All-optical logic NOR gate using two-cascaded semiconductor optical amplifiers

The authors present a novel all-optical logic NOR gate using two-cascaded semiconductor optical. amplifiers (SOAs) in a counterpropagating feedback configuration. This configuration accentuates the gain nonlinearity due to the mutual gain modulation of the two SOAs. The all-optical NOR gate feasibility has been demonstrated delivering an extinction ratio higher than 12 dB over a wide range of wavelength.     

All-optical signal processing based on semiconductor optical amplifiers

In this paper,we review the recent progress in the optical signal processing based on the nonlinearity of semiconductor optical amplifiers (SOAs).The four important optical signal processing functional blocks in optical switching are presented,i.e.,optical wavelength conversion,optical regeneration,optical logic,and optical format conversion.We present a brief overview of optical wavelength conversion,and focus on various schemes to suppress the slow gain recovery of the SOA and improve the operating speed of the SOA-based optical switches.Optical regeneration including re-amplification,re-shaping and re-timing is also presented.Optical clock recovery that is essential for optical regeneration is reviewed.We also report the recent advances in optical logic and optical format conversion,respectively.After reviewing the four important optical signal processing functional blocks,the review concludes with the future research directions and photonic integration.     

Spectral properties of amplified spontaneous emission insemiconductor optical amplifiers

We present a theoretical investigation of the spectral properties of spontaneous emission in semiconductor optical amplifiers. We use an extended (3×3) transfer matrix formalism to derive in the spectral domain an expression for the total longitudinally averaged internal field, which is valid regardless of the levels of optical input and bias current. The material parameters are saturated not only by the monochromatic signal, but also by the amplified spontaneous emission, filtered into the resonance modes of the structure, and integrated over its whole spectral range     

Transfer matrix analysis of the amplified spontaneous emission ofDFB semiconductor laser amplifiers

Analytical expressions are derived for the amplified spontaneous emission of a DFB (distributed-feedback) semiconductor laser amplifier with reflective cavity ends. The analysis is extended to a multisection DFB structure including a phase-shifted DFB semiconductor laser amplifier. It is shown that the spontaneous emission power per unit frequency bandwidth emitted from one facet is proportional to the transmission gain and to a quantity which at threshold becomes the inverse of the differential quantum efficiency of the other facet. The analysis is applied to two practical cases: (1) calculation of emission spectra of a DFB semiconductor laser biased below the threshold, and (2) assessment of the signal-to-noise ratio performance of DFB semiconductor laser amplifiers     

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.     

All-optical XOR gate using semiconductor optical amplifiers without additional input beam

The novel design of an all-optical XOR gate by using cross-gain modulation of semiconductor optical amplifiers has been suggested and demonstrated successfully at 10 Gb/s. Boolean AB~ and A~B of the two input signals A and B have been obtained and combined to achieve the all-optical XOR gate. No additional input beam such as a clock signal or continuous wave light is used in this new design, which is required in other all-optical XOR gates.     

Multiwavelength lasers based on semiconductor optical amplifiers

Stable multiwavelength lasing is demonstrated with a novel laser, in which a semiconductor optical amplifier offers optical gain and cascaded sampled fiber gratings serve as a comb filter. Five lasing lines are obtained with a fixed wavelength spacing of 0.8 nm. Optical power fluctuations among the lasing lines are improved by adjusting the reflectivity profile through the cascade of two sampled gratings     

All-optical signal up-conversion for radio-on-fiber applications using cross-gain modulation in semiconductor optical amplifiers

The authors present a novel scheme of up-converting optical intermediate frequency (IF) signals with an optical local oscillator (LO) signal using cross-gain modulation in a semiconductor optical amplifier. This scheme provides high conversion efficiency and is independent of the incident light wavelength and polarization. It can be useful for radio-on-fiber transmission system applications in which one remote LO signal is provided for several wavelength-division-multiplexing IF signals.     

Characterization and modeling of amplified spontaneous emission in unsaturated erbium-doped fiber amplifiers

The generation of amplified spontaneous emission (ASE) in erbium-doped fiber amplifiers (EDFAs) is characterized. A theoretical model, leading to closed-form analytical expressions for the backward and forward ASE power spectra, is developed for the unsaturated gain regime. This study shows that for the unsaturated gain regime, both power and spectral distributions of the ASE can be well described through the closed-form expressions, which require only measurable experimental parameters.<>     

Reduced crosstalk semiconductor optical amplifiers based on Type-IIquantum wells

It is shown theoretically that semiconductor optical amplifiers (SOAs) with type-II quantum-well active regions in SOAs will have up to 10 dB lower interchannel crosstalk at high (>2.5 Gb/s) data rates. That reduction is attained via the corresponding increase in saturation energy without any reduction in the efficiency     

Experimental study of the statistical properties of nonlinearly amplified signals in semiconductor optical amplifiers

We examine the effect of nonlinear amplification on the noise properties of an amplified signal. We show that the output noise statistics can be approximated as Gaussian over a wide range of practical parameters. In addition, we show that nonlinear amplification of noise carrying signals may result in an enhancement of the signal-to-noise ratio (SNR). Basic principles dictate that this can not improve the bit error rate performance of a communication link, as long as an optimal detection scheme is used. Hence, we conclude that for communication systems that exploit nonlinear amplification in semiconductor optical amplifiers, evaluation of performance on the basis of the SNR can be misleading and should be made with great care.     

