Optical phase difference measurement and correction using AlGaAs integrated guided-wave components

A Y-junction interferometer phase measurement technique that is independent of the power or power ratio in the input arms has been developed. The technique is intended for use in the basic module of a proposed integrated optical system for use at GaAs wavelengths that produces a flat-phase output wavefront. A proof-of-concept AlGaAs guided-wave Mach-Zehnder interferometer was used to demonstrate measurement and correction of a phase difference between the arms using this phase measurement technique. Results have been obtained for the cases of successive steps in the phase difference between the interferometer arms, of random phase differences, and of a power imbalance of up to 30% between the arms.<>     

Access control module for local integrated optical network

The implemented access control module (ACM) for a multiservice high-speed network, which performs the access protocol functions, is presented. The operating speed of the module is at 18 Mbyte/s and the protocol delimiter recognition time is 30 ns. The use architecture provides a low cost implementation well suited for the use of custom or semi-custom VLSI implementation.<>     

Finite difference methods for the analysis of integrated optical waveguides

A finite difference method based on a Crank-Nicolson discretisation procedure has been implemented and applied to the analysis of propagation of optical beams in dielectric waveguides. It is based on a new formula which takes into account the correct boundary conditions. Comparisons with the well known BPM technique show a definite improvement in computer time saving, accuracy and ease of use.<>     

Finite element/finite difference propagation algorithm for integrated optical device

A propagation algorithm based on finite elements and a finite difference discretisation of the scalar wave equation is investigated as an alternative to the beam propagation method. The new approach overcomes the assumption of low contrast media in the BPM and allows the propagation of arbitrary input fields in strongly guiding structures.<>     

Integrated AlGaAs waveguide components for optical phase differencemeasurement and correction

A Y-junction interferometer phase measurement technique has been developed that is independent of the power or power ratio in the input arms. This technique was incorporated into a proof-of-concept AlGaAs guided-wave Mach-Zehnder interferometer to demonstrate the measurement and correction of a phase difference between the arms. In the first part of this paper, we describe the design, fabrication, and characterization of the individual AlGaAs dielectric-loaded rib waveguide components that were chosen to fabricate the proof-of-concept interferometer. These components include passive waveguides, bends and Y-junctions, and reverse-biased phase modulators. The composition of the waveguide layer was chosen so that these modulators would have low loss at the applied voltage required for maximum phase correction. The choice was based on electroabsorption measurements on test modulators as a function of the energy difference between the bandgap of the waveguide layer and the operating wavelength. The average propagation loss at 862 nm of the passive single-mode guides used was 1.1 dB/cm. The abrupt bend insertion loss was ~0.20 dB/bend for a 0.5° bend angle, and the Y-junction insertion loss was ~0.37 dB for 1.0° full angle. Two-mm-long p⁺ -n^--n⁺ phase modulators typically had V_π voltages of ~6.8 V. On a slightly modified structure, V _π voltages as low as 2.65 V were measured. In the last part of the paper, the proof-of-concept interferometer and test setup are described and recent phase difference measurement and correction data with intentional power imbalances greater than 90% between the interferometer arms are presented. These results demonstrate conclusively that the phase difference measurement and correction performance of the Y-junction interferometer technique are independent of the power ratio in the interferometer input arms for power ratios >10:1     

A DFB-LD module integrated with 60 dB optical isolator for coherentlightwave transmission systems

The coupling efficiency between the distributed feedback-laser diode (DFB-LD) chip is presented and the single-mode fiber is as high as -5.7 dB (27%) including the insertion loss of the isolator. The spectral linewidth measurement using the self-delayed heterodyne method shows 26 MHz under the condition of IF=I_th+50 mA. No changes in the DFB-LD chip properties are observed after packaging. The comparison to another DFB-LD module with a 30-dB isolator confirms the immunity of the spectrum against -14-dB Fresnel reflection. The results show that the DFB-LD module is sufficiently stable to be applied to the coherent lightwave transmission systems     

Passive phase correction for stable radio frequency transfer via optical fiber

The transfer of radio frequency (RF) signal via optical fiber is widely adopted in distributed antenna systems and clock standard disseminating networks. To suppress the phase variation caused by fiber length fluctuation, passive phase correction technique based on frequency mixing has been proved as a promising approach due to its significant advantages over the traditional active compensation technique in terms of complexity, compensation speed, and compensation range. The phase correction can be done either in the transmitter or in the receiver, but it usually requires many stages of electronic mixing and auxiliary microwave signals, which not only increases the cost of the link but also degrades the quality of the transmitted signal. In addition, the effect of chromatic dispersion, polarization mode dispersion, and coherent Rayleigh noise in the optical fiber will further deteriorate the phase noise of the signal after transmission. In this paper, an analytical model for the stable RF transfer system based on passive phase correction is established, and the techniques developed in the last few years in solving the problems of the method are described. Future prospects and perspectives are also discussed.     

