On crosstalk and noise in an optical amplifier with gain clamping by vertical laser field

We have calculated the transient behavior and noise figure of a semiconductor optical amplifier (SOA) with the gain clamped by a vertical cavity laser (VCL). The characteristic behavior of the more conventional gain-clamped SOAs and SOAs with no gain-clamping is also studied and compared with the vertically gain-clamped amplifier. The calculations are based on a numerical stochastic rate equation model including several forward- and backward-propagating channels that are coupled to the vertical laser field through the active medium. The noise model takes into account the input noise, randomly amplified spontaneous emission, and random gain. Numerical simulations have been carried out to study the relaxation oscillations, crosstalk, and noise in a system with a strong input signal switched on and off while observing the output signals, VCL photon density, and carrier density. Results show that the VCL field captures most of the disturbances, in agreement with available experimental data.     

Longitudinal spatial hole burning and associated nonlinear gain ingain-clamped semiconductor optical amplifiers

The longitudinal spatial hole burning (LSHB) in gain-clamped semiconductor optical amplifiers (GCSOAs) is investigated by means of a numerical model, which is based on position-dependent rate equations for the carrier density and the propagation equations for the optical power. The simulation results show that the carrier densities are nonuniformly distributed within the active layer of GCSOAs. The nonuniformity can be large, especially for high currents and optical signal powers near the saturation. It is found that the LSHB induces a gain nonlinearity, which causes interchannel cross talk when GCSOAs are used in wavelength division multiplexing (WDM) applications. In order to reduce this gain nonlinearity, two methods are analyzed: the use of low resistivity devices and the use of unbalanced Bragg mirror reflectivities     

Effects of gain saturation in semiconductor laser amplifier links

The effects of gain saturation due to amplified spontaneous emission in systems comprising cascaded semiconductor laser amplifiers and attenuators are investigated. The influence of the relative spatial distribution in the link of gain and loss is analyzed numerically, and conclusions regarding noise optimal structures are drawn. It is shown that the performance of links with gain saturation can be quite different from the ideal, unsaturated case     

Investigation of semiconductor optical amplifier integrated with DBR laser for high saturation power and fast gain dynamics

A detailed theoretical investigation of an integration of a semiconductor optical amplifier (SOA) and distributed Bragg reflector (DBR) laser is presented. The dependence of the device performance on those key design parameters such as the lasing wavelength, light injection direction (co- and contra-propagation), lasing power of the DBR laser, and the biasing condition of the SOA is examined systematically by means of a comprehensive time-domain traveling-wave model. As this integrated structure is particularly designed for high saturation power and fast gain dynamics, these characteristics are simulated and compared with the results from the conventional structures. Depending on different requirements, superior performance on either saturation power or noise figure without compromise on the optical gain can be achieved by different integration configurations (i.e., by different light injection directions). For the structure with the light injection from the output end of the SOA (namely, the integrated SOA-laser structure), the fast gain dynamics is found through simulation, which helps to reduce the large-signal waveform distortion in the amplification of narrow pulses.     

Asymmetric gain induced by longitudinal spatial carrier burning in semiconductor lasers

Nonlinear gain caused by dielectric corrugation resulting from the cavity standing wave of a lasing mode in semiconductor lasers is investigated using the perturbation approach. The results show that the nonlinear gain spectrum is asymmetric when the linewidth enhancement factor alpha not=0, and the possibility of single mode operation is greater at alpha =0.<>     

Pulse energy gain saturation in subpico- and picosecond pulseamplification by a traveling-wave semiconductor laser amplifier

Optical pulses with durations ranging from 0.49 to 21 ps are amplified by a traveling-wave semiconductor laser amplifier. The pulse energy gain is determined by pulse energy only. The dependence of pulse energy gain on output pulse energy does not change in the pulse duration range. The saturation characteristics are successfully explained by a four-level system model     

