基于迈克耳孙干涉的毫米波本振信号相位稳定传送

提出了一种毫米波本振信号的相位稳定传送技术。采用迈克耳孙干涉原理,将传输过程中的信号相位扰动信息调制在信号臂上,通过反射部分信号臂信号,并与参考臂信号干涉拍频,获得传输过程中的相位扰动信息,从而反馈控制光纤延时器,对系统进行相位校正。在建立传送系统的理论模型和实验系统的基础上,实验测试了本振信号的相位漂移与光纤长度漂移及干涉拍频输出信号之间的关系,理论和实验结果取得了一致。研究结果表明,这一本振信号传送方案的可行性。     

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210km实地通信链路的高稳定性光学频率信号传递

利用西安和咸阳之间的电信省级骨干光纤网构建了210km的光学频率信号传递测试链路,链路损耗为0.23dB/km。实验中采用可搬运、基于光纤干涉仪、线宽约为200 Hz的激光器作为光源,利用两台低噪声双向掺铒光纤放大器(EDFA)补偿光纤链路损耗和增加光信号的传输距离,放大器平均增益控制在15dB左右,以防止激射。通过测量和分析不同情况下光纤链路的附加相位噪声,可观测到铁路震动引起的规律性干扰。当噪声抑制系统在锁定状态时,链路的相位噪声被抑制了23dB,在剔除铁路干扰时段数据后,获得的210km实地通信链路的秒级频率稳定度达到了1.51×10-14,万秒频率稳定度达到了5×10-17。利用210km通信链路进行了光学频率信号的远程传递测试,分析了限制频率稳定度的主要影响因素,并针对现行光纤布设方式提出了补充要求。该研究为基于通信链路的高精度光学频率信号的传递与比对提供理论支撑。     

基于光梳状谱发生器和注入锁定本地激光器的相干正交频分复用无源光网络系统

提出一种基于光梳状谱发生器(OFC)和注入锁定本地激光器的相干正交频分复用无源光网络(OFDM-PON)系统,通过理论计算及实验得出OFDM信号功率、本振光(LO)功率和注入比的最佳值。并对经过25 km单模光纤(SMF)传输后用半导体光放大器(SOA)、宽线宽从属激光器和窄线宽从属激光器提供外差接收本振光波的3种下行传输方案的误码率(BER)性能进行对比。实验结果表明激光器注入锁定不仅可以改善接收灵敏度,而且接收性能不受从属激光器固有线宽的影响,并能为上行传输提供相干光源。因此系统成本大大降低,为光相干检测技术在接入网和数据中心互联中的应用提供了可能性。     

贝尔实验室的光纤通信实验传输距离超过两万公里

贝尔实验室在美国圣迭戈举行的 1991年光纤通信会议(OFC’91)上报道了新的一轮Hero实验.在这些实验中,他们实现了传输距离超过两万公里的超高速光纤传输,其重大意义是不言而喻的,因为地球上任何两地之间的距离都不超过两万公里. 在美国新泽西州Holmdel贝尔实验室的N.S.Bergano等人完成了两个实验:在一个实验中,光信号以2.4 Gb/s的数据传送速率传输了21000km 多;在另一个实验中,光信号以5Gb/s 的数据传送速率传输了9000km.他们在这两个实验中让光信号反复通过一个循环圈.这个循环圈包括四个10dB的掺铒光纤放大器和三段变色散光纤,每段长…     

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.     

光纤水听器远程全光放大系统相位噪声研究

光功率冗余不足及相位噪声增加是制约光纤水听器传输距离及探测性能的关键因素。基于光纤水听器全光模拟传输系统，建立远程放大相位噪声模型，设计大有效面积低损耗光纤组合传输链路，在100 km传输4波分×8时分复用系统中，远程放大引入的相位噪声仅为-98.1 dB@1 kHz(1 kHz为频率)，优于常规单模光纤4.3 dB，模型的有效性得到了验证。将模型应用于150 km传输系统，对远程增益单元位置进行优化，获得了-93.2 dB@1 kHz的远程放大噪声性能。所提噪声模型及优化方法可应用于不带电中继的光纤水听器系统设计及研制中，对增大全光传输距离及提升远程探测性能具有重要意义。     

光自差法生成微波/毫米波技术中偏振失谐研究

对光外差法生成微波/毫米波技术中的偏振失谐进行了分析. 首次推导出偏振失谐对微波/毫米波功率影响的计算公式. 利用自行制作的基于双波长保偏光纤光栅激光器的微波/毫米波发生器生成30 GHz左右的微波/毫米波信号, 其偏振失谐的实验结果与理论分析结果一致, 证明了理论分析的正确性. 最后, 应用分析结果模拟仿真了偏振失谐对60 GHz毫米波信号的影响, 得出了不同情况下系统的误码率及不同传输距离下的眼图. 结果表明, 在光纤无线传输链路中采用偏振失谐控制技术会大大提高链路的可靠性, 在对链路进行偏振失谐控制的前提下, 传输30 km仍可保持误码率10^-9以及很好的眼图, 说明了偏振失谐控制的重要性.     

