A Low-Cost 16 Quadrature Amplitude Modulation Direct-Detection–Orthogonal Frequency-Division Multiplexing Radio-over-Fiber System Using Low-Cost Direct-Modulation Laser to Generate Optical mm-Wave

Abstract

This article demonstrates a novel scheme to generate 16 quadrature amplitude modulation orthogonal frequency-division multiplexing signals for radio-over-fiber systems using a low-cost direct-modulation laser to generate an optical millimeter-wave. Mathematical analysis of that system is also investigated. The fiber Bragg grating is employed because the repetitive frequency of the radio frequency source and the bandwidth of the optical modulator are largely reduced, and the architecture of the radio-over-fiber system is simpler. Because no expensive broadband external modulator is used, the overall system is considered a low-cost solution. The simple structure and low cost of the radio-over-fiber system is attractive for the future cost-effective systems.     

Alternative Wired and 60-GHz Wireless Full Duplex Access Based on a Polarization Orthogonal Dual-Tone Optical Millimeter-Wave Signal

Abstract

A novel full duplex fiber wireless link providing alternative wired and 60-GHz wireless access is proposed based on a polarization orthogonal dual-tone optical millimeter-wave signal. In a hybrid optical network unit, the downlink optical signal can be decomposed as a single-sideband optical millimeter-wave signal (baseband optical signal) for wireless (wired) access by a polarization controller and polarization beam splitter. The uplink optical carrier abstracted from the downlink optical signal makes the hybrid optical network unit free from the optical source. The simulation results show that both downlinks and uplinks for either wired or wireless access can maintain quite good performance over 60 km of fiber.     

A full-duplex radio-over-fiber system using direct modulation laser to generate optical millimeter-wave and wavelength reuse for uplink connection

In this paper, we present a full-duplex radio-over-fiber system incorporating both optical millimeter-wave (mm-wave) generation and wavelength reuse for uplink connection. The optical double sidebands (DSB) signal is generated by using only one inexpensive broadband direct modulation laser (DML), to which a mixing RF signal is applied. An optical interleaver is then used to separate the first-order optical sidebands from the optical carrier of optical DSB signal. The separated first-order optical sidebands are beat to generate mm-wave signal that has double the frequency of the RF drive signal, while the separated optical carrier is reused as light source to remodulate uplink signal. Both detailed theoretical analysis and experiments to demonstrate the feasibility of the proposed system are presented. Experiment result shows that the bidirectional 2.5 Gb/s data can be successfully transmitted over 40 km standard single-mode fiber (SSMF) with less than 2 dB power penalty.     

Full-Duplex Radio-over-Fiber System Based on a Novel Octupling mm-Wave Generation Scheme

Abstract

A novel mm-wave generation scheme based on two phase modulators and two unbalanced Mach-Zehnder interferometers is proposed. Compared with the conventional Mach-Zehnder modulator-based scheme, the phase-modulator-based scheme can work steadily without an electrical control circuit for the DC bias, and it has smaller insertion loss. A full-duplex radio-over-fiber system was investigated by simulation, and its performance is not affected by chromatic dispersion for both downstream and upstream transmission. A 40-GHz mm-wave is generated from a 5-GHz driving signal. The system performance is analyzed by using eye diagrams and bit error rate. Results demonstrate that the performance is still very good, even after a 50-km transmission.     

基于综合光学调制技术的光纤无线双向通信系统设计

提出并研究了一种使用单光源的光纤无线双向传输系统.该系统只需在中心站配置一个可调谐激光器,以产生频率恒定的激光光源,通过综合光学调制（频率调制、强度调制）技术将基带信号调制到光载波上,最终形成60 GHz毫米波下行信号|同时,相同的光载波在基站被重用,作为上行链路传输光源.系统结合光载波重用技术和综合调制技术特点,合理利用资源,基站结构更为简化.仿真结果表明,该系统可以将速率达2.5 Gbit/s的数据在单模光纤中双向传输20 km,功率代价小于0.5 dB,相对已有的技术方案,该传输系统在传输功率、传输距离、传输性能方面具有明显优势.     