大视场光学系统畸变曲线拟合

大视场光学系统由于非共轴、视场、焦距等因素的影响,光学设计比较复杂,光学系统的畸变比较大。针对这一问题,本文给出了一种准确、实用且易于实现的畸变曲线拟合方法,并提供了相应的计算机算法。该方法也为其它复杂光学系统的畸变校正提供了一种新思路。     

An integrated error correction and detection system for digitalaudio broadcasting

Hybrid in-band on-channel digital audio broadcasting systems deliver digital audio signals in such a way that is backward compatible with existing analog FM transmission. We present a channel error correction and detection system that is well-suited for use with audio source coders, such as the so-called perceptual audio coder (PAC), that have error concealment/mitigation capabilities. Such error mitigation is quite beneficial for high quality audio signals. The proposed system involves an outer cyclic redundancy check (CRC) code that is concatenated with an inner convolutional code. The outer CRC code is used for error detection, providing flags to trigger the error mitigation routines of the audio decoder. The inner convolutional code consists of so-called complementary punctured-pair convolutional codes, which are specifically tailored to combat the unique adjacent channel interference characteristics of the FM band. We introduce a novel decoding method based on the so-called list Viterbi algorithm (LVA). This LVA-based decoding method, which may be viewed as a type of joint or integrated error correction and detection, exploits the concatenated structure of the channel code to provide enhanced decoding performance relative to decoding methods based on the conventional Viterbi algorithm (VA). We also present results of informal listening tests and other simulations on the Gaussian channel. These results include the preferred length of the outer CRC code for 96-kb/s audio coding and demonstrate that LVA-based decoding can significantly reduce the error flag rate relative to conventional VA-based decoding, resulting in dramatically improved decoded audio quality. Finally, we propose a number of methods for screening undetected errors in the audio domain     

基于FFT相位差修正的伪码快捕方法

针对大频偏下高动态直扩接收机伪码捕获时间长的问题,提出了一种新的基于FFT相位精确估计频偏的改进方法。利用分段FFT频谱的相位差信息修正估计误差,以达到精确估计频偏的目的。理论分析和仿真结果表明,与传统的方法相比,该算法简单有效,具有较高的估计精度。     

Multigigabit multichannel optical interconnection module forbroadband switching system

This paper describes optical transmitter and receiver modules for package-to-package interconnection in broadband switching networks such as an asynchronous transfer mode switch fabric. These modules, which include the multiplexer and demultiplexer, can reduce the number of connections and the problem of skew between links. Five-channel optical transmitter and receiver modules were fabricated and demonstrated at 2.8 Gbit/s with a power dissipation of 4.5 W per channel. Moreover, temperature-insensitive optical interconnection was successfully demonstrated by driving a laser with a constant bias current over the threshold and by deducting the optical signal offset. The output power of the transmitter module was -4.2 dBm. Nonuniformity of the transmitter output powers across the range of optical channels was <2.1 dB. Receiver sensitivity for a bit error rate of 10^-11 was -9.3 dBm. Nonuniformity of the receiver sensitivities was <1.5 dB. The power penalty of the receiver sensitivity due to crosstalk was 1 dB. The connection distance was >250 m     

DWDM optical millimeter-wave generation for radio-over-fiber using an optical phase modulator and an optical interleaver

We have proposed and experimentally demonstrated a novel scheme to generate a dense wavelength-division multiplexing (DWDM) optical millimeter-wave source by using an optical phase modulator and an optical interleaver. The stability of the DWDM optical millimeter wave generation is largely improved because we use an optical phase modulator without a dc-bias controller and an optical interleaver is subsequently employed to suppress the optical carrier of the DWDM source, which is not as temperature sensitive as a fiber Bragg grating. Moreover, the limitation of chromatic dispersion is greatly reduced due to avoiding the generation of higher order sidebands via driving the phase modulator with optimized RF signal.     

