Vertical-cavity Semiconductor Optical Amplifiers Research Articles

High efficient net gain and low noise figure based vertical cavity semiconductor optical amplifiers for wavelength division multiplexing applications

Abstract This paper has demonstrated the high efficient net gain and low noise figure based vertical cavity semiconductor light amplifiers for wavelength division multiplexing applications. Previous study on the chip reflective gain variations versus SOA current under temperature effects is clarified. We have transferred light semiconductor amplifiers for wavelength multiplexing schemes applications. Amplifier output power is demonstrated with bias current and amplifier active layer region length variations based input signal power of 3, 6.5, 10 dBm, 1550 nm wavelength and optimum amplifier confinement factor of 0.45. The amplifier output noise variations are clarified against the bias current and amplifier active layer region width variations based input signal power of 3, 6.5, 10 dBm, 1550 nm wavelength and optimum amplifier confinement factor of 0.45. The output OSNR variations are studied clearly and deeply against the bias current and amplifier active layer region length variations based input signal power of 3, 6.5, 10 dBm, 1550 nm wavelength and optimum amplifier confinement factor of 0.45. The signal loss is demonstrated versus both active layer width/length and temperature based optimum 30 % gallium core dopant ratio and 28 % arsenide cladding dopant ratio at optimum input signal power of 10 dBm, 1550 nm wavelength and optimum amplifier confinement factor of 0.45. SOA amplifier output power can be enhance with the management of both bias current and input signal power and the reduction of active amplifier length. The amplifier output noise can be enhance with the management of both bias current and input signal power and the reduction of active amplifier width. Output OSNR system can be improved with the management of both bias current and input signal power and the reduction of active amplifier length. The SOA amplifier gain can be improved with the management of both bias current and input signal power and the reduction of active amplifier length. The SOA amplifier noise figure can be improved with the management of both bias current and input signal power and the reduction of active amplifier width. The signal loss can be controlled and managed by adjusting optimum 30 % gallium core dopant ratio and 28 % arsenide cladding dopant ratio, optimum active layer/with and the presence of room temperature.

Plastic Photonic Synapse Based on VCSOA for Self-Learning in Photonic Spiking Neural Network

We propose and demonstrate a plastic photonic synapse to achieve all-optical synaptic plasticity based on the potentiated and depressed dynamics in commercially available vertical-cavity semiconductor optical amplifier (VCSOA). The effects of presynaptic and postsynaptic spike powers, bias current, initial wavelength detuning between presynaptic spike and VCSOA on the potentiated and depressed time windows are investigated. The numerical results show that all-optical synaptic plasticity can be achieved successfully based on VCSOA with delayed self-feedback loop. The proof-of-concept experimental results show that plastic photonic synapse can be achieved based on the VCSOA with subsequent iterations. Besides, the curve of VCSOA gain in the potentiated and depressed time windows is similar to that of spike timing dependent plasticity. Furthermore, all-optical unsupervised self-learning and recognition of first spike timing of an input pattern are realized numerically in the photonic neural network including two proposed plastic photonic synapses. The plastic photonic synapse based on a VCSOA is interesting and valuable for the self-learning in all-optical neural networks. Moreover, the proposed plastic photonic synapse offers great potential for dense, high-performance neuromorphic photonic systems.

Design, Modeling, and Characterization of Hot Electron Light Emission and Lasing in Semiconductor Heterostructure-VCSOA with Optical Gain up to 36 dB

Vertical-cavity semiconductor optical amplifiers (VCSOAs) are interesting devices for optical communication applications. In this work, we have studied the characteristics of gain spectra and amplifier bandwidth in reflection mode at 1300 nm GaInNAs/GaAs hot electron light emission and lasing in semiconductor heterostructure-VCSOA structure using MATLAB program. The device contains 16 Ga0.7In0.3N0.038As0.962 multiple quantum wells (QWs) in its intrinsic region; the active region is bounded between eight pairs of GaAs/AlAs top distributed Bragg reflectors (DBRs) mirror and 25 pairs of AlAs/GaAs bottom DBRs mirror. Simulation results suggest that the resonance cavity of QW of HILLISH-VCSOA is varied with temperature and number of DBRs periods. We compare the relation between the wavelength and gain at a different single-pass gain in both reflection and transmission modes. The highest gain at around 36 dB is observed in reflection mode. Moreover, we calculated the amplifier bandwidth at different periods of top mirror’s reflectivity, in which when the peak reflection gains increases, the amplifier bandwidth decreases.

