Wavelength reused upstream transmission scheme for WDM passive optical networks

A novel technique facilitating wavelength reused upstream transmission in a WDM passive optical network, eliminating wavelength source at ONUs, is proposed and experimentally demonstrated. A subcarrier frequency is used for downstream transmission and the pure optical carrier is filtered and reused for upstream transmission. The scheme requires only simple baseband receivers at both ONU and OLT terminals.     

利用基带直调信号注入锁定半导体激光器产生全光上变频信号的研究

提出了一种将低速基带信号直调产生的宽谱信号,注入至用于上变频的分布反馈式半导体激光器(DFB-LD),利用调制信号光谱中的高阶分量对从激光器进行相位锁定,从而产生光学上变频信号的方法。对直调信号注入锁定DFB-LD产生光学上变频信号的机理进行了理论分析,完成了2.5Gb/s伪随机码基带信号通过直调并注入从激光器,分别产生了30,35,40GHz副载波频率的全光上变频信号的实验,并在时域和频域上,对上变频信号的特征进行了研究。该方案结构简单,无需高速外调制器及高频本振,具有集成潜力,理论上可产生更高载频(如60GHz),对目前的光-无线混合接入提供了一种可行的解决方案。     

Optical Front-Ends to Generate Optical Millimeter-Wave Signal in Radio-Over-Fiber Systems With Different Architectures

We have proposed and experimentally demonstrated three different optical front-ends to implement in wavelength-division-multiplexing (WDM) radio-over-fiber (ROF) networks to minimize the cost of the ROF system. When the number of WDM channels is small, such as smaller than four channels, the simplest front-end to generate WDM optical millimeter (mm)-wave signals is to use only broadband direct-modulation laser (DML) for each WDM channel. In this case, the expensive external modulator can be removed. However, when the number of WDM channels is large, such as larger than four, the frond-end to generate WDM optical mm-wave signals can be realized by using an external modulator to upconvert simultaneously all channels after the WDM channel signals are multiplexed. In this way, the cost of the expensive external modulator will be shared by all channels. For seamless integration of WDM signals that come from the existing backbone with ROF system, a broadband external modulator can be used to upconvert WDM signals.     

Reconfigurable 2.5-Gb/s Baseband and 60-GHz (155-Mb/s) Millimeter-Waveband Radio-Over-Fiber (Interleaving) Access Network

In this paper, we propose a dynamic reconfigurable wavelength division multiplexed (WDM) millimeter-waveband radio-over-fiber (RoF) and baseband access network. We also demonstrate dynamic channel allocation capability of millimeter-waveband optical RoF and baseband signals in WDM access network using a supercontinuum (SC) light source, arrayed-waveguide gratings, and a reconfigurable optical crossconnect switch. The dynamic reconfigurable RoF and baseband network architecture is presented and its features are described. Two 155-Mb/s RoF channels and two 2.5-Gb/s baseband channels are effectively generated, transmitted through 25 km of fiber, switched, and then transmitted again through 2 km of fiber and detected with error-free operation (bit error rate $≪ 10^{-9}$). The proposed architecture allows the RoF and baseband to coexist and is highly scalable, both in terms of channel counts and access point (AP) counts.      

A 4-wavelength optical multi/demultiplexer for WDM subscriber loop systems using analog baseband video transmission

This paper describes the design principles and performance of optical multi/demultiplexers (MUX/DEMUX's) in wavelength-division multiplexing (WDM) subscriber-loop systems over a 50- μm core diameter, graded-index (GI), multimode fiber, which employ analog baseband video transmission using laser diodes (LD's). In this WDM arrangement, requirements for MUX/DEMUX's are: 1) low insertion loss; 2) no signal degradation caused by optical interchannel crosstalk; 3) only a small amount of analog baseband signal degradation caused by the use of MUX/DEMUX; 4) a small size and simple structure capable of multiplexing three or four wavelengths; and 5) good stability. The newly developed 4-wavelength MUX/DEMUX satisfies the preceding requirements and is suitable for application to WDM subscriber-loop systems using analog baseband signals along with digital signals.     

Converged Wireless and Wireline Access System Based on Optical Phase Modulation for Both Radio-Over-Fiber and Baseband Signals

We propose and experimentally investigate a scheme for transmitting a phase-modulated radio-over-fiber (RoF) signal along an existing fiber infrastructure without degradation of the existing baseband signal. Optical phase encoding of both signals, namely a baseband 21.4-Gb/s nonreturn-to-zero differential quaternary phase-shift keyed signal and a 5.25-GHz RoF carrying 1.25 Gb/s, enables the use of identical optical receiver structures. The experimental results show that both receivers achieve error-free operation after 80-km standard single-mode fiber transmission. The proposed scheme has potential applications for converged wireless and wireline optical access networks.      

