External optical feedback effects on intensity noise ofvertical-cavity surface-emitting lasers

The authors have experimentally evaluated the effect of external optical feedback on the relative intensity noise (RIN) of a vertical-cavity surface-emitting laser (VCSEL) diode. In the absence of optical feedback, the smallest RIN is found to be -135 dB/Hz. For optical feedback levels approaching -25 dB, the RIN is degraded by about 20 dB. The authors have measured feedback-induced power penalties in a 500-Mb/s intensity-modulation/direct-detection (IM/DD) link and determined that the penalty exceeds 1 dB if the optical feedback ratio is larger than -30 dB     

Receiver performance evaluation of various digital optical modulation-demodulation systems in the 0.5-10 µm wavelength region

Error rate characteristics of various digital optical modulation-demodulation schemes are studied. The main concern is whether we can improve receiving power levels to achieve a prescribed error rate by employing a coherent optical transmission system in place of the presently available amplitude-shift-keyed (ASK) baseband direct detection system. The receiving power level reduction in various modulation-demodulation schemes is calculated by taking into account the optical carrier wavelength, data rate, photodetector performance, local oscillator power level, and number of levels in multilevel codes. The phase-shift-keyed (PSK) homodyne detection system requires the least receiving power. The improvement in the receiving power level compared to the conventional ASK baseband direct detection system is expected to be 16-22 dB at the carrier wavelength oflambda_{c} = 0.5-3 mum, 31-36 dB atlambda_{c} = 3-5 mum, and 35-40 dB atlambda_{c} = 5-10 mum.     

17圆柱形混合棒塑料光纤耦合器中的串扰及其功率代价

研究17圆柱形混合棒塑料光纤耦合器(CMRC)中由于混合棒端面反射造成的结构性串扰,建立不同误码率条件下串扰与功率代价的关系。串扰与功率代价的关系表明,在误码率为10-9的条件下,17 CMRC的串扰小于-20dB时其功率代价接近于零。实验制作了17 CMRC,测得其端口间串扰为-23.5dB。为了进一步降低17 CMRC的串扰,试验了在混合棒的失配面上涂覆光吸收介质的方法。测量结果表明该方法可以使串扰降低5dB。     

采用半导体光放大器的多波长光纤环形激光器

报道了一种插入马赫-曾德尔(M-Z)光纤干涉仪的半导体光放大器(SOA)多波长光纤环形激光器,实现了信道间隔为100 GHz的稳定的多波长连续光激射,其输出光谱3 dB带宽为19.5 nm,消光比大于30 dB.其中在17.9 nm范围内获得了22个波长的连续光,功率不平坦度为1.2 dB,总输出功率为5.1 dBm.对该结构的多波长激光器输出光谱宽,不同波长间功率波动小的特性进行了分析,提出在较低环腔损耗下,半导体光放大器的增益饱和及四波混频(FWM)效应的共同作用使环腔内多波长光功率获得自动均衡;并对实验观测到的激光器输出光谱带宽及中心波长随半导体光放大器驱动电流降低或环腔损耗增大而减小的现象进行了讨论.     

Optimal design of a multi-mode interference splitter based on SOI

In this paper, the multimode waveguide lengths and the output port locations of a SOI （silicon on insulator） material-based 1×4 MMI （multimode interference） optical splitter are optimized by means of FD-BPM （finite difference - beam propagation method）. An improved 1×4 MMI optical splitter is designed. Compared with an usual optical splitter, a smaller loss 0. 12dB and a better output port power uniformity 0.11dB are achieved for the optical signal transmission.     

基于3 μm-SOI的波分复用/解复用器与电吸收型VOA的单片集成

波分复用/解复用器与可调光衰减器的是光通信系统中的重要元器件。为了得到制备工艺简单、响应速度快的二者的单片集成芯片,并且考虑到其与其他不同光器件的集成可能性,在绝缘体上硅材料制作了16通道、信道间隔200 GHz的阵列波导光栅复用/解复用器与电吸收型可调光衰减器的单片集成。该器件的片上损耗小于7 dB,串扰小于-22 dB。电吸收型VOA在20 dB的衰减量下的功耗为572 mW （106 mA,5.4 V）。此外,该器件可以实现光功率的快速衰减,在0~5 V的外加方波电压下,VOA上升及下降时间分别为50.5 ns和48 ns。     