Photonic implementation of spike timing dependent plasticity with weight-dependent learning window based on VCSOA

Based on the well-known Fabry–Pérot approach, after taking into account the variation of bias current of the vertical-cavity semiconductor optical amplifier (VCSOA) according to the present synapse weight, we implement the optical spike timing dependent plasticity (STDP) with weight-dependent learning window in a VCSOA with double optical spike injections, and numerically investigate the corresponding weight-dependent STDP characteristics. The simulation results show that, the bias current of VCSOA has significant effect on the optical STDP curve. After introducing an adaptive variation of the bias current according to the present synapse weight, the optical weight-dependent STDP based on VCSOA can be realized. Moreover, the weight training based on the optical weight-dependent STDP can be effectively controlled by adjusting some typical external or intrinsic parameters and the excessive adjusting of synaptic weight is avoided, which can be used to balance the stability and competition among synapses and pave a way for the future large-scale energy efficient optical spiking neural networks based on the weight-dependent STDP learning mechanism.

Weight adjustable photonic synapse by nonlinear gain in a vertical cavity semiconductor optical amplifier

In this paper, we report a high-speed and tunable photonic synaptic element based on a vertical cavity semiconductor optical amplifier (VCSOA) operating with short (150 ps-long) and low-energy (μW peak power) light pulses. By exploiting nonlinear gain properties of VCSOAs when subject to external optical injection, our system permits full weight tunability of sub-ns input light pulses, just by varying the VCSOA's applied bias current. Not only is the VCSOA-based synapse able to adjust the strength of incoming optical pulses, but it can also provide gain (applied weight factors >1). Moreover, we show that this simple approach permits dynamical weight tuning at high-speed (ns rates) with up to an 11.6-bit precision. These results are realized with commercially sourced, inexpensive vertical cavity surface emitting lasers, operating at the key telecom wavelengths of 1300 and 1550 nm and hence making our approach compatible with optical network and data center technologies. This VCSOA-based system, therefore, offers a hardware friendly, low-energy, and high-speed solution for photonic synaptic links with high potential for use in future neuromorphic photonic systems.

A Comparison of Top Distributed Bragg Reflector for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers Based on III–V Compound

In this work, the design of GaAs/AlGaAs distributed Bragg reflector (DBR) has been implemented for 1300 nm vertical cavity semiconductor optical amplifiers (VCSOAs) for optical fiber communication applications. The top DBR period and Al concentration are varied, the peak reflectivity of the DBR is increasing from 50% to 97.5% for 13 periods with increasing Al concentration, whereas the reflectivity bandwidth is increased to almost 190 nm. The relation between wavelength and incidence angle variation on DBR reflectivity is increasing with the incident angle (0°, 20°, 30°, and 50°), the resonant wavelength and bandwidth of the measured reflectance spectra shifts to shorter wavelength and wider bandwidth, respectively. In addition, a comparison between the linear, the graded, and the parabolic DBRs has been achieved with transfer matrix method using MATLAB software to show the influence of layer in DBRs and its effect on lasing wavelength. It is shown that using grading DBR mirror is much more beneficial compared to abrupt DBR, whereas it has lower reflectivity of almost 10% due to VCSOAs device which needs less number of top layers until prevent reaching lasing threshold.

