This PDF file contains the front matter associated with SPIE Proceedings Volume 12440, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

This paper investigates the role of the insertion of trapping layers, above and below the active region, in improving the reliability of 1.31 μm InAs quantum-dot laser diodes epitaxially grown on silicon substrate. The study is based on an extensive set of characterization and accelerated aging experiments carried out on two groups of quantum-dot lasers, featuring the same geometry and epitaxial structure, but differing in the presence or absence of defect trapping layers. The results of our work demonstrate that devices with trapping layers exhibit i) higher optical performance in terms of L-I characteristics, ii) longer lifetime, when aged at similar temperatures and identical current densities, and iii) similar degradation modes with respect to the devices without trapping layers. This latter point highlights the role of epitaxial structure optimization in the improvement of the lifetime of the IR optical sources for next-generation silicon photonics. The selective reduction in concentration of specific defects, misfit dislocations rather than threading dislocations in this case, can effectively improve the reliability of the devices.

We present a novel hybrid 800 nm laser with a wide tuning range, high optical power and ultra-narrow linewidth with ⪆kHz tuning speeds and a small footprint. Tunable, narrow linewidth hybrid lasers around 800nm serve as an attractive choice for e.g. OCT, LIDAR and atomic transition locking in e.g. atomic clocks. The laser has a microring resonator based optical cavity. The laser has a tuning range of 45 nm and a maximum output power of 5 dBm. The intrinsic linewidth of the laser is measured at 22 kHz.

Time and Frequency applications, such as time synchronization of complex networks, are in need of high accuracy and stability clocks. Optically pumped Cesium tube atomic clocks satisfy these demands. However, Size, Weight and Power (SWaP) are very important parameters considering easier implementation of atomic clocks in systems. The innovative principal of Coherent Population Trapping (CPT) clocks can meet these challenges. They require a 894nm (Cs D1 line) DFB laser modulated at half the clock frequency (4.6GHz). The modulation generates the side bands separated by 9.2GHz. The laser should also keep a linewidth below 1MHz. We grow the layers of our laser structure two steps Metal Organic Vapor Phase Epitaxy, with an Aluminum free active region. It includes a single GaInAsP compressively strained Quantum Well (QW) and a GaInP waveguide, on GaAs substrates. The use of Al free materials allows for the realization of a buried Bragg grating which induces a very stable single frequency operation as a function of current and temperature. We have investigated our actual 2mm long laser in light current characteristics, optical spectra, linewidth and direct modulation, showing high stability at different temperatures. The Cs D1 line is achieved near room temperature with a very high SMSR (50dB) and a low linewidth (<1MHz). The actual -3dB bandwidth is 2.3GHz at 80mA (48mW) at 25°C. We have designed a new laser structure allowing 10 GHz bandwidth, without reducing the cavity length.

Shifted Excitation Raman Difference Spectroscopy (SERDS) is a powerful technique to separate disturbing background signals such as fluorescence and ambient light from Raman signals. Depending on the sample under investigation the requirements for SERDS excitation light sources can vary. In addition to narrow spectral dual-wavelength emission, the nature of the target might demand large inspection areas and herewith high output powers. Dual-wavelength Y-branch distributed Bragg reflector (DBR) diode lasers with output powers exceeding 100 mW have been proven to be suitable light sources for SERDS. Spectral stabilization is provided by deeply etched 10^th order DBR gratings, manufactured using e-beam lithography. One way to increase the inspection area is a dual-wavelength Y-branch DBR diode laser array for the excitation of multiple spots and herewith gaining more information about the sample under study. Here, we present a 5 mm wide, ten emitter dual-wavelength Y-branch DBR diode laser array. Electro-optical and spectral characteristics will be discussed with respect to the application SERDS. The individual emitters have a spectral emission width of less than 20 pm. At 1 W optical output power the spectral emission from the ten emitters has a full width at half maximum of 60 pm or less at both wavelengths. The narrow emission proves homogeneously manufactured DBR gratings, which are designed to provide dual-wavelength emission at 784.0 nm and 784.6 nm at 1 W optical output power. Lifetime of 5,000 h was exemplarily demonstrated. The influence of the emitters of the array on each other will be investigated and compared to the single chip Y-branch diode laser properties.

