On the carrier generation and HD signal transmission using the millimeter-wave radio over fiber system

The dual sideband optical carrier suppression (DSB-OCS) technique is employed in the optical carrier generation for 40 GHz radio over fiber (ROF) system. A dual electrode Mach-Zehnder modulator (DE-MZM) with the minimum transmission bias (MiTB) technique is employed to build the system. The results show that, a 40 GHz carrier is successfully generated with the amplitude up to −29 dBm and signal to noise ratio (SNR) of 35 dB and a high definition (HD) signal is successfully transmitted using the system. Finally, the bit error rate (BER) measurement is carried out for the system with 1.25 Gbps OOK signal showing an error free 40 GHz ROF system with almost no penalty between the back to back and 20 km fiber for a BER of 10⁻⁹.     

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.     

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.     

Single tone and multi tone microwave over fiber communication system using direct detection method

In this paper, an analog microwave over fiber link for long haul distance based upon Rate Equation Laser is demonstrated. This system uses the advantage of high potential bandwidth of fiber in transmission of microwave signal. The interface of the two systems needs an up-conversion of microwave band into baseband (at which fiber operates). An Intensity Modulation Direct Detection (IMDD) technique is used to achieve this purpose. The Rate Equation laser is operated in a dynamic state, where its intensity oscillates at a microwave frequency that varies with the input signal fed by wave generator. This system can also use for two modulating tones. The frequency of the first tone is varied from 1 to 20 GHz and second is set at 5 GHz. A data signal of 10 Gbps is transmitted over long haul single mode fiber by single tone system. A very good bit error rate (BER) 10^?40 performances for 100 km and 25 km fiber link is achieved for both single tone and two tones respectively in proposed microwave over fiber communication system.     

Generation of radio signals using a novel Mach-Zehnder modulator with four arms

We have proposed and demonstrated a novel Mach-Zehnder modulation technique which employs a 1 × 4 multimode interference MMI coupler and four optical phase-modulator waveguides to generate optical single sideband (SSB) signals in radio-over-fiber (ROF) transmission link. It is shown that when the RF (radio frequency) modulation index is large, the optical SSB signal generated by conventional modulation scheme contains a significant part of undesired higher order harmonics, accordingly, much distortion in the RF signal was detected at the base station (BS). However, the main undesired higher order harmonics can be suppressed using our proposed modulation scheme and the performance of the transmission links were largely improved in single-channel and dense wavelength-division multiplexing (DWDM) cases.     

A novel approach for simultaneous millimeter wave generation and high bit rate data transmission for Radio over Fiber (RoF) systems

We propose a novel method for simultaneous transmission of OC-192 (9.95328 Gbps) digital data and 60 GHz RF generation in a Standard Single Mode Fiber (SSMF) link utilizing Stimulated Brillouin Scattering (SBS). The system comprises of a 1550 nm DFB Laser diode, Mach Zehnder modulator (MZM), 50 km SSMF and Optical receiver. The receiver includes laser diode for optical pump, a regenerator for data retrieval and a RF bandpass filter for RF generation. This system requires minimum number of RF and optical components for the generation of 60 GHz RF. The remotely generated 60 GHz RF signal may be used for wireless transmission of data. The entire link is simulated in Optisystem software to analyze the system performance.     

Impact of interferometer delay time on the performance of ODSB-SC RoF system with wavelength interleaving

In this paper, we investigate the impact of interferometer delay time in a 5 Gb/s optical double sideband-suppressed carrier (ODSB-SC) RoF system transmitting two wavelength interleaved radio frequency (RF) signals at 10 and 15 GHz over an optical fiber. Here, an optical Mach–Zehnder modulator is used for both optical carrier suppression and signal modulation. At the receiver, delay interferometer is used for the separation of RF frequency signals. We analyze the performance of the RoF system by varying the value of delay time of interferometer from 0.02 to 0.14 ns. The result shows that the RoF system performance is optimum for the time delay of 0.1 ns. Further, the optical spectrums, RF spectrums and eye diagrams of two interleaved RF signals have been compared.     

