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.     

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.     

采用级联相位调制器和强度调制器产生四倍频光载毫米波的光纤无线通信系统

理论和实验研究了基于载波抑制原理采用级联的相位调制器和强度调制器产生四倍频光载毫米波的原理。基于此原理,在中心站利用10 GHz的本振射频信号,通过调节两个调制器的相位差和强度调制器的偏置电压产生40 GHz光载毫米波信号,2.5 Gb/s的基带数据信号直接调制在光载毫米波上,经过20 km标准单模光纤传输至基站。实验研究表明,下行链路信号通过20 km标准单模光纤传输后,传输功率代价小于0.8 dBm,基带信号眼图依然清晰张开,简化了系统配置,信源稳定可靠。     

基于光载波抑制调制的可调谐高倍频毫米波信号发生器

提出了一种基于改进的光载波抑制调制方式的光学生成高倍频可调谐毫米波的方案.该方案利用均匀光纤光栅型声光可调谐滤波器选取光载波抑制信号中的两个边带分量进行拍频,实现高倍频且倍频因子可调的毫米波信号的生成.为避免色散所致的码元时移效应,将基带数据信号仅调制到光载波抑制信号的一个边带分量上.仿真验证了倍频因子分别为2,6,10,14,18和22的毫米波信号的生成.另外,对22倍频下的光载无线电系统的链路性能进行了仿真分析,毫米波信号在调制2Gbit/s的非归零码型数据信号经50km的光纤传输后,系统的眼图仍保持良好的睁开度,链路的功率代价仅为0.4dB.系统具有良好的传输性能,可以满足通信系统的需求.     

面向光载无线系统的混合频相调制信号产生

为提高光载无线系统传输容量,提出一种混合频相调制信号光学产生技术。利用保偏光纤布拉格光栅对不同输入偏振态响应不同的特性,将加载到信号偏振态的基带信息转换到输出波长上,并通过在接收端的外插拍频实现频率调制。同时通过光学相位调制将信息映射到拍频产生的微波信号上,最终产生混合频相调制信号。搭建基带传输式光载无线系统,验证了该信号产生方法的有效性。产生了码率为1Gbit/s、频率为12.5GHz/9.5GHz的混合频相调制信号,该信号经过5km光纤传输后由接收端解调。信号的时域波形及解调后信号眼图与星座图等结果证明了所产生的混合频相调制信号的可靠性。     

一种基于相干检测的双向输出信号频率可选的光纤无线系统

提出了一种单光源、双向输出信号频率可选的光纤无线系统,该系统在单光源条件下,利用相干检测技术、数字信号处理技术,结合并行相位调制器以及波长选择开关结构,在上下行链路实现基带信号、多个毫米波信号输出.仿真验证表明,针对20Gbit/s 16-QAM调制信号,经30km光纤传输,系统下行输出信号频率实现0~60GHz可选,其传输最小矢量误差为6.53%(0GHz)~7.61%(60GHz);上行输出信号频率实现0~120GHz可选,其传输最小矢量误差为6.89%(0GHz)~8.30%(120GHz).理论分析和仿真结果表明,该系统双向链路均可实现频率可选的信号输出,且双向传输具有较好的性能表现.     

42.8 Gbit/s DPSK信号的波分复用传输实验

实现了42.8 Gbit/s 差分相移键控调制信号的三信道波分复用传输实验.传输链路为410 km的标准单模光纤,分为四个放大段,采用色散补偿光纤进行色散补偿和掺铒光纤放大器/分布式喇曼放大器混合放大方式.给出了差分相移键控信号及其解调后的信号在背对背和传输后的光谱和眼图(中路波长信号).在接收端使用单端检测,给出中路波长的差分相移键控信号背对背情况和传输后的误码率曲线,并与单信道传输时进行比较.经过传输后的中路信号的误码率可维持在1.0E-3左右.     

42.8 Gbit/s DPSK信号的波分复用传输实验

实现了42.8 Gbit/s 差分相移键控调制信号的三信道波分复用传输实验.传输链路为410 km的标准单模光纤,分为四个放大段,采用色散补偿光纤进行色散补偿和掺铒光纤放大器/分布式喇曼放大器混合放大方式.给出了差分相移键控信号及其解调后的信号在背对背和传输后的光谱和眼图(中路波长信号).在接收端使用单端检测,给出中路波长的差分相移键控信号背对背情况和传输后的误码率曲线,并与单信道传输时进行比较.经过传输后的中路信号的误码率可维持在1.0E-3左右.     