A Comparative Study of Electrical Characterization of P-Doped Distributed Bragg Reflectors Mirrors for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers

This paper presents an electrical analysis of various diameters of two p-types of GaAs/Al0.9Ga0.1As and two p-types of GaAs/Al0.3Ga0.7As/Al0.9Ga0.1As distributed Bragg reflectors (DBRs) mirrors structure grown on undoped and on p-doped GaAs, which affects the characteristics of 1300 nm vertical cavity surface emitting lasers (VCSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs). Electrical characterizations and Hall measurements of current−voltage (IV) for GaAs/Al0.9Ga0.1As linear DBRs and GaAs/Al0.3Ga0.7As/Al0.9Ga0.1 As graded DBRs were also performed at temperatures between 13 and 300 K. Consequently, p-type DBRs are designed with graded composition interfaces technique. The smaller mesa diameters are used to reduce vertical and longitudinal resistances and to limit the heating effect and improve the characteristics of VCSEL/VCSOA devices.

Computing Primitive of Fully VCSEL-Based All-Optical Spiking Neural Network for Supervised Learning and Pattern Classification.

We propose computing primitive for an all-optical spiking neural network (SNN) based on vertical-cavity surface-emitting lasers (VCSELs) for supervised learning by using biologically plausible mechanisms. The spike-timing-dependent plasticity (STDP) model was established based on the dynamics of the vertical-cavity semiconductor optical amplifier (VCSOA) subject to dual-optical pulse injection. The neuron-synapse self-consistent unified model of the all-optical SNN was developed, which enables reproducing the essential neuron-like dynamics and STDP function. Optical character numbers are trained and tested by the proposed fully VCSEL-based all-optical SNN. Simulation results show that the proposed all-optical SNN is capable of recognizing ten numbers by a supervised learning algorithm, in which the input and output patterns as well as the teacher signals of the all-optical SNN are represented by spatiotemporal fashions. Moreover, the lateral inhibition is not required in our proposed architecture, which is friendly to the hardware implementation. The system-level unified model enables architecture-algorithm codesigns and optimization of all-optical SNN. To the best of our knowledge, the computing primitive of an all-optical SNN based on VCSELs for supervised learning has not yet been reported, which paves the way toward fully VCSEL-based large-scale photonic neuromorphic systems with low power consumption.

Theoretical investigation of weight-dependent optical spike timing dependent plasticity based on VCSOA

We propose an implement scheme of the weight-dependent optical spike timing dependent plasticity (STDP) based on the vertical-cavity semiconductor optical amplifiers (VCSOAs) subject to double optical spike injections, and numerically investigate the effects of the internal and external parameters of VCSOAs on the optical STDP curve by the well-known Fabry-Pérot approach. Additionally, the optical weight-dependent STDP is realized by introducing the various bias current according to the feedback signal. The simulation results show that, the width and height of the optical STDP curve window can be effectively controlled by adjusting the relevant parameters of VCSOAs. Moreover, the optical weight-dependent STDP is analogous to the biological STDP synapses and can be used to balance the stability and competition among synapses. These results can offer great potential for constructing a large-scale energy efficient optical spiking neural networks (SNNs).

Performance Evaluation of SD-WDM System to Mitigate the Effect of XPM using HOA

This paper has dealt with the mitigation effect of cross-phase modulation (XPM) which is a nonlinear effect of fiber losses. To control the losses, we have used a quantum dot vertical cavity semiconductor optical amplifier with vertical cavity semiconductor optical amplifier as hybrid optical amplifier (HOA). Further, an analysis of 560 channels with a data rate of 40 Gbps has been done to achieve the acceptable rating of gain, quality factor and noise figure. The final suggestion has recommended that the proposed HOA is most suitable to control the XPM with a received quality factor from 40 to 16 dB.

Optical Analysis of 1300 nm GaInNAsSb/GaAs Vertical Cavity Semiconductor Optical Amplifier

Vertical cavity semiconductor optical amplifiers (VCSOAs) based on GaInNAsSb active region is designed to operate in reflection mode at wavelength of 1300 nm. Addition of antimony Sb to the GaInNAs has dramatically improve the performance of VCSOAs, where the wavelength shifts to longer wavelength. This study is aimed to design GaInNAsSb/GaAs quantum wells (QWs) enclosed between various periods of front and 25-periods of back of AlGaAs/GaAs distributed Bragg mirrors (DBRs) by using MATLAB. GaInNAsSb can be grown and lattice matched to GaAs with a very small band gap and it can be grown monolithically on high quality GaAs/AlGaAs distributed Bragg reflector. Peak reflection gain at around of 53.2 dB at single pass gain of 1.076 is observed. In addition, amplifier bandwidth at various front back mirrors reflectivities is simulated to achieve high gain and wide optical bandwidth at low reflectivity of front mirrors.   