A novel full-duplex radio-over-fiber system based on dual octupling-frequency for 82 GHz W-band radio frequency and wavelength reuse for uplink connection

A novel full-duplex radio-over-fiber system is proposed and demonstrated, in which an external modulator and an optical interleaver are used to generate dual octupling-frequency optical millimeter waves for two base stations and wavelength reuse for uplink connection. This scheme is simplified and low-cost because no additional laser is utilized for uplink connection at two base stations and one laser at central office works for two base stations simultaneously. The frequency of local oscillator signal is reduced largely due to frequency octupling. The theorem about how to generate optical millimeter waves is analyzed. The simulation results show that the bidirectional 5 Gb/s system has a perfect performance because the power penalty for the downlink and uplink signals of two base stations are less than 0.6 dB after successful transmission over 60 km standard single mode fiber.     

A full-duplex radio-over-fiber system based on frequency decupling

A full-duplex radio-over-fiber system using frequency-decupling optical millimeter-wave based on external modulation via a Mach–Zehnder modulator is proposed and analyzed theoretically. The simulation results show that the power penalties for both the downstream and upstream signals are less than 0.5 dB. In this scheme, the configuration of a base station is simplified due to no laser at a base station, and the frequency of local oscillator signal is largely reduced due to the frequency-decupling millimeter-wave technique. The costs of central office and base station are largely reduced.     

The transmission performance of the single sideband optical millimeter-wave with BPSK signal in the duplex radio-over-fiber link

This paper has investigated the transmission performance of the single sideband (SSB) optical millimeter (mm)-wave with signal carried by the sideband in BPSK format in duplex radio-over-fiber (RoF) system theoretically and numerically. The SSB optical mm-wave signal is generated by a LiNbO₃ Mach–Zehnder modulator and there exists an optimal modulation index to generate the SSB optical mm-wave with a maximal RF photocurrent. The SSB optical mm-wave is much suitable for the duplex ROF link with the uplink lightwave recovered from the downlink because the optical carrier carries no signal. In such a duplex RoF link, although there are the spurs on the optical carrier, they have little influence on the downlink and the uplink signal even if the modulation index is large.     

Generation of millimeter-wave in optical pulse carrier by using an apodized Moiré fiber grating

A novel scheme is proposed to transform a Gaussian pulse to a millimeter-wave frequency modulation pulse by using an apodized Moiré fiber Bragg grating in radio-over-fiber system. The relation between the input and output pulses is analyzed theoretically by Fourier transformation method and the requirements for the proposed fiber grating are presented. An apodized Moiré fiber Bragg grating is designed and its characteristics are studied. It is shown that the proposed device is feasible, and the new scheme is believed to be an effective solution for the generation of millimeter-wave sub-carrier in future radio-over-fiber systems.     

Full-duplex radio-over-fiber system based on a modified single-side band modulation

A full-duplex radio-over-fiber system based on a modified single-sideband using external modulator is proposed and demonstrated. At the central station, a CW lightwave is intensity-modulated by a RF signal to generate a DSB signal. After the central carrier and the two first-order sidebands are separated by a FBG, the central carrier is modulated with a baseband data at 2.5 Gbit/s. Then, it is recombined with the un-modulated first-order sidebands to generate optical millimeter-wave by an optical coupler with a certain coupling coefficient and transmitted to the base station over single-mode fiber. The central carrier and one of the first-order sidebands are beaten to generate the mm-wave when they are detected by an optical receiver. Another first sideband is reused as carrier for uplink connection. The dispersion performance of the generated mm-wave is theoretically analyzed; one can see that the effect of dispersion and requirement of the optical power are reduced. The PIN-PD can avoid working in a high-DC saturation range which may distort the RF components and depress the responsibility of the detector. The stimulant results show that the system can reduce the effect of dispersion effectively, and immune the fading effect and the walking-off signals. It is suitable for a long distance transmission.     

