effects on the semiconductor laser performance. As an alternative method, Si_xO₂/SrF₂ bilayer films with a thin Si_xO₂ dielectric layer is employed to obtain high epitaxial quality during annealing with small penalty on the suppression effect. We demonstrate record large ΔE of 125 meV. Broad area laser diodes were fabricated by the IFVD process. Fabricated high-power semiconductor lasers demonstrated conservation of quantum efficiency with high intermixing selectivity. The differential quantum efficiencies are 81%, 74%, 66% and 46% for as grown, bilayer protected, SrF₂ protected and QWI lasers, respectively. High power laser diodes using bilayer dielectric films outperformed single-layer based approach in terms of the fundamental operational parameters of lasers. Comparable results obtained for the as-grown and annealed bilayer protected lasers promises a novel method to fabricate high power laser diodes with superior performance and reliability.

To establish highly performing vertical cavity surface-emitting lasers (VCSELs), it is essential to have an adequate understanding of the intrinsic laser dynamics of these devices. However, this is done while bearing in mind that extrinsic parasitic elements in VCSELs play an important role in limiting the intrinsic modulation bandwidth. In this work, we analyse different electrical parasitic equivalent circuit models in the aim of comparing them and selecting the one that can best describe and represent the physical properties of our high-performance VCSELs. Through measuring the microwave reflection coefficient S₁₁(f), then fitting it with the calculated one from the equivalent circuit impedance model, the parasitic components of the equivalent circuit model can be extracted. The S₁₁(f) data was collected over different ranges of operating bias currents and using a 7 μm oxide aperture diameter VCSEL. This allows us to observe the variations of these circuit elements with respect to the current and compute the transfer function and the resulting parasitic cut-off frequencies (bandwidth limitation) for each model. After plotting and comparing the transfer functions of the different models together, under the same driving current, it was found that the discrepancy between the two curves, in a specific frequency range, is rather small over the VCSEL bandwidth of interest, hence allowing us to use the first-order low pass filter to de-embed the parasitic contributions and separate them from the device intrinsic response. However, over higher frequency ranges, the deviation is found to be substantial and the extract parasitic transfer function should be taken into consideration.

Another issue to be addressed is the reliability of the simple circuit models to extract accurate circuit component values, especially when the deviation between the measured microwave reflection coefficient S₁₁(f) and the fitted model is substantially large. This discrepancy is due to the oversimplification imposed on the equivalent circuit model, leading to a high level of uncertainty in the extracted circuit component values. Thus, sufficient modelling and accurate fitting strategies are needed for a reliable parasitic de-embedding approach.

Open resonant optical devices such as an oxide-confined vertical cavity surface emitting laser (VCSEL) can be characterized by a quasi-normal mode (QNM) expansion. In contrast to eigenmodes of a closed system, QNMs exhibit an exponential divergence in the exterior of the device and are no longer normalizable. This behavior renders the mathematical treatment and physical understanding very challenging. As an alternative we investigate the constant-flux mode (CFM) expansion which avoids the divergence in the exterior domain. Besides numerical studies, we present results for different oxide aperture sizes and positions inside the investigated VCSEL. Here, we apply CFMs to describe the impact on the resonance wavelength and on the mode profile.

Self-injection locking, an efficient method to improve the spectral performance of semiconductor lasers without active stabilization, has already demonstrated its high potential for operation with single-longitude-mode fiber lasers urgently demanded by new applications in optical metrology and spectroscopy, coherent optical communications, distributed fiber sensing. The laser operation stability remains to be a crucial issue for such laser applications. Here, we present a theoretical framework for modeling of semiconductor laser coupled to an external fiber-optic ring resonator. The developed approach has shown good qualitative agreement with theoretical predictions and experimental results for particular configuration of a self-injection locked DFB laser delivering narrow-band radiation and particular employed in Brillouin fiber laser configurations. The model is capable of describing the main features of the experimentally measured laser outputs such as laser line narrowing, spectral shape of generated radiation, mode-hoping instabilities and makes possible exploring the key physical mechanisms responsible for the laser operation stability.

Passively mode-locked lasers are compact photonic sources delivering high-repetition rate (RR) pulse trains and picosecond short optical pulses. An excellent stability of the generated optical pulse train is crucially important towards their application in optical communications,¹ optical sampling² or as photonic clocks.³ Controlled RR transitions in a multi-section monolithic quantum-dot (QD) laser have been experimentally demonstrated by a reconfigurable absorber placement⁴ or a double-interval technique.⁵ In this contribution, we study the optical pulse train stability improvement and higher harmonic RR transitions in a monolithic semiconductor laser with interdigital absorber placement by the simulation tool FreeTWM.⁶ The laser under investigation is 4 mm long, corresponding to a fundamental RR of 10 GHz, and consists of 2 gain and 2 absorber sections. All gain sections are biased with the same current density and the absorber sections are equally reverse biased. The total absorber lengths contribute with 10 % to the total cavity length. One absorber is placed at the high reflective facet, the second at 1/3 of the total cavity length with one gain section in between and the second gain section following the second absorber. Numerically transitions from fundamental mode-locking (n=1; 10 GHz) to higher harmonic mode-locking (n=3; 30 GHz) occur by increasing the injected current density using numerical continuation. Associated with that transition is an improved timing stability by a factor of 333. Simulations confirm experimental results obtained by timing stability and RR transition studies.

