Tunable wavelength filter using nano-sized droplets of liquidcrystal

An electrically tunable optical filter has been developed that uses a polymer containing fine droplets of nematic liquid crystal as the active cavity in a Fabry-Perot interferometer (FPI). This FPI filter, whose finesse was 62, had a free spectral range of 37 nm in the 1.55-μm range with a full-width at half maximum of 0.6 nm and a transmission loss of 2.4 dB. The polarization dependent loss was smaller than 0.17 dB. The transmitted peak wavelength decreased with an electric field. This resulted in a tuning range of 10 nm at 300 V. The switching time was about 370 μs     

Part II: An example of the use of the comsis software: simulation of an optical network which uses wavelength multiplexing,fsk modulation format and direct detection

This second article deals with using the Comsis software for a particular application. Simulation is used to determine the maximum channel density in presence of crosstalk. In a first part, the modelling of the system is described. The simulation parameters of different optical elements are given. The results show that in the case of channels modulated at 500 Mbitls using fsk modulation format, and a direct detection operation at 1,5 μm, a minimum spacing of 6 GHz can be obtained with a 2 dB penalty. Thus if only the bandwidth of the erbium doped fibre amplifier is taken into account, the maximum number of channels which can be used is 250. However if the fsr (free spectral range) of optical filter is taken into account, the maximun number of channels is limited to 30.     

A wavelength-tunable semiconductor amplifier/filter for add/drop multiplexing in WDM networks

Reconfigurable channel drop in a wavelength-division multiplexed system is demonstrated using a packaged semiconductor amplifier/filter. The filter is electrically tunable over 9.0 nm with a 0.9-nm width and is used with an optical circulator to demultiplex three 5.0-Gb/s WDM channels spaced by 2.25 nm. A receiver sensitivity improvement and low optical crosstalk is observed over a dynamic range of nearly 10 dB.     

Tunable birefringent wavelength-division multiplexer/demultiplexer

A tunable wavelength-division multiplexer/demultiplexer, based on a polarisation-insensitive birefringent optical filter design, is described. The two channels of the device can each be tuned, with the channel separation adjustable over a wide range. Experiments with 6 to 30 nm laser channel separations have yielded optical crosstalk values of less than ?20 dB.     

级联臂长差啁啾MZI型带通滤波器的分析设计

为了设计出自由频谱区(FSR)较大和3dB带宽较小的带通滤波器,拟合级联马赫-曾德尔干涉仪(MZI)与阶梯形滤波器原理的相似性,在MZI中引入啁啾臂长差以有效扩展FSR.采用传输矩阵法建立带通滤波器的理论模型,进而分析其滤波性能(3dB带宽、FSR)与结构参数(级联级数、衍射阶数)的对应关系.结果表明,当合理选取啁啾系数,该滤波器在保持3dB带宽不变的前提下有效扩展了FSR,并且在整个FSR内具有高边模抑制比.在设计实例中,对应低于.5nm的3dB带宽和高于100nm的FSR(要求边模抑制比高于35dB)的滤波性能,器件的级联级数、衍射阶数、最佳啁啾系数分别对应16,5和5.     

Demonstration of a 15×15 arrayed waveguide multiplexer on InP

By interconnecting two star couplers with a waveguide grating, the authors built a monolithic 15×15 multiplexer on InP. The grating order of 148 gives a free spectral range of 10.5 nm (1.3 THz) and a channel spacing of 0.7 nm (87 GHz) at 1550 nm wavelength. A crosstalk between adjacent channels of less than 18 dB and a residual crosstalk of less than 25 dB were obtained. The on-chip insertion loss is typically 2-4 dB     

Frequency tuning characteristics and WDM channel access of thesemiconductor three-branch Y3-lasers

We describe frequency tuning and channel access characteristics of the new, widely-tunable, multi-quantum-well three-branch Y3-lasers. The Y3-lasers are tuned discretely with two independent current controls: coarse tuning (5.5 nm, 680 GHz tuning steps) selects the desired optical frequency range, fine tuning selects the desired frequency channel (0.4 nm, 50 GHz channel spacing). For example, we demonstrate access to 50 channels over the ~31 nm free spectral range of the Y3-laser; 36 contiguous channels are accessed using three independent current controls. The coarse/fine “digital” tuning makes Y3-lasers very useful for wavelength-division-multiplexed (WDM) multi-channel optical communication systems     

Bragg gratings on InGaAsP/InP waveguides as polarizationindependent optical filters

The fabrication and operation of Bragg gratings for future wavelength-division multiplexing (WDM) devices in integrated optical circuits are discussed. Crosstalk attenuation of more than 20 dB with respect to the optical power and spectral bandwidths of up to 2.2 nm were achieved. Polarization-independent operation of the gratings, an important qualification for their operation in fiber optical transmission systems, was demonstrated with a filter bandwidth of 0.2 nm at -10 dB and channel spacings as small as 1 nm     