Optical Microwave Frequency Up-Conversion Via a Frequency-Doubling Optoelectronic Oscillator

We propose and demonstrate an optical microwave modulator that incorporates a low phase-noise optoelectronic oscillator (OEO) for frequency up-conversion in a radio-over-fiber system. A single Mach-Zehnder lithium-niobate waveguide modulator working as a local oscillator in a frequency-doubling OEO directly up-converts the baseband signals to a carrier band. We demonstrate frequency up-conversion to the 20-GHz band for optical analog signals in the intermediate-frequency (IF) band and for optical digital signals at 1.25 Gb/s. The measured transmission bandwidth for IF modulated signals is greater than 1.5 GHz for transmission over 50.5 km of single-mode fiber.     

归零码信号注入FP-LD实现无本振光子上变频系统

提出了一种低速率归零码（RZ-OOK）信号注入法布里-珀罗腔激光二极管（FP-LD）的无本振光子上变频系统。利用外部注入信号光对FP-LD的一个自由振荡模式进行锁定从而得到一个微波的高频振荡,基于注入锁定机理进行了上变频原理分析,并通过实验方式验证了方案的可行性。实验中,2 Gb/s的RZ-OOK信号分别被上变频到12 GHz、14.28 GHz成为副载波信号。     

Optical Tandem Single-Sideband-Based WDM Interface for Millimeter-Wave Fiber-Radio Multisector Antenna Base Station

We propose and demonstrate a spectrally efficient wavelength division multiplexed (WDM) optical interface for millimeter-wave radio access networks with the capability of being integrated within a standard 100-GHz WDM infrastructure. The proposed WDM optical interface is realized by the use of a multiport optical circulator in conjunction with fiber Bragg grating filters. The interface supports demultiplexing of wavelength-interleaved optical tandem single-sideband modulated signals for a millimeter-wave fiber radio backbone with a sectorized antenna interface at the remote base station. The functionality of the interface is verified experimentally for RF signals at 29 and 31.6 GHz with 155-Mb/s binary phase-shift keying data. The effects of optical impairments on the transmission performance of WDM channels are experimentally analyzed. The experimental results demonstrate that the WDM optical interface performs efficiently with very low channel impairments due to optical crosstalk.      

ROF系统中基于SOA非线性效应的光子上变频技术研究

在光载射频（ROF）系统中,为了将承载信息的光基带信号上变频到微波／毫米波波段,本文基于半导体光放大器（SOA）中的交叉增益调制（xGM）和交叉相位调制（XPM）效应实现了光子上变频：即实现了1．25Gb／s基带信号到30GHz的毫米波信号的转换。文中分析了SOA驱动电流的变化（50～200mA）和信号光与本振光波长间...     

A novel hybrid WDM/SCM-PON sharing wavelength for up- and down-link using reflective semiconductor optical amplifier

A hybrid wavelength-division multiplexed/subcarrier multiplexed passive optical network (WDM/SCM-PON) which shares the same wavelength both up-link and down-link is presented by using a reflective semiconductor optical amplifier (RSOA) as a modulator. We investigated down-link of 622 Mb/s using distributed feedback laser diode with direct modulation and 100-Mb/s up-link using an RSOA as a modulator with 900-MHz SCM signal. In our scheme, a novel efficient and cost-effective WDM/SCM-PON using the same wavelength for down/up-link at each optical network unit is proposed and experimentally demonstrated.     

Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

Generation of optical millimeter-wave (mm-wave) signal using a Mach–Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM).      

Multiple input detection and digital signal processing for uncooled ONUs in a TWDM-PON with a commercial WDM demultiplexer

A simple uplink transmission scheme with multiple-input direct detection and digital signal processing has been proposed and experimentally demonstrated for the time and wavelength division multiplexed passive optical networks (TWDM-PONs), to allow wavelength drift of lasers at the uncooled optical network units (ONUs). In our experiment, after passing by the commercial 100-GHz WDM demultiplexer, three 10-Gb/s NRZ signals with minimum signal wavelength separation of 50-GHz can be recovered successfully after 50-km standard single-mode fiber (SSMF) transmission. Simulation results are also obtained to analysis the receiver sensitivity at different wavelength separations and discuss methods improving power budget.     