全双工60 GHz的光纤无线通信系统

基于光纤无线通信(ROF)的无线网络被认为是提供高带宽、交互式和多媒体无线通信服务很有前景的实现方式,但目前毫米波频段的光纤无线通信系统都存在色散严重或基站结构复杂等问题。设计完成了一个全双工60 GHz的光纤无线通信系统,利用双光源技术和60 GHz的电吸收收发器(EAT)分别在下行和上行链路实现单波长和双波长调制,完成基站的探测、调制、射频上变频和下变频四种功能,在基站中实现了电吸收收发/混频器(EATX),从而避免了制作电吸收收发/混频器件,同时也解决了光纤无线通信系统中常见的色散和基站结构复杂等问题。     

Influence of the modulation index of Mach-Zehnder modulator on RoF link with ASK millimeter-wave signal

In this paper, the influence of the modulation index of LiNbO₃ Mach-Zehnder modulator on the radio over fiber (RoF) link based on single sideband (SSB) optical millimeter (mm)-wave with ASK signal is theoretically and numerically investigated. Our investigation shows that there exists an optimal modulation index to generate the SSB optical mm-wave with a maximal RF photocurrent. Although the fiber dispersion distorts the code form and degrades the performance of the RF signal demodulated from the SSB optical mm-wave after fiber transmission, it does not cause the closure of the eye diagram. However, the influence of the fiber dispersion becomes more obvious as the modulation index increases. For the duplex RoF link with the optical carrier of the uplink recovered from the downlink, a larger modulation index of the downlink causes a worse crosstalk from the downlink to the uplink.     

Optical access transmission with improved channel capacity using non-orthogonal frequency quadrature amplitude modulation

A new modulation scheme that improves the bandwidth efficiency of an optical access link is proposed in this paper. It is implemented using non-orthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM) simultaneously. We call the proposed technique non-orthogonal frequency quadrature amplitude modulation (NOFQAM). Especially, non-orthogonal FSK based on digital signal processing (DSP) is proposed for the first time. DSP-aided non-orthogonal FSK allows us to select RF carrier frequency irrespective of the channel bandwidth to allocate FSK symbols, unlike the existing orthogonal FSK. The non-orthogonality is implemented using a sequential correlation, where a received NOFQAM signal is correlated with only one RF carrier at a time by using DSP. After the sequential correlation is completed, both the FSK and the QAM symbols are recovered successfully and merged to generate the NOFQAM symbols. For experimental verification, a 20-km optical access link, which can transmit a 64-NOFQAM signal sampled at 10 Gsample/s, is implemented. We observed no increase in occupied channel bandwidth and a power penalty <0.5 dB compared to the 16-QAM scheme. A bit error rate lower than 10^?11 was obtained for the frequency spacing considered herein, which corresponds to 3% of the used RF carrier (1.5 GHz) when there are 50 sampling points per 64-NOFQAM symbol.     

Generation of linearized optical single sideband signal for broadband radio over fiber systems

We propose a new scheme to generate broadband linearized optical single-sideband （OSSB） signal for radio over fiber systems. By using an unbalanced dual parallel Mach-zehnder modulator （DPMZM） followed by optical filtering, a linearized OSSB signal is obtained. With coherent detection, radio frequency （RF） signal can be recovered with simultaneously suppressed second-order distortion and third-order intermodulation. This scheme can be used to realize broadband systems with wide dynamic range.     

Stable RF transfer over a fiber-optic ring with DSBCS modulation and a DSB RF signal

We propose a radio frequency(RF)transfer technique with passive phase noise compensation over a fiber-optic ring.By adopting different frequencies and same wavelength transmission and double sideband(DSB)with carrier suppression(DSBCS)modulation,the impact of backscattering can be effectively suppressed.A stable RF signal can be obtained via frequency mixing at an arbitrary access site along the fiber-optic ring.As the two directional transmissions adopt the same fiber and same wavelength from the same laser,the bidirectional propagation symmetry can be maximally guaranteed.We experimentally demonstrate 2 GHz RF signal transfer along a 100 km standard single-mode fiber-optic ring.     

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.     

