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.     

Optical Generation of mm-Wave Signal Through Optoelectronic Phase-Locked Loop

In this paper, we propose a scheme for the generation of low phase noise tunable mm-wave signal by beating two lightwaves in a photodiode. These two lightwaves are made phase coherent by an optoelectronic phase locked loop.Calculated mm-wave power at a frequency of 60 GHz is found to be -4 dBm.     

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.     

Analysis of an optical mm-wave generation scheme with frequency octupling using two cascaded Mach-Zehnder modulators

We propose a novel method to generate optical mm-wave signals with frequency octupling using two cascaded Mach-Zehnder modulators (MZMs). First, the scheme is investigated both theoretically and by simulation, and results show that an 80 GHz mm-wave is generated by a 10 GHz RF oscillator. Then, an analytical expression is developed to describe the performance of the scheme. The influences caused by non-ideal factors are discussed in detail, and undesired sidebands suppression ratios are plotted and analyzed. At last a RoF system using the mm-wave generation scheme is demonstrated and its BER curves indicate that the performance of the system is still good even if the parameters deviate from the ideal values to a certain degree.     

Tunable microwave photonics filter with dual pass-band based on PM-FBG and PS-FBG

In this paper, a dual pass-band microwave photonics filter with simple, commercial structure is proposed and demonstrated. The key devices are the specially designed polarization maintaining fiber Bragg grating and the phase shift fiber Bragg grating. They are employed to extract out two orthogonally polarized sidebands and remove the undesired sideband, respectively. The simulation results show that without any extra operations or electrical processing, the dual pass-band can be achieved with the two central frequencies of 3.5 GHz and 8 GHz when the frequency spacing between the two orthogonally polarized sidebands is 12 GHz, their 3-dB bandwidth are about 500 MHz. The central frequencies of the two pass-bands can be simply tuned by adjusting the frequency spacing in a range of 4 GHz. In addition, the spurious free dynamic ranges for the two pass-bands are 75.71 dB Hz^2/3 and 70.17 dB Hz^2/3 respectively. Finally, a brief experiment is also carried out to demonstrate the feasibility.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Frequency-octupled phase-coded signal generation based on carrier-suppressed high-order double sideband modulation

An approach for photonic generation of a frequency-octupled phase-coded signal based on carrier-suppressed high-order double sideband modulation is proposed and experimentally demonstrated. The key component of the scheme is an integrated dual-polarization quadrature phase shift keying modulator, which is used to achieve the carrier-suppressed high-order double sideband modulation. At the output of the modulator, two fourth-order optical sidebands are generated with the optical carrier suppressed. After that, a Sagnac loop incorporating a fiber Bragg grating and a phase modulator is employed to separate the two optical sidebands and phase modulate one sideband with a binary coding signal. The approach features large carrier frequency tuning range for the generated phase-coded signal from several megahertz to beyond the W-band. A proof-of-concept experiment is carried out. The 2 Gbit/s phase-coded signals with frequencies of 16.48, 21.92, and 29.76 GHz are generated.     

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.     

噪声免疫腔增强光外差分子饱和光谱线型的理论分析

噪声免疫腔增强光外差分子光谱(NICE-OHMS)作为世界上最灵敏的光谱技术可以被应用到痕量气体检测、频率标准、原子分子光谱以及超灵敏引力波测量等领域中,高精细度谐振腔吸收池的使用在增长激光与腔内物质相互作用路径的同时,极大的提高了腔内激光功率,这就会饱和低气压下的气态样品吸收线从而获得亚多普勒光谱结构,因此NICE-OHMS技术不仅具有高灵敏、还具有超高分辨的优点。该研究基于光与二能级分子相互作用的密度矩阵理论对NICE-OHMS技术中包含亚多普勒的多普勒展宽光谱线型进行了理论推导,获得了光谱线型的表达式,同时以该表达式对光谱线型进行了数值模拟,其中调制频率、饱和参量、频率调制系数分别设置为384 MHz,10和0.2。由模拟结果可见吸收光谱由两个边带的吸收信号构成,在包络上存在四个亚多普勒饱和结构;色散光谱由载频以及边带的色散三者决定,并在包络上存在五个亚多普勒饱和结构,获得了与已有实验一致的结果。最后重点分析了不同探测相位、不同饱和参量下的NICE-OHMS光谱线型尤其是亚多普勒结构的变化,由于饱和参量按照调制系数分配给载频和边带,因此虽然载频饱和参量很大,但NICE-OHMS吸收光谱幅度变化不大,主要是由于该光谱信号只与边带饱和参量有关,可以看出NICE-OHMS多普勒展宽信号具有饱和效应免疫的特性,与已有实验结果也符合较好。为更进一步的实验研究提供了必要的理论基础。     

