Interband Cascade Lasers (ICLs) subject to optical feedback can produce periodic oscillations. In this work, we investigate experimentally the influences of current modulation on nonlinear dynamics of an optical feedback ICL operating at period-one (P1) oscillation. By varying the power and frequency of current modulation, we can examine the variations in the time series, power spectrum, and phase portrait of the laser output resulting from the introduction of current modulation. The results show that, the P1 fundamental frequency of the optical feedback ICL exhibits a frequency drift after introducing a current modulation with a relatively low modulation power. When the modulation power is set at a relatively high level, the optical feedback laser may behave the locking phenomenon, period-three (P3) state or period-two (P2) state under a modulation frequency close to theP1 fundamental frequency of the optical feedback ICL.
Reservoir computing (RC) is a computational framework for information processing based on neural network. It can be implemented with different physical platforms, principally, electronic architectures and photonic architectures. Photonic RC shows potential path to ultra-fast and efficient processing beyond the traditional Turing-von Neumann computer architecture. Typical photonics RC consider specifically a semiconductor laser (SL) with delayed feedback as reservoir substrate. Basically, the SL is a kind of type B laser, needing enough long delay feedback for the high dimensional chaos generation and for the RC mapping. But on the other hand, long delay feedback leads to the setup big size, being nonconductive of integration implement and stable operation performance in real world. To solve the problem of a huge size, we propose a new photonics RC scheme that using chaotic SL hybrid with Si3N4 micro-resonator, which works as the storage layer and feedback loop. The Si3N4 micro-resonator could help SL producing high-dimensional chaos and reaching high-complexity RC. Meanwhile, the size of Si3N4 micro-resonator is highly compressed at the level of ten micrometers, thereby realizing a size compression of over ten times than that of typical photonics RC setup. In our experiment, we make the free spectrum range (FSR) of micro-resonator is 35GHz, reaching the nonlinear frequency of SL. Then, with careful operation, two-mode mixing chaos can be realized, being very conductive for the photonics RC applications. These results are conducive for the development of on-chip photonic RC.
Convolutional neural network (CNN) has attracted widespread attention in image feature extraction and speech recognition owing to greatly reducing the complexity of model parameters and the number of weights, but it cannot be separated from the support of hardware accelerator. The limitations of electronic devices in terms of power, speed, and size make it difficult for current electron accelerators to meet the computational power requirements of future large-scale convolution operations. Here, we proposed a photonic vector architecture. This structure combines time, space and wavelength, and the non-volatile phase change material and the integrated microcomb form an optical matrix multiplier to realize memory calculation, thus reducing the energy consumption of reading weight data. The tooth spacing of the integrated microcomb is more than 100 GHz, and the microcomb coverage is from 1510 nm to 1610 nm. Finally, we replace the weight values in the CNN with the optimal weight values that the optics can achieve. The final recognition accuracy reached 97.04%, which is comparable to the efficiency of the first electronic equipment. Our results could be helpful for the development of non-volatile and ultra-fast optical neural network (ONN) with feathers of low energy consumption and high integration.
We proposed an integrated semiconductor laser scheme that combines an ultra-high Q silicon nitride microresonator with a DBR semiconductor laser, resulting in a tunable ultra-narrow linewidth laser. The experiment achieves tuning within the wavelength range of 1554.2-1557.15nm (about 370GHz), being almost ten times larger than that of reported DFB scheme. Moreover, the sidemode suppression ratio is low to 52dB with a ultra-narrow linewidth about 6.6kHz. It needs the joint adjustment of DBR operating current, coupling of the high-Q silicon nitride external cavity. These results can be applied in fields such as dense wavelength division multiplexing systems and integration LiDAR System.
We propose a scheme to generate wavelength-tunable broadband Optical Frequency Combs (OFCs) based on an optical injection gain-switched Weak-Resonant-Cavity Fabry-Perot Laser Diode (WRC-FPLD). Firstly, a sinusoidal signal with frequency of 1.6 GHz and power of 19 dBm is utilized to drive the WRC-FPLD into the gain-switched state. Then, external optical injection is introduced into the gain-switched WRC-FPLD for generating wavelength-tunable broadband OFCs. The experimental results demonstrate that, when the wavelength of injected light is in the middle of the two modes, the OFCs with larger bandwidth can be obtained. When the wavelength and power of the injection light are 1545.6522 nm and 3.397 μW, respectively, the maximum bandwidth of generated OFC can arrive at 76.8 GHz (49 comb lines), and the single sideband phase noise for the fundamental frequency of the beat signal is as low as -125.5 dBc/Hz@10 kHz. The coherence of comb lines increases with the decrease of modulation frequency. Through varying the wavelength of injection light and selecting the matched injection power, the central wavelength of OFC can be adjusted within the range of (1525 nm, 1565 nm).