Performance improvement and wavelength reuse in millimeter-wave radio-over-fiber links incorporating all-fiber optical interleaver

Simultaneous downlink performance improvement and uplink wavelength reuse in a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) system by using a simple and cost-effective all-fiber optical interleaver are proposed and demonstrated. The MMW RoF downlink performance improvement is based on suppressing optical carrier-to-sideband ratio (OCSR), with which the mechanism is confirmed by theoretic analysis and derived experimental results. Measured results show that, by suppressing OCSR using a fabricated all-fiber optical interleaver, the downlink optical receiver sensitivity is improved about 2.1 dB. The downlink data rate is 1.25 Gbit/s and the carrier frequency is 58.1 GHz; the link consists of 6 km optical single-mode fiber and 1 m wireless connection. On the other hand, with the interleaver suppressing downlink OCSR, simultaneously an optical carrier is recovered from the RoF downlink and is reused for RoF uplink transmission. The uplink is operated at 62.9 GHz and the data rate is the same 1.25 Gbit/s. With the recovered optical carrier, a laser-free remote access point is achieved. The principle, structure, and fabrication of an all-fiber optical interleaver are also presented in this paper.     

A novel OCS millimeter-wave generation scheme with data carried only by one sideband and wavelength reuse for uplink connection

We propose a novel optical carrier suppression (OCS) millimeter-wave generation scheme with data carried only by one sideband using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system, and the transmission performance is also investigated. As the signal is transmitted along the fiber, there is no time shifting of the codes caused by chromatic dispersion. Simulation results show that the eye diagram keeps open and clear even when the optical millimeter-waves are transmitted over 110 km and the power penalty is about 1.9 dB after fiber transmission distance of 60 km. Furthermore, due to the +1 order sideband carrying no data, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over a 40 km standard single mode fiber with less than 0.8 dB power penalty in the simulation. Both theoretical analysis and simulation results show that our scheme is feasible and we can obtain a simple cost-efficient configuration and good performance over long-distance transmission.     

Novel 60 GHz RoF system with optical single sideband mm-wave signal generation and wavelength reuse for uplink connection

In order to improve RF frequency to achieve higher bandwidth and larger capacity, we propose a novel scheme to generate optical single sideband (SSB) millimeter-wave, in which frequency doubling of local radio frequency (RF) is obtained by using one integrated Mach–Zehnder modulator (MZM), and we theoretically investigate the generating principle of SSB. The optical SSB modulation scheme is employed to generate 60 GHz optical mm-wave and the 2.5 Gb/s baseband signal is simultaneously up-converted at the central station (CS) for downlink transmission, and the optical carrier is reused for uplink connection at the base station (BS). The full-duplex 2.5 Gb/s data are successfully transmitted over 40 km standard single-mode fiber (SMF-28) for both uplink connection and downlink connection with less than 2-dB power penalty. Results show the novel 60 GHz RoF system with optical SSB mm-wave signal generation using optical frequency doubling is feasible and we can obtain simple cost-efficient configuration and good performance over long-distance transmission.     

基于相位调制器产生六倍频光毫米波的OFDM信号光传输系统研究

提出了两个并行相位调制器产生六倍频光毫米波并传输正交频分复用信号的全双工光纤无线通信系统.将2.5 Gbt/s的正交频分复用信号调制到60 GHz光毫米波上.从理论上分析了毫米波产生的原理,并分别模拟了毫米波信号承载OOK信号和正交频分复用信号在光纤中的传输性能.从而验证系统的可行性.仿真模拟结果表明,在光纤无线通信系统中,正交频分复用比非归零码更具有优势.     

A full-duplex radio-over-fiber system based on dual quadrupling-frequency

We proposed and simulatedly demonstrated a novel full-duplex radio-over-fiber system using an external modulator and an optical interleaver to generate dual quadrupling-frequency optical millimeter waves for carrying two base station downstream data and wavelength reuse for uplink connection. The simulation results reveal that the power penalties for the downstream and upstream signals of both base stations are less than 0.8 dB. In this new scheme, the configuration of the both base stations is simplified further because there is no additional laser at two base stations. The frequency of local oscillator signal is reduced due to frequency quadrupling. The cost of the new system is largely reduced.     

