Coherent Transmission Direct Detection MIMO Over Short-Range Optical Interconnects and Passive Optical Networks

Building on a recently introduced quadratic multiple-input multiple-output (Q-MIMO) channel model making use of quadratic forms instead of linear channel matrices, we explore diverse signaling formats over the Q-MIMO channel in the frequency flat regime, highlighting the unique characteristics of optical multimode fiber (MMF) systems versus their wireless counterparts. In particular, we treat multiple-input single-output multimode fiber systems, comparing them with single-input single-output MMF systems and obtaining insight into the possibility of efficiently coupling the output of an MMF into a single-mode fiber. We further treat vector amplitude modulation over MMF MIMO and study the receiver zero-forcing (ZF) technique for MMF MIMO transmission, deriving its performance and comparing with a recently introduced ZF beamforming technique based on precoding at the transmitter, which is shown to be superior to receiver ZF.      

OWC中DPPM调制解调技术研究

调制解调技术一直是光无线通信(OWC)领域中的研究热点之一.较之脉冲位置调制(PPM),差分脉冲位置调制(DPPM)是一种光功率利用率和带宽利用率都较高的调制方式.本文对PPM调制和DPPM调制进行了比较分析,提出了基于FPGA的DPPM调制解调系统的设计方案.硬件仿真结果表明,该系统性能稳定,可以应用到光无线通信系统中.     

Discrete Multitone Modulation for Maximizing Transmission Rate in Step-Index Plastic Optical Fibers

The use of standard 1-mm core-diameter step-index plastic optical fiber (SI-POF) has so far been mainly limited to distances of up to 100 m and bit-rates in the order of 100 Mbit/s. By use of digital signal processing, transmission performance of such optical links can be improved. Among the different technical solutions proposed, a promising one is based on the use of discrete multitone (DMT) modulation, directly applied to intensity-modulated, direct detection (IM/DD) SI-POF links. This paper presents an overview of DMT over SI-POF and demonstrates how DMT can be used to improve transmission rate in such IM/DD systems. The achievable capacity of an SI-POF channel is first analyzed theoretically and then validated by experimental results. Additionally, first experimental demonstrations of a real-time DMT over SI-POF system are presented and discussed.      

Decision-Feedback Equalization for Pulse-Position Modulation

In this paper, we propose a minimum mean squared error (MMSE) decision feedback equalizer (DFE) for pulse position modulated (PPM) signals in the presence of intersymbol interference (ISI). While traditional uses of PPM may not have had ISI, PPM is increasingly being considered for use in situations where ISI is an issue, such as high-performance optical communication systems and ultrawideband communications. First, we review previous work on the subject which used the zero-forcing criterion under strict assumptions about the channel and equalizer lengths. Then, we derive a computationally efficient MMSE equalizer which removes these restrictions, and is suitable for use with training-based stochastic gradient-descent algorithms. Finally, we demonstrate the performance of the proposed equalizer with simulations.     

Loop-Back Optical Heterodyne Technique for 1.0-Gb/s Data Transmission Over 60-GHz Radio-On-Fiber Uplink

An optical-heterodyne-detection method for a 60-GHz radio-on-fiber uplink is proposed and verified in this paper. The main point of this proposal is that all the functions needed for the optical heterodyne detection, i.e., the local/carrier light sources, the automatic frequency control of these light sources, and a polarization-diversity-detection circuit, are consolidated in one transmitting-side module to realize a simple system configuration. This proposal realizes an adequate optical uplink budget with low-cost optical receivers that consist of just one IF-band photodetector and one envelope detector. A 1.0-Gb/s transmission experiment over 10 km of single-mode fiber, which represents access-network transmission, is demonstrated using a 61.0-GHz amplitude-shift-keying signal as a 60 GHz-band uplink signal. A BER of less than 10-9 was obtained at an uplink SSB signal power of -40 dBm regardless of the polarization state of the optical uplink signal, and no significant dispersion-induced degradation was noted.     

激光外差对不合作目标的探测研究

利用激光外差探测原理实现综合孔径激光雷达探测越来越受到关注.文中通过二极管泵浦固体激光外差探测实验,实现了实验平台上接受目标反射微弱回波信号的外差探测,并进一步实现了对表面粗糙的若干漫反射目标,即不合作目标的外差探测.总结了实现激光外差探测应用于综合孔径激光雷达领域的必要条件.     

Spectrally Efficient Compatible Single-Sideband Modulation for OFDM Transmission With Direct Detection

A combination of orthogonal frequency-division multiplexing (OFDM) and compatible single-sideband modulation (CompSSB) using a standard direct-detection scheme is suggested to overcome chromatic dispersion without explicit compensation. Since the proposed type of SSB modulation does not require a spectral gap between optical carrier and subcarriers, it is highly spectrally efficient and the complexity in the analogue part is reduced compared to known direct-detection schemes for OFDM.     

Applications of Optical Fibers for Overhead Transmission Lines

Optical fibers are increasingly in use for overhead transmission lines. Optical fiber cables for overhead transmission lines can be classified into three types; composite type, winding type, and self-supporting type. For the composite type, an FRP-covered optical fiber unit is suitable because of its good thermal and mechanical characteristics. Winding-type fiber cable is least expensive to install on existing overhead transmission lines. A dc arc test showed that the winding type can be applied to a ground wire because of its resistance to lightning. The winding type was applied to the ground wire of a 275-kV line, using a remote-controlled winding machine.     

