Filter-free all-optical wavelength conversion using Sagnac interferometer integrated with parallel-amplifier structure (SIPAS)

A Sagnac interferometer integrated with a parallel-amplifier structure (SIPAS) is proposed for filter-free all-optical wavelength conversion. A Mach-Zehnder interferometer with a semiconductor optical amplifier in each arm is monolithically integrated with a Sagnac interferometer. Clear eye opening and low power penalty of 0.9 dB were achieved at a bit rate of 10 Gbit/s using the fabricated SIPAS.     

Theoretical Study on Wavelength Conversion Based on Cross Phase Modulation Using Semiconductor Optical Amplifiers

Performances of wavelength converted signal by cross phase modulation (XPM) using semiconductor optical amplifiers (SOA's) were studied by the use of the multi-section model. Results show that they are related to both the phase arm bias current of the XPM wavelength converter and its operation. When the conversion is under the in-phase operation, the peak extinction ratio (ER) and the chirp frequency of the converted signal increase according to the decrease of the phase arm bias current, but the input signal power dynamic range decreases. When the converter is under the out-of-phase operation, the chirp frequency decreases with the decrease of the phase arm bias current, while the peak ER and the input power dynamic range keep almost the same when the phase arm bias current changes.     

Basic module for an integrated optical phase difference measurementand correction system

A basic module for an integrated optical phase difference measurement and correction system was developed and fabricated in the AlGaAs-GaAs material system. The relative phase difference between two waveguides is measured using waveguide couplers to sample the optical field in each waveguide, a Y-junction interferometer with a small sinusoidal phase dither applied to one arm and a vertically integrated metal-semiconductor-metal detector. P⁺-n^-n⁺ phase modulators are used to control the phase difference between the waveguides. This implementation makes it possible to measure and correct the relative phase difference between adjacent waveguides using only a few percent of the optical power of each guide     

Experimental investigation into conversion efficiency of cascading four-wave mixing

We have proposed and experimentally demonstrated a scheme for cascading four-wave mixing (CFWM) by exploiting nonlinearity in highly nonlinear fiber (HNLF). Through utilizing optical spectrum analyzer (OSA), the second-order sideband products are observed in our experiment by only launching two waves into HNLF, and the conversion efficiency from the injected wave to each sideband is discussed in detail. It is found that only the conversion efficiency of the satellite wave will be increased with the power of the tunable injected wave when the power and the wavelength of the other one are fixed. Furthermore, the conversion efficiency of all the sidebands will be decreased with the absolute value of detune of injected wavelengths increasing. Also, the authors have demonstrated that the power of the satellite wave will be influenced most among all the sidebands if tuning the injected wave power. The proposed scheme can find potential applications in parametric amplification, frequency conversion, and optical quantum-information processing.     

一种新颖的复合环形谐振腔的理论分析

文章基于环形谐振腔所具有的非线性相位传输特性,提出了一种新型的动态光谱滤波器结构,它将全通环形谐振腔调相器接入平衡马赫-曾德干涉仪,实现复合结构的动态滤波特性.与传统的马赫-曾德干涉仪相比,此复合滤波结构可利用远小于π的相移调整实现输入光信号的开关,因此,在提高开关速度、降低调相器功耗等方面具有重要的应用价值.     

基于掺锗光子晶体光纤的可调谐多波长转换器

为了提高光网络中波长资源的使用效率,利用光纤中瞬态受激拉曼散射效应分析理论,设计了一种基于掺锗光子晶体光纤的可调谐四通道波长转换器。由于受激拉曼散射效应的增益随信号光与探测光波长之间的频移量变化,波长转换器各个转换信道波长可由探测光波长调谐。分析了泵浦信号光输入功率对多波长转换器性能的影响,结果表明:随着输入泵浦功率的增大,多路波长转换器的转换性能更好。用OptiSystem对四通道可调谐波长转换进行仿真,结果表明:所设计的波长转换器能够同时实现四通道波长转换,各信道波长可在1 511~1 569nm进行调谐。     

基于STM32的光功率实时监测系统设计

设计了一种基于Cortex-M3内核的32位ARM产品STM32F103ZE的光功率实时监测系统,并给出了设计的原理、实现方法及软硬件结构。介绍了被监测光分别通过光电转换电路、对数放大电路、A/D转换电路转换成的数字信号通过现场总线传递给主控单元,再经GPRS通信模块进行数据传输,可形成对通信光缆的实时自动监测。该设计具有可靠性高、方便扩展等优点。     

Remote downconversion with wavelength reuse for the radio/fiber uplink connection

The authors present a novel technology for uplink transmission in radio-over-fiber distribution systems. The technique employs remote downconversion of the uplink data to intermediate frequency (IF) in the base station (BS). The local oscillator signal for the downconversion is optically generated in the central station (CS) and sent to the BS via optical fiber. The IF uplink data is then modulated onto an optical carrier, retrieved from the downlink signal, and sent to the CS, where the baseband conversion takes place. By employing this method of uplink connection, simplicity and cost efficiency of the BS is achieved.     