Harmonic RF carrier generation and broadband data upconversion using stimulated Brillouin scattering

We propose and experimentally demonstrate a harmonic radio frequency (RF) carrier generation and broadband data upconversion technique with single mode and single sideband (− SSB) modulation for radio-over-fiber (RoF) systems using stimulated Brillouin scattering (SBS). The optical carrier-to-sideband ratio (CSR) of the single mode and SSB modulated signal can be easily adjusted to achieve the best received sensitivity performance of the RoF system. By using this method, we successfully demonstrate generation of third-harmonic RF carrier at 32.625 GHz with f_LO of 10.875 GHz and upconversion of 1.25-Gb/s data to the RF carrier band. In addition, the data bandwidth is independent of the Brillouin gain profile. Finally, the transmission performance of the RoF downlink system is examined.     

基于光电振荡器的宽带射频下转换及在高清视频传输的应用

以无压缩全高清视频的光载无线传输为背景,通过研究宽带射频光子下转换技术,从而构建全高清视频的实时传输系统,其中下转换系统主要基于光电振荡器实现.由于光电振荡器的注入锁定,光微波信号中的载波信号被提取出来,并反馈至调制器,与宽带光微波信号混频,在光域实现信号下转换.实验论证了载频为10GHz,码率大于2Gb/s的信号下转换和有线无线传输.利用天线和光纤实现了距离为0.5m的无线分发和距离为10km的有线传输.本文还成功实现了1.5Gb/s无压缩高清视频信号的实时传输.实验结果表明,该系统具有大带宽、抗电磁干扰等优点,同时利用光电振荡器的自动相位跟踪技术,无须外加锁相等操作.整个下转换系统简单稳定,为高清视频的有线无线传输提供了论证和演示平台.     

基于光电振荡器的宽带射频下转换及在高清视频传输的应用

以无压缩全高清视频的光载无线传输为背景,通过研究宽带射频光子下转换技术,从而构建全高清视频的实时传输系统,其中下转换系统主要基于光电振荡器实现.由于光电振荡器的注入锁定,光微波信号中的载波信号被提取出来,并反馈至调制器,与宽带光微波信号混频,在光域实现信号下转换.实验论证了载频为10GHz,码率大于2Gb/s的信号下转换和有线无线传输.利用天线和光纤实现了距离为0.5 m的无线分发和距离为10km的有线传输.本文还成功实现了1.5Gb/s无压缩高清视频信号的实时传输.实验结果表明,该系统具有大带宽、抗电磁干扰等优点,同时利用光电振荡器的自动相位跟踪技术,无须外加锁相等操作.整个下转换系统简单稳定,为高清视频的有线无线传输提供了论证和演示平台.     

86-km optical link with a resolution of 2 × 10<Superscript>-18</Superscript> for RF frequency transfer

RF frequency transfer over an urban 86 km fibre has been demonstrated with a resolution of 2×10^-18 at one day measuring time using an optical compensator. This result is obtained with a reference carrier frequency of 1 GHz, and a rapid scrambling of the polarisation state of the input light in order to reduce the sensitivity to the polarisation mode dispersion in the fibre. The limitation due to the fibre chromatic dispersion associated with the laser frequency fluctuations is highlighted and analyzed. A preliminary test of an extended compensated link over 186 km using optical amplifiers gives a resolution below 10^-17 at 1 day.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

Clock recovery from 40 Gbps optical signal with optical phase-locked loop based on a terahertz optical asymmetric demultiplexer

10 GHz clock recovery from 40 Gbps optical time-division-multiplexed (OTDM) signal pulses is experimentally demonstrated using optical phase lock loop based on a terahertz optical asymmetric demultiplexer (TOAD) with a local-reference-oscillator-free electronic feedback circuit. The clock pulse that was used as the control pulse had energy of 800 fJ and the SNR of the time-extracted 10 GHz RF signal to the side components was larger than 40 dB.     

Multi-functional fibre-optic microwave links

The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition to signal transmission. All three functionalities are presented and experimentally demonstrated with a remote heterodyne detection link based on a dual-frequency laser transmitter with two offset phase locked semiconductor lasers. In the modulating link a 1Gbit/s baseband signal is QPSK modulated onto a 9GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100Mbit/s PSK signal from a 2GHz carrier to a 9GHz carrier with penalty-free transmission over 25km of optical fibre. Finally, the transparent signal recovering link transmits a standard FM video 7.6GHz radio-link signal over 25km of optical fibre without measurable distortion.