Optical millimeter-wave signal generation by frequency quadrupling using one dual-drive Mach–Zehnder modulator to overcome chromatic dispersion

We propose a novel approach to generate quadrupling-frequency optical millimeter-wave using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system. By properly adjusting the phase difference in the two modulation arms of MZM, the direct current (DC) bias, the modulation index and the gain of base-band signal, the quadrupling-frequency optical millimeter-wave with signal only carried by one second-order sideband is generated. As the signal is transmitted along the fiber, there is no time shift of the codes caused by chromatic dispersion. Theoretical analysis and simulation results show that the eye diagram keeps open and clear even when the quadrupling-frequency optical millimeter-wave are transmitted over 110 km and the power penalty is about 0.45 dB after fiber transmission distance of 60 km. Furthermore, due to another second-order sideband carrying no signals, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over 40 km standard single mode fiber with less than 0.6 dB power penalty in the simulation.     

基于偏振稳定双波长保偏光纤光栅激光器的可调谐微波/毫米波产生技术

首次提出了一种基于偏振稳定双波长保偏光纤光栅激光器的可调谐微波/毫米波产生技术, 利用保偏光纤光栅选频产生两个偏振稳定的激光信号, 采用扰偏器确保激光输出的两个正交偏振态功率的一致性, 最后输入高速光电探测器产生微波/毫米波. 通过对保偏光纤光栅施加不同大小的侧向应力, 可以灵活调谐输出的毫米波频率. 实验制作了基于偏振稳定双波长保偏光纤光栅激光器的可调 谐微波/毫米波产生装置, 通过对保偏光纤光栅施加不同的轴向拉力分别产生了20.407 和22.050 GHz的微波信号. 仿真产生了60 GHz的毫米波信号, 并分析该毫米波在光纤无线通信下行链路的传输性能, 结果表明该毫米波作为副载波调制到光波上从中心站传输80 km至基站后经天线发射至用户端, 解调后仍然得到很好的眼图, 充分证明了本方案的优越传输性能.     

Performance Improvement of Optical Single Sideband Signal Using an Integrated Mach-Zehnder Modulator

Abstract

A novel integrated Mach-Zehnder modulator consisting of three phase modulators to generate an optical single sideband with carrier signals in the radio-over-fiber system has been proposed. By adjusting the direct current voltage applied in the modulation arm, named the “direct current arm,” the power of the optical carrier in the optical single sideband signal is controllable, and the optimal carrier-to-sideband ratio of 0 dB can be achieved for any modulation index. The simulation results show that the receiver sensitivity can be greatly improved, and the radio-over-fiber system based on the proposed technique has better robustness.     

基于新型偏振稳定毫米波发生器的光载无线通信下行链路

为了降低ROF系统成本,增加传输距离,提高系统性能, 提出了一种基于新型偏振稳定毫米波发生器的光载无线通信下行链路传输系统.与传统ROF系统相比, 该系统利用保偏光纤光栅选频产生的两个偏振稳定激光信号拍频产生毫米波, 易于实现并降低了功率噪声对系统的影响.仿真分析了该系统中环形激光器强度、谱线宽度、保偏光纤光栅反射谱特性对毫米波性能的影响;分析了系统中保偏光纤光栅的群时延、长度、色散,双波长激光信号脉冲包络宽度、啁啾系数对毫米波频率的影响.优化保偏光纤参数, 差频产生60 GHz的毫米波信号,并分析该毫米波信号在ROF下行链路的传输性能,结果表明该毫米波 作为副载波调制到光波上从中心站传输80 km至基站后经天线发射至用户端,解调仍然得到很好的眼图, 充分证明了本方案的优越性能.     

RoF downlink transmission system using FWM effect of SOA for generating MM-Wave

We propose a millimeter wave radio-over-fiber system to provide downlink service by using four-wave-mixing effect in semiconductor optical amplifier for millimeter-wave generation. At the central station, microwave source is 5.4-GHz. The optical carrier suppression modulation scheme and semiconductor optical amplifier are employed to simultaneously generate 32.4-GHz (sextuple fundamental) optical millimeter wave and up-convert data signal. At the base station, the downstream is received by a high-speed photodiode and base data are recovered by an electrical mixer. Theoretic analysis and experimental results show that the downlink 2.5-Gb/s data is successfully transmitted over 20-km single mode fiber with less than 0.15-dB power penalty.