新颖的掺铒光纤放大器无源复合组件的研究

报道了一种将光波分复用器与光隔离器集于一体的适用于掺铒光纤放大器的新颖复合组件。根据复合组件的性能指标对组件的结构参数进行了优化设计。实际制作的复合组件，得到泵浦光插入损耗＜０．６ｄＢ，信号光的插入损耗＜１．５ｄＢ，反向隔离度＞４２ｄＢ，体积为９×４５ｍｍ３。将复合组件用于掺铒光纤放大器中（前向泵浦方式）得到约３０ｄＢ的小信号增益，１０ｄＢｍ的饱和输出功率。     

High-sensitivity detection of narrowband light in a more intense broadband background using coherence interferogram phase

This paper describes an optical interferometric detection technique, known as the interferogram phase step shift, which detects narrowband, coherent, and partially coherent light in more intense broadband incoherent background light using changes in the phase gradient with the optical path difference of the coherence interferogram to distinguish the bandwidth or coherence of the signal from that of the background. The detection sensitivity is assessed experimentally by measuring the smallest signal-to-background ratio or signal-to-clutter ratio (SCR), which causes a detectable change in the self-coherence interferogram phase. This minimum detectable SCR (MDSCR) is measured for the multimode He-Ne laser, resonant-cavity light-emitting diode (LED), narrowband-filtered white light, and LED signal sources in a more intense tungsten-halogen-lamp white-light background. The highest MDSCRs to date, to the authors' knowledge, are -46.42 dB for coherent light and -31.96 dB for partially coherent light, which exceed those of existing automatic single-domain techniques by 18.97 and 4.51 dB with system input dynamic ranges of 19.24 and 11.39 dB, respectively. The sensitivity dependence on the signal-to-system bandwidth ratio and on the relative offset of their central wavelengths is also assessed, and optimum values are identified.     

Spectral filtering criteria for U-band test light for in-service line monitoring in optical fiber networks

In the fiber-to-the-home era, thousands of optical fibers will have to be accommodated in the central offices of optical access networks. To reduce maintenance costs and improve the service reliability of optical fiber networks, the authors must develop an optical fiber line testing system with a function for in-service line monitoring that uses a test light with a wavelength different from the communication light wavelength. To monitor an in-service line in an optical network, the effective rejection ratio of the test light must be taken into account. This ratio depends on the spectrum of the test light from the optical time-domain reflectometer and the rejection band of the filter in front of the optical network unit. The dependence of the effective rejection ratio as a function of the sideband suppression ratio (SBSR) and of the ratio of the rejection band to the bandwidth of the sideband noise d/D is clarified. When d/D=0.1 and the target effective rejection ratio of the filter is -40 dB, the SBSR and the filter loss of the termination cable must be -70 and -43 dB, respectively, or the SBSR must be -80 dB. When d/D<0.5 and the target effective rejection ratio of the filter is -40 dB, the SBSR is also required to be -80 dB. In-service line monitoring for a 10-Gb/s transmission using a 1650-nm test light with an SBSR of -80 dB is also demonstrated.     

玻璃基离子交换型宽带22 3dB耦合器研究

为满足2N光功率分配器的制作和应用的需求,对宽带集成化22 3dB耦合器进行了深入的理论和实验研究。采用3-D光束传播法,对传统的非对称X结进行了模拟改进,设计了低损耗且具有较宽工作带宽的22 3dB耦合器。采用Ag+-Na+离子交换技术在玻璃基上成功制作了非对称X结结构的宽带22 3dB耦合器。通过对1260nm~1360nm和1460nm~1600nm两个波段宽带光源的光谱测试,得到在宽带范围内小于4.0dB的插入损耗,光谱谱线相对平坦,波长依赖性较小,均匀性小于0.5dB。结果表明,采用这种非对称X结并结合离子交换工艺,可以在玻璃基上制作出宽带的22 3dB耦合器,这为进一步优化器件性能,研制成功具有应用价值的器件奠定了基础。     

Polarization properties of fused fiber couplers and polarizingbeamsplitters

The polarization properties of fused taped fiber couplers were investigated experimentally by changing cross-sectional shapes at the coupler waist. The coupling difference between x and y polarized light was studied for many test fused fiber couplers with various cross-sectional shapes. On the basis of the experimental results, two polarizing beamsplitters with the aspect ratio of 1.1 and 1.8 were produced, and their chromatic characteristics were measured. It was evident that the aspect ratio should be more than 1.7 to manufacture polarizing beamsplitters with few power transfer cycles, i.e. long spectral period. Splitting ratios of polarizing beamsplitters with the aspect ratio of 1.1 and 1.8 were 17.6 and -12.7 dB for x polarized light and -16.1 and 11.7 dB for γ polarized light, respectively. Their losses were less than 0.6 and 0.3 dB     

Noise figure of phase-sensitive parametric amplifier using a Mach-Zehnder interferometer with lossy Kerr media and noisy pump

The noise figure (NF) of a phase-sensitive parametric amplifier using a nonlinear Mach-Zehnder interferometer (NMZI) with Kerr media is analyzed for amplitude-modulation signals. In the analysis, the distributed loss of the Kerr media and the excess noise of the pump light are taken into account. As for the distributed loss of the Kerr media, the quantum Langevin equation for the NMZI is derived and solved. The results elucidate a simple degradation factor in the NF representation of the amplifier. This factor implies that the NF can be less than the standard quantum limit (SQL) of 3 dB, even if the total loss of the Kerr media exceeds 3 dB. As for the excess noise of the pump light, the semi-classical small signal analysis is utilized. The results clearly indicate that the signal-to-noise ratio of the pump light must be four times higher than that of the input signal in order to realize a low-noise optical amplifier under the SQL of 3 dB.     