光纤混沌相位编码保密通信系统理论研究

通过耦合激光混沌相位控制同步系统和光纤信道，提出外部光注入半导体激光器激光混沌相 位控制光纤同步以及混沌相位相移键控外调制光纤保密通信系统理论模型，数值实现了在相 位控制器控制下的远程光纤混沌同步.理论分析了光纤自相位调制对混沌信号以及对同步的 影响，导出了光纤混沌最大传输距离公式.通过连续键控调制相位控制器实现了光纤激光混 沌相位相移键控编码调制发射，设置接收系统相位控制器控制激光相位相移实现了光纤激光 混沌同步解调.数值模拟了具有比特率50Mbit/s远程光纤混沌数字编码通信系统的应用，详 细地进行了在远距离光纤传输中的系统参数失配以及系统抗噪声能力的数值分析. 关键词： 混沌 同步 光纤混沌通信 半导体激光器 相位     

光纤时间频率传输的时延抖动主动补偿

介绍了使用飞秒锁模激光实现稳定的时间频率传输的实验进展。采用1.2 km通信光纤传输89.7 MHz飞秒激光脉冲,同时其中插入一个主动延迟线,通过比较光纤返回的脉冲信号与激光器本地信号的第10次谐波的相位,将180 ps的时延补偿到了36 ps,证明了此方法在光纤传输时频信号的有效性。理论上本系统的延迟时间测量分辨率应为10 fs,由于噪声的原因,实际分辨率有所降低。进一步的工作正在进行,以提高信噪比和系统的稳定性。     

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.     

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.     

Design of millimeter-wave fiber-wireless downlink with remote local-oscillator delivery by using dual-electrode Mach-Zehnder modulators configured for optical single-sideband modulations

An optical fiber-wireless system operating in millimeter-wave (MMW) bands may include numerous optical remote access points (RAPs) of which the cost is critical to implement such systems in real market. In this paper, we design an optical fiber communication system for MMW optical fiber downlink transmission with remote MMW local-oscillator (LO) delivery for intermediate frequency (IF) fiber uplink transmission. The new design is based on two dual-electrode Mach-Zehnder modulators in parallel both configured for optical single-sideband modulations. By using the proposed design, a conventional RAP can be simplified in structure to reduce the cost. Our numerical results show that, with the proposed design, 1-Gbit/s binary-phase-shift-keying (BPSK) data at a 42-GHz sub-carrier frequency can be transmitted over a 20-km standard single-mode optical fiber followed by a wireless transmission of several kilometers. Moreover, a MMW LO at 37-GHz frequency can be remotely delivered over tens of kilometers of a standard single-mode fiber with acceptable deterioration in the LO phase noise for IF uplink fiber transmission.     

Using dual-mode self-locked semiconductor laser for optical millimeter-wave application

In this study, an optical millimeter-wave (mm-wave) generator is proposed and experimentally demonstrated by using a self-injected Fabry-Perot laser diode (FP-LD), having mode spacing of 1.11 nm, for dual-mode beating in 140 GHz band (terahertz band). The created dual-wavelength also can be also modulated at 1.25, 2.5, and 10 Gb/s with on-off keying (OOK) modulation format by external optical modulator, respectively, in 20 km fiber transmission. Moreover, the dual-mode laser can be selected in difference wave-lengths by tuning the optical filter inside cavity for the future WDM applications.     

60 GHz Radio over Fiber Technology for Wireless Access by employing Narrow-Angle PSK Modulation

This paper investigates two key techniques used in 60 GHz Radio over Fiber (RoF) technology for wireless access, namely, the generation of 60 GHz signals and the distribution of 60 GHz local oscillator (LO). In the proposed model, a 60 GHz PSK signal is generated by a heterodyne of two subcarriers with narrow-angle PSK (NA-PSK) modulation, whose phase shift is equal to one half that of a normal PSK signal. Then we use a 60 GHz mixer to frequency mix two PSK signals in two different bands, 60 GHz and baseband. By doing this, the modulation information can be fully eliminated, resulting in a 60 GHz LO. In the wireless terminal, coherent demodulation is realized by a self-mixing of the transmitted 60 GHz PSK signal and LO. Thus no millimeter-wave (mm-wave) band oscillator is needed in the wireless terminal.     