We propose and experimentally demonstrate a wideband multi-channel chaotic source using a Weak Resonator Cavity Fabry-Perot Laser Diode (WRC-FPLD) with Self-Phase Modulated Optical Feedback (SPMOF), in which, phase modulation is introduced into the external optical feedback loop to improve the bandwidth of the generated multi-channel chaotic signals. The experimental results show that under appropriate optical feedback intensity, WRC-FPLD with SPMOF can generate wideband multi-channel chaotic signals, when the feedback intensity is in the range of -45 dB to -15 dB, the lasing modes in the range of 1530 nm to 1570 nm can be simultaneously driven into chaos state. In addition, the Time Delay Signature (TDS) characteristics of the generated multi-channel chaotic signals are also investigated. To highlight the advantages of the proposed scheme, we also conducted comparative experiments on the conventional optical feedback scheme without phase modulation. Using SPMOF scheme, the obtained bandwidth of multi-channel chaotic signals is improved obviously, the standard bandwidth reaches 11.5 GHz, the TDS of chaotic signal is suppressed to an indistinguishable level. Relative to traditional Fabry-Perot laser diode, WRC-FPLD used in the experiment has a smaller front reflectance, about 1/90 of the rear reflectance, and a longer cavity, so it can excite more lasing modes. The proposed scheme can generate wideband multi-channel chaotic signals with a small mode spacing, which is an ideal light source for the chaotic optical communication system using wavelength division multiplexing technology.
We propose and demonstrate a scheme for improving ranging performance of Frequency-Modulated Continuous-Wave (FMCW) radar, in which the transmitting signal is generated by a Semiconductor Laser (SL) under intensity-modulated optical injection. Previous investigations have demonstrated that, through introducing optical injection, SLs can be driven into period-one (P1) oscillation under suitable injection parameters, and the oscillation frequency depends on the injection strength. As a result, through modulating the intensity of injection light, FMCW can be obtained. In this work, we adopt a triangular Frequency-Modulated (FM) signal with a frequency of 11.579 MHz (period of 86.362 ns) to modulate the injection strength, an original FWCM signal with bandwidth of 2.59 GHz (from 13.59 GHz to 16.18 GHz) is generated. Taking such a signal as the transmitting signal of radar, the relative error is within the range of (17.74 % to 26.36 %) for ranging the targets within 2.600 m. The large relative error is due to poor repeatability of the transmitting signal, which can be characterized by the frequency comb contrast of FMCW signal. In order to generate the promoted FMCW signal with higher repeatability, optical feedback with delayed time of 86.362 ns is further introduced into the SL under intensity-modulated optical injection. Under optimized feedback strength, the comb contrast of promoted FMCW signal can arrive at 32.35 dB. Taking the promoted FMCW signal as the transmitting signal of radar, the relative error for ranging the targets within 2.600 m is decreased into the range of (0.42 % to 4.61 %).
KEYWORDS: Field programmable gate arrays, Heterodyning, Laser frequency, Digital filtering, Simulink, Process modeling, Feedback control, Tunable filters, Signal generators, Signal filtering
Heterodyne Optical Phase-Locked Loop (HOPLL) is an important technology for laser frequency stabilization. In this work, a digital HOPLL system for realizing frequency offset locking of a Distributed Feedback Semiconductor Laser (DFB-SL) is designed and implemented. The system is composed of a Frequency Synthesizer (FS), a passive third-order loop filter and an adjustable gain module. The effectiveness of the system is tested by measuring the frequency offset locking of DFB-SL. The results show that the designed system provides a cost-effective, sensitive, and reliable way to lock the DFB-SL with suitable parameters, and the drift caused by environmental variations can be suppressed effectively.
In this work, a new scheme based on a Si3N4 microresonator for generating parallel pulsed chaos is proposed, and the performances of the parallel pulsed chaos and its application in imaging are experimentally investigated. Under optical injection with suitable injection parameters, the Si3N4 microresonator can output a continuous wave (CW) chaotic microcomb including nearly 100 comb lines. After passing through an acousto-optic modulator, the CW chaotic microcomb can be transferred into pulsed chaotic microcomb, in which each comb line provides a pulsed chaos. Therefore, parallel pulsed chaos signal can be generated. Taken the parallel pulsed chaos signal as the emitting resource of lidar, the quality of imaging has been analyzed. The experimental results show that clear target imaging can be achieved.
Due to many advantages of compact structure, high efficiency, good beam quality, etc., diode-pumped all-solid-state passively Q-switched lasers have a bright future in military, industrial processing, medicine, and other fields. At present, the relevant reports on diode-pumped all-solid-state passively Q-switched lasers mainly focus on the characteristics of the period-1 dynamic state, while there are few reports on the characteristics of other nonlinear dynamic states. In this work, we experimentally investigated the dynamic characteristics of a diode-pumped all-solid-state passively Q-switched Nd:LaMgAl11O19 laser by using a semiconductor saturable absorber mirror. The experimental results show that, under different absorbed pump power and cavity loss, the laser can display various dynamic states such as period-1, period-2, period-4, period-5, period-7, and chaotic pulsing states. Through changing the cavity loss, the laser goes through period- 1, period-2, period-4 to chaos, or period-1, period-5, period-7 to chaos.
We propose and experimentally demonstrate a stable and tunable PT-symmetric single-longitudinal-mode (SLM) fiber ring laser using a nonreciprocal Sagnac loop. To suppress multiple-longitudinal-mode oscillation, the Sagnac loop only including a 3-dB optical coupler (OC) and a polarization controller (PC) is incorporated into the fiber ring cavity, which induces nonreciprocal light transmission and coupling between the frequency-degenerate clockwise (CW) and counterclockwise (CCW) resonator modes. The two light paths traveling along the CW and CCW directions in the Sagnac loop are defined as the gain loop and loss loop, respectively. By adjusting the polarization states of the two light waves, when the gain and loss coefficients are larger than the coupling coefficient, the PT symmetry is broken, singlemode lasing is thus generated in the fiber laser cavity.