Characteristics of regenerative erbium-doped fibre ring amplifier

A study is presented into the dynamic characteristics of a unidirectional regenerative erbium-doped fibre ring amplifier at below laser threshold. A considerable improvement in gain and noise figure performance was observed due to the suppression of amplified spontaneous emission in the regenerative amplification process. It was found that lower feedback power provides higher optical gain. An optical signal of -33.5 dB was found to experience a gain of ⩾35 dB at and near the resonance wavelength using 1% feedback by an optical fibre coupler for an optical pump (1480 nm) power as low as 10 mW     

Long-wavelength monolithic GaInNAs vertical-cavity optical amplifiers

We report on the continuous-wave amplification characteristics of an optically pumped 1.3-/spl mu/m multiple-quantum-well GaInNAs-GaAs vertical-cavity semiconductor optical amplifier (VCSOA). The VCSOA structure was monolithically grown by molecular beam epitaxy and operated in reflection mode in a fiber-coupled system. The maximum on-chip gain attained, limited by the onset of laser action, was 15.6 dB at 196 mW of 980-nm pump power. For a chip gain of 10.4 dB, the optical bandwidth was 10.8 GHz and the saturation output power was -9 dBm. By varying the pump laser power, a maximum extinction ratio of 22.3 dB was obtained. Temperature-controlled tuneable operation of the device is also presented and demonstration of 9 dB of chip gain obtained over 9.5 nm with an optical bandwidth of 12 GHz is reported.     

Novel architectural schemes for wavelength conversions in optical cross connect systems

This paper proposes simple, cost-effective schemes for wavelength conversions in optical cross-connect (OXC) systems using wavelength-fixed light sources and an optical space switch, and provides improved performance in stability and conversion range of wavelengths and channel spacing. In addition, the schemes avoid the need for the wavelength locking control that is generally needed after changing the probe beam wavelength from one wavelength to another. The technical feasibility of the proposed pre-fix scheme is investigated in terms of probe beam power through experiment of wavelength conversions based on the cross-gain modulation. The results show that the proposed wavelength conversion scheme in OXC allows a ±4 dB deviation in the probe beam power to afford a 2 dB power penalty deviation from the minimum power penalty. As long as the insertion loss deviation of an optical space switches are within ±4 dB, the proposed pre-fix scheme can be used for wavelength conversions in OXC systems for a 2 dB power penalty deviation, whereas the proposed post-fix scheme does not require an optical space switch.     

High-density and alignment-tolerant integration of monitoringphotodetector arrays onto polymeric guided-wave components

We report on a hybrid integration concept which allows high-density and alignment-tolerant surface mount assembly of top-illuminated photodetector (PD) arrays onto polymeric guided-wave components by means of a micromachined submount with an integrated mirror. This research aims at the development of polymeric waveguide based devices with an embedded optical power monitoring capability for applications in optical fiber communication networks. A prototype integrated multichannel optical power monitor comprising an eight-channel PD module and a polymeric waveguide splitter array was demonstrated which exhibited an average insertion loss of 5.2 dB, a PD coupling efficiency of -2.6 dB, and a crosstalk value of -17.1 dB between adjacent channels. Low polarization and wavelength sensitivity (σ<0.1 dB) was confirmed over a spectral range of 40 nm in both telecom wavelength windows     

两段级联内插差异损耗功率箝制掺铒光纤放大器

针对全光网中信道路径不同所引起的功率失衡问题 ,设计了一种利用商用光纤波分复用器实现两段级联内插差异损耗环的功率箝制掺铒光纤放大器 (EDFA)光路结构 ,并从理论和实验上研究了光路结构参数对放大器动态范围和噪声特性的影响。得出损耗插入最佳位置在 6 0 %附近 ,最佳插入损耗大小 5～ 8dB依抽运功率和光纤长度而定。所研制的功率箝制EDFA在信号波长 15 5 3nm处 ,动态范围大于 2 0dB ,动态范围内平均输出功率超过2 90 μW。     

Increased linear dynamic range by low biasing the Mach-Zehndermodulator

Operating a Mach-Zehnder modulator at an optical bias below the conventional 50% (quadrature) bias is investigated. Theoretical distortion curves as a function of bias have been calculated and experimentally verified. These curves show that (single octave) linear dynamic range increases as the bias is lowered, so long as optical power at the detector can be maintained just below the saturation level or laser noise limit. This method thus provides a way for very large optical power to be used to benefit linear dynamic range. Theoretically, 20 dB of excess optical power, attenuated through low biasing, can result in an increase in linear dynamic range of 15 dB     

Peripheral-coupled-waveguide MQW electroabsorption modulator for near transparency and high spurious free dynamic range RF fiber-optic link

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.     

