Four-wave mixing in Raman fibre amplifiers in the 3rd telecommunications window

The efficiency of four-wave mixing (FWM) between two wavelength channels in Raman amplifiers operating around 1550 nm has been investigated. Measurements of FWM in Raman amplifiers utilizing different gain fibre types demonstrated that choice of gain fibre and pump power can seriously impact channel cross talk via four-wave mixing.     

基于半导体光放大器四波混频原理的光采样

建立了可研究强超短光脉冲放大特性且包含自由载流子吸收、受激辐射、双光子吸收、光谱烧孔和超快非线性折射效应的半导体光放大器理论模型,用以建立脉冲四波混频模型,并进一步仿真了基于半导体光放大器的光采样过程,重点讨论了自由载流子吸收、双光子吸收效应对采样特性的影响。仿真结果与实验结果相符。     

Frequency converters based on FWM in traveling-wave optical amplifiers: Theoretical aspects

We summarize the results of a theoretical model, developed to investigate the performance of a frequency converter based on four-wave mixing in a bulk traveling wave amplifier. The theory predicts very high values of conversion efficiency and signal-to-background ratio in the bandwidth of the converted signal. These results, whose experimental confirmation is reported elsewhere, increase the potential of using four-wave mixing in semiconductor amplifiers in actual optical systems.     

Distortions compensation in linear optical links adopting wavelength converters based on FWM in semiconductor amplifiers

Wavelength conversion by four-wave mixing in high-speed, long-distance optical links compensates for fiber dispersion and source chirping. Wavelength converters based on four-wave mixing in semiconductor amplifiers could be key components in wavelength-switched networks. The link performances are estimated by simulation using a physical model of all devices; the bit error rate is evaluated by a semianalytical model.     

光纤参量器件研究进展

综述介绍基于光纤四波混频效应的一些参量器件(放大器、频率转换器、相位共轭器等)的物理特性和工作性能;以及基于这些参量器件的新应用,比如可调谐辐射产生、相位敏感放大器、基于频率转换和色散的缓存以及实时采样等;最后就量子信息实验中的光子产生和频率转换等方面进行一些介绍。     

四波混频在长距离相干光纤传输中的影响

本文研究光纤非线性现象之一的四波混频对长距离相干多路光纤传输系统的影响.通过对一条长度为550km,采用9个掺铒光纤放大器的频分复用系统的实验,清楚地观察到了四波混频这一光纤非线性.实验的结果符合对四波混频的理论分析与计算.结果表明:对信息容量在每秒10~9bit数量级,采用常规的不归零码作信号方式的多路传输,光纤中的四波混频现象将严重地影响其传输性能.     

Method of implementation of frequency encoded all optical half adder, half subtractor and full adder based on semiconductor optical amplifiers and add drop multiplexers

A novel frequency encoded all optical half adder, half subtractor and full adder are proposed. The implementation is ultrafast one and the frequency encoding makes it intensity loss dependent problem free. The use of polarization insensitive four-wave mixing makes the design polarization independent and the hardware simple. The frequency conversion by the reflective semiconductor optical amplifiers (RSOA) makes the design faster compared to other semiconductor optical amplifiers (SOA) based design.     

Experimental verification of the existence of optically induced carrier pulsations in SOAs

Experimental investigation of the role of interband effects in four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is reported. Carrier density pulsations (CDP) in SOAs, caused by optical wave beating, are measured in the RF domain. This gives strong experimental confirmation of the link between CDP and wave mixing, as usually assumed in theory of FWM in SOAs. The dependence of CDP amplitude on bias current and optical power is also established.     