In this work, a filter-free scheme of photonic generation of a high-quality 32-tupling millimeter-wave signal based on four dual-port MZMs (DP-MZMs) is proposed and simulated. In this scheme, four DP-MZMs are recombined into the two parallel DP-MZMs and the two cascaded DP-MZMs, respectively. After being modulated by a local oscillation signal, the light from the two parallel DP-MZMs is converted by a photodetector into an electrical signal, which is imposed on the electrodes of the two cascaded DP-MZMs. The simulation results show that the performances of the photonic microwave signal are affected by the modulation index, extinction ratio, and bias voltage of the DP-MZMs. Under the optimized operation parameters, a high-quality 32-tupling millimeter-wave signal with 46 dB radio frequency sideband suppression ratio (RFSSR) and 40 dB optical sideband suppression ratio (OSSR) is generated without using the filter. Because the two cascaded DP-MZMs are modulated by a small signal and there is no filter in the system, the high stability and high utilization rate of the sideband can also be realized in this scheme.
We experimentally investigated multi-channel chaos synchronization characteristics based on two asymmetrical mutually coupled Weak-Resonant-Cavity Fabry-Perot Laser Diodes (WRC-FPLDs). Experimental results show that, through adjusting the center wavelength of the Tunable Optical Filter (TOF) and the injection power, different modes can be selected and induced into chaotic state with wideband. Under proper asymmetrical injection power and frequency detuning, stable leader-laggard chaos synchronization with the maximal correlation coefficient about 0.90 between two asymmetrical mutually coupled WRC-FPLDs can be achieved. In addition, the effects of injection power and frequency detuning between the two lasers on chaos synchronization performance have also been discussed.
Based on a four-level rate equation model, we numerically simulated the nonlinear dynamics of a diode-pumped solidstate passively Q-switched laser. A Nd:YAG and a Cr4+:YAG is used as the gain medium and the saturable absorber in this system, respectively. Through setting the pumping rate or the round-trip optical loss at different values, the diodepumped solid-state passively Q-switched Nd:YAG/Cr4+:YAG laser may operate at the period-one, period-two, multiperiod or chaotic states. For a certain specific state, the time series, the power spectra and the Poincaré maps are represented. Moreover, the route for the diode-pumped solid-state passively Q-switched Nd:YAG/Cr4+:YAG laser entering into chaos is revealed by mapping the bifurcation.
KEYWORDS: Microsoft Foundation Class Library, Modulation, Signal to noise ratio, Semiconductor lasers, Microwave radiation, Laser optics, Frequency combs, Picosecond phenomena, Optoelectronics, Nonlinear dynamics
Based on a current modulated semiconductor laser (SL) subject to optical injection, tunable and broadband microwave frequency comb (MFC) generation is theoretically investigated. For a SL under only current modulation, a seed MFC with relatively narrow bandwidth can be generated. Then, an optical injection is introduced to improve the quality of seed MFC. Furthermore, the influences of operation parameters on the performance of MFC are also discussed. The numerical results show that after introducing optical injection with injection coefficient k = 1.8×10-4 and detuning frequency Δf = 6.0 GHz, the MFC bandwidth can be further increased by 15.6 GHz and the signal-to-noise ratio can be improved by more than 20 dB.
We proposed a reconfigurable all-optical logic gate (AND, OR) based on a vertical-cavity surface-emitting laser with saturated absorber (VCSEL-SA) subject to dual pulse injection and numerically investigated the effects of injection delay, injection strength and bias current on the system performance. The results show that, through adjusting bias current, the pulse injection strength and the injection delay between two pulses, the reconfigurable all-optical logic gate (AND, OR) can be realized. For a suitable injection intensity, all-optical logic AND and OR gates can be implemented within a certain bias current range. Moreover, both AND and OR gates have good robust to noise under suitable injection strength. These results are expected to open a new window for future ultra-fast neuromorphic computing systems to solve complex classification and decision-making tasks
Based on a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) with dispersive optical feedback provided by a linearly chirped fiber Bragg grating (LCFBG), we propose a scheme for simultaneously generating multi-channel chaotic signal with time delay signature (TDS) suppression. The experimental results show that under LCFBG feedback, 45 longitudinal modes within a 30-dB amplitude variation in the WRC-FPLD can be simultaneously driven into chaotic states. With the increase of feedback strength, the effective bandwidth of the generated chaotic signal gradually increases while the TDS value firstly decreases and then increases. For feedback strength from -35 dB to -15 dB, the generated chaotic signals by WRC-FPLD under LCFBG feedback possess lower TDS compared with those under mirror feedback or ring cavity feedback. Under an optimized feedback strength of -32.88 dB, the TDS value is about 0.01, which means the TDS is almost completely suppressed.
Based on a master-slave frame, we propose and numerically simulate a scheme for generating frequency-modulated continuous-wave (FMCW) signals with broad bandwidth. In such a master-slave system, a semiconductor laser under current modulation with single-tone electrical signal is taken as the master laser (ML), and its output optical signal with modulated power is injected into another semiconductor laser (taken as the slave laser, SL) for generating FMCW. The simulated results show that, under suitable operating condition, the bandwidth and the sweep rate of generated FMCW signal can reach 15.4 GHz and 4.83 GHz/ns, respectively. Through further introducing optoelectronic feedback into SL for suppressing the phase noise, the contrast of the frequency comb in the FMCW signal can be increased by 20.22 dB.