一种降低列阵波导光栅相邻信道串扰的方法

阵列波导光栅 (AWG)作为波长滤波器在光通信领域具有很大的应用前景。串扰是影响阵列波导光栅应用的重要因素之一。为了降低阵列波导光栅相邻信道的串扰 ,本文提出并研究了一种降低阵列波导光栅的新方法。该方法利用阵列波导光栅的衍射特点性 ,通过调节阵列波导光栅的自由光谱范围 (FSR)、罗兰圆焦距和阵列波导数目 ,使得各信道信号的输出极小值处于其它信道输出波导中心 ,无次极大处于其它波导中 ,从而降低了阵列波导光栅的串扰 ,特别是相邻信道之间的串扰。通过光束传播方法 (BPM)的模拟了具有不同FSR的 1× 16阵列波导光栅 ,结果显示 ,该方法能将相邻信道之间的串扰降低约 5 .7dB。     

An adaptive wavelength tunable optical filter employing anangle-tuned interference filter and an intelligent digital controller

This paper describes an adaptive wavelength tunable optical filter, which is composed of an angle-tuned interference optical filter and an intelligent digital controller. The new angle-tuned interference filter consists of a dielectric interference optical filter and a piezoelectric angle-tuning mechanism. It achieves quick wavelength switching within 2.5 ms in a 30 nm tuning range and a sufficiently low crosstalk less than -30 dB. The intelligent digital controller has two functions: wavelength tracking and wavelength channel selection. Combining these technologies, we have developed a practical low-cost tunable filter suitable for a post-optical-amplifier filter in a high-sensitivity detection system and a channel selector in a WDM system that requires 10-100 ms channel selection time. With a wavelength tracking operation, we have confirmed -35 dBm high-sensitivity detection in 20 nm wavelength range in a 10 Gb/s system. We have also confirmed a wavelength channel selection operation within 18 ms in a three-channel wavelength division multiplexed (WDM) system whose channel spacing is 4.4 nm     

Cascaded coupler Mach-Zehnder channel dropping filters forwavelength-division-multiplexed optical systems

We describe the design and characteristics of cascaded coupler Mach-Zehnder (CMZ) channel adding/dropping filters that select every nth channel (n=2,3,4,...) from the wavelength-division-multiplexed (WDM) optical signal. Using the truncated binomial coupling weight distribution, which appears to be optimal, such filters achieve low (<-30 dB) sidelobe levels and good finesse with just a modest number of stages. We also show that the number of filter stages grows only linearly with the required filter finesse and thus the number of selectable channels. Such WDM filters can be conveniently implemented using the silicon or InP integrated optical technology     

High-gain low-noise mid-infrared quantum cascade optical preamplifier for receiver

Optical preamplifier (OPA) in the mid-infrared can boost weak signals in systems such as lidars or optical wireless links to improve the receiver sensitivity. Quantum-cascade-based traveling-wave OPA with off-normal Bragg-grating (BG) coupled surface-emitting configuration have been developed with a net small-signal gain up to 13 dB over a spectral range /spl sim/70 nm around 4.7 /spl mu/m, limited by the wafer gain bandwidth, and the linear dynamic range was >20 dB. Amplified spontaneous emission (ASE) was measured and the spontaneous emission factor was determined N/sub sp//spl sim/1, indicating near quantum-limit noise behavior. Surface-emitting BG devices yielded diffraction-limited output beam, and provided simultaneous wavelength dispersion and ASE filtering. The OPA was coupled with a detector to form a receiver that is polarization-selective, has a net gain 8-13 dB with a corresponding optical filter bandwidth 25-50 GHz. These results suggest that BG-coupled OPA receivers can be useful for multispectral/wavelength-division-multiplexing systems in free space applications.     

Design and Application of Compact and Highly Tolerant Polarization-Independent Waveguides

In this paper, the design, fabrication, and application of a highly tolerant polarization-independent optical-waveguide structure suited for operation in the third communication window is presented. The waveguide structure has been optimized toward minimized sensitivity to technological tolerances and low fabrication complexity. The tolerance analysis has been based on the typical processing tolerances of the widely applied silicon-oxynitride technology, being plusmn3times10 ^-4 in refractive index, plusmn1% in thickness, and plusmn0.1 mum in channel width. The optimized waveguide design fulfills the criterion of a channel birefringence within 5times10^-5, including processing tolerance. It also enables a fiber-to-chip coupling loss below 1 dB/facet and is suited for the realization of low-loss bends with a radius down to 600 mum. Based on this waveguide design, a passband-flattened optical wavelength filter with 50-GHz free spectral range has been realized and tested. The measured TE-TM shift of 0.03 nm confirms the polarization dependence of the optical waveguides being as low as 3times10^-5     

