半导体光放大器的稳态增益饱和特性

高速全光逻辑门是实现光分组交换、光计算和未来高速大容量光传输的关键器件,近年来受到广泛的关注。半导体光放大器（SOA）因为具备体积小、工作波长范围宽、响应时间短及良好的非线性特性等优点,成为研制高速全光逻辑器件的首选。采用分段模型分析了SOA的稳态增益饱和特性,通过数值求解载流子速率方程和光传输方程对其特性进行了仿真实现。结果表明,SOA在入射光功率不同时会表现出明显的非线性;在一定范围内增加光功率,SOA增益持续增加,继续增加入射光功率,SOA逐渐进入饱和吸收状态,增益反而降低。     

基于磁通压缩技术的爆炸磁频率发生器的参数选择

 爆炸磁频率发生器是一种结构简单、小型化的电磁脉冲产生和辐射装置。为了优化其性能,从数学模型入手进行研究,得出输出信号所满足的Bessel函数,分析了在不同电参数下输出信号的模式及电路中的能量分配。研究结果表明,当电感变化到初始值的1/e所需时间与初始载波频率的乘积较大时,发生器的输出信号为振荡模式,且二者乘积越大,载波频率越高,对其辐射越有利。     

基于光纤传感的核信号读出方法中的调制驱动模块设计和实现

基于光相位调制的核信号读出方法将探测器信号调制进光纤中,并使用光纤作为模拟信号的传输介质。在该读出方案中,调制驱动模块负责载波信号的产生及放大,是该方案读出电子学系统的重要组成部分。为了产生低相位噪声,幅度大且幅度可调的载波信号,本工作提出了基于锁相环的载波产生电路和基于MMIC射频放大器的载波放大电路的设计方案,该方案结构简单,尺寸小,性能优异。对载波产生电路使用了ADIsimPLL仿真软件进行了环路滤波器的设计和仿真,同时也对载波放大电路使用ADS仿真软件进行了设计和仿真,并在实验室条件下进行了测试。测试结果表明,输出26 dBm载波信号相位噪声好于–110 dBc/Hz@100 kHz,能够用于信号解调。     

Distortion in optical pulse equalization through phase modulation and dispersive transmission

By combining phase modulation and dispersive transmission we propose an adjustable optical device to compress a time-varying input signal for producing ultrashort light pulses of high optical power. The relationship between the required properties of the input signal and the device parameters to get well-conformed sharp pulses with large energy concentration was established. High-order aberrations effects of the electro-optical modulator acting as the time lens of the employed setup are also considered. We found a mathematical analogy between the output signal of the analyzed device and the signal which would be obtained by using an equivalent first-order dispersive line. Some numerical simulations are shown which illustrate the feasibility of the method.     

Application of a continuously tunable, cw optical parametric oscillator for high-resolution spectroscopy

We report the use of a smoothly tunable, single-frequency continuous-wave optical parametric oscillator (OPO) for high-resolution spectroscopy. The OPO is based on potassium titanyl phosphate and is resonant for both signal and idler fields, resulting in a device with a very low pump power threshold of 30 mW. The frequency-selective nature of the doubly resonant oscillator ensures that the signal and idler modes can be tuned across the entire phase-match bandwidth without the need for additional intracavity frequency-selective components. Smooth frequency tuning of the output of the OPO is obtained by tuning of the pump laser. To demonstrate the practicality of our OPO we recorded the absorption spectrum of cesium vapor in the 1-microm spectral region.     

Spectral hole burning for wideband, high-resolution radio-frequency spectrum analysis

We present experimental results for what is to our knowledge the first spectral-hole-burning based rf spectrum analyzer to cover 10 GHz of rf analysis bandwidth. The rf signal of interest is modulated onto an optical carrier, and the resultant optical sidebands are burned into the inhomogeneously broadened absorption band of a Tm3+:YAG crystal. At the same time a second, frequency-swept laser reads out the absorption profile, which is a double-sideband replica of the rf spectrum, and thus the rf spectrum can be deduced after spectral calibration of the nonlinear readout chirp. This initial demonstration shows spectral analysis covering 10 GHz of bandwidth with >5500 spectral channels and provides 43 dB of dynamic range.     