基于ED-NALM的全光波长变换理论模型

提出了应用非线性掺饵光纤放大环镜进行全光波长变换的理论模型.详细研究了反转光脉冲的峰值功率、脉冲宽度和消光比等重要物理参量以及反转光脉冲继续在常规单模光纤中传输时的演变特性.结果表明:应用此模型,反转光脉冲除具有较高的峰值功率和消光比外,脉冲的宽度也比初始信号脉冲的宽度窄,而且脉冲的中心部分带有一定量的线性上啁啾,当其在常规单模光纤中传输时,在光纤的初始阶段,脉冲的峰值功率将经历先增加后减小的变化过程,而脉冲宽度的变化趋势与其正好相反.     

激光二极管抽运Nd∶YAG双薄片激光器

激光介质的热效应是高平均功率固体激光器面临的最大挑战,采用薄片激光介质是解决热效应的有效手段之一。当在抽运区尺寸远大于薄片厚度并且抽运光均匀分布的条件下,热流近似为沿厚度方向的一维分布,从而大大降低介质的热透镜效应和热致应力双折射。设计了四通光学耦合系统,通过提高二极管激光器阵列输出激光强度分布的均匀性,并优化经微柱透镜准直后光束的发散角,实现了抽运光的近平顶分布。采用两片1 mm厚的Nd∶YAG薄片激光介质,在两个峰值功率2000 W,占空比为15%的二极管激光器阵列抽运下,获得了峰值功率1440 W,平均功率216 W的准连续激光输出,光光转换效率达到36%,电光转换效率超过16%,在稳腔下测得的光束质量M2因子约为12×13。     

A Microwave Ferrite Single-Sideband Modulator

A microwave single-sideband modulator has been designed utilizing two reflection types of Faraday rotation ferrite-balanced modulators. Power is fed to the two balanced modulators by means of a 3-db quadrature hybrid such that each modulator has equal incident power with a 90-degree phase difference. The output power of the balanced modulators is combined by means of a magic tee sum and difference circuit. It is shown that if the modulation signals applied to the balanced modulators are in phase quadrature, the upper sideband will appear at the output sum arm and the lower sideband will appear in the output difference arm. An analysis of the device relates the spurious and undesired sidebands to the conversion loss, and a method is proposed for minimizing carrier output. The drive power is reduced due to the use of reflection-type balanced modulators, and experimental data is presented for the modulation frequency impedance and drive power requirements. The temperature and frequency sensitivity of the undesired sidebands have also been measured. A number of applications of the device are discussed.     

Spatial Quantized Analog-to-Digital Conversion Based on Optical Beam-Steering

A novel optical spatial quantized analog-to-digital converter (ADC) is presented and the performance enhancements through employing this architecture are analyzed theoretically. A high-speed low-jitter ADC sampling clock is provided by a mode-locked laser. A high sampling rate is maintained by avoiding any speed-limiting conversion from optical to electrical domain in an all-optical quantization technique. A high quantization bandwidth is achieved by employing the all-optical quantization technique, benefiting from the high bandwidth characteristics of optical modulation. A high ADC resolution is obtained by using a single-channel quantization configuration and detecting a single image at each sampling step. A high power efficiency is achieved by extracting some portions of the required power from the analog electrical signal and optical sampling clock, directly. Various ADC-resolution limiting factors including the ambiguity of photodetectors, jitter of the optical sampling-clock, the limited beam deflector bandwidth, dispersion, phase modulator nonlinearity/mismatch, noise, and crosstalk have been identified and the contribution of each effect has been discussed.      

Optical 90 degrees hybrid Costas-type receivers

A 90 degrees hybrid which consists of a beam combiner and two polarisation separators is proposed for optical preprocessing in Costas homodyne receivers. It utilises all the available optical power. The power distribution between the inphase and the quadrature arm can be arbitrarily adjusted.<>     

Noise analysis for optical frequency conversion using nearlydegenerate four wave mixing in semiconductor optical amplifier

For future wavelength-division-multiplexed (WDM) networks, optical frequency conversion will enable the flexible and efficient use of optical frequency bandwidth. However, the signal degradation at frequency converters limits the maximum size of the network. Noise due to optical frequency conversion using nearly degenerate four wave mixing in a semiconductor optical amplifier is investigated, and it is found that the crosstalk from one of the two pump lasers can impose the power penalty on the bit error rate (BER) characteristics after optical frequency conversion. Analytical expressions for BER are developed and used to evaluate the receiver sensitivity penalty caused by optical frequency conversion. On the basis of these results the optimal setting of the frequency difference between the signal and pump lasers and the power ratio of the two pump lasers are discussed. A 155-Mb/s frequency-shift keying (FSK) transmission with 1750-GHz (14 nm) optical frequency conversion has been carried out, using a novel phase noise cancellation method. The BER performance is in good agreement with the calculated results     