Optoelectronic reservoir computing (RC) is a supervised training algorithm implanted in an optoelectronic time-delay system, which possesses simple structure and can be utilized to realize pattern recognition. In this work, based on double reservoir layers composed of two Mach-Zehnder modulators (MZMs), a novel optoelectronic RC system is proposed and the system performances for processing handwritten numeral recognition (HNR) are analyzed. For such a system, a masked handwritten numeral information is injected into the first reservoir layer, the different value between two adjacent node states of the first reservoir layer is sent to the second reservoir layer, and the virtual node states of the second reservoir layer are extracted for training and testing. The simulated results show that, by optimizing the system parameters, a word error rate (WER) of 0.11 for processing HNR can be achieved. By comparing with an optoelectronic RC with a single reservoir layer, the optoelectronic RC with two reservoir layers possesses better performances for processing HNR.
In this paper, we propose and numerically demonstrate a security-enhanced high-speed chaotic communication system by introducing phase modulation and phase-to-intensity conversion. The driving laser (DL) with delayed optical feedback can be used to generate the chaotic driving signal, which is simultaneously injected into two response lasers (RLs) through a phase modulator (PM) and a dispersion component (De). The simulated results show that, due to the phase modulation and phase-tointensity conversion, TDS of injected chaos signal from DL can be effectively suppressed and its bandwidth can be increased to 39.6 GHz under suitable parameter conditions. Simultaneously injecting the chaos signal into two identical RLs, high-quality chaos signals with weakened TDS and enhanced bandwidth between two RLs can be achieved even under certain parameter mismatches, but the synchronization quality between DL and any one of RLs is extremely bad. Based on the system synchronization, secure transmission of 20 Gbit/s messages can be realized and the transmission distance can be over 200km.
We experimentally demonstrate a diode-pumped passively Q-switched Yb:Lu3Al5O12 ceramic laser operating at 1031 nm or 1047 nm based on a semiconductor saturable absorber mirror (SESAM) and an output coupler (OC) of different transmission (T). For an OC of T=7.5% and an absorbed power of 9.25 W, the laser operates at 1031 nm with a maximum average output power of 1.47 W, the corresponding optical-to-optical efficiency of 15.85%, and the slope efficiency of 19.04%, respectively. The pulse width and the pulse repetition frequency (PRF) are about 1.23 μs and 245.04 kHz, respectively. For an OC of T=1.6% and an absorbed power of 9.25 W, the laser operates at 1047 nm with a maximum average output power of 0.85 W, the corresponding optical-to-optical efficiency of 9.21%, and the slope efficiency of 8.43%, respectively. The pulse width and the PRF are 1.49 μs and 112.63 kHz, respectively.
Based on a slave vertical-cavity surface-emitting laser (S-VCSEL) simultaneously driven by dual chaotic optical injection (DCOI) from two master VCSELs (M-VCSELs) with double optical feedback (DOF), an unpredictability-enhanced broadband chaotic signal generation scheme is proposed and numerically investigated. The unpredictability degree (UD) and bandwidth of chaotic signals are evaluated by the peak value (σ) of self-correlation function (SF) at the feedback time and the effective bandwidth (EBW), respectively. The results show that, M-VCSEL with DOF can generate chaos signals with lower time delay signature (TDS) than that with single optical feedback (SOF). Under suitable injection strength and frequency detuning, both two orthogonal polarization components (X-PC and Y-PC) of the S-VCSEL can be driven to generate unpredictability-enhanced broadband chaotic signals with suppressed TDS (σ < 0.1) and wide EBW (EBW < 50GHz). Moreover, a relatively large parameter space to achieve this high-quality chaos signals can be determined.
In this work, we propose and experimentally demonstrate a scheme for generating fast physical random bits (PRBs). For such a scheme, the chaotic signal output from an optoelectronic delay loop (OEDL) pumped by a semiconductor laser (SL) under modulated optical feedback is utilized as the chaotic entropy resource, and the m least significant bits (m-LSBs) extraction and local XOR operation are selected as the post-processing methods. Firstly, through analyzing the influences of some typical parameters on the properties of the chaotic signal, the optimized parameter regions for achieving high quality chaotic signals with weak time-delay signatures and broad bandwidths are determined. Secondly, a high quality chaotic signal under optimized parameters is selected as a chaotic entropy resource, which is sampled and transferred to an original digital bit sequence by an 8-bit analog-to-digital converter (ADC) at a rate of 80 GS/s. Finally, through adopting the m least significant bits (m-LSBs) extraction and logical exclusive OR (XOR) operation to process the original digital bit sequence, a PRB at a rate up to 400 Gbits/s can be generated, which has passed all the NIST tests.
Photonic generation of frequency-modulated continuous wave (FMCW) based on period-one (P1) oscillation of an optically injected semiconductor laser (OISL) is numerically investigated. A modulated optical injection can drive an OISL into P1 oscillation for generating an FMCW signal, and an optical feedback is further introduced to reduce the phase noise of the generated signal. The influences of operation parameters on the performance of the generated FMCW signal are discussed. The numerical results show that under proper operating conditions, a photonic FMCW signal with a sweep range of 12.41 GHz can be obtained. After adopting optical feedback, the frequency comb contrast can be increased to a level more than 30 dB.