基于被动补偿的点到多点微波信号光纤稳相传输

微波信号的稳相传输在雷达、空间观测以及卫星导航等领域有广泛的应用。针对目前点对点稳相传输方案传输效率不高以及主动补偿速度较慢等问题,研究并提出了一种基于被动补偿的适用于大范围、多站点微波信号光纤稳相传输的方案。微波信号在本地端经功分器分为两路,分别作为待传信号和分频后的探测信号;待传信号在本地端与经光纤往返传输的探测信号混频获得下变频信号;该下变频信号传输到远端与前向探测信号混频后生成相位稳定的微波信号,通过结构的合理设计实现点到多点稳相传输。经过实验验证后可知:2 GHz信号在10 km光纤链路下多链路分布结构的均方根(RMS)延时抖动为0.968 ps,在11 km光纤链路下单链路分布结构的均方根延时抖动达到1.606 ps。     

基于偏振旋转光反馈下的外光注入VCSEL产生高性能毫米波

本文提出一种基于偏振旋转光反馈下的外光注入垂直腔 表面发射激光器(VCSEL)产生高性能毫米波的方案, 并利用描述外部扰动下VCSEL动态特性的自旋反转模型(SFM), 对所产生的毫米波的特性进行了数值研究. 研究结果表明: 一个受到主VCSEL(M-VCSEL)光注入的副VCSEL(S-VCSEL)在一定条件下可以产生单周期(P1)振荡, 即在光波上调制了一个微波信号. 通过调节外光注入强度ξ_i以及S-VCSEL与M-VCSEL之间频率失谐Δν, 可以获得频率在30---60 GHz范围内连续可调的毫米波信号. 在外光注入VCSEL中引入偏振旋转光反馈, 通过选取合适的反馈强度ξ_f以及反馈延迟时间τ, 产生的毫米波信号的线宽可以得到明显窄化. 对于光注入S-VCSEL所产生的线宽为5.509 MHz的毫米波, 在引入偏振旋转光反馈后, 毫米波线宽可以降低到230.2 kHz. 本文的研究对高速光载无线(RoF)系统中优质毫米波信号的获取具有一定的参考意义.     

Frequency sextupling technique using two cascaded dual-electrode Mach–Zehnder modulators interleaved with Gaussian optical band-pass filter

A frequency sextupling technique for the generation of millimeter-wave (mm-wave) is proposed and investigated. The proposed technique is comprised of two cascaded dual-electrode Mach–Zehnder modulators (MZMs), which are interleaved with Gaussian optical band-pass filter (GOBF). The first MZM, biased at minimum transmission, is only used for optical carrier suppression modulation, and the second MZM, biased at maximum transmission, is used for both even-order optical harmonic generation and data signal modulation. The GOBF between two MZMs is used to suppress the high-order optical harmonics beyond the first-order optical harmonics. On the basis of theoretical analysis and simulated demonstrations, it is concluded that with the use of an RF signal at 10 GHz, which carries the data signal and drives the MZMs, an mm-wave signal at 60 GHz can be obtained. The simulation results show that the proposed sextuple leads to a 7 dB improvement in receiver sensitivity in comparison with the modulation technique, i.e. using two cascaded dual-electrode MZMs without GOBF. Furthermore, the eye diagrams show that the quality of generated mm-wave signal is satisfactory. The proposed technique is verified by experiments.     

A novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators

We propose a novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators (MZMs) for the first time. First, the scheme is investigated theoretically, which suggests that it can be used for sextupling, 12-tupling, and 18-tupling mm-wave generation. Then simulation results are given, 60 GHz mm-wave is generated from 5 GHz, or 10 GHz RF oscillator based on frequency 12-tupling or sextupling, and 90 GHz mm-wave is generated from 5 GHz RF oscillator based on frequency 18-tupling. The optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are analyzed by simulation, in which several non-ideal factors are taken into consideration. Results indicate that all the three mm-wave generation methods are practical and very good performance can be obtained when the extinction ratio of the MZM is 30 dB, even if the extinction ratio of the MZM is 20 dB, the performance is still good, especially for the sextupling mm-wave generation method, whose performance is excellent and insensitive to the extinction ratio of MZM, the non-ideal RF driving voltage and the non-ideal DC bias. At last, we set up a RoF system by simulation to verify the transmission performance of the scheme. The BER performance and eye diagrams are given.     

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.     

Injection-locked fiber laser for tunable millimeter-wave generation

A dual-ring injection-locked fiber laser consisting of a ring of optoelectronic oscillator (OEO) and a ring of fiber laser is proposed and demonstrated for tunable millimeter-wave (mm-wave) generation. The approach combines the advantages of mm-wave generation based on OEOs and fiber lasers, which can generate a high-frequency, low-phase-noise, and a mode-hopping-free mm-wave signal with a large tuning range. A low-phase-noise mm-wave signal with a tunable frequency of 30-50 GHz and a tuning step of 10 GHz is obtained in a proof-of-concept experiment. The tuning range can be as large as 140 GHz if a high bandwidth photodetector is applied.     