Raman spectroscopy of heterogenous samples requires measurements with larger spot size and herewith larger excitation power. The former leads to an increase of collected background light. Shifted excitation Raman difference spectroscopy, which requires two neighboring excitation wavelengths, is a powerful technique to spectrally separate Raman signals from the background. Master oscillator power amplifier systems using a Y-branch distributed Bragg reflector ridge waveguide diode laser as master oscillator and tapered laser as power amplifier can meet the spectral and power requirements. In this work, a comparison of 785 nm micro-integrated dual-wavelength master oscillator power amplifiers on 5 mm x 25 mm micro-optical benches is presented. To study the impact of potential back reflections from the amplifier into the master oscillator, Y-branch lasers with front facet reflectivity of 5% and 30% are investigated. The branches of the master oscillators are operated subsequently during characterization. At 25°C and 50 mW pump power, the master oscillator power amplifiers provide 2.7 W of near-diffraction limited dual-wavelength laser emission. Spectral widths < 20 pm and spectral distances of 0.6 nm (10 cm^-1) between both laser wavelengths are measured, suitable for shifted excitation Raman difference spectroscopy. A higher front facet reflectivity significantly reduces feedback related mode hopping. Additional longitudinal modes still measured in both cases are separated by 30 pm, corresponding to the free spectral range of the master oscillators. These modes remain within spectral windows < 0.15 nm (< 3 cm^-1) along the entire power ranges, sufficient to resolve Raman signals of most solid and liquid samples. As expected, the integration a compact 30 dB optical isolator eliminates the observed optical feedback effects.

We present a novel Dual DFB laser for high-speed direct modulation. The design comprises two identical quarter wavelengths shifted DFBs in mirrored configuration separated by a passive waveguide. This structure utilizes the effect of photon-photon resonance to increase the modulation bandwidth of 57.6 GHz. Operation of these devices under large signal modulation at 56 Gbps and 72 Gbps is demonstrated.

The aging behavior of Quantum Wells (QW) in UVB-emitting devices is analyzed. In addition to the standard lifetime tests, we measured the non-equilibrium carrier lifetime in the QW by time-resolved photoluminescence (PL) and performed spatially resolved PL measurements. In this way, we distinguish the different contributions that lead to a decrease in the emission power of the device. We show that the aging-induced increase of spatial inhomogeneities of the PL also affects the transient PL behavior.

Buried heterostructure quantum cascade lasers (BH-QCLs) operating at high temperature in mid-infrared (MIR) to THz spectral range are desired for chemical sensing and free-space optical communication (FOC). In this work, Fe doped semi-insulating InP (SI-InP) regrowth is demonstrated in a hydride vapor phase epitaxy (HVPE) reactor for advanced MIR and THz BH-QCLs grown by MBE and MOCVD. SI-InP regrowth is implemented in THz QCL pillar arrays and narrow width and reverse-taper MIR BH-QCLs for efficient heat dissipation. By exploiting SI-InP regrowth, the parasitic capacitance in MIR distributed feedback BH-QCL can be suppressed, which is exploited for high speed FOC application.

Type-II Quantum Well (QW) Interband Cascade Lasers (ICLs) have become the most efficient laser source in the mid-infrared spectral range spanning 3 μm to 6 μm. In order to use ICLs for gas sensing applications, they must be fabricated for single-mode emission. Distributed feedback (DFB) ICLs are commercially available single-mode lasers and offer low threshold currents for these types of applications but this technology is expensive and time consuming to fabricate since they require e-beam lithography. Slotted waveguides are explored in this work as an inexpensive alternative to electron beam (e-beam) lithography since standard UV photolithography can be used to fabricate the larger, reflective defects (slots) in the waveguide. The geometry of the slot pattern must be simulated beforehand in order to design a photolithography mask for the ICL growth so limitations and behavior of key design parameters will be presented. For 8 μm narrow ridge slotted ICLs emitting near 3.5 μm around 20 °C, single-mode emission was achieved with threshold currents in the range of 60 mA to 80 mA and output power of 2+ mW/facet. Single-mode emission was only reached for certain temperatures and injected current values, but for all operating conditions the number of longitudinal cavity modes supported was suppressed with respect to a Fabry-Pérot ICL; thus, validating the success of the first Sb based slotted laser.