Quantum well vertical light modulator

A waveguide modulator is proposed whose operation is based on the dissipative coupling of light from a waveguide into an appropriate quantum-well structure. This approach uses the electric-field-induced change of the refractive index for light modulation. A particular geometrical configuration is numerically evaluated. The advantages of this configuration are that the combination of high switching speed ( approximately=1 ps), high on/off ratios (e.g. 1/16 dB or 2/25 dB), and low-driving voltage (4 V) could be combined in one device. The proposed modulator exhibits negligible phase shifts when the attenuation is smaller than about 10 dB.<>     

超长距离通信系统中远程泵浦的优化设计

文章介绍了一种用于密集波分复用(DWDM)超长距离通信系统中远程泵浦的传输设计方案.为了得到较大的增益与较小的噪声指数,我们选择了数值孔径小、掺杂浓度低的掺铒光纤,同时光路中还采用了对信号光全透、对泵浦光全反的二色镜来提高泵浦光的利用率.通过优化的光路设计,我们得到了增益＞17 dB、噪声指数＜7 dB的远程泵浦放大器.     

开环双波段人眼视网膜成像液晶自适应光学系统设计

设计了一套基于开环双波段模式的人眼视网膜成像液晶自适应光学系统。该光学系统分别采用夏克-哈特曼波前传感器和液晶空间光调制器来探测和校正波前畸变。探测波段采用830nm近红外光,成像波段采用790nm近红外光。采用开环模式以提高光能利用率和系统的稳定性,采用双波段模式以增大视场。新加入了瞳孔监控子系统和响应矩阵测量子系统,使系统更加灵活方便。介绍了系统的关键参数,并通过ZEMAX软件对光学系统进行模拟分析,认为系统可以达到接近衍射极限的效果。传递函数MTF@50lp/mm达到0.25(对应视网膜上3μm),满足设计要求。     

基于高稳定性的PGC解调算法研究

为了解决传统相位生成载波(PGC)解调算法在光强扰动和调制深度漂移引起的解调失真现象, 采用基波混频和差分自乘的改进PGC解调算法, 进行了相关的理论分析和仿真验证。结果表明, 该算法能很好地抑制光强扰动引起的失真, 在引入1.5rad~3.5rad的光强扰动时可以达到近30dB的信纳比, 比传统的离散余弦变换算法高出近15dB; 同时能消除对调制深度C的依赖性, 可以实现低于0.1%的总谐波失真和30dB的信纳比, 比传统算法高出近10dB, 线性度高达99.99%。该研究为光纤干涉型传感的解调提供了一种新的方案。     

超宽带平坦多载波光源结构设计

为了解决波分复用系统中传统光源稳定性差、成本高、带宽小等问题,本文提出了一种超宽带平坦光源发生器结构,该结构基于级联的电吸收调制器和两个频率调制器,得到了频率间隔相同且可调的高带宽、平坦度小的多载波光源。在单波长光信号输入下,产生了大范围频率间隔可调平坦度小于0.2 dB的21个子载波的多载波光源,当驱动信号频率为8 GHz和9 GHz时,平坦度可达到0.07 dB;在多波长光信号输入下,得到了频率间隔为15 GHz,平坦度小于0.9 dB子载波数为275的超宽带平坦光源,频谱宽度可以达到THz以上。最后研究了10 GHz驱动信号下,电吸收调制器与频率调制器驱动信号的相位差、频率调制器的频率偏移以及电吸收调制器的啁啾因子对多载波光源的影响,结果表明,驱动信号的相位差在±10°上下波动时,平坦度最大改变了1.05 dB,频率调制器的频率偏移在±10 GHz范围内变化时,平坦度波动幅度仅为0.1 dB,表明该结构具有良好的稳定性和可控性。     

A tunable polarization-independent liquid-crystal Fabry-Perotinterferometer filter

The authors propose a simple structure for a tunable polarization-independent wavelength-selective filter. This successfully fabricated filter consists of a liquid crystal Fabry-Perot interferometer, a γ/4 plate, and a mirror. The input light is divided into a transmitted light and a reflected light. The polarization of this reflected light is rotated 90° by the γ/4 plate and the mirror and then this light is input again into the filter. The bandwidth is 0.48 nm and the tuning range is 50 nm. Fiber-to-fiber loss is approximately 3.9 dB and polarization dependence of the loss is approximately 0.3 dB     

Influence of reflected light on erbium-doped fiber amplifiers foroptical AM video signal transmission systems