Based on vertical-cavity surface-emitting lasers (VCSELs) with optical injection and polarization-rotated optical feedback, we propose and numerically demonstrate a scheme for generating synchronized random bit sequences (SRBS) for two legal users at different locations. For the scheme, the chaotic signal generated by a driving VCSEL (D-VCSEL) subject to chaotic optical injection are utilized to simultaneously drive two VCSELs (A-VCSEL and B-VCSEL) with polarization-rotated feedback, then the chaotic outputs from A (B)-VCSEL are used as physical entropy sources to generate SRBS. The simulated results show that, the SRBS at a rate up to 400 Gbits/s can be achieved after adopting suitable post-processing method. The security of this scheme can be ensured by a high-quality synchronization between A-VCSEL and B-VCSEL while relatively low-quality synchronization between D-VCSEL and A (B)-VCSEL. Moreover, the BER and the randomness of generated SRBS are also discussed.
A scheme for generating frequency-modulated continuous-wave (FMCW) based on an optically injected semiconductor laser (SL) is proposed and demonstrated experimentally. A modulated light injection drives an SL into period-one (P1) state with modulated microwave frequency for generating FMCW, and then an optical feedback is introduced to further enhance the frequency comb contrast of the generated FMCW. Under proper operation conditions, a FMCW signal with a sweep range of 11.39 GHz (10.08 GHz-21.47 GHz) and a sweep rate of 0.72 GHz/ns is obtained, and the frequency comb contrast is increased by 20 dB after introducing the suitable optical feedback.
We propose a scheme for acquiring dual-channel physical random bits based on a vertical-cavity surface-emitting laser (VCSEL) under dual-path polarization-preserved chaotic optical injection (DP-PPOI). The injection chaotic light is generated by a master VCSEL (M-VCSEL), which is subjected to polarization-preserved optical feedback from a fiber Bragg grating (FBG). Under suitable operation parameters, the outputs of X polarization component (X-PC) and Y polarization component (Y-PC) in the M-VCSEL are chaotic signals with weak time-delay signatures (TDS), which are injected into another VCSEL (named as the slave VCSEL, S-VCSEL) via DP-PPOI. Through selecting the injection parameters, the X-PC and Y-PC in the S-VCSEL can simultaneously output chaotic signals with wide bandwidth and suppressed TDS, which are used as entropy sources for generating dual-channel random bits. The results demonstrate that the rates of generated dual-channel random bits can be up to 500 Gbits/s.
We theoretically investigate the propagation characteristics of inhibited spiking dynamics between two unidirectionally coupled VCSEL-based photonic neurons. The results show that, the inhibition of spiking regimes in a transmitter VCSEL (T-VCSEL), in response to the arrival of external perturbation, can be propagated to another receiver VCSEL (R-VCSEL) and two VCSEL-based photonic neurons have similar responses to the external perturbation. With increasing perturbation strength, the spikes with higher amplitude and lower oscillation frequency can be observed during the perturbation time. The spikes can be entirely suppressed for enough perturbation strength. Additionally, the spiking inhibition window can be controlled through adjusting perturbation duration.
Under suitable filtered optical feedback, a weak-resonant cavity Fabray-Perot laser diode (WRC-FPLD) is rendered into chaotic state, and the central wavelength of chaotic output can be tuned through varying the central wavelength of filter. The output chaotic signal with wavelength-tunability is unidirectionally injected into another WRC-FPLD and drives it into chaotic state, and then wavelength-tunability chaos synchronization can be realized. The experimental results demonstrate that, under suitable injection strength and frequency detuning, chaos synchronization between two unidirectionally coupled WRC-FPLDs with maximal correlation coefficient about 0.900 can be achieved under different wavelengths.
Based on a nonlinear fiber loop mirror (NOLM) composed of a fiber coupler (FC) and a highly nonlinear fiber (HNLF), a scheme is proposed to simultaneously realize the bandwidth enhancement and the time-delay signature (TDS) suppression of a chaotic signal generated from an external cavity optical feedback semiconductor laser. The simulation results show that, after passing through the NOLM, the bandwidth of chaotic signal can be efficiently enhanced and the TDS can be well suppressed under suitable operation parameters. Furthermore, the influences of the power-splitting ratio of the FC, the averaged power of the chaotic signal entering into the FC and the length of the HNLF on the chaotic bandwidth and TDS are analyzed, and the optimized parameters are determined.
High-quality photonic microwave generation is experimentally demonstrated based on the period-one (P1) dynamical state output from an optically injected 1550 nm vertical-cavity surface-emitting laser (1550 nm-VCSEL) subject to optoelectronic negative feedback. The experimental results show that, under suitable injection condition, the 1550 nm-VCSEL can generate a photonic microwave signal with single sideband optical spectrum structure, but the linewidth of the microwave signal is relatively wide (on the order of MHz). After further introducing optoelectronic negative feedback, the linewidth of the microwave signal can be narrowed two orders of magnitude to 105.7 kHz. Furthermore, for the case that the feedback strength is set at an optimized value, the frequency of the microwave signal can be tuned continuously within a certain range through simply adjusting the injection strength.