We report the first implementation of an advanced waveguide structure, consisting of GaSb Separate Confinement Layers (SCLs), n-doped InAs/AlSb superlattice (SL) intermediate cladding layers, and n⁺ -doped InAs_0.91Sb_0.09 plasmon enhanced cladding layers for GaSb-based interband cascade lasers (ICLs) with lasing wavelengths at 3.3 and 3.4 µm. This advanced waveguide structure is intended to improve the optical confinement and the overall thermal conductivity of these ICLs. A room temperature (RT) threshold current density (J_th) as low as 176.9 A/cm² for a Broad Area (BA) device emitting at 3.28 µm was measured with the pulsed operation extending up to 390 K. A second ICL emitting at 3.42 µm exhibited a RT pulsed J_th of 195.6 A/cm² . The ICLs tested here had characteristic temperatures (To) of nearly 60 K, which is the highest among RT ICLs with similar lasing wavelengths, suggesting advantages of the advanced waveguide in these devices.

The low cross-plane thermal conductivity of Quantum Cascade Lasers (QCLs) is a significant limitation in their Continuous-Wave (CW) performance. Structural parameters such as individual layer thicknesses and interface density vary for QCLs with different target emission wavelengths, and these design parameters are expected to influence the cross-plane thermal conductivity. Though previous works have used theoretical models and experimental data to quantify thermal conductivity, the correlation between target wavelength and thermal conductivity has yet to be reported for QCLs. In this work, we observe a general trend across a group of QCLs emitting from 3.7 to 8.7 𝜇m: as the QCL design changes to reduce wavelength, the thermal conductivity decreases as well. Numerically, we measured an approximate 70% reduction in thermal conductivity, from 1.5 W/(m·K) for the 8.7 m device, to 0.9 W/(m·K) for the 3.7 𝜇m device. Analysis of these structures with the Diffuse Mismatch Model (DMM) for Thermal Boundary Resistance (TBR) shows that the largest contribution of this effect is the impact of superlattice interface density on the thermal conductivity. The observed changes in conductivity result in significant changes in projected CW optical power and should be considered in laser design.

Probabilistic Markov Chains modelling to define the relationship between microscopic scattering and macroscopic device level losses of photonic crystal surface emitting lasers (PCSEL) is reported. Here, we assume a priori knowledge of the microscopic scattering via simulation or measurement. The commissioning of the simulator, and convergence criteria are discussed.

We have demonstrated a single-mode lasing with a narrow single-lobe beam emission from InP-based double-lattice photonic-crystal surface-emitting lasers (PCSELs) in a wide temperature range from 25°C to 80°C under CW condition. A high output power of 240 mW is achieved at a temperature of 25°C. The lasing occurs even at a high temperature of 80°C, and the output power is 48 mW. The single-mode lasing and the narrow single-lobe beam with divergence angle below 1.5°, which is a unique feature of PCSELs, are maintained even at a high temperature of 80°C.

We report epitaxially regrown Photonic Crystal Surface-Emitting Lasers (PCSELs) utilizing self-assembled InAs quantum dots (QDs) exhibiting lasing at room temperature. The ability to utilize both the ground-state (GS) and excited-state (ES) of the QDs allows multiple emission wavelengths from one heterostructure. The choice of the grating periods of the photonic crystal allows lasing from neighbouring devices at the GS (~1230 nm) or ES (~1140 nm) of the QDs, 90 nm apart in wavelength. The threshold current densities are 0.69 kA/cm² and 1.05 kA/cm² for GS and ES respectively. The effect of PC structures, specifically etch depth of the PC on lasing performance is also discussed.