弹光调制光电转换放大电路设计

弹光调制干涉具调制的干涉光被探测器接收后输出高速变化的微弱电信号,能否将该电信号提取并放大输出对弹光调制-傅里叶变换光谱仪的研制至关重要。通过对调制干涉光进行理论分析,设计一种具有高信噪比和较高带宽的光电转换放大电路,主要由电源电路、光电转换电路、放大电路、理论通频带为100 kHz~3.5 MHz的带通滤波电路组成。实验结果表明:设计的电路能够将探测器输出的最大频率为1.6 MHz的信号放大至670 mV左右,实现了将探测器输出的微弱速变电信号从背景噪声中有效提取与放大,为后续傅里叶变换提供可靠数据。     

On the output characteristics of a semiconductor optical amplifier driven by an ultrafast optical time division multiplexing pulse train

A comprehensive theoretical analysis of a semiconductor optical amplifier (SOA) that is subject to an ultrafast optical time division multiplexing pulse stream is presented with the help of a simple but efficient model developed for this purpose. The model combines the necessary set of mathematical equations with the appropriate simplifying assumptions to describe in the time domain gain saturation and recovery for the case of multiple incoming pulses. In this manner, analytical expressions can be obtained for the power and chirp profile of the amplified pulses, essentially extending the work that has been performed for a single pulse only. This allows to identify the critical operational parameters and to investigate and evaluate their effect on these two output characteristics. The derived simulation curves are thoroughly studied to specify the limitations imposed on the SOA small signal gain and carrier lifetime as well as on the full-width at half-maximum (FWHM) and energy of the input pulses and, based on a series of logical arguments, to extract useful rules concerning their selection so as to achieve improved performance with respect to the practical applications of all-optical switching and pulse compression. The obtained results indicate that due to the continuous insertion of pulses, the requirements for the SOA small signal gain and the input pulse energy are stringent than those for the case of isolated pulse amplification. The combination of these two parameters determines also the regime in which the amplifier must be biased to operate in order to ensure distortionless pulse amplification and enhanced chirp for efficient pulse compression and it has been found that low saturation is necessary for the former case whilst heavy saturation for the latter. The scopes of the corresponding requirements for the carrier lifetime and the FWHM are also tight but to a less extent and can be simply satisfied with the available photonics technology. These results are in good agreement with the available experimental data essentially proving the validity and robustness of the model. The model can be thus applied to predict the behavior of more complex all-optical circuits of enhanced functionality in which the SOA is the basic functional device.     

缓变截面波导型回旋共振放大器理论

本文先采用波动法对缓变截面波导型回旋共振放大器进行理论分析,推导出它的色散方程,这仅适用于小信号情况。另外还利用场与电子流的动功率守恒定理对这类放大器进行理论计算,它可不受小信号限制,可用来计算放大器的饱和输出功率和效率。针对由三段角锥组成的变截面波导系统,对这放大器进行了具体计算。理论计算表明:这种结构的放大器的突出优点是在高功率输出下磁场变化对输出功率影响较小。此外,与均匀波导的同类放大器相比,在相同的输出功率与增益下有更宽的工作频带,互作用长度则有所缩短。 关键词：     

A novel scheme of optical pulse width compression using a feedback optical phase modulator

This paper presents a scheme for the compression of optical pulse widths by using a feedback optical phase modulator. In the first part of the proposed circuit, the carrier and two fourth-order sidebands on either side of the carrier are amplified and phase shifted before getting combined by an optical power combiner to generate a picosecond optical pulse. The optical pulse generated by this part of the circuit has a calculated width of 3.5 ps. This optical pulse when passed through a feedback optical phase modulator produces a compressed optical pulse at the output. By making the drive frequency of the feedback optical phase modulator equal to 100 GHz, we found the output optical pulse to have a calculated width of 1.0 ps. PACS 42.65.Re; 42.79.Sz; 42.62.-b; 42.30.Lr; 42.55.Px; 42.60.Fc; 42.70.Mp     

