Analysis of the Physical Impairments on Maximum Size and Throughput of SOA-Based Optical Burst Switching Nodes

In this paper, the physical limitations of semiconductor optical amplifier (SOA)-based switching nodes for optical burst switching (OBS) are investigated. The investigation covers two broadcast-and-select (BAS)-based architectures. Their maximum size and throughput are analyzed for nodes at different bit rates. As main impairments for signal degradation amplifier noise, crosstalk, SOA gain saturation and dynamics, and SOA chirp are evaluated by simulations. In conclusion, general rules for design burst switching nodes are established.      

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.     

SOA的增益响应特性及其对TOAD解复用器开关窗口的影响

通过数值求解半导体光放大器的增益动力主程,研究了ＳＯＡ的增益响应特性及ｚ光学非对称解复用器开关窗口的影响。     

双辅助光作用下半导体光放大器性能分析

半导体光放大器以其良好的非线性在全光网络中具有广泛应用,但较长的载流子恢复时间一直是制约其用于超快全光信号处理的速率瓶颈,基于包含自发辐射噪声的半导体光放大器模型,探讨了提高半导体光放大器增益恢复时间的有效途径,通过对制约透明波长移动,增益饱和与有效载流子寿命的相关因素进行数值分析,得出以下结论:与单辅助光相比,采用双辅助光可以在不牺牲信号增益的前提下进一步缩短载流子寿命,因而是提高半导体光放大器增益恢复时间的有效途径,这一点对工程设计和应用具有一定的指导意义.     

半导体光放大器的超快动态增益特性

提出了一种包括载流子密度脉动(CDP)、载流子加热(CH)和光谱烧孔(SHB)效应在内的半导体光放大器(SOA)的时域动态模型。利用该模型分析了半导体光放大器中的增益饱和、超快增益动态以及光脉冲在增益饱和半导体光放大器中的波形畸变,其中重点考虑了超短脉冲的情况。模拟计算表明,对于10ps量级以下的短脉冲,分析半导体光放大器的动态增益特性时,不能忽略载流子加热和光谱烧孔等带内超快非线性效应的影响。     

Simulation of mode-locking by nonlinear polarization rotation in a semiconductor optical amplifier

We present a theoretical investigation of a mode locked laser that has a semiconductor optical amplifier (SOA) in its ring cavity. A mode-locked train of narrow pulses is obtained by combining nonlinear polarization rotation in the SOA and a polarization filter whose polarization axis is set such that the tail of optical pulses is removed in each cavity round-trip. The pulse narrowing process is demonstrated numerically and good qualitative agreement with experiments in our previous work is achieved. The pulse performance is largely determined by the ultrafast SOA gain dynamics and the cavity dispersion. Our simulation shows that the laser can produce a pulse train of subpicosecond pulsewidth at a repetition rate of 28 GHz for a moderate SOA current level. We observe that the laser can switch itself on or off depending on the initial pulse.     

Measurements and Simulations of nonlinear noise redistribution in an SOA

Measurements and numerical simulations of the noise statistics after a semiconductor optical amplifier (SOA) demonstrate nonlinear noise redistribution. The redistribution, which relies on self-modulation due to gain saturation and carrier dynamics, shows a strong power and bandwidth dependence and can be important for SOA-based regenerators.     

Detailed theoretical investigation of the input power dynamic rangefor gain-clamped semiconductor optical amplifier gates at 10 Gb/s

A detailed theoretical investigation of the input power dynamic range for gain-clamped semiconductor optical amplifier (GC-SOA) gates at 10 Gb/s is presented. We show that although the gain is clamped, the dynamic changes of the carrier distribution in the GC-SOA causes pattern effects on a time scale given by the relaxation frequency of the GC-SOA. Combined with a higher noise figure compared to a conventional SOA, this results in a dynamic range only ~0.5 dB better than for an optimized SOA gate     

Intensity noise suppression in fibre DFB laser using gain saturated SOA

Experimental results of a simple, all-optical technique to reduce low-frequency intensity noise in an Er-Yb codoped fibre distributed feedback (DFB) laser are reported. This method utilises the gain dynamics of a saturated semiconductor optical amplifier (SOA) to produce a reduction of 30 dB in the relaxation oscillation noise component of the fibre laser.     