Laser sources, since their invention, have proved to be the right solution in practically all conceived applications. Recently, the so-called second quantum revolution and quantum technologies like sensing, computing, simulation or communication are triggering a new generation of sub-classical sources to tackle such novel and challenging applications. First concepts and experimental results aimed to endow quantum cascade lasers and other infrared sources with truly quantum properties will be shown.

Mid-Wave Infrared (MIR) free-space optical communication offers multiple advantages, such as improved transmission capacity through the atmosphere and immunity to electromagnetic interference. In addition, MIR transmission between 8-12 microns provides stealth for the communication signal thanks to the random thermal blackbody radiation having a strong background at these wavelengths, hence greatly reducing the probability of adversaries intercepting a MIR laser signal. Quantum Cascade Lasers (QCL) are optical sources of choice to target this wavelength domain. They are unipolar semiconductor lasers from which stimulated emission is obtained via electronic transitions between discrete energy states inside the conduction band. This work reports on a full unipolar quantum optoelectronics communication system based on a 9-micron QCL and on a Stark-effect modulator. Two different receivers are considered for high-speed detection, namely an uncooled Quantum Cascade Detector (QCD) and a nitrogen-cooled Quantum Well Infrared Photodetector (QWIP). We evaluate the maximum data rate of our link in a back-to-back (B2B) configuration before adding a multi-pass Herriott cell so as to increase the transmission length of the light path up to 31 meters. By using pulse shaping, pre- and post-processing, we reach a record bitrate both two-level (OOK) and four-level (PAM-4) modulation scheme for a 31-meter propagation link and a Bit Error Rate (BER) compatible with standard error-correction codes. Overall, we believe that our unipolar quantum system is of paramount importance for the development of cost-effective, reliable and versatile free-space optics data links.

Diode lasers providing nanosecond high power optical pulses are key components for light detection and ranging (LiDAR) systems used for, e.g., distance measurements. For autonomous vehicles, good beam quality is an important aspect to achieve the required high spatial resolution. While 30 μm broad area devices can achieve pulse powers >20 W emitting at 905 nm, the beam quality factor M2 is about ten and further degrades with increasing stripe width. Tapered-Ridge-Waveguide (TRW) lasers with 23 μm wide output apertures reduced the M² to about 2.2 without power loss. However, deployment of such lasers also requires a low temperature-dependent wavelength shift allowing for narrowband spectral filters. Here, we present TRW Distributed Bragg Reflector (DBR) lasers with a 23 μm wide output aperture. For emission around 905 nm the active region comprises an InGaAs single quantum well embedded in an AlGaAs waveguide. A surface Bragg grating is implemented into an unpumped section of the device enabling a wavelength shift of only 0.07 nm/K. The electrical interface realized by a nanosecond pulse driver developed in-house delivers pulse currents up to some 10 A within 2 ns to 5 ns pulses at 10 kHz. We investigate different designs of the trenches etched to define the ridge-waveguide. Beam quality factors of about three are achieved at pulse powers of about 10 W. Experimental results on the optical power, the near and far field profiles, and spectral characteristics are presented. Integration into an electrical driver module allows for reliability tests on an application relevant testbed.

In the area of smart mobility, a major challenge is to insure secure transportation. LIDAR are acknowledged as key enablers for Advanced Driver Assistance Systems (ADAS) and autonomous driving. Our approach for the Time of Flight (ToF) LIDAR is to use an Optical Phase Array (OPA), for the optical beam steering, together with a high peak power and high beam quality laser diode emitting at 905nm. To the best of our knowledge, a high-power laser diode at 905nm directly compatible with an OPA does not exist. We report on the design, realization and characterization of laser diode, with different geometries, emitting several watts (>10W) in a short pulse (typically 10ns) operation, in order to be coupled into the silicon nitride waveguide input of the OPA developed by the CEA LETI. The high power 905nm LASER coupled into the OPA, and their respective drivers, will constitute the optical steerable source, without no moveable parts, of the medium range TOF LIDAR developed within the European VIZTA project. The Aluminum free active region laser structure have been grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on 3” GaAs substrates. It contains a single GaInAsP compressively strained Quantum Well (QW) for emission at 905nm, located in a GaInP waveguide. This structure exhibits high internal quantum efficiency η_qi of 0.99, low internal losses α_i of 1.3cm^-1 and low transparency current density J₀ of 59A/cm². Peak optical powers of 11.4W at 15.4A and 7.7W at 10.2A are obtained, respectively, for two different geometries.