全双工光载无线隧道通信系统

鉴于长距离隧道内复杂的无线传输环境,传统通信技术不能满足旅客高质量的通信需求,提出了一种基于波分复用无源光网络的光载无线（RoF）分布式隧道通信系统。采用波分复用技术实现不同业务在光域的物理隔离,协同分布式天线技术,在隧道内部提供高频无线接入,提升系统带宽的同时解决了隧道内部信号急剧衰减的问题。通过实验搭建了全双工的光载无线试验平台,实现了用光学的方法产生和传输载频为24 GHz的16/64QAM矢量信号,并且通过测量上下行链路的EVM值验证了方案的可行性。     

Multiband Signal Generation and Dispersion-Tolerant Transmission Based on Photonic Frequency Tripling Technology for 60-GHz Radio-Over-Fiber Systems

We designed and experimentally demonstrated an efficient photonic frequency-tripling technology for 60-GHz radio-over-fiber systems to simultaneously realize millimeter-wave (mm-wave), microwave, and baseband signal generation. The technique utilizes vestigial sideband filtering in combination with optical carrier suppression to generate novel alternate subcarrier modulation for high tolerance of fiber dispersion. Experimental verification of the proposed scheme is presented with generation and error-free transmission of 2.1-Gb/s data on the 63-GHz mm-wave and 21-GHz microwave carriers over 50-km single-mode fiber (SMF-28) without dispersion compensation. The power penalty for both signals is less than 1.0 dB.      

A bidirectional lightwave transport system based on PON integration with WDM VLC

A novel bidirectional lightwave transport system employing phase modulation (PM) scheme and light injection-locked distributed feedback laser diode (DFB LD) as a duplex transceiver for passive optical network (PON); as well as employing laser pointer lasers (LPLs) with directly modulating data signals for wavelength-division-multiplexing (WDM) visible light communication (VLC) is proposed and experimentally demonstrated. Impressive and low bit error rate (BER) operation is achieved for PON integration with VLC application. Such bidirectional PON integration with VLC system has been successfully demonstrated, which can not only present its advancement in PON/VLC application but also reveal its simplicity and convenience to be installed. Whereby, our proposed system is suitably applicable to the PON in combination with VLC system in wire and wireless transmission.     

All-Optical Subcarrier Demodulation in Up-Link of WDM mm-Wave Radio-Over-Fiber System

We have proposed and experimentally demonstrated a scheme of all-optical broadband subcarrier demodulation in the up-link of wavelength-division-multiplexing (WDM) millimeter-wave radio-over-fiber systems. In this scheme, the subcarriers of all the WDM channels can be demodulated by only one optical demodulation module, hence its cost can be reduced remarkably. Because of its all-optical implementation, it can offer more bandwidth. The radio-frequency power degradation introduced by the channel dispersion is also avoided in this scheme even when the conventional simple double-sideband modulation method is employed in the base stations.     

Integrated optical multi-/demultiplexer using acoustooptic effectfor multiwavelength optical communications

Optical integrated switching systems using collinear acoustooptic (AO) interactions for wavelength division multiplexing (WDM) systems are discussed. The AO switch module has excellent advantages compared to electrooptic switches. Optical WDM signals can be wavelength-selectively switched by frequency multiplexed surface acoustic waves. WDM switching systems are proposed as an application of this AO switch, and optical insertion loss, crosstalk, and optical frequency shift are discussed. Wavelength-selective characteristics in the AO module are established. The crosstalk from other wavelengths is found to be reduced by decreasing slightly the switching transfer efficiency. The wavelength-selective switching was experimentally demonstrated with a slab-type module of a 4-mm interaction region, where the WDM interval of 25.2 Å was realized. This wavelength interval can be decreased by increasing the interaction length     

Carrier-Reuse WDM-PON Using a Shared Delay Interferometer for Separating Carriers and Subcarriers

We propose a novel optical carrier-reuse scheme for the wavelength-division-multiplexed passive optical network. The scheme is based on a single delay interferometer (DI) at the remote node and reflective semiconductor optical amplifiers (RSOAs) at optical network units as the colorless devices for upstream transmission. The downstream subcarrier signals are optically separated by the DI for baseband detection of the downstream data and the separated optical carriers are used for seeding the RSOAs. Eight-channel upstream and downstream transmission is demonstrated at 1.25 Gb/s using the proposed scheme. The impact of optical carrier-to-subcarrier ratio of downlink signal and seeding light power on performance is also investigated     

基于光学倍频技术的WDM-ROF-PON系统设计

设计了一种将光载无线技术融合于波分复用无源光网络结构的系统。在发射端,系统采用光学倍频技术生成40GHz光毫米波载波,加载2.5Gbit/s的基带数据信号,下行链路传输性能良好且受色散影响小;在接收端,利用光波重用技术从下行信号中提取上行光载波,加载2.5Gbit/s上行基带数据信号。采用光学倍频技术降低了毫米波生成成本,提高了系统的实用性。