Monolithic passively mode-locked (PML) semiconductor lasers with multi-GHz repetition rate (RR) emitting at wavelengths of around 1070nm are attractive ultrafast sources for seeding ytterbium doped fiber amplifiers and for photonic communication at high data rates. The timing stability quantified by the timing jitter (TJ) and the RR tuning range of a PML multi quantum-well (QW) semiconductor laser emitting at 1070nm subject to dual-cavity optical self-feedback (DC-OFB) consisting of one very short cavity for a high RR tuning range and one very long cavity for strong TJ reduction is investigated. The 3mm long PML QW semiconductor laser with a saturable absorber section length of 10% of the total cavity length has a RR of 13.61 GHz and a TJ of 83 fs with a pulse width amounting to 8 ps at the investigated injected gain current, absorber reverse bias voltage and cooling block temperature. For the combination of the long fiber-based cavity amounting to 5.9m combined with the short free-space cavity amounting to a few laser cavity lengths a RR tuning range over 1 GHz is achieved. Furthermore a minimal TJ of approximately 330 as with full sideband suppression in the radio-frequency (RF) spectrum is achieved which is an improvement by factor 250 in comparison to the free-running laser.

In this contribution we investigate experimentally and by modeling the mode spacing tuning range and stability of optical frequency comb lines generated by a 1 mm long self mode-locked single section quantum dot semiconductor laser subject to dual-cavity all optical self-feedback. The external optical feedback cavities have an optical length of 9.4 m and 16.5 m and are implemented by optical fibers. The optical feedback strengths are below 0.02% back reflected onto the as-cleaved laser facet. The line-width of the laser mode-beating frequency equals optical frequency mode spacing of 40.67 GHz amounts to 1.4 MHz in the free-running case. By fine-delay tuning of both optical feedback lengths, we find a comb-line spacing tuning range of 70 MHz. The radio-frequency linewidth decreases by a factor of 700 down to 2 kHz for particular adjusted optical feedback cavity lengths, thus improve the mode spacing stability. We validate the experimental findings by a simple and universal stochastic time-domain model.

Optical frequency combs generated by self mode-locking of single-section quantum dot based semiconductor lasers are ideal sources for applications in high capacity optical interconnects or high precision dual comb spectroscopy. We investigate a 1mm long InAs/InGaAs quantum dot semiconductor laser both experimentally and by simulations using a time-domain traveling-wave model. We observe that by increasing the injection current, the laser output exhibits an unlocked multi-mode behavior above the lasing threshold up to a certain current were the modes lock due to an internal non-linear effect in the active laser medium. This phase locking is experimentally and numerically observed by RF beat note line width analysis as well as by integrated relative intensity noise analysis. Both of these properties are significantly reduced above this locking threshold. The lowest experimentally measured RF line width amounts to 20 kHz, while for lower currents prior to the threshold the line width can be as high as hundreds of MHz. Our simulations confirm this threshold behavior and the simulated spectra are in good qualitative and quantitative agreement.

Optical feedback (OF) system plays an important role in nonlinear dynamics because of low cost, less complexity, and well-maintained. Rich nonlinear characteristics of semiconductor laser under optical feedback are investigated, including period-one oscillation (P1), period-two oscillation (P2), quasi-period (QP), and chaotic oscillation (CO) states. However, the stability of the states generated is the most important issue to be solved and improved. In this paper, the polarization rotated feedback is purposed to be an alternative approach that possesses the characteristic of improving the signal quality compared to optical feedback. We focused on the generation of P1 states and on the performance of the noise reduction of the P1 states by utilizing incoherent OF. The polarization rotated feedback system is built up by OF systems under the orthogonally polarized feedback. The optical components that we used in the scheme for generating of the polarization rotated feedback are Faraday rotator (FR) and polarizer to provide the incoherent optical feedback, rich dynamics is obtained compared to those observed in traditional feedback system. Moreover, noise reduction of the P1 states caused by the delay loop frequencies in feedback scheme is realized by applying the orthogonally polarized feedback to the already-generated P1 states by the traditional scheme. To explore the quality of the generated P1 states, the measurements of the amplitude of side peaks, the spectral linewidths, and amplitude variation of P1 states under traditional OF and polarization rotated feedback in both frequency and time domain observed by electrical power spectrum and oscilloscopes are examined and analyzed, respectively. As a result, effective noise reduction in P1 states is achieved while applying a polarization rotated feedback.