Wavelength channel data rewriter using semiconductor optical saturator/modulator

A wavelength channel data rewriter (WCDR) is a device that erases the data on an incoming signal by utilizing the saturation characteristic of a semiconductor optical amplifier (SOA) and then modulates it with new data to generate an upstream signal. This paper describes a theoretical and experimental investigation designed to improve the performance of the WCDR. Through numerical calculations, this paper shows that an SOA with a long waveguide with a large small-signal gain better suppresses optical bit patterns. This paper also uses calculated and experimental results to show that the amplified-spontaneous-emission noise in the SOA input signal degrades the bit-pattern suppression. This paper then describes the semiconductor optical saturator/modulator (SOSM), which this paper has developed for use in the WCDR based on the results of the author's theoretical investigations. This paper outlines the SOSM specifications and provides experimental results that confirm the improved WCDR performance obtained using the SOSM.     

Optical preamplifier using antireflection-coating-free semiconductor optical amplifier with signal-inverted ASE

We fabricated an antireflection (AR)-coating-free semiconductor optical amplifier (SOA) with an absorbing region for an optical preamplifier. In the fabricated SOA, the resonance of light was fully suppressed so that the amplitude of the ripple of amplified spontaneous emission (ASE) spectra was as small as 0.36 dB, which is comparable to conventional SOAs with AR coating at both facets. We formed an optical preamplifier using the AR-coating-free SOA. The gain saturation of the SOA gives us the signal conversion to ASE and the amplification of the signal. The small-signal fiber-to-fiber and chip gain of the preamplifier were 11.4 and 20.0 dB, respectively. The 3-dB optical gain bandwidth of the preamplifier was about 30 nm.     

Analytical Model for Cross-Gain Modulation and Crosstalk in Quantum-Well Semiconductor Optical Amplifiers

An analytical model of the dynamic characteristics of a quantum-well (QW) semiconductor optical amplifier (SOA) is developed. Closed-form expressions for the optical gain and cross-gain modulation (XGM) for arbitrary input pulses are derived. The model takes into account the carrier capture and escape transitions between the QW and the continuum states. This model is also used to derive a closed-from expression for interchannel XGM crosstalk in multichannel SOA systems. The model/analysis provides insight into the effect of the SOA parameters on the performance of a wavelength-division multiplexed system. We found that crosstalk in a multichannel SOA system can be reduced by reducing the escape lifetime.     

All-Optical Format Conversion From NRZ to BPSK Using a Single Saturated SOA

All-optical format conversion from nonreturn-to-zero (NRZ) to binary phase-shift keying format is experimentally demonstrated at 8 Gb/s using a single semiconductor optical amplifier (SOA). The conversion is based on the gain and phase modulations of the SOA on an input NRZ signal of finite extinction ratio     

Operational design on high-speed semiconductor optical amplifier with assist light for application to wavelength converters using cross-phase modulation

Using the newly developed time-dependent transfer matrix method with nonlinear effects, we analyzed the characteristics of cross-phase modulation (XPM), cross-gain modulation and gain recovery time of a semiconductor optical amplifier (SOA) with an assist light injection, which is introduced to speed up the gain recovery of the SOA. Particularly for the application to high-speed wavelength converters using XPM with an interferometer structure where /spl pi/-phase change is required, various parameters such as SOA lengths, wavelengths and powers of injected lights, and their propagation directions are designed via numerical simulation. Discussions concerning the conditions of an SOA structure and the parameters of injected lights for high-speed operation are described to show the potential of fast gain recovery with a response time as low as 25 ps.     