光子型远程分布式微波信号接收码元速率估计

基于光子学技术,设计了一种针对远程分布式微波信号接收的码元速率估计方案。首先,远程终端将接收的微波信号经电光调制器对连续激光源进行载波抑制双边带调制,生成携带微波信号的两个光边带信号;此光信号经光纤链路传输至中心站在光域滤除其中一个边带;其次,进行光电探测,通过分析电频谱的谐波实现微波信号码元速率估计。针对此方案,搭建仿真及实验系统装置:仿真成功地从60 GHz微波信号中提取出0.8 GBaud和6 GBaud的二进制伪随机码(PRBS)信号码元速率、从25 GHz微波信号中提取出3GBaud的PRBS码元速率;实验成功地从25 GHz的微波信号中提取出3 GBaud和5 GBaud的PRBS码元速率。     

基于偏振模干涉的可变系数微波光子滤波器

基于偏振调制和光的干涉原理,设计了同时具有正系数和负系数特性的微波光子滤波器,并通过搭建实验模型证实了方案的可行性。利用偏振调制及光的偏振特性实现载波和一阶边带的正交偏振,并通过改变偏振调制器的偏置电压分别对载波和一阶边带引入相移。当载波和一阶边带的相位差为0或90时,利用保偏光纤快慢轴上两正交偏振光在同一偏振态上的干涉效应,分别对应实现具有负系数或正系数特性的微波光子滤波器。最后,测量并验证了0~15 GHz频率范围内滤波器的频率响应。     

Reduction of frequency fading and imperfect frequency response with pre-emphasis technique in OFDM-ROF systems

In this paper, a novel technique is proposed and experimentally demonstrated to reduce the effect of frequency fading (FF) and imperfect frequency response in direct-detection (DD) optical orthogonal frequency division multiplexing-radio-over-fiber (OFD-MROF) systems. To overcome FF effect in the optical fiber and imperfect frequency response in the optical and electrical devices at the high frequency, we pre-emphasize the power of the millimeter wave (mm-wave) OFDM sub-carriers appropriately in the center station. Experimental result of the proposed system shows the received sensitivity has been improved about 2 dB at the BER of 1 × 10^− 4 after 50 km SSMF transmission for 2.5 Gb/s OFDM signal carried on 60 GHz optical mm-wave compared to the original system without pre-emphasis technique.     

相位调制信号对窄线宽光纤放大器线宽特性和受激布里渊散射阈值的影响

高功率窄线宽光纤放大器的输出功率主要受限于受激布里渊散射(SBS)效应,通过相位调制进行线宽展宽可以有效抑制SBS效应.基于窄线宽光纤放大器中的SBS动力学模型,研究了正弦信号、白噪声信号和伪随机编码信号(PRBS)对窄线宽光纤放大器光谱特性与SBS阈值的影响.研究发现,采用不同信号进行相位调制时,调制频率和调制深度等参数对调制后激光光谱的谱线间隔、谱线数目与光谱平整度的影响存在较大差异,进而影响放大器的线宽特性和SBS阈值.通过对比分析,给出了调制信号的类型选择和参数优化原则,能够为窄线宽光纤放大器的相位调制系统设计提供参考.