Blue diode and diode arrays became recently available commercially and offer a promise for high-power, excellent beam quality, compact and efficient light source for wide variety of applications including phototherapy, sanitization, underwater sensing and communication devices, and directed energy. Due to relatively recent availability on commercial market, these type of diodes and arrays have not yet been extensively studied, for example compared to their near-infrared counterparts. We experimentally investigated two external-cavity schemes involving single broad-area blue lasers and arrays of blue lasers. The feedback provided by a surface grating in Littrow configuration allowed demonstrations of spectral linewidth narrowing, wavelength tuning and paves the way towards locking of multiple diodes in a common external cavity for high-power applications.

Remote sensing techniques are critical in atmospheric research, such as the monitoring of the low tropospheric temperature and the water vapor distribution. Lidar is one type of remote sensing technique that can deliver an atmospheric measurement with high spatial and temporal resolutions¹. In this paper, we describe a diode-laser-based laser source at 828 nm in a master oscillator power amplifier (MOPA) architecture designed to be compatible with a water-vapor differential absorption lidar (DIAL). Two tapered amplifiers with a pulse duration of 1 μs and a repetition rate of 10 kHz are injected by a single-frequency DBR seed laser diode and coherently combined. The performance of the seed DBR laser diode and the tapered amplifiers are characterized. The phase dynamics during the pulse are analyzed, and we demonstrate that they do not significantly reduce the combining efficiency. The combined power is stabilized by a hill-climbing algorithm which actively corrects the low-frequency environmental noise. The average combined pulse energy is highly stable with relative fluctuations σ_on = 0.4%. The combined pulse energy reaches 10.3 μJ at the maximal operation current of 8.1 A with a combining efficiency above 82% ± 5%. This work demonstrates the coherent beam combination of micropulse tapered amplifiers and the interests of these techniques in lidar applications.

In recent years, red Laser Diodes (LDs), especially, longer wavelengths of “deep red” have been used in the biomedical and quantum technology fields. In light-based cancer therapies such as Photodynamic Therapy (PDT) and near-infrared photoimmunotherapy (NIR-PIT), and in skin care, high power red LDs are required. We have demonstrated highly reliable 1.2 W multi-mode LDs with the wavelength of 630, 635, 652, 659, 665, 675, 683, and 690 nm. Life test results showed stable operation in 2,700 hours at 20°C, 1.2 W for 630 nm LD, and in 10,000 hours at 75°C, 1.2 W for 675 and 690 nm LDs. These multi-mode LDs are suitable for fiber coupling because of their small emitter size of 80μm, and high power and high reliability make them ideal light sources for biomedical applications. In addition, deep red high power single-mode LDs are desired for optical lattice clocks and laser cooling. We have demonstrated AlGaInP-based 200 mW single-mode LDs with the wavelength of 690, 700, and 705 nm. Life test results showed stable operation in 4,000 hours at 75°C, 200 mW for all three wavelengths. Of all AlGaInP-based material, the 705 nm LD which demonstrated reliable operation is the world’s longest wavelength LD to the best of our knowledge. These single-mode LDs wavelength can be adjusted for the specific value by controlling temperature, which makes them ideal light sources for quantum technology. We believe that these new light sources will contribute to solving social challenges and explore the future.