Optical time-division multiplexed transmission at 8 Gbit/s using single laser and semiconductor optical power amplifier

The authors report transmission over 57 km of single-mode fibre in a two-channel, 8 Gbit/s optical time-division multiplexed system experiment using a transmitter with a single laser and a semiconductor optical power amplifier at the transmitter output. The amplifier operates with a net gain of 11.5 dB, which corresponds to 0.8 dB gain compression, and a fibre coupled output power of +6 dBm. The amplifier facet output power for which the gain is compressed by 3 dB is +13 dBm. The experimental system uses neither an isolator nor an optical filter.<>     

Fabrication of large-core 1/spl times/16 optical power splitters in polymers using hot-embossing process

Large-core (42 /spl times/43 /spl mu/m) 1/spl times/16 optical power splitters in polymers have been fabricated. Y-branch waveguide structures with and without offsets in the arc-bending regions were designed by the beam propagation method software and molded by a silicon-mold master using a hot-embossing process. The optical power splitters were produced by epoxy core filling and ultraviolet curing processes. The average insertion losses at a wavelength of 850 nm were measured to be 19.8 dB with offset and 17.1 dB without offset, respectively. The maximum uniformities were 3.3 dB with offset and 3.9 dB without offset, respectively.     

Sampled-grating DBR laser-based analog optical transmitters

Sampled-grating distributed Bragg grating (SGDBR) laser-based widely tunable optical transmitters are investigated for application in high-performance analog links. More than 45 nm tuning range, 40 dB sidemode suppression ratio, and peak relative intensity noise below -153 dB/Hz is measured. SGDBR lasers integrated with semiconductor optical amplifiers and electroabsorption modulators (EAMs) are characterized with spurious free dynamic range of 125-127 dB/spl middot/Hz/sup 4/5/ over the wavelength tuning range. It is also shown how the modulation response of the EAM is affected by the optical power to limit the performance of the analog transmitter.     

An ultrawide-band semiconductor optical amplifier having an extremely high penalty-free output power of 23 dBm achieved with quantum dots

A semiconductor optical amplifier (SOA) having a gain of >25 dB, noise figure of <5 dB, and 3-dB saturation output power of >19 dBm, over the record widest bandwidth of 90 nm among all kinds of optical amplifiers, and also having a penalty-free output power of 23 dBm, the record highest among all the SOAs, was realized by using quantum dots.     

中间链路光学相位共轭补偿相干光正交频分复用系统的光纤非线性损伤

由于相干光正交频分复用(CO-OFDM)系统具有很高的峰均功率比(PAPR)以及非常近的子载波间隔,使得光纤非线性损伤成为系统的决定因素。提出中间位置光学相位共轭(OPC)补偿算法补偿CO-OFDM的Kerr损伤,由于OPC两端链路对称,可以最大限度地保证满足补偿条件,具有很好的非线性补偿效果。而且无链路色散补偿和有链路色散补偿系统均适用。该算法能使单信道40 Gb/s CO-OFDM的最大Q因子提高3 dB,非线性阈值提高4 dB;波分复用(WDM)系统的最大Q因子能提高1.1 dB,非线性阈值提高1 dB。     

An experimental diffuse optical wireless link employing DPIM

The paper presents the design for an experimental indoor optical wireless (OW) diffuse link using the digital pulse interval modulation (DPIM) scheme. Complete system implementation and procedure for carrying out the measurement are given. The system performance in the presence of artificial ambient light (AAL) sources is given. A high pass filter (HPF) with a cut-on frequency of 50?kHz is found to be sufficient to reject the interference signal from all AAL sources with the exception of the high-frequency (HF) fluorescent lamp (FL). Optical filtering reduces the average optical power penalty by 1?dB and 0.2?dB for the low-frequency (LF) FL, and the daylight. For the lowest error rate, the optimum HPF cut-on frequency in the presence of the HF-FL is found to be 884?kHz. The incandescent bulb introduces the largest average optical power penalty of 2.3?dB.     

The performance of a traveling-wave-type semiconductor laseramplifier as a booster in multiwavelength simultaneousamplification

In this study, the theoretical worst and the average interchannel crosstalk are shown as a function of normalized input power. The validity of normalization by saturation input power is confirmed by experimental data. This normalized input power must be set below -20 and -10 dB for multiwavelength numbers of 20 and 4, respectively, to attain an average interchannel crosstalk of under -10 dB. The optical loss, including interchannel crosstalk, that can be compensated by a traveling-wave-type semiconductor laser amplifier (TWA) is analyzed. The experimental results indicate that the compensable optical loss could be evaluated by using the average interchannel crosstalk in multiwavelength transmission system design. Applying a TWA as a preamplifier is more effective in systems that include excess optical loss in the receiver