Photonic generation of high-purity 60 GHz millimeter-wave signal requiring only 10 GHz radio frequency local oscillator

A novel approach to generate 60 GHz millimeter-wave from a 10 GHz radio frequency signal using an integrated nested DD-MZM without optical filter is proposed and demonstrated. The simulation results show that the generated frequency sextupling optical mm-wave has high purity with an OSSR exceeding 29 dB and a RFSSR of 25 dB, which is consistent with the theoretical analysis. Besides, a RoF link model is established to investigate the transmission performance. The eye diagram keeps clear even when the optical mm-wave is transmitted over 60 km and the power penalty is about 0.4 dB after fiber transmission of 50 km.     

The transmission performance degradation of the optical millimeter-wave signals by fiber chromatic dispersion

The influence of the fiber chromatic dispersion on double sideband (DSB), optical carrier suppression (OCS), and single sideband (SSB) optical mm-wave signals is investigated based on the Taylor expansion of the propagation constant and is verified by simulation. According to our theoretical results, the fading effect suppresses the signal power of the DSB optical mm-wave periodically in a cosine-like pattern, and it can be described by the zero-order Taylor expansion of the propagation constant. For the optical mm-wave with the signal modulated on two or more tones, the bit pulses of the mm-wave signal are distorted by the dispersion-inducing bit walk-off effect between tones, which is expressed by the first-order Taylor expansion of the propagation constant. Moreover, as the signal rate and the transmission distance are increased further, higher-order Taylor expansion of the propagation constant still degrades the optical mm-wave signal even if both the fading effect and the bit walk-off effect are eliminated completely. The distortion of the signal pulses of SSB optical mm-wave is derived based on the second-order Taylor expansion of the propagation constant. This degradation is verified by the simulation with the eye diagram evolution of the SSB optical mm-wave signal.     

Low Noise mm-Wave Amplifier Design Methodology

A design methodology for mm-wave LNAs is presented. The optimum bias point selection is outlined. The stabilisation strategy is described, and the impact of packaging requirements on the amplifier design is discussed. A bond wire compensation technique is detailed. The tradeoff between input match and noise figure is presented, and a design with a suitable tradeoff is¹ developed. A very simple inter-stage match requirement is a novel outcome of this design approach. An effective means of achieving a broadband response is also outlined. A four stage 30 – 50 GHz LNA design was fabricated and characterised in a customised package. A maximum MMIC gain of 28 dB at 32 GHz was achieved, and the gain exceeded 20 dB over the frequency range 26 – 44 GHz. A noise figure of 4.5 dB and a P1dB of +11 dBm were also obtained. It is the authors' opinion that the methodology presented in this paper will be of significant interest to other mm-wave LNA designers.     

A Very Low-Noise Integrated 3MM-Wave Schottky Diode Mixer and PHEMT IF Amplifier

An integrated 3mm-wave Schottky diode mixer and pseudomorphic high-electron-mobility transistor (PHEMT) IF amplifier with record noise performance at room temperature is described. The design has shown the room-temperature double-sideband (DSB) receiver noise temperature T_R^DSB of 190 K at 100 GHz due to a very low conversion loss in the full-height waveguide mixer and an ultra-low noise of the PHEMT IF amplifier. The receiver noise temperature has been reduced by a factor of 1.5 in comparison with the best previously reported 3mm-wave Schottky diode mixer receiver.     

Polarization insensitive wavelength conversion based on four-wave mixing for polarization multiplexing signal in high-nonlinear fiber

We have theoretically and experimentally investigated polarization insensitive of all optical wavelength conversion for polarization multiplexing signal based on four-wave mixing (FWM) in nonlinear optical fiber. Optical polarization multiplexing technique can be used to double the transmission bit rate by adding data on each of two orthogonal optical states. At the receiver side, the two orthogonal signals can be obtained by direct detection. The eye diagrams of the original signals have been probed and compared with the converted one in this experiment. The characteristics of the converted signal have been fully studied and a little crosstalk which leads a better corresponding eye diagram has been obtained after polarization demultiplexing.     

Photonic mm-Wave Generation Using a Double Passband Fiber Bragg Grating Filter

We report a simplified version of a mm-wave generator employing the sideband filtering technique which uses a single optical sideband filter. Instead of using a Mach-Zehnder-like fiber network to select a pair of sidebands, we employ a single Fabry-Perot fiber Bragg grating with a pair of passbands separated by the mm-wave frequency. Using a single filter eliminated the need for polarization control and pathlength matching that was required by the former interferometer-like arrangement. We describe a 30 GHz generator design and present its mm-wave signal spectrum showing an instrument-limited linewidth of ~20 Hz. The generation of such an extremely narrow signal spectrum from a laser with a 1 MHz linewidth demonstrates the remarkable laser frequency noise cancellation property of the sideband filtering technique.