垂直腔半导体光放大器增益的理论分析

针对研究增益饱和时,现有的垂直腔半导体光放大器(VCSOA)速率方程模型在确定输入信号的功率注入因子方面存在难题,根据法布里-珀罗腔边界条件,从行波方程和与位置相关的载流子方程出发,引入随轴向位置发生变化的增益增长因子刻画微腔内的驻波效应,构建出VCSOA的增益模型。利用该模型通过求方程的自洽得到了腔内载流子、光子的分布,并分析了反射增益,其结果与已报道的理论及实验基本一致。     

锥形有源条半导体光放大器增益和饱和特性分析

以行波半导体光放大器速度方程为基础，采用传输矩阵方法，对锥形结构半导体光放大器的增益和饱和特性进行理论研究。讨论了不同锥形长度，不同结构时的增益和饱和特性差异。理论研究表明，锥形结构能改善半导体光放大器的偏振灵敏度。在同一锥度下，长锥形长度能提高饱和增益，降低偏振度。在进行半导体光放大器有源条结构设计时要综合考虑锥度及锥形长度的影响，以实现结构优化 。     

Gain saturation enhancement of longitudinal hole burning viastanding wave induced wave coupling in a semiconductor laser

It is shown by a simple theoretical model that the large scale longitudinal hole burning in a semiconductor laser will enhance by about 2.6 times the gain saturation caused by the cavity standing wave induced wave coupling     

Effects of multiple wave mixing and gain saturation in an idealtraveling wave semiconductor laser amplifier

Nonlinear distortions induced by four-wave mixing and gain saturation in a semiconductor laser amplifier can affect the overall performance of lightwave systems using such devices. A model which includes both types of distortion in a three-channel optical transmission system is presented. Large-signal analysis is used to calculate distortion in amplifiers operating near saturation. The technique provides more realistic predictions than the small-signal rate equation analysis used in previous theoretical studies of four-wave mixing in optical amplifiers     

Analytical model of a semiconductor optical amplifier

The spatial dependence of the material gain is introduced in the model of a semiconductor optical amplifier. Analytical expressions of the profiles of the carrier density, spontaneous emission, and amplified fields are obtained for amplifiers with arbitrary facet reflectivities. The nonuniformity of the carrier density is demonstrated in the case of low facet reflectivities. The model predicts the output saturation power and gain ripple, with good agreement with experimental results in resonant and traveling-wave amplifiers. Very low-gain ripple measured in low facet reflectivities amplifiers is explained by the model. A comparison with the uniform gain model shows that important deviations can occur in the case of low facet reflectivities. It is also shown that with the currently achievable low facet reflectivities, the maximum available gain is limited by spontaneous emission     

High-gain 1310 nm semiconductor optical amplifier modules with a built-in amplified signal monitor for optical gain control

A compact high-gain 1310-nm semiconductor optical amplifier (SOA) module incorporating two photodiodes to detect radiation emitted from the two opposite facets of the amplifier chip is reported. By subtracting their signals, a measure of the amplified signal is obtained without the need for optical filtering, Using this, amplified signals can be stabilized within 0.5 dB over a 25-dB range of input signals.     

Optical gain and saturation characteristics of quantum-dot semiconductor optical amplifiers

Detailed theoretical analysis of the gain characteristics of quantum-dot semiconductor optical amplifiers (QD-SOA) is presented. An analytical expression for the optical gain is derived from the quantum dot and wetting layer rate equations. Due to the better confinement of carriers in the quantum dots, our calculation shows that large unsaturated optical gain can be obtained at low operating current. Also, we found that the output saturation intensity of QD-SOA is higher than the output saturation intensity of bulk-SOA. This fact lends itself to the design of efficient low-power SOAs.     

双电极半导体光放大器的放大自发辐射谱和增益特性的实验研究

设计并制作了双电极多量子阱半导体光放大器（SOA）,对其放大的自发辐射(ASE)谱和增益特性进行了测试和分析。结果表明,注入电流密度分布对多电极SOA的ASE谱和增益特性有非常大的影响。通过调节注入电流密度比,ASE谱的半高全宽、峰值波长、峰值功率以及增益特性能够得到很好的调控。     

Amplified spontaneous emission spectrum and gain characteristic of a two-electrode semiconductor optical amplifier

A two-electrode multi-quantum-well semiconductor optical amplifier is designed and fabricated.The amplified spontaneous emission(ASE)spectrum and gain were measured and analyzed.It is shown that the ASE spectrum and gain characteristic are greatly influenced by the distribution of the injection current density.By changing the injection current density of two electrodes,the full width at half maximum,peak wavelength,peak power of the ASE spectrum and the gain characteristic can be easily controlled.     