部分校正自适应光学系统的激光导星阵

讨论了斯特列尔(Strehl)比为0.5的部分校正自适应光学望远镜所需要的人造导星数对望远镜口径及大气相关长度r0的依赖以及子孔径大于r0时对导星亮度的要求,最后给出在相应条件下产生钠导星所需要的激光能量。     

A DIL-type miniature optical transceiver module using an InGaAsPhalf-transmittance photodiode for TCM optical access networks

A compact DIL-type miniature optical transceiver module has been developed without using a conventional 3 dB optical coupler. This transceiver is composed of a newly designed InGaAsP half-transmittance photodiode (HT-PD) and a 1.3-μm multiquantum-well laser diode (MQW-LD). An HT-PD is used both as a photodetector and as a window for laser diode (LD) light. Fiber output power of 0 dBm at the drive current of 33.8 mA and responsivity of 0.58 A/W at the reverse-voltage of 2 V were obtained. The fundamental characteristics of the HT-PD are studied and discussed     

Non-reciprocity compensation correction and antenna selection for optical large MIMO system

This paper exploits an optical large multiple input multiple output (MIMO) system. We first establish the non-reciprocity compensation correction factor to solve the channel non-reciprocity problem. Then we propose an antenna selection algorithm with the goal of realizing maximum energy efficiency (EE) when satisfying the outage EE. The simulation results prove that this non-reciprocity compensation correction factor can compensate beam energy attenuation gap and spatial correlation gap between uplink and downlink effectively, and this antenna selection algorithm can economize the number of transmit antennas and achieve high EE performance. Finally, we apply direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) modulation in our system and prove that it can improve the bit error rate (BER) compared with on-off keying (OOK) modulation, so the DCO-OFDM modulation can resist atmospheric turbulence effectively.     

直接检测光OFDM相位特性分析

理论分析了直接检测光正交频分复用(DDO-OFDM)传输系统中信号的相住特性.分别讨论了与频率有关的非随机性噪声和其他随机性噪声对信号的影响;并在此基础上提出了一种简便的相位均衡方法.推导了系统Q参数与光信噪比之间的关系式.仿真验证了此相位特性和均衡方法的可行性.     

Resource management in an integrated optical network

We propose a novel integrated optical network switching architecture. The proposal offers an approach to signaling for the purpose of transport on an all-optical network of optical and nonoptical legacy network traffic. In order to provide effective end-to-end control and efficient transport services, new signaling and control techniques are required. Standard organizations such as Optical Interworking Forum (OIF) and Internet Engineering Task Force have developed interface methods between client and transport networks, as well as signaling processes for resource allocation. We propose a network controller, which implements interfaces for such integration in the intermediate future, as well as provides a feasible path for the long-term objective of all optical networking. Performance and capacity issues for these systems introduce new dimensions to the existing set of networking problems, since optical paths can now be set up in real-time. There are two main contributions in this paper: (1) functional composition of a network controller, which translates legacy signaling to optical connection signaling and path establishment and (2) determining when to issue an optical connection request based on the current network conditions such as link utilization, so that the integrated optical network can operate efficiently. Analytical approximations, as well as simulation results for call blocking performance are also presented.     

Dynamic range of an optical amplifier cascade in an ASK system withsignificant phase noise

The authors present detailed results concerning the dynamic range of an amplitude-shift keyed (ASK) heterodyne optical communication system where the transmitted signal is impaired by significant amounts of laser phase noise. Theoretical results are evaluated for a system with up to ten in-line optical amplifiers and a significant influence of the laser phase noise is found for the maximum allowable transmission span and the dynamic range. With ten amplifiers, a linewidth of 11% of the bit rate causes the span to be reduced by 12.2 dB and the dynamic range to be reduced by 5.7 dB. The results have been confirmed using two amplifiers in a field trial experiment at a bit rate of 636 Mb/s with an IF linewidth of 70 MHz     

光网监测系统的GIS模块实现技术

主要研究了GIS技术在光缆网络监测系统中的应用.针对系统GIS模块实现中的三个关键问题,提出了图形、属性数据分开独立存储管理同时通过图元ID值建立关联的数据管理思想,并在此基础上提出两类数据双向查询的模型,最后讨论了故障点地理位置的映射标注算法.