同步脉冲泵浦抑制光纤放大自发辐射实验研究

放大的自发辐射(ASE)是影响掺Yb3+光纤放大器效率的重要因素之一。为了抑制ASE,本文从放大器的泵浦方式着手,设计并搭建了同步脉冲泵浦的掺Yb3+双包层光纤放大器,证实了其具有明显抑制ASE的效果。在重复率400 Hz时,将平均功率15 mW,脉宽500 ns的信号光放大至170 mW,实现增益10.5 dB。同时实验研究了不同泵浦脉宽对于ASE生成的影响。     

Sampling pulses with semiconductor optical amplifiers

We demonstrate three techniques to measure the instantaneous frequency and intensity of optical pulses using semiconductor optical amplifiers (SOAs). Four-wave mixing, gain-saturation, and interferometric switching through a nonlinear optical loop mirror are three mechanisms by which sampling is done. We have experimentally measured the intensity and chirp profiles of pulses with energies as low as 10 fJ. Since the nonlinearity in the SOA is relatively slow, these measurement techniques are most appropriate for picosecond pulses often found in telecommunication applications. The temporal resolution of these methods are limited by timing jitter, which was ≈0.5 ps for the mode-locked laser diodes we used in our experiments, and by the width of the switching window     

Noise figure monitoring of optical amplifiers via backwardamplified spontaneous emission

A new configuration of an optical amplifier is proposed that provide in-service noise figure (NF) monitoring. It is difficult to determine the NF of traditional optical amplifiers in operation because the amplified spontaneous emission (ASE) power cannot be measured separately from the output signal power. The proposed technique measures the NF from the backward ASE power. The discrepancy between the NF measured from forward ASE (using the traditional technique) and backward ASE (proposed technique) is found to be less than 1.0 dB at input powers below -6.2 dBm. A prototype optical amplifier is successfully used as a linear repeater, in a 10 Gbit/s 200 km transmission experiment     

Analysis of optical DEMUX characteristics based on four-wave mixingin semiconductor optical amplifiers

We have analyzed the basic characteristics of all-optical demultiplexing (DEMUX) based on four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) by solving a modified nonlinear Schrodinger equation by the finite-difference beam propagation method. Amplified spontaneous emission noise was not included in our model. The optimum pump pulsewidth for obtaining the high ON-OFF ratio is 1~3 ps for 1 ps, 250 Gb/s probe pulses. The shorter limit of the pulsewidth is due to detuning between the pump and probe frequencies, which is determined by the gain bandwidth of the SOA. In order to achieve faster DEMUX operation, an SOA with broader gain bandwidth is required. We also simulated pattern effects in the FWM signal. Power fluctuation in the FWM signal can be reduced by using a strong energy pump pulse and/or weak energy probe pulse. The energy fluctuation of the FWM signal decreases to less than 1% for a 30-bit, 250-Gb/s input probe pulse train with a pulse energy of 0.01 pJ. This small fluctuation should not disturb DEMUX operation. We have also examined DEMUX from time multiplexed signals by repetitive pump pulses. Strong energy pump pulses decrease the FWM signal intensity. However, there is no pattern effect due to gain saturation because the pump pulses are injected continuously     

Theoretical and experimental investigation of amplified spontaneous emission in electron-beam-pumped semiconductor lasers

Linear and nonlinear theories of amplified spontaneous emission in longitudinally-pumped semiconductor lasers have been developed. Spatial inhomogeneity in three dimensions and spectral inhomogeneity of gain and spontaneous emission are taken into account. Experiments to investigate the dependency of lasing threshold and differential efficiency of electron-beam-pumped semiconductor lasers on excited region diameter have been performed. The results of threshold measurements have agreed well with the linear theory calculations, while accounting for the results of differential efficiency measurements has required the development of a nonlinear theory. The data for non-linear calculations were provided by experiments on saturation of spontaneous emission. The results of experiments have definitely proved the inhomogeneity of gain. Based on the data obtained from experiments, the nonlinear calculations have explained the dependence of differential efficiency on the excited region diameter.     

Tunable wavelength filters based on nonlinear optical interactionsin semiconductor amplifiers

A novel class of narrow-band tunable wavelength filters is proposed and evaluated. Wavelength selectivity of the proposed filters Is derived from the finite time response of an optical nonlinearity. The nonlinearity is gain saturation in semiconductor optical amplifier structures. The filters are shown to have very narrow passbands tunable over the entire semiconductor gain bandwidth. The key to filter implementation is a device configuration in which the wave-mixing products can be isolated from the amplified inputs. Three integrated optics compatible configurations are considered and shown to have high filter throughputs 34 to 180% and subangstrom bandwidths     

Equivalent circuit theory of spontaneous emission power insemiconductor laser optical amplifiers

An equivalent circuit model for a semiconductor laser amplifier (SLA) has been developed. This model can be used with a transfer matrix method (TMM) to analyze the performance of a SLA. The validity of the model is explored in this paper by analyzing the spontaneous emission noise power in a Fabry-Perot SLA with a uniform distribution of material gain coefficient. The result is found to be identical with that derived by the Green function approach. The physical reasons for the validity of the equivalent circuit model are also discussed, and possible further applications of the model are suggested