激光器型全光波长转换器的小信号分析

当外部光子注入到激光器有源腔中时 ,载流子把被注入光子消耗的一部分放大 ,进而激光器自身的输出功率将降低。基于此 ,可以实现全光波长转换。理论上基于载流子消耗机制 ,对激光器型波长转换器进行了小信号分析 ,给出了频率响应函数。理论分析表明 ,激光器型全光波长转换器的转换速度取决于激光器光子寿命以及激光器腔内的光子密度。     

Optimization of the UTC-PD Epitaxy for Photomixing at 340?GHz

We present a method to optimize the epitaxial layer structure of an InGaAs/InP uni-traveling-carrier photo-diode (UTC-PD) for continuous THz-wave generation. The design approach used is general in that it can be applied for any target frequency while this study focuses on 340 GHz. The photodiode epitaxy is modeled and optimized using a TCAD software implementing the hydrodynamic semiconductor equations. This physical device model was found to be in good agreement with reported experimental results. It is shown that the UTC-PD can generate ~1 mW at 340 GHz by choosing the optimum absorption layer and collection layer thicknesses.     

A comprehensive equivalent circuit model for the study of thermal and spectral characteristics in laser diodes

An improved electrical equivalent model for multimode laser diode incorporating thermal effects and spectral behavior is developed from the multi mode rate equations. The temperature dependent optical power, wavelength shift, spectral widths are determined in the dc sweep simulations. The output power, frequency chirp and temperature rise are evaluated under pulse modulation conditions. Further, the laser diode bandwidth dependence on temperature is also evaluated. Analysis is carried out in the temperature range of 283–343 K, by simulating the equivalent circuit, using PSpice circuit simulator.     

Large amplitude noise reduction in ultrashort pulse trains using a power-symmetric nonlinear optical loop mirror

We analyse numerically the capabilities of a power-symmetric nonlinear optical loop mirror (NOLM) in the ultrashort pulse regime for high-quality amplitude regeneration of an optical signal. The device, which operates through nonlinear polarisation rotation, includes twisted, anomalous-dispersion fibre and a quarter-wave retarder. For particular adjustments of the retarder orientation, and a circularly polarised input beam, the output energy characteristic flattens near the switching energy, a property that can be used to eliminate large amplitude fluctuations in an optical signal. The group velocity mismatch between polarisation components introduced by twist is mitigated by the interplay between anomalous dispersion and the nonlinear Kerr effect, although strong twist should be avoided as it still introduces substantial pulse distortion. Contrary to other designs, where a plateau characteristic requires a large power imbalance between the counter-propagating beams, both pulses in the present scheme can be simultaneously close to fundamental solitons, which allows a substantial widening of the plateau for particular pulse parameters. Good quality, nearly transform-limited pulses are obtained in this case at the NOLM output. The device is applicable for the regeneration of ultrafast data streams in which the signal-to-noise ratio is severely deteriorated.     

基于布里渊载波相移的宽带可调谐二倍频微波信号生成

本文提出并实验验证了一种基于光纤中受激布里渊散射效应的光子二倍频微波信号生成技术.利用布里渊增益谱内的强色散特性,对光强度调制器产生的双边带调制信号的载波进行π/2相移,可实现载波与±1阶边带拍频仅生成二倍频微波信号.由于光纤中受激布里渊散射的窄带特性以及仅对双边带调制信号的载波进行相移,不影响调制信号两个边带的幅值和相位,因而生成的二倍频微波信号可实现宽带调谐,调谐范围仅受其他光器件的工作带宽限制.此外,信号光和产生受激布里渊散射的抽运光均来自同一光源,因而不受波长漂移的影响,系统具良好的稳定性.     