A novel frequency sextupling scheme for optical mm-wave generation utilizing an integrated dual-parallel Mach-Zehnder modulator

A novel scheme is proposed for frequency sextupling mm-wave generation based on a laser and an integrated dual-parallel Mach-Zehnder modulator (MZM) without optical filter. Theoretical analysis is presented to suppress the undesired optical sidebands for the high quality generation of frequency sextupling mm-wave signal. The performance of the proposed scheme is evaluated by simulations. Utilizing the integrated MZM consisted of two sub-MZMs with extinction ratio of 30 dB, the optical sideband suppression ratio (OSSR) is as high as 29.9 dB and the radio frequency spurious suppression ratio (RFSSR) exceeds 24 dB without any optical or electrical filter. The impact of the nonideal RF driven voltage and phase difference of RF driven signal applied to two sub-MZMs of the integrated MZM on OSSR and RFSSR is discussed and analyzed. After transmission over fiber, the generated optical mm-wave signal demonstrates good performance. Furthermore, the performance of two cases for the proposed scheme is also compared.     

水下平台对卫星上行激光通信研究

在合理选择通信系统参量和通信信道参量的基础上,利用Monte Carlo方法模拟了卫星接收到的水下平台上行激光通信信号.分析了卫星接收信号的空间和时间分布特性,以及与望远镜接收视场角的关系,并计算了接收信号的信噪比,得出了3°望远镜视场角和15 μs信号积分时间的优化参量.基于计算结果,根据激光脉冲的PPM调制方式和最大似然检测方法,计算了系统的通信误码率,同时分析了海气界面、云等传输介质对通信的影响.研究结果表明:根据文中给定通信系统参量,在典型海水、海气界面、云等环境条件下,卫星与激光信号中心水平距离5 km范围内信号误码率<10－4.因此位于水下60 m的水下平台可能实现对卫星上行激光通信.     

Fiber-optic distributed sensor based on phase-sensitive OTDR and wavelet packet transform for multiple disturbances location

A novel location scheme based on the wavelet packet transform (WPT) for the phase-sensitive optical time-domain reflectometry (OTDR) is proposed. The wavelet packet energy of the backscattered signal at a time interval over the sensing fiber is provided to discriminate the disturbances regions from other regions. It is insensitive to the frequency drift of the laser. The simultaneous measurement of two disturbances at 5 km and 7 km positions is achieved by the location technique based on the WPT over a 9 km monitored length with a 50 m spatial resolution even when a laser with a frequency drift rate of 230 MHz/min is utilized. During 100 times experiments the false alarm rate is only 2% and the maximum location error is 150 m.     

Optical millimeter-wave generation and transmission system for 1.25 Gbit/s downstream link using a gain switched laser

In this paper, we propose a novel and cost effective system for optical millimeter-wave (mm-wave) generation and transmission of downstream data based on a gain switched laser (GSL). The GSL produces an optical comb spectrum that can be appropriately filtered to generate two optical sidebands spaced by more than 4 times the repetition rate of the GSL. These sidebands are modulated by baseband data and then transmitted via optical fiber to the remote antenna unit (RAU). At the RAU, the two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal, before demodulation using self mixing. We demonstrate the distribution of 1.25 Gbit/s data OOK modulated onto a 60 GHz carrier, similar to that used in the IEEE 802.15.3c draft standard, over fiber lengths up to 62 km.     

Influence of laser linewidth on performance of Brillouin optical time domain reflectometry

The effects of optical sources with different laser linewidths on Brillouin optical time domain reflectometry (BOTDR) are investigated numerically and experimentally. Simulation results show that the spectral linewidth of spontaneous Brillouin scattering remains almost constant when the laser linewidth is less than 1 MHz at the same pulse width; otherwise, it increases sharply. A comparison between a fiber laser (FL) with 4-kHz linewidth at 3 dB and a distributed feedback (DFB) laser with 3-MHz linewidth is made experimentally. When a constant laser power is launched into the sensing fiber, the fitting linewidths of the beat signals (backscattered Brillouin light and local oscillator (LO)) is about 5 MHz wider for the DFB laser than for the FL and the intensity of the beat signal is about a half. Furthermore, the frequency fluctuation in the long sensing fiber is lower for the FL source, yielding about 2 MHz less than that of the DFB laser, indicating higher temperature/strain resolution. The experimental results are in good agreement with the numerical simulations.