基于光纤环的光缓存器

提出了一种基于光纤环的光缓存器的结构,对结合半导体光放大器作光开关的此结构的物理模型进行了详细描述,并根据此模型分析了其增益、噪声、信噪比等方面的特性.     

基于半导体光放大器交叉增益饱和的波长转换的理论分析

建立了基于半导体光放大器交叉增益饱和的波长转换的理论模型。分别讨论了小信号下波长转换特性和大信号下转换波形的畸变情况。结果表明,半导体光放大器的载流子寿命是导致输出波形畸变的主要因素。     

Optimization of the frequency response of a semiconductor opticalamplifier wavelength converter using a fiber Bragg grating

Cross-gain modulation in a semiconductor optical amplifier (SOA) is one of the simplest techniques for all-optical wavelength conversion. However, the finite gain recovery time of the semiconductor optical amplifier causes distortion and pattern dependence at high bit rates. Here we show that filtering the output of a semiconductor optical amplifier wavelength converter with the transmission edge of a fiber grating filter improves its frequency response. The grating sharpens the transition between the bits by converting the phase modulation at the edge to useful amplitude modulation. We determine the filtering condition that produces the optimum frequency response and reduces bit-pattern dependence for nonreturn-to-zero (NRZ) data. For small modulation, the apparent frequency response increases by the linewidth enhancement factor α_H of the SOA. In this case, pattern dependence is eliminated completely by the fiber grating filter. For large modulation, pattern dependence can be substantially reduced, but not completely eliminated. We show that after spectral filtering, the residual pattern dependence of an SOA depends only on modulation depth. For a given SOA, we find the optimum grating for minimum conversion penalty at 12 Gb/s for a wide range of operating parameters. Using a fiber grating filter reduces the required optical power for conversion in a semiconductor optical amplifier     

Gain and phase recovery of optically excited semiconductor optical amplifiers

An investigation of the recovery dynamics of semiconductor optical amplifiers (SOAs) explains why the ultrafast component of the gain recovery is largely absent in the phase response. The time-resolved gain and phase dynamics of a bulk GaInAs SOA are measured using a pump-probe technique and differences between the gain and phase recoveries are highlighted and explained using Kramers-Kronig analysis. These have important implications for optical signal processing.     

Phase dynamics of semiconductor optical amplifiers at 10-40 GHz

The phase dynamics that occur in bulk InGaAsP-InP semiconductor optical amplifiers (SOAs) in response to picosecond pulse excitations at 10 and 40 GHz are studied experimentally and numerically for various amplifier lengths. The time dependencies of the phase changes and of the absolute gain of the amplifier are measured simultaneously. The total phase shifts induced by 1.5-ps pulses at 10 GHz are higher than /spl pi/ in SOAs with active region lengths between 0.5 and 2 mm and exceed 2/spl pi/ in a 1.5-mm-long amplifier. Phase shifts above /spl pi/ are measured at 40 GHz in 1.5- and 2-mm-long SOAs. The dependence of the total phase shift on the amplifier bias current and length and on pump pulse energy is investigated. Numerical simulations based on a comprehensive time-domain SOA model allow us to confirm the experimental results for a wide range of amplifier parameters. In particular, SOAs with lengths up to 5 mm have been modeled, and the calculations suggest that the maximum phase shifts occur in amplifiers of approximately 2-mm length. The phase dynamics measurements are illustrated at the example of an optical time division multiplexing add-drop multiplexer, based on a SLALOM switch, gated by 10- or 40-GHz control pulses. We find that simultaneous good dropping and clearing is possible if the length and the operating conditions of the SOA in the switch are chosen such as to induce a full /spl pi/ phase shift.     

22 dB gain semiconductor optical amplifier module using high numerical aperture aspheric lenses

A polarisation-insensitive semiconductor optical amplifier (SOA) module with a net gain of 22 dB is demonstrated. High numerical aperture, low aberration aspheric glass moulded lenses are efficiently used for optical coupling between the SOA chip and singlemode fibres.<>