Performance analysis and improvement of semiconductor optical amplifier direct modulation with assistance of microring resonator notch filter

We demonstrate through numerical simulations that a passive single-bus microring resonator (MRR) employed as notch filter enables to directly modulate an ordinary semiconductor optical amplifier (SOA) at 10 Gb/s. This data rate constitutes a fourfold increase in the speed that it is possible to modulate the SOA due to its finite differential carrier lifetime. The theoretical analysis unveils how the MRR radius and detuning must be selected so that the MRR-based filtering scheme efficiently overcomes the pattern-dependent impairments incurred by the SOA narrow electrical bandwidth. Moreover, the small-signal analysis conducted to correlate the perturbations in power of the modulated optical signal inserted in the MRR with those at the MRR output confirms the enhancement in the electrical bandwidth of the SOA–MRR combination. Provided that the MRR response is tailored as suggested, which is technologically feasible, the MRR action permits the encoded signal to exhibit at extended data rate a pulse and eye diagram profile of acceptable quality, tolerable amplitude difference indices, an error probability below the forward error correction limit, and a sufficient system net gain for medium-haul transmission in standard single-mode fiber with dispersion compensation. These performance improvements can be beneficial for the direct modulation of standard SOAs. Together with SOAs inherent amplification capability, they can open new perspectives in using these active elements as external modulators in various target applications.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

10 Gb/s broadband silicon electro-optic absorption modulator

Here we propose a design for a novel broadband silicon electro-optic absorption modulator. The device is simply a 100 µm long silicon waveguide with a Schottky diode integrated in it. Modulation is achieved through free-carrier absorption, not interference effects, enabling operation over the entire bandwidth of the waveguide. The high overlap between the modulated carrier density and the optical mode enables high speed (> 10 Gb/s), small footprint and modulation depths of ∼ 4.6 dB.     

Modeling the power of an optical parametric generator by discrete mode summation

An analytical expression for calculating the signal output power of an optical parametric generator (OPG) configuration was developed. The model is based on Heisenberg equations in space and radiation mode theory. A simple analytical expression can be obtained by assuming that all modes within the gain bandwidth of the nonlinear crystal have the same gain and the same interaction length. Another derivation considers the gain and interaction length of each individual mode. The model predictions are in excellent agreement with the measured signal power of OPGs based on 25- and 35-mm periodically poled LiNbO₃ crystal (with effective quadratic nonlinearity of ∼14.5 pm/V) and 47-mm periodically poled LiTaO₃ crystal (with effective quadratic nonlinearity of ∼9 pm/V). In addition, a comparison was made between the summation over discrete modes approach and the traditional approach of continuous integration over the beam parameters and pump frequency. We have found that the first approach, which is developed in this paper, predicts more accurately the output power of the OPG.     

基于同步载波提取的光纤传感器相位生成载波解调方法

利用3×3耦合器和法拉第旋转镜等光学元件,构造了一个基于迈克尔逊干涉系统的光纤振动传感器.使用外调制的方法对传输光进行相位生成载波调制,并将该光纤振动传感器应用于长距离的安全监测中.通过对该传感器的干涉输出信号进行贝塞尔展开分析,发现干涉输出信号中含有与外调制所使用的载波频率相同的信号成分.因此,使用一个中心频率为载波频率且通带很窄的带通滤波器,可以同步地提取载波信号.同步提取的载波信号用于干涉输出信号的相位生成载波被动零差解调,可以得到作用于光纤振动传感器上的外界振动信号.本文提出了从输出信号中同步提取载波的方法,通过理论推导得出了该方法的可行性,并且通过软件仿真和实验验证了该理论的正确性.文中还对提取的载波受低频信号干扰,造成其幅度不稳定的现象进行分析并提出了解决方法.研究表明,同步载波提取法适用于相位调制器与干涉信号输出端距离较远,相位生成载波解调需要的同源载波获取较困难的情况.