Cascadability of Optical 3R Regeneration for NRZ Format Investigated in Recirculating Loop Transmission Over Field Fibers

This letter demonstrates optical 3R regeneration in 10-Gb/s nonreturn-to-zero field transmission. The 3R regenerator utilizes semiconductor-optical-amplifier-based Mach–Zehnder interferometer wavelength converters, a synchronous modulator, and a Fabry–PÉrot filter to realize optical 3R regeneration including all-optical clock recovery. The cascadablity of the 3R regenerator is investigated in recirculating loop transmission experiments with various regeneration spacings up to 462 km (corresponding to an input optical signal-to-noise ratio (OSNR) of 22 dB). Transmission with the 3R regenerator shows significant performance improvement over that without 3R regeneration. A 66-km-spaced 3R regeneration with a 33-dB input OSNR achieves 1000-hop cascaded error-free transmission (66 000 km in distance) with no hop-to-hop power penalties. A 264-km-spaced 3R regeneration with a 25-dB input OSNR also achieves 100-hop cascaded transmission (26 400km in distance) with a bit-error-rate error floor at$sim 1times 10 ^-8$.     

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.     

单模光纤中光脉冲啁啾的分析

论述了啁啾光脉冲在单模光纤中传输时啁啾和脉宽的变化，以及此变化与相应的频谱相位变化的关系．详细分析了啁啾变化的规律，并讨论了其物理图像及该规律在光纤通信中的应用．实验中所获得的脉宽变化与理论计算相符。     

RF Carrier Frequency Selection for Incoherent MIMO Transmission Over MM Fibers

In this paper, incoherent multiple-input multiple-output (MIMO) systems operating over multimode fiber are analyzed theoretically. In particular, investigated is the influence of selection of the RF carrier frequency and other system parameters on the value of SNR at the MIMO receiver. It is shown that the RF carrier frequency should be greater than the baseband (3 dB) frequency. Furthermore, it is proved that the MIMO channel SNR reduction is smaller if the mode groups used for communication between transmitter/receiver pairs are different.     

Full-Duplex 1.0 Gbit/s Data Transmission Over 60 GHz Radio-on-Fiber Access System Based on the Loop-Back Optical Heterodyne Technique

Full-duplex transmission over a 60 GHz radio-on-fiber access system based on the optical heterodyne technique is verified in this paper. With this technique, an optical carrier generator on the transmitting side consolidates the functions of wavelength and polarization control for optical heterodyne detection in uplinks and optical millimeter-wave generation in downlinks, on behalf of each optical transmitter/receiver. Therefore, the whole system configuration can be significantly simplified. A full-duplex 1.0 Gbit/s transmission experiment over 10 km of single-mode fiber, which represents an access network transmission, is demonstrated using the simultaneous modulation/photodetection operation of an electroabsorption modulator (EAM). Bit error rates of less than 10$^{-9}$ were obtained in both the uplink and downlink without noticeable mutual interference, even though the laser source and the EAM is shared by both links, and no significant dispersion-induced degradation was observed. Moreover, the experimental results showed that an optical link budget of 9.2 dB can be achieved with the experimental configuration.      

光纤中的互相位调制效应及其应用

单模光纤中的互相位调制是一种很重要的非线性光学效应.在介绍互相位调制原理的基础上,系统地综述了其应用情况,指出了应用中存在的一些问题,以及若干情况下互相位调制效应对系统性能的不利影响.     

Analysis of the Additional Modulation of Semiconductor Lasers Using Optical Heterodyne Techniques

In this letter, the power spectrum of a cooled distributed feedback laser module is measured using the self-heterodyne technique. Periodical oscillation peaks have been observed in the measurement. Further investigation shows that the additional modulation signal is coupled from the thermal electric cooler (TEC) controller to the laser driver, and then applied to the laser diode. The additional modulation can be eliminated by properly isolating the laser driving source from the TEC controller.     

Receiver Performance for Heterodyne Optical Communication

A model for the heterodyne optical channel that is consistent with experimental observations is introduced, and a general maximum-likelihood sequence estimation receiver that accounts for laser phase instabilities is proposed using the generalized log-likelihood functional. The performance of various suboptimal "estimator-correlator" receivers, obtained from optimal, nonimplementable receiver equations, is studied by simulation and compared to that of an incoherent receiver for practical parameter values. It is observed that, for hard decisions, the proposed receiver performs significantly better than an incoherent receiver for bit intervals larger than about half the coherence time of the laser oscillators, with larger gains to be expected when soft decisions on long sequences are made. A way of reducing the complexity of the soft-decisions receiver for long sequences is discussed.     

利用光外差检测技术的光纤温度传感器

本文报导以频率稳定的纵向塞曼激光器为光源,高度内禀双折射偏振保持光纤为传感元件,并利用光外差检测技术而制作的温度传感器。理论分析了实验系统工作机理,并给出系统主要性能参数。     

半导体激光器微腔结构调制的脉码在光纤中的传输

对于平面结构微腔半导体激光器的微腔结构调制，数值模拟了其输出二进制脉码在光纤中的传输眼图，给出了双态对应的微腔结构参数与脉码在线性光纤中无误码传输最大距离的数值对应关系。     

具有饱和非线性的非克尔光纤中自相位调制效应所致啁啾

在考虑光纤损耗下,从理论上推导出具有饱和非线性的非克尔光纤中自相位调制效应产生啁啾的解析表达式;并在计算机上模拟了光纤中啁啾的演变过程。结果表明,非克尔光纤中的饱和效应越强,自相位效应所产生的啁啾越小;随着光纤传输,啁啾不断增大;而且啁啾与光纤损耗、入射脉冲的峰值功率等因素有关。     

Cross-Polarization Modulation Domain Wall Solitons for WDM Signals in Birefringent Optical Fibers

Nonlinear cross-polarization modulation between two wavelength multiplexed channels propagating in an elliptically birefringent optical fiber leads to polarization domain wall solitons. These solitons represent a switching of the polarization of both waves between two stable orthogonal states. The potential application of polarization domains to nonlinear loss-free polarizers is described.