基于微环谐振器的超紧凑微波光子滤波器的设计

设计了一个基于硅基微环的超紧凑的微波光子滤波器,用以提高硅基微波光子器件的集成密度及增大其自由光谱范围。根据波导光学的耦合模理论,推导出双环并联谐振器的光强传递函数,并通过仿真得到了微波光子滤波器的输出特性。结果表明:当微环半径为0.79 m时,谐振器中直波导宽度为0.3 m,环形波导宽度为0.25 m,滤波器的自由光谱范围为140 nm,插入损耗为0.5 dB,半峰全宽为7 nm,此滤波器的性能完全满足粗波分复用系统的要求。     

Parallel-cascaded semiconductor microring resonators for high-order and wide-FSR filters

We demonstrate an optical channel dropping filter (OCDF) using three parallel-cascaded vertically coupled microrings with improved rolloff, bandpass flattening, and wide free spectral range (FSR) compared to a single-ring OCDF using single-mode tightly confined waveguides in both GaAs-AlGaAs and GaInAsP-InP. We achieve FSRs of 30 nm for GaAs-AlGaAs and 40 nm for GaInAsP-InP devices, which are three and four times greater, respectively, than those for single rings. The rolloff is 2.8 times faster than that for a single ring.     

热光聚合物微环谐振腔滤波器的研究

设计并制备了一种热光聚合物微环谐振腔滤波器。微谐振环采用跑道型结构,通过光束传播法(BPM)对其弯曲半径进行了设计和优化。采用传统的接触式光刻曝光工艺制备了微环谐振腔滤波器并对其进行了光谱测试,实验结果表明,所设计的器件在1 550nm附近的自由光谱范围(FSR)为112pm,消光比约为12.8dB,3dB带宽约为0.026nm,品质因子Q为5.96×104,调制效率是6.13pm/mW;同时测量了器件的响应时间,得到的响应时间约为1.5ms。     

Polymer micro-ring filters and modulators

Micro-ring wavelength filters and resonant modulators using polymer materials at 1300 nm and 1550 nm are analyzed, designed, and demonstrated. The rings are integrated with vertically coupled input and output waveguides. The devices are fabricated using optical lithography. Filters with a finesse of 141 and free spectral range of 5 nm at 1300 nm and finesse of 117 with a free spectral range (FSR) of 8 nm at 1550 nm are demonstrated. Ring resonators with a Q as high as 1.3 /spl times/ 10/sup 5/ at 1300 nm are demonstrated. The filters can be temperature tuned at the rate of 14 GHz//spl deg/C. Resonant ring modulators, which use an electrooptic polymer, are demonstrated. The resonance wavelength voltage tunes at the rate of 0.82 GHz/V. The modulators have a bandwidth larger than 2 GHz. Using the resonant modulator, and open eye diagram at 1 Gb/s is demonstrated.     

Four-channel integrated-optic wavelength demultiplexer with weakpolarization dependence

A planar four-channel wavelength demultiplexer with weak polarization dependence is proposed and demonstrated. This demultiplexer is based on an optical-phased array. An experimental device with dimensions 4.5×3.2 mm² was designed and fabricated, using conventional (high-quality) optical lithography. The demultiplexer operates in the wavelength range 776.5-781.2 nm, with a channel spacing of 1.55 nm. Insertion loss was 0.6 dB for the central channels and 1.2 dB for the outer channels for transverse-electric (TE) polarization, excluding 1.3-dB waveguide propagation loss. Crosstalk values measured 15.4-29.7 dB for the TE and 13.4-22.2 dB for the transverse-magnetic (TM) polarization     

Wide tuning range and low operating power AWG-based thermo-opticwavelength tunable filter using polymer waveguides

Two types of polymer thermo-optic wavelength tunable filter (TOWTF) have been developed, each with a pair of triangular phase shifters. One filter is designed for a large-scale WDM system (32 channels, 0.8 nm spacing), the other for a small-scale WDM system (10 channels, 0.8 nm spacing). The arrayed waveguide number is optimised thus reducing the operating power required by the filters. Moreover, both filters operated with a low crosstalk of <-25 dB     

基于硅纳米线波导的16通道200GHz阵列波导光栅

设计了基于硅纳米线波导的16通道,通道间隔为200GHz的阵列波导光栅(AWG)。传输函数法模拟了器件传输谱,结果表明器件的通道间隔为1.6nm,通道间串扰为31dB。器件利用SOI材料,由193nm深紫外光刻工艺制备。光谱测试结果分析表明,通道串扰为5-8dB,中心通道损耗2.2dB,自由光谱区长度24.7nm,平均信道间隔1.475nm。详细分析了器件谱线畸变的原因。