Nonlinear dynamics associated with polarization switching (PS) in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) with orthogonal optical injection is investigated theoretically by scanning the injected power. The results show that, adjusting injected powers may induce complex variation of dynamical state of each polarization mode and PS. When the PS happens, its dynamical states can be located at an injection locking state or not, which depends on the frequency detuning between the injected field and the VCSEL. Detailed mappings of polarization-resolved nonlinear dynamical states are calculated to unveil a rich variety of dynamical scenarios for different scanning routes of injected power in the parameter space of injected power and frequency detuning, and show that the dynamical states and PS are critically dependent on the scanning routes of the injected power under the case of larger current.
Time-delay (TD) signatures of chaotic output in 1550nm vertical-cavity surface-emitting lasers (VCSELs) with double
variable-polarization optical feedback (DVPOF) are investigated theoretically by using self-correlation function (SF).
The effects of delay feedback time, feedback strength, polarizer angle, and injection current on the TD signature are
discussed comprehensively. As a result, the optimal parameters setting for the TD signature suppression have been
specified.
A bidirectional chaos communication system, composed of 1550nm semiconductor lasers (SLs) and fiber links, is
experimentally and numerically investigated. Based on the robust chaos synchronization between two authorized SLs,
0.5Gbits/s pseudo-random data bidirectional message transmission between the two SLs has been preliminarily realized
experimentally. Moreover, related theoretical simulations are also given, which basically conforms to our experimental
observations.
In this paper, a new style state-bistability has been experimentally observed by back and forth sweeping the current of a
semiconductor laser nearby its threshold. Moreover, the influence of the injection power on the width of state-bistability
loop has been analyzed and discussed in detail.
We experimentally and numerically investigated the time delay (TD) signature suppression in a mutually delay-coupled
semiconductor lasers (MDC-SL) system. The results show that excellent TD signature suppression can be achieved and
all TD signatures are suppressed into background noise level. Meantime, two chaotic sequences are obtained
concurrently and the corresponding self-correlation curves exhibit almost perfect δ function profile.
We experimentally and numerically investigate the chaos synchronization characteristics of mutually coupled system
consisted of two semiconductor lasers (SLs) with asymmetrical bias currents. The results show that, for the case of the
two SLs with identical free running oscillation frequencies, the mutually coupled system can achieve excellent chaos
synchronization under relatively large asymmetrical bias currents. Frequency detuning Δ (Δ=1-2, where 1, 2 are the
free running frequencies of SL1 and SL2, respectively) has obvious influence on the synchronization performance. For
the case of the SL1 biased at a relatively much larger current compared with that of SL2, the synchronization
performance will be degraded with the increase of the positive frequency detuning (1>2), while the synchronization
performance can be further improved with suitable negative frequency detuning. The simulated results are basically
consistent with experimental results.
Based on the framework of the spin-flip model (SFM), for the GHz level modulation frequency, the polarization
performances of current-modulated vertical-cavity surface emitting lasers (VCSELs) subject to weak optical
feedback have been theoretically investigated. The results show that, for type I polarization switching (PS), under
small signal modulation, the variation of the modulation frequency does not affect the polarization direction of the
VCSEL output, but due to the influence of the optical feedback, the VCSEL output may behave period, doubling
period and chaos state with modulation frequency variation. For the case of the large signal modulation, optical
feedback can result in the generation of a new style of PS with the variation of the modulation frequency.
Based on the theory describing the optical feedback semiconductor lasers (SLs) under optical injection, the
effects of the feedback strength and delay time, injected strength and frequency detuning on the self-correlation
performance of the output chaotic signal are investigated. The results show that the full-width at half-maximum
(FWHM) and peak sidelobe level (PSL) of the output self-correlation function is critically dependent on
parameters related to injection and feedback. By reasonably selecting the parameters, the self-correlation
function with 0.02ns FWHM can be obtained, which is prior to reported results.
The dynamics of a semiconductor laser with delayed optoelectronic feedback are theoretically investigated when the
delay time is continuously varied. The results show that, for a fixed feedback time, the output dynamics state of the
semiconductor laser with delayed optoelectronic feedback is dependent on the continuous variation route of delay
feedback time; the bistability can be obtained for a given varying range of the delay feedback time. Further more, by
adding modulation signal, the characteristics of the bistability states become more complex, and some new types of
dynamic bistability states are observed.
Based on the coupled mode theory, the transfer matrix approach is presented to investigate the fiber grating external
cavity semiconductor lasers (FGECSL). As a result, the P-I curve, the lasing wavelength and the side-mode-suppression-ratio
(SMSR) have been investigated numerically in detail. With the length of the fiber grating increasing, the reflection
spectrum of FGECSL changes obviously, the threshold current and threshold carrier density decreases, the mode
distribution is irregular, and the output spectrum becomes complex. Moreover, the optical bistablility is also observed.