STDP-Based Unsupervised Spike Pattern Learning in a Photonic Spiking Neural Network With VCSELs and VCSOAs

We propose a photonic spiking neural network (SNN) consisting of photonic spiking neurons based on vertical-cavity surface-emitting lasers (VCSELs). The photonic spike timing dependent plasticity (STDP) is implemented in a vertical-cavity semiconductor optical amplifier (VCSOA). A versatile computational model of the photonic SNN is presented based on the rate equation models. Through numerical simulation, a spike pattern learning and recognition task is performed based on the photonic STDP. The results show that the post-synaptic spike timing (PST) is eventually converged iteratively to the first spike timing of the input spike pattern via unsupervised learning. Additionally, the convergence rate of the PST can be accelerated for a photonic SNN with more pre-synaptic neurons. The effects of VCSOA parameters on the convergence performance of the unsupervised spike learning are also considered. To the best of our knowledge, such a versatile computational model of photonic SNN for unsupervised learning and recognition of arbitrary spike pattern has not yet been reported, which would contribute one step forward toward numerical implementation of a large-scale energy-efficient photonic SNN, and hence is interesting for neuromorphic photonic systems and spiking information processing.

Integrated VCSOA and PIN with high sensitivity

An integrated vertical cavity semiconductor optical amplifier (VCSOA) and PIN photodetector was proposed in attempting to raise the sensitivity in high speed fiber-optic communication systems. Two slightly different structures have been studied under this configuration. For the cascade and the resonance structure, our simulation results showed that their sensitivity could reach -33dBm and -36dBm at a bit rate of 10Gb/s, respectively. We also managed to fabricate the cascade structure and demonstrated a 7dBm improvement on sensitivity as compared to the conventional PIN photodetector.

Slow light in quantum dot vertical cavity semiconductor optical amplifiers

Slow light in the Technologically important devices InGaAs/GaAs quantum dot (QD) Vertical Cavity Semiconductor Optical Amplifiers (QD-VCSOAs) is studied. The presented work benefits from the possibility offered by QD-VCSOA structures for operation exclusively at the amplifying regime without reaching threshold unlike Quantum Well (QW) VCSOAs. The mathematical formulation of the main slow down metric based on gain dispersion is presented. The effects of various functional (current, input signal) and structural (inhomogeneity, cavity length, density of dots etc) properties on the optical delay properties of the QD-VCSOA are identified and relevant design strategies are outlined. The numerical investigation concludes that considerably higher Group Delays can be achieved in QD-VCSOAs compared to QW-VCSOAs by means of static (i.e. structural design) and dynamic (i.e. injection current) properties. The results highlight the flexibility (tunability) offered by the QDs in tailoring SL properties of the VCSOA.

Analysis of pulse amplification characteristics in vertical cavity semiconductor optical amplifiers

Based on the transfer matrix method (TMM), a comprehensive dynamic numerical model describing the optical pulse amplification in vertical cavity semiconductor optical amplifiers (VCSOAs) is established, which treats the whole VCSOA as one multilayer dielectric structure, including the two Distributed Bragg Reflectors (DBRs) and the middle active region. In this model, the spatial dependence of the carriers and optical field in the longitudinal direction and the discontinuity of refractive index distribution in the resonant cavity are accounted for. Moreover, in this study the influence of the two photon absorption (TWP) is also taken into consideration. By employing this model, we investigate the signal distortion and the pulse energy gain characteristic in single pulse amplification of VCSOAs operated in reflection mode in detail. The numerical results show that the pulse distortion can be mitigated in a satisfactory manner via reducing the period of top DBR. It further shows that the energy gain during the pulse amplification can be increased by enhancing the pump power; larger saturation input pulse energy (SIPE) could be obtained by either lowering the period of top DBR or reducing the pump power; for the input pulse with duration ranging from several to tens of picoseconds, the energy gain characteristics of VCSOA is pulsewidth independent.