DBR tapered lasers reach output powers of more than 10 W, narrow spectral linewidth, and nearly diffraction limited beam quality. Partly independent, the ridge waveguide (RW) current controls the fundamental mode and tapered current the output power. Concerning spectral stability and tuning, Master Oscillator Power Amplifiers (MOPAs) promise higher independent control. Recently, devices with 9.5 W output power, narrow spectral emission, and a beam quality factor of 1.5 were presented. In this contribution, the reliability of 1064 nm 6 mm long DBR tapered lasers and monolithic MOPAs will be investigated. 7th order DBR-gratings were implemented together with a 3.5 mm long tapered sections with full taper angles of 6°. The tapered lasers consist of 1.0 mm DBR-grating, 1.5 mm RW-section, and tapered section. The MOPA devices consist of 1.0 mm DBR-grating, 0.75 mm RW-section, 0.25 mm DBR grating, 0.5 mm RW preamplifier and tapered section. 3 different MOPA layouts including a straight design, 4° tilted master oscillator and 4° tilted power amplifier (PA) were tested. The reliability of two devices from each layout was investigated. At 5 W, the DBR tapered lasers reach a Mean Time To Failure (MTTF) of 2,800 h, whereas the MOPA devices with tilted PA show a MTTF of 13,000 h. For such devices tests at 7 W demonstrate reliable operation over 5,000 h. Intermediate measurements of spectral and beam parameters show, that before the occurrence of a failure, the spectral width remains smaller than 20 pm and the beam quality factor smaller than five.

In this work, Ridge Waveguide Amplifiers (RWA) with a gain wavelength around 1122nm and different device geometries are analyzed in detail using electro-optical measurements. The measurement results are compared with simulations based on a beam propagation approach to evaluate them and gain a better understanding of the device behavior. Optimized operating conditions are derived with respect to the electro-optical and amplification efficiency of the amplifier. The potential of RWAs with a combination of diffraction-limited beam quality and high output power is demonstrated in miniaturized laser modules supplied with polarization-maintaining optical fibers for input and output and optional nonlinear crystals. More than 200mW of yellow-green laser light with a wavelength of 561nm is provided through the fiber, enabling applications in the bio-medical field.

4.6um QCL arrays with different emitter number are fabricated and their device results are reported; an 8-emitter laser array, epi-down mounted on copper heat sink, outputs ~12 watts peak optical power @ 20us pulse width 4% Duty Cycle, and ~8 Watts with 100us pulse width 20% duty cycle, at 9.6A current, room temperature. A similar laser array with 7 emitters was measured to have a Visibility (V) greater than 0.9 in an external cavity. A 3D thermal model has been established to simulate QCL arrays, including all the epi-layers and packaging elements; suggestions to improve the performances further are proposed.

The beam quality of ridge-waveguide quantum cascade laser arrays with broad-area emitters and Multi-Mode Interference (MMI) couplers is investigated both experimentally and numerically. Previous demonstrations of MMI QCL arrays had narrow ridge waveguides to ensure fundamental mode operation and phase locking between elements of the array. In the interest of scaling optical power with lateral waveguide dimensions, we demonstrate broad area tree-arrays with MMI couplers at a wavelength of 4.65μm and ridge widths between 13 μm and 17μm. The emitted beams from the stem’s side are characterized with M2 measurements. We show that the MMI coupled arrays generally have significantly improved beam quality compared to Fabry Perot resonators with the same dimensions. Optimized tree-array devices will be the cornerstone of the next generation high power infrared systems.

InAs-based quantum cascade lasers (QCL) demonstrated high performance in the long-wavelength mid-infrared range. Hard baked photoresist usually employed for electrical insulation in these devices exhibits some drawbacks related to the polymer nature of this material. Wire bonding is difficult because of the mechanical softness of the photoresist. Besides, optical properties of such insulator can be altered when the laser is operated at elevated temperature. Conventional dielectrics with potentially suitable characteristics introduce optical loss and/or current leakage when fabricated using standard deposition techniques. We report manufacturing of InAs-based QCLs using spin-on-glass that ensured high performance of the devices.

We present a study of the generation of subterahertz pulses in multi-section quantum dot (QD) ring lasers based on an improved version of the well-established delayed differential equation model, and taking into account an arbitrary number of gain and absorber sections. Results of the analysis of an 8-section ring laser emitting at 1.3 μm are presented. The proposed approach provides a significant insight for the understanding of the onset of the harmonic mode-locking in this family of devices and shows to be an effective tool for the optimization of the real devices in terms of pulses quality and generated RF intensity.