In this paper, the total output power features and the mode power characteristics of the extremely short external cavity
semiconductor lasers (ESECSLs) have been investigated experimentally and theoretically, and a new type of variation of
ESECSL's mode power is reported. The results show that with the variation of the external cavity length at the order of
lasing wavelength, the total output power and the mode power of ESECSLs will hop periodically, and the different mode
presents diverse power characteristics. Especially, some modes, locating at the material gain center of ESECSL, present
unique double peak characteristics. Moreover, the primarily theoretical simulations and the physics explanation about
these double peak characteristics have been given. The theoretical simulation results agree well with the experimental
results. These new type characteristics of ESECSL's mode power may be useful in improving the sensitivity of all-optical
sensors and developing the new type of optical data read-write head.
In this paper, the influences of the external light injection on the chaotic carrier fundamental frequency of
vertical-cavity surface-emitting lasers (VCSELs) with optical feedback have been investigated. The results show that, for
the fixed frequency detuning between the master laser diode and the slave VCSEL, the chaotic carrier fundamental
frequency can be increased generally with the increase of injected strength; the chaotic carrier fundamental frequency
can be improved significantly by adjusting frequency offset and injected strength. For the normalized injected parameter
K is 330 and frequency detuning is 42GHz, chaotic output with 47.3GHz fundamental frequency can be obtained.
Based on the theoretical model of the synchronization system with incoherent optical feedback, message encoding
and decoding of the chaotic system have been investigated. The results show that message can be hidden efficiently in
the chaotic signal during the transmission with three encryption schemes (i.e., chaos shift keying (CSK), chaos masking
(CMS) and additive chaos modulation (ACM)); the message of 250Mb/s can be decoded in the receiver with CSK and
CMS; when the bit rate increases to 2.5Gb/s, the message can not be decoded with CSK and the quality of message
decoded with CMS becomes bad; and when the bit rate increases to 12.5Gb/s, the message can not be decoded with CSK
and CMS, however the message can be decoded perfectly by adopting ACM.
In order to supply a theoretical guide for chaotic telecommunication, the influences of the chromatic dispersion and
nonlinearity in fiber on the chaotic synchronization have been investigated based on the theoretical models used to
describe the dynamics of semiconductor laser subjected to the external optical feedback and signal transmission in fiber
channel. The numerical simulation results show that, the fiber nonlinear effect is responsible for the phase varying of
chaotic signal and do not affect the amplitude of the chaotic signal; due to chromatic dispersion, the amplitude
characteristics of chaotic signal are distorted significantly and the system synchronization quality will be impaired; after
propagating 200km in dispersion shifted fiber, a desirable system chaotic synchronization with a synchronized
coefficient 0.99 can be achieved by adopting a amplifier before the received laser to compensate the fiber loss.
In this paper, after taking into account two situations that the polarization of the injection light is parallel or orthogonal
with the solitary vertical-cavity surface-emitting laser (VCSEL) output light, the nonlinear dynamic characteristics of an
optical injection VCSEL are investigated numerically. The simulated results show that VCSEL can exhibit periodic
oscillations, deterministic chaos and other complex instabilities under optical injection. For parallel or orthogonal optical
injection, the same injection coefficients have different effects on the output of VCSEL. By properly adjusting the
injection strength or detuning frequency, the dynamical state of the laser output can be controlled to a fixed state, and the
polarization of the VCSEL output light can also be controlled.
Based on the coupled mode theory by using the reversely recursive transmission matrix method, the switching
characteristics of the λ/4 phase-shifted fiber grating and the influence of introducing chirp on the switching
characteristics have been numerically studied when the reflection of the transmission facet is taken into consideration.
The results show: for coherent superposition reflection strengthening, it can reduce the threshold switching energy of the
λ/4 phase-shifted grating, but the switching contrast will decline; with the introduction of negative chirp in λ/4
phase-shifted grating, the switching contrast will be greatly improved, but the threshold switching energy will increase;
with the introduction of positive chirp in λ/4 phase-shifted grating, the switching threshold can be further reduced, but
the switching contrast will decline; and the hysteresis loop width will be influenced obviously by the introducing chirp.
All-optical wavelength conversion based on four-wave mixing (FWM) is one of the key techniques for building
dynamic optical networks. In this paper, the cavity enhancing effect of the residual F-P cavity mode on the
non-degenerated four-wave mixing (NDFWM) in a distributed-feedback semiconductor laser diode (DFB-LD) have
been investigated both experimentally and theoretically. The conversion efficiency of NDFWM is obtained at small or
large frequency detuning range. The results show that the NDFWM can be enhanced obviously when the probe
wavelength matches one of the F-P cavity modes, and the high conversion efficiency can be achieved even if the
frequency detuning between the injection probe frequency and free-running frequency of the DFB-LD is up to THz.
Based on the ray tracing method, the implicit expression of the output spectrum of the extremely short external cavity
semiconductor Laser (ESECSL) is derived, and the output spectrum and P-I characteristic of the ESECSL are
investigated. The results show that: when the length of external cavity is changed at the order of wavelength, the P-I
characteristics of the ESECSL will undergo significant changes; with the variation of the external cavity length, the
lasing wavelength of ESECSL will behave cyclical jump in the range of 10nm. Especially, for the external cavity length
changed within the range of 40μm-70μm, the jump range of the lasing wavelength will reach the maximum. The
simulations well agree with the experimental results reported.
Based on the theoretical model of the synchronization system with incoherent optical feedback, the influence of the
internal parameter mismatch on the synchronized characteristics of the chaotic system has been investigated. The result
shows that the chaotic system with incoherent optical feedback can be realized more easily than the complete
synchronized system, and has higher security than injection locking synchronization system. Using encoding of chaos
shift keying, the message can be hidden efficiently during the transmission in the system and decoded easily in receiver.