Numerical Implementation of Wavelength-Dependent Photonic Spike Timing Dependent Plasticity Based on VCSOA

We propose to realize photonic spike timing dependent plasticity (STDP) by using a vertical-cavity semiconductor optical amplifier (VCSOA) subject to dual optical pulse injections. The computational model of the photonic STDP is presented for the first time based on the well-known Fabry–Perot approach. Through numerical simulations, the dependences of photonic STDP on the bias current of VCSOA and the input powers are analyzed carefully. Besides, the effect of the initial wavelength detuning on the photonic STDP is also explored. It is found that, the current scheme requires much lower bias current and input power to obtain controllable STDP curve when compared with the previously reported photonic STDP circuits; the initial wavelength detuning is an effectively controllable parameter to realize wavelength-dependent photonic STDP. The computational model of the photonic STDP based on a VCSOA is interesting and valuable for numerically simulating of large-scale photonic spiking neural network, and provides a guideline to design low power consumption photonic neuromorphic systems.

Simple semi-analytical model for bistable cross-gain modulation in quantum dot VCSOAs

A novel semi-analytical model for cross-gain modulation (XGM) in quantum dot vertical-cavity semiconductor optical amplifier has been derived. The derived model, which is simple, requires small computational time compared with numerical simulation and can efficiently be used to investigate the optical bistable/stable characteristics of the device. Large XGM bandwidth can also be obtained when the device operates in the bistable region and in the stable region close to the bistable edge. A figure of merit is proposed to optimize the complicated tradeoff between the XGM bandwidth, efficiency, applied current and the input pump to probe ratio. We find that optimum characteristics can be obtained in our investigated device when the probe wavelength is detuned by 9 A above the resonant wavelength and when a specific CW probe density is applied to the input of the device.

Contrast ratio and hysteresis width of optical bistability in quantum-dot vertical-cavity semiconductor optical amplifiers integrated with MEMS membrane

The characteristics of optical bistability in quantum dot vertical cavity semiconductor optical amplifier integrated with MEMS membrane have been investigated, and a closed-form model is derived taking into account the effect of the quantum dot discrete states and the membrane deflection and reflectivity. We show that small membrane deflection significantly adjusts the resonant wavelength, the contrast ratios and the hysteresis width. The shape of the input–output characteristics of the device can be adjusted to display clockwise, butterfly and counterclockwise hysteresis loops depending on the membrane deflection and the initial wavelength detuning. Our analysis reveals that the contrast ratios of the upper and lower bistable levels are totally different. Also, it has been shown that the characteristics of the bistability are strong function of the active layer linewidth enhancement factor and the membrane reflectivity.

Analysis of Quantum Dot Vertical Cavity Semiconductor Optical Amplifier with Saturable Absorber

We analyze the bistable characteristics of quantum dot vertical cavity semiconductor optical amplifier integrated with saturable absorber. The device demonstrates bistable characteristics in the input-output powers which can be controlled by changing the voltage of the saturable absorber. We observe that the lower trigger level is more sensitive to variation of the absorption coefficient of the saturable absorber than that of upper trigger level. For clockwise and butterfly loops, we find that the upper and lower trigger levels increase as the absorption coefficient increases, and consequently the hysteresis width decreases. For counter clockwise, the upper and lower trigger levels decrease as the absorption coefficient increases and the corresponding hysteresis width increases.

Novel Tunable Bistable Quantum-Dot Vertical-Cavity Semiconductor Optical Amplifiers

We propose and theoretically demonstrate a novel type of tunable bistable device. Detuning is achieved by introducing deflectable microelectromechanical systems (MEMS) membrane suspended above the top distributed Bragg reflector (DBR). By applying external voltage at the MEMS, the membrane deflects, which detunes the resonant wavelength of the vertical-cavity semiconductor optical amplifiers, and consequently changes the bistability of the device. Therefore, the hysteresis width and the shape of the input–output characteristics of the device (clockwise, butterfly, and counterclockwise hysteresis loops) can be controlled electronically.