Experimental investigation of stability properties for a semiconductor laser with optical feedback

The stability limits for a semiconductor laser exposed to optical feedback have been measured as a function of the feedback level and the phase of the reflected field. The experimental results are in good agreement with a detailed theoretical analysis. They include a determination of the absolute feedback level in a practical set-up and of the R-parameter, which for the actual laser is found to be ?3.0 ± 0.3.     

Linewidth broadening in a distributed feedback laser integrated with a semiconductor optical amplifier

The problem of the linewidth degradation in systems using distributed-feedback lasers together with strained-layer multi-quantum-well semiconductor optical amplifiers (SOAs) is examined. A modified expression for the linewidth in the case of anti reflection-coated SOA output facets is derived and simulation results are given in the case of output facets with a nonvanishing reflectivity. A numerical model combining finite-element calculations in the transverse x-y plane and a longitudinal model based on the Green's function method is used for that purpose.     

Automatic frequency control in a semiconductor laser and an optical amplifier

Automatic frequency control (AFC) in an injection locked or resonant type amplifier in an AlGaAs semiconductor laser was achieved through using the terminal voltage change induced by light injection. Signal-to-noise ratio in the control signal of 10 dB was obtained when the input optical power was -47 dBm and the optical gain Was 51 dB. The AFC was maintained for 3 h with an 0.3-percent output power fluctuation for 2°C ambient temperature change and 65-MHz frequency stability. Step response showed that the system response time was 1.5 s. Sensitivity to input optical power deteriorates at -49 dBm, with a 53-dB locking gain, because of frequency deviation caused by temperature modulation. The second derivative of the induced voltage and it's relation to the optical frequency is constant at5 times 10^{-10}[V/(MHz)²] for all input power levels in a buried-heterostructure (BH)-AlGaAs laser. Terminal voltage change induced by light injection is calculated by simple rate equations with a Gaussian-Halperin-Lax (GHL) bandtail model. Good agreement with experimental results was seen.     

Analysis of gain and saturation characteristics of a semiconductorlaser optical amplifier using transfer matrices

The transfer matrix method (TMM) has been applied to analyze the gain and saturation characteristics of semiconductor laser optical amplifiers. This method approximates the amplifier cavity by dividing it into M discrete subsections, and TMM has been applied to analyze the stepwise longitudinal field distribution at each subsection along the amplifier cavity. By incorporating also the carrier rate equations into the analysis, it has been shown that the approximation can accurately describe the carrier density and longitudinal field distribution along the amplifier cavity if M is sufficiently large (i.e., the size of each subsection is about an order of magnitude of one wavelength of the input signal). By assuming that the amplifier is biased below oscillation threshold such that the contribution of spontaneous emissions to the gain characteristics can be neglected, we have shown that our proposed method yields a fast and efficient algorithm in analyzing the gain and saturation characteristics of laser amplifiers. We have compared the results produced by our method to those analyzed using the average photon density (AVPD) approximation technique, as well as to experimental results on a 1.5-μm buried heterostructure semiconductor laser amplifier     

Characteristics measurement of gain and refractive index of traveling-wave semiconductor optical amplifier

A novel method to measure the gain and refractive index characteristics of traveling-wave semiconductor optical amplifier（TMA） is presented. In-out fiber ends of TWA are used to construct an external cavity resonator to produce big ripple on amplified spontaneous emission（ASE） spectrum. By this means,Hakki-Paoli method is adepted to obtain the gain spectra of TWA over a wide spectral range. From measured longitudinal mode spacing and peak wavelength shift due to increased bias current, we further calculate the effective refractive index and the refractive index change. Special feature of refractive index change above lasing threshold is revealed and explained.