A hybrid actively and passively mode-locking semiconductor optical amplifier fiber ring laser based on nonlinear
polarization rotation was presented, where intensity modulator not only acted as modulator but also polarizer. Under the
hybrid mode-locking mechanism, output pulse is with some new characters. So, a theoretical model that describes the
SOA fiber ring laser was developed and system parameters effects on mode-locking pulse are discussed.
The dynamic single-mode and modulation performance of λ/4 phase-shifted distributed feedback laser
diode with chirped grating (QWS-CG-DFB) are analyzed theoretically. The numerical simulation
shows that, In contrast to purely QWS-DFB laser, the enhanced dynamic single-mode suppression ratio
(SMSR) can be reached by QWS-CG-DFB laser; Under the smaller biasing current, the modulation
band-width in presence of chirped grating is narrower, this difference shrinks for larger biasing current;
For large signal modulation, the chirped grating is helpful to increase the output extinction ratio, but
worsens the frequency chirping.
In this paper, based on self-reproduction theory, harmonic mode-locked (HML) and rational harmonic mode-locked (RHML) fiber ring lasers consisting of two semiconductor optical amplifiers (SOAs) was numerically researched, respectively. Harmonic mode locking makes a target of obtaining ultra-short pulse, but, in rational harmonic mode locking, it urgently needs to be solved that pulse amplitude becomes uneven with the increase of the order of rational harmonic, which results in the different work conditions of both. After obtaining the optimal work condition, the system parameters effects on the characteristic of HML pulse and the quality of pulse-amplitude equalization in rational harmonic mode locking have been investigated, respectively.
In this paper, a novel scheme for adiabatic pulse compression using silica-based functional fibers with enhanced nonlinearity is proposed and investigated in detail. The numerical results show that the pulse compression in this kind of fiber satisfies the adiabatic condition by selecting the reasonable systematic parameters. Although the higher order nonlinear effects, especially the Raman self-frequency-shift, are obvious due to the increased gradually nonlinearity, high quality compressed pulse can also be obtained except generating an extra-time-delay according to retarded frame.
In this paper, after considering the facet residual reflectivity of the semiconductor optical amplifier (SOA), a theoretical model of the SOA based harmonic mode-locked fiber ring laser has been established. Using this model, the influence of the facet residual reflectivity on the shape, peak power, and pulse width of the pulse output from the harmonic mode-locked fiber ring laser, has been investigated.
A novel scheme for all-optical frequency multiplication/recovery based on the semiconductor optical amplifier (SOA) ring cavity is proposed and investigated numerically. The results show, for a 2.5GHz driving pulse train, it can be generated 5-25GHz repetition rate pulse trains with low clock amplitude jitter (CAJ), polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence (PRBS) signal can be realized based on the proposed scheme.
After taking into account the multiple reflections of light in external cavity, the influence of the optical feedback on the large signal modulation characteristics of the external cavity semiconductor laser (ECSL) has been theoretically investigated. The numerical simulations show that, with the increase of the modulation index, the peak photon number of the ECSL tends to higer level on the whole. When the optical feedback is strong or weak, the peak photon number of the ECSL shows single period. However, the peak photon number exhibits bifurcation or chaos for different modulation index when the optical feedback is intermediate.
The carrier lifetime is usually treated as a constant (called as the constant carrier lifetime assumption (CCLA)) during modeling theoretically the chaotic behaviors of semiconductor lasers. In this paper, after considering the actually recombination mechanism of the carriers in the semiconductor and the variation of the carrier lifetime with the time, the chaotic characteristics of semiconductor laser with optical feedback have been investigated numerically, and the obvious differences can be observed compared with those obtained with the CCLA.
It is well known that the compressed pulse by the high-order soliton effect in dispersion-shifted fiber (DSF) accompanies by undesired pedestals. In this paper, a novel method by combining a nonlinear Fabry-Perot cavity (NLFPC) and EDFA is proposed for pedestal suppression, which is based on the optical bistability effect of the NLFPC. The numerical simulations demonstrate that obvious pedestal suppression can be realized by selecting reasonably the facet reflectivity of the NLFPC, and the detuning between the central frequency of the input pulse and the resonant frequency of the NLFPC.
After presenting an improved theoretical model that describes the dynamic process of optical pulse amplification by the semiconductor light amplifiers (SLAs), both the rising and falling time of amplified picosecond optical pulses by the SLAs have been investigated numerically. The results show that with the increase of the bias current of SLAs, the rising time will decrease and the falling time increase; the input pulse with a large peak power will accelerate the rising time shortening and the falling time lengthening; the gain compression has an obvious influence on the rising and falling time for several picosecond width input pulses; the gain asymmetry and shift violently affects the rising and falling time.
After taking into account the wavelength-depended reflectivity distribution profile of a fiber Bragg grating, the oscillation wavelength ?l of fiber Bragg grating semiconductor lasers has been investigated theoretically. The results show that the laser oscillation wavelength ?l is not fixed at the Bragg reflection wavelength ?B of fiber Bragg grating, and the offset between ?B and ?l depends on the reflectivity distribution profile of fiber Bragg grating and the gain profile of semiconductor gain medium.
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