基于PolSK调制的四波混频型超快全光译码器

提出了一种新型的基于半导体光放大器（semiconductor optical amplifier, SOA）中四波混频（four-wave mixing, FWM）效应的超快全光译码器方案,方案中采用了偏振移位键控（polarization-shift-keying, PolSK）信号光.考虑SOA的偏振相关性,建立了这种全光译码器完整的偏振相关宽带理论模型.通过数值模拟的方法,从理论上实现了超快全光译码器,并研究了两输入信号光功率、SOA注入电流和SOA的偏振相关性对全光译码器输出特性的影响. 关键词： 全光译码器 偏振移位键控 四波混频 半导体光放大器     

Detection of weak optical signals with a laser amplifier

Detection of weak and extremely weak light signals amplified by linear and four-wave mixing laser amplifiers is analyzed. Photoelectron distributions are found for different input photon statistics over a wide range of gain. Signal-to-noise ratios are calculated and analyzed for preamplification schemes using linear and four-wave mixing amplifiers. Calculations show that the high signal-to-noise ratio (much higher than unity), ensuring reliable detection of weak input signals, can be attained only with a four-wave mixing preamplification scheme. Qualitative dependence of the signal-to-noise ratio on the quantum statistical properties of both signal and idler waves is demonstrated.     

Theory of frequency shift, injection-locking, and appearance of sidebands in class-C laser amplifiers

The second-order nonlinear amplification features of an optical signal by a single-mode class-C laser are discussed in detail. Due to a four-wave mixing process, the laser amplifier demonstrates a multiple frequency region in which a spectrum of the new signal and image sidebands is produced; simultaneously the free-running laser intensity is weakened and its frequency is pulled toward the amplified input signal frequency. The main aim is to find the ranges of input signal intensity and frequency detuning for which the four-wave mixing process occurs for class-C laser amplifiers. Our results satisfy the energy conservation law and they are in complete agreement with the previous results derived for class-A and -B laser amplifiers.     

Properties of Optical Phase-Locked Loop Based on Four Wave Mixing in Semiconductor Laser Amplifiers

In this paper, the properties of the optical phase-locked loop(PLL) based on the four-wave mixing in the semiconductor laser amplifiers (SLAs) are discussed. The components that achieve the function of detecting the bit phase of the input optical signal are concerned and discussed in detail together as a function module named as the optical bit phase detector referred to the general electronic PLL. Therefore, most of the properties of the optical PLL can be analyzed by applying the general phase-locked theory. Here the stability of the optical PLL is discussed. It's shown that the variance of input signal power in the practical application will cause optical PLL system unstable because of its long loop delay. The influence on the output phase jitter of the optical PLL is also investigated.     

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲产生四波混频及孤子效应的实验研究

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲,实验产生了一对由四波混频引起的信号波带和闲频波带,及一对由脉冲内拉曼散射和非孤子辐射引起的孤子和色散波带,并观察到功率饱和现象.利用有限元法理论模拟了光纤的色散和非线性特性,用四波混频的相位匹配条件模拟了光纤在满足相位匹配条件下所产生的信号波带和闲频波带出现的可能位置,并与实验结果符合得很好.结果表明:即使在光子晶体光纤的正常色散区抽运激光脉冲亦可以产生四波混频和孤子效应;研究发现四波混频的产生是由四阶色散参量引起的;并进一步从理论上解释了孤子及色散波的产生原因.     

Four-Wave Mixing in Microwires to All-Optical Signal Processing in Mode-Division Multiplexing Systems

Abstract

Mode-division multiplexing requires all-optical signal processing techniques that are able to deal with a new coding dimension, the spatial mode. In this context, optical microwires emerge as a potential highly non-linear and multi-modal waveguide envisioning the development of all-optical signal processing devices to mode-division multiplexing systems based on the four-wave mixing process. The inter- and intramodal phase-matching conditions for the four-wave mixing process are mapped as a function of the microwire diameter and the wavelength of signals. Moreover, the efficiency of four-wave mixing considering a strong guiding regime is investigated in the multi-modal regime.     

All-optical error-bit amplitude monitor based on NOT and AND gates in cascaded semiconductor optical amplifiers

This paper proposes and simulates a novel all-optical error-bit amplitude monitor based on cross-gain modulation and four-wave mixing in cascaded semiconductor optical amplifiers （SOAs）, which function as logic NOT and logic AND, respectively. The proposed scheme is successfully simulated for 40 Gb/s return-to-zero （RZ） signal with different duty cycles. In the first stage, the SOA is followed by a detuning filter to accelerate the gain recovery as well as improve the extinction ratio. A clock probe signal is used to avoid the edge pulse-pairs in the output waveform. Among these RZ formats, 33% RZ format is preferred to obtain the largest eye opening. The normalized error amplitude, defined as error bit amplitude over the standard mark amplitude, has a dynamic range from 0.1 to 0.65 for all RZ formats. The simulations show small input power dynamic range because of the nonlinear gain variation in the first stage. This scheme is competent for nonreturn-to-zero format at 10Gb/s as well.     