波长锁定878.6 nm LD调制泵浦Nd: YVO4自拉曼激光器

报道了一款基于调制共振泵浦技术的Nd:YVO₄自拉曼激光器。针对全固态自拉曼激光器中热效应严重导致的激光器输出功率及光光效率普遍偏低的问题,合理地将共振泵浦技术和调制泵浦技术相结合,实现了激光器的有效热管控,缓解了激光器的热效应,提高了泵浦上限,从而实现了激光器输出功率和光光效率的大幅提高。当泵浦源的调制频率为10 kHz、占空比为40%、平均泵浦功率为30 W、声光Q开关的调制频率为100 kHz时,获得了最大平均功率为8.57 W的1176 nm斯托克斯光输出,相应光光转换效率28.6%。相较于相同泵浦功率的连续泵浦机制下的实验结果,斯托克斯光平均输出功率提高了42%,光光效率提高了8.5%。实验结果表明:共振泵浦和调制泵浦技术相结合的方式可以有效缓解热效应,提高泵浦功率上限,从而提高自拉曼激光器的输出功率和光光效率。     

纳秒量级光参量放大技术研究进展

基于非线性频率变换技术的中红外固体激光器,受限于光学晶体的损伤阈值、镀膜工艺和逆转换效应,输出功率相对较低,而光参量放大技术可以有效改善这个问题。介绍了光参量放大技术的典型结构、特点以及常用光学晶体,评述了光参量放大技术提高纳秒量级中红外固体激光器输出功率的研究进展,分析了光参量放大技术在提高纳秒量级中红外固体激光器输出功率方面面临的挑战。     

交叉增益型波长转换器的实验研究

全光波长转换器是全光网络中的关键光电子器件.基于半导体光放大器的交叉增益型波长转换器具有结构简单容易实现、转换效率高、波长转换范围宽以及转换速率高的特点.文中在自行研制半导体光放大器的基础上,对交叉增益型波长转换器进行了实验研究.讨论了实现波长转换的基本原理,描述了实验系统结构,实现了速率为140Mbit/s的1315nm和1301nm之间的波长转换.研究了波长转换器泵浦光功率、探测光功率以及放大器注入电流转换效率、消光比和噪声特性的影响,研究结果与文献中报道的相同.研究表明,不同因素对不同指标的影响是相互制约的,要全面提高波长转换器的性能,必须折衷考虑各方面的因素.研究结果对半导体光放大器结构参数的优化和波长转换工作条件的优化有一定的指导作用.     

基于微波光子的射频信号功率测试方法

功率是微波信号的基本参数之一。传统的功率测量方法受限于同轴电缆传输损耗大、体积大等因素，难以适应分布式长距离组网应用。文章提出基于电光转换的微波功率测量方法，将微波功率测量转换为对光边带抑制比的测量。分别分析了采用相位调制和强度调制的电光转换方法时，微波功率与光边带抑制比之间的映射关系。实测对比了测量值与理论计算值之间的符合性。该方法经过电光转换后，可以采用光纤传输信号，进行长距离远拉测试，在分布式长距离组网中具有较好的应用前景。     

Estimating the Maximum Attainable Efficiency in Dye‐Sensitized Solar Cells

For an ideal solar cell, a maximum solar‐to‐electrical power conversion efficiency of just over 30% is achievable by harvesting UV to near IR photons up to 1.1 eV. Dye‐sensitized solar cells (DSCs) are, however, not ideal. Here, the electrical and optical losses in the dye‐sensitized system are reviewed, and the main losses in potential from the conversion of an absorbed photon at the optical bandgap of the sensitizer to the open‐circuit voltage generated by the solar cell are specifically highlighted. In the first instance, the maximum power conversion efficiency attainable as a function of optical bandgap of the sensitizer and the “loss‐in‐potential” from the optical bandgap to the open‐circuit voltage is estimated. For the best performing DSCs with current technology, the loss‐in‐potential is ～0.75 eV, which leads to a maximum power‐conversion efficiency of 13.4% with an optical bandgap of 1.48 eV (840 nm absorption onset). Means by which the loss‐in‐potential could be reduced to 0.4 eV are discussed; a maximum efficiency of 20.25% with an optical bandgap of 1.31 eV (940 nm) is possible if this is achieved.     

Fabrication and test of an efficient photovoltaic cell for laseroptical power transmission

An AlGaAs photocell designed for efficient optical-to-electrical power conversion of monochromatic radiation has been fabricated and tested. A power conversion efficiency of 59% and a fill factor of 82% were measured when the device was illuminated by a laser diode source at 826-nm wavelength. The conversion efficiency of the cell remained constant for optical powers up to 1.7 W (54 W/cm²), which was the limit imposed by the intensity of the available laser diode source. Such a device is needed for use in applications that require optical power transmission to remote sensors or electrical systems