Investigates experimentally the influence of reflected light on an erbium-doped fiber amplifier for use in optical AM frequency-division multiplexing (FDM) video distribution systems when reflection points exist before and after the amplifier. It is found that amplifier distortion is not affected by reflected light but that the signal gain and the noise figure of the fiber amplifier degrade with increased reflectivity. Gain was decreased by 3 dB when reflectivity after the amplifier was -12 dB. It was theoretically and experimentally clarified that the noise figure degradation was related to the internal reflection of the erbium-doped fiber, in addition to the reflection before and after the fiber amplifier. This internal reflection is caused by input signal light scattered within the erbium-doped fiber     

Low-loss singlemode amorphous silicon waveguides

Amorphous silicon waveguides were obtained by plasma-enhanced chemical vapour deposition and anisotropic plasma etching. Rectangular multimode waveguides as well as singlemode ridge waveguides were fabricated. Scattered light measurements at 1550 nm (1300 nm) wavelength showed a low propagation loss of /spl les/0.5 dB/cm (1.6 dB/cm) for multimode waveguides and 2.0 dB/cm (5.0 dB/cm) for highly-confined singlemode waveguides.     

Linearisation of optical transmitters by a quasifeedforward compensation technique

A quasifeedforward linearisation scheme is described suitable for linearisation of optical transmitters using GaAlAs double heterostructure Burrus-type light emitting diodes. Experimentally, an improvement was observed of, respectively, 33 dB and 17 dB in 2nd and 3rd order distortion for a figure of ?70 dB down on fundamental at 100 mA d.c, 100 mA peak-to-peak modulation currents.     

Low-loss planar lightwave circuit OADM with high isolation and nopolarization dependence

A passive optical add-drop multiplexer with 1 dB of insertion loss and 36 dB of isolation is fabricated by writing Bragg gratings in a waveguide Mach-Zehnder interferometer using ArF excimer laser light. The spectral properties and bit-error-rate performance of the device are fully characterized using polarized light     

Topology optimised broadband photonic crystal Y-splitter

A planar photonic crystal waveguide Y-splitter that exhibits large-bandwidth low-loss 3 dB splitting for TE-polarised light has been fabricated in silicon-on-insulator material. The high performance is achieved by utilising topology optimisation to design the Y-junction and by using topology optimised low-loss 60/spl deg/ bends. The average excess loss of the entire component is found to be 0.44/spl plusmn/0.29 dB for a 100 nm bandwidth, and the excess loss due to the Y-junction is found to be 0.34/spl plusmn/0.30 dB in a 175 nm bandwidth.     

An effective nonreciprocal circuit for semiconductor laser-to-optical-fiber coupling using a YIG sphere

A practical nonreciprocal optical circuit for laser-diode (LD)-to-optical-fiber coupling in the 1.3-μm wavelength region is described. It consists of a yttrium iron garnet- (YIG) sphere graded-index (GRIN) rod lens and a polarizer. The YIG sphere can function not only as a Faraday rotator but also as an effective coupling lens. High coupling efficiency of more than -5 dB for a single-mode fiber, and more than -2 dB for a multimode fiber, is easily achievable. Alignment sensitivities and coupling characteristics of the proposed circuit are also discussed theoretically and experimentally. The increase in LD relative intensity noise (RIN), caused by light injected into the LD, is estimated using the reciprocal characteristics of LD-to-single-mode-fiber coupling. By comparing the LD-RIN increase in the proposed non-reciprocal circuit with that of the reciprocal, high isolation of about 32 dB is confirmed. The fact that reflected light from the proposed circuit has little influence on LD characteristics is also clarified.     

Highly stabilized millimeter-wave generation by using fiber-opticfrequency-tunable comb generator

A novel optical generation and transport technique for millimeter-wave (mm-wave) signals by using the fiber-optic frequency-tunable comb generator having a discrete emission spectrum as the light source is proposed. 60 GHz mm-wave signal generation and transmission over a 108 km-long optical fiber link at λ=1560 nm is demonstrated. Excellent stability of both the frequency and amplitude of the mm-wave carrier is attained, so that the 3 dB linewidth is less than 0.3 kHz and the variance of the amplitude fluctuation is 0.07 dB. The advantages include tunability of the carrier frequency, handling ease, and no need for a high-speed external light modulator     

LiNbO3traveling-wave light modulator/switch with an etched groove

A Ti dffused lithium niobate traveling-wave interferometric light modulator/switch with a groove excavated at the electrode gap has been fabricated and tested at microwave frequency. The groove suppresses the undesirable light coupling between the two parallel waveguides for the phase shifting section so that the drive voltage is decreased by reducing the separation of the parallel waveguides, or of the electrodes. In addition, the groove decreases the effective index for the modulating wave to reduce the velocity mismatch between light wave and microwave so that the bandwidth is broadened. The modulation experiment was carried out from dc to 15 GHz at 633 nm light wavelength. For the modulator with the electrodes 6 mm long and 10 μm apart, the half-wave or switching voltage was 3 V, the extinction ratio was 18 dB, the 3 dB bandwidth was 12 GHz and aP/Delta fof 1.5 mW/GHz was obtained.