Reduction of fiber-nonlinearity-enhanced amplifier noise by means of phase-sensitive amplifiers

In optical fiber transmission systems near the zero-dispersion wavelength that use in-line erbium-doped fiber amplifiers (EDFA's), the enhancement of optical amplifier noise caused by four-wave mixing (FWM) in transmission fibers degrades signal-to-noise ratio (SNR) excessively. We theoretically show that the enhancement of amplifier noise by the FWM in transmission fibers can be effectively eliminated by implementing in-line phase-sensitive amplifiers (PSA's). Small-signal analysis of the nonlinear Schr?dinger equation shows that the transmission distance limited by the SNR of an in-line PSA system is expanded four times more than that of an in-line EDFA system.     

Analysis of format conversion from optical 16QAM to QPSK based on cascaded four-wave mixing in semiconductor optical amplifier

A scheme of format conversion from optical 16-ary quadrature amplitude modulation (16QAM) to quadrature phase shift keying (QPSK) signal based on cascaded four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is proposed. Theoretical analysis and simulations of the format conversion scheme are conducted to validate the feasibility of the proposal. In this proposal, the phase conjugated of 16QAM signal is generated after the first FWM process in an SOA, and then the QPSK signal is converted due to the second non-degenerate FWM (ND-FWM) process in another SOA. The performance and the optimal design of the 10 Gbit/s format conversion system under various key parameters of SOAs are evaluated and discussed. Simulation results present useful to enable interconnection between backbone network and access network.     

Generation of a reference frequency comb by cascaded four-wave mixing enhanced by Raman amplification

The generation of standard reference frequencies close to the ITU channels is essential for the frequency calibration of DWDM systems. This paper describes the generation of a reference frequency comb based on the combination of a cascaded four-wave mixing in two semiconductor optical amplifiers and Raman amplification in a dispersion-shifted optical fiber. As a result we have achieved a stable frequency comb with 36 reference lines separated by a constant frequency spacing of 177 GHz. The seed of the comb is combination of two narrow-linewidth semiconductor lasers which are locked to two absorption lines of the acetylene (¹²C₂H₂).     

Complete experimental characterization of the influence of parametric four-wave mixing on stimulated Raman gain

We present what is to our knowledge the first complete measurement of the dependence of Raman gain on chromatic dispersion, fully revealing the influence of parametric four-wave mixing on stimulated Raman scattering. In particular, a threefold increase of the Raman gain is observed under phase-matching conditions, in excellent agreement with theoretical predictions. Our experiments, which were performed in a photonic crystal fiber, demonstrate that these unique fibers can be exploited to boost the performances of fiber Raman amplifiers.     

A novel all optical method of implementing an n-bit wavelength encoded complete digital data comparator using nonlinear semiconductor optical amplifiers

Data comparator is the integral part of arithmetic and logical unit of any electronic or optical data processor. Due to some inherent limitations of electronics it cannot be possible to obtain a super fast operation (over terahertz limit) from electronic comparators. Again wavelength encoding technique has been established as an excellent one over other existing optical data encoding techniques. Semiconductor optical amplifier (SOA) technologies have shown their strong potentiality of realizing many all-optical systems. In this communication the authors have proposed a new scheme of developing all-optical wavelength encoded n bit binary comparator exploiting the four-wave mixing, wavelength filtering, wavelength conversion and nonlinear polarization rotation capabilities property of nonlinear semiconductor optical amplifiers. The scheme can be used for comparing signed and unsigned optical binary data of any bit wide numbers as well. The comparator is especially suitable for use as a building block in a larger optical circuit, such as in an all optical telecommunications switch.