Nonlinear dynamics of semiconductor lasers under individually optoelectronic feedback (OEF) and optical feedback (OF) is attracted much attention in these two decades. In this paper, nonlinear dynamics of single-mode distributed feedback (DFB) semiconductor laser subject to dual feedback composed of both optical feedback and optoelectronic feedback are investigated experimentally. The dynamical states shown in individual system are observed, quasi-periodic (QP) oscillation and pulsation, regular pulsation (RP), chaotic oscillation (CO) and pulsation (CP). To explore the microwave signals generated by quasi-periodic states in the dual feedback system, we also measure the suppression ratio of unwanted frequency side peak and RF spectral linewidth in frequency domain. On the other hand, the corresponding time series are also considered and discussed by calculating the amplitude variation of regular pulses and pulse widths. Moreover, a side peak suppression ratio of about 56 dB is achieved when applying the hybrid feedback scheme. The amplitude variation ratio of regular pulses is optimized to 0.008 and the pulse-width is approximately 0.12 ns which is smaller than those coefficient when applying individual OF and OEF system. The improved percentage of averaged amplitude variation in regular pulses of around 60 percent is also obtained. Furthermore, the complexity of chaotic waveforms generated by hybrid feedback system are discussed and calculated.

We analyze the properties of a unidirectional class-A ring laser containing a nonlinear amplifying loop mirror (NALM). The NALM is a Sagnac interferometer consisting of an amplifier and a Kerr-type nonlinear element, and has a reflectivity that periodically varies with the intra-cavity power. To model the dynamics of these lasers, we use the approach based on Delay Differential Equations (DDEs) that has been successfully applied to describe the properties of passively mode-locked semiconductor lasers. The proposed model allows us to investigate mode locking operation in this laser. The analysis of this DDE model for mode-locked operation was performed numerically and analytically in the limit of large cavity round trip times. We demonstrate that mode-locked pulses are born though a modulational instability of the steady state solutions when the pseudo- continuous branch crosses the imaginary axis. These asymmetric pulses always co-exist with the stable laser-off solution. Hence, they can be viewed as temporal cavity solitons having similar properties with localized structures observed in bistable spatially-extended systems.

The objective of this research is to design, develop and test the InP based multichannel transceivers dedicated for application in WDM access systems. The transmitters are making use of DBR lasers and Mach-Zehnder modulators. The satisfying parameters of transceivers were obtained like low threshold current and good side mode suppression ratio.

The main optical output power limitation in high power laser diodes is the catastrophic optical mirror damage (COMD) initiated by facet heating due to optical absorption, which limits the reliable power and lifetime of a single laser. Facet heating correlated with current injection near laser facets can be reduced by unpumped window structure. However, the high-power laser slope efficiency drops as the length of the window increases. In this work, separately pumped window (SPW) method is proposed and experimentally demonstrated to significantly reduce the facet temperature of the semiconductor lasers without compromising their performance. We used 5-mm long high-power laser diodes and compared its performance and facet temperature to the devices integrated with SPW facet sections, which are electrically isolated from the laser section. The slope efficiencies of the lasers with SPW and that of 5-mm lasers without SPW are comparable when SPW is pumped at its transparency current, illustrating that SPW integrated lasers preserve their slope efficiency. As the window pumping current increases, the threshold current of the laser with SPW decreases when the SPW approaches transparency. The facet temperature rise (ΔT) of the lasers were measured by the thermoreflectance method. The ΔT measured at waveguide regions of lasers was shown to be reduced by 42% implementing SPW region to conventional lasers. Therefore, SPW technique was shown to be a promising approach to increase the COMD level of the high-power laser diodes and it opens up a new avenue for reliable semiconductor laser operation at very high output power levels.

An optical system is designed to shape the rectangular beam which emitted by direct high power laser diode stack for laser material processing. Beam parameter product theory and inverted Kepler telescope system principle are applied to analyze and design the optical system, the fast and slow axis beams of LD stack are focused in same focal plane. Firstly, two LD stacks with different wavelength are collimated by micro-lens array respectively. Then they are combined by dichroic beam splitter. Because of the divergence angle in slow axis direction is still big, the inverted Kepler telescope system is applied to expand and collimate the slow axis beam. Finally, the fast and slow axis beams are focused simultaneously. The whole optical path is simulated by ZEMAX software in the non-sequence mode and the simulated focused spot size and optical power density is obtained after ray tracing. Based on the theoretical calculation and software simulation, we perform the experiment and obtain a focused spot whose size is 2.0mm×5.0mm with 300mm focal length and 5 kilowatts power. The optical power density can reach to dozens of thousands of watts level. We discuss the influence factors of the focused spot size, and analyze the merit and demerit of the optical system. We also point out the improving orientation in the future. The laser beam after shaping by this optical system can be directly applied to laser cladding because of its long focal length and high optical power density.

We demonstrate frequency modulation (FM) in an external cavity III-V/Silicon laser, comprising a Reflective Semiconductor Optical Amplifier (RSOA) and an SU8 polymer waveguide vertically coupled to a 2D Silicon Photonic Crystal (PhC) cavity. Laser FM was achieved by local heating of the PhC using a resistive element of Ni-Cr metal as a microheater to change the refractive index in the cavity hence changing the lasing frequency. Presented is a thermal study of the laser dynamics and observations of the shift in lasing frequency.