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.     

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.     

Carrier generation and IF signal up-conversion using optical injection locking and stimulated Brillouin scattering

We theoretically investigate the intermediate frequency (IF) signal up-conversion with dual modes modulation (DMM) and single-mode modulation (SMM) of two single sideband (SSB) modulation modes for radio-over-fiber (RoF) systems. The simulation results indicate that the SMM can overcome the dispersion-induced power penalties of the generated carrier and up-converted IF signals. Then, we experimentally demonstrate an approach for RF carrier generation with SSB modulation and IF signal up-conversion with SMM using a combination of direct modulation in an injection-locked distributed feedback (DFB) laser and stimulated Brillouin scattering (SBS). The experimental results are compared with the predictions of the numerical simulation in SMM condition, and both are in good agreement with each other. The advantages and limits of the proposed method are discussed.     

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.     

Single-sideband modulated radio-over-fiber system based on long period fiber grating

We present a prototype for optical single-sideband (SSB) modulated radio-over-fiber (RoF) system by employing a long period fiber grating (LPFG). A LPFG with 13.78 nm base width of transmission spectrum and 0?23.2 dB of transmission depth was designed by using commercial software. Then it is used in RoF SSB modulation scheme. In the scheme, a Mach?Zehnder modulator modulates the light wave with millimeter-wave driving signals to realize optical double-sideband (ODSB) modulation, the generated ODSB modulation signals pass through a LPFG. Due to the negative slope in transmission spectrum, the lower sideband experiences higher attenuation than the upper sideband. Thus the conversion from ODSB to optical single sideband with carrier (OSSB + C) can be easily achieved by using only one LPFG. Also, the carrier to sideband ratio (CSR) can be reduced by using a LPFG, results show the CSR can be decreased from 12.49 dB to 1.1 dB.     

The optimization design of tilt-Spectral fiber Bragg grating and its application in SSB modulation based Radio over Fiber system

Based on theoretical analysis and simulation software, the paper researched the performance of transmission after using tilt-Spectral fiber Bragg grating for SSB modulation in Radio over Fiber system. The study concluded that DSB signal can be converted to SSB signal by using tilt-Spectral fiber Bragg grating, and inhibit the carrier power. There are two ideal conditions for a best grating. First, one side of DSB signal will be completely filtered, while the other side remains the same power. Secondly, carrier power equals to sideband power in SSB signal, which means that carrier-to-sideband ratio is 0 dB. As the result, the best tilt-Spectral fiber Bragg grating is designed. Transmitting the SSB signal which is filtered by the best grating in optical fiber not only eliminates the phenomenon that output amplitude change with the transmission distance cyclically, it also enhances the transmission efficiency and receiver sensitivity.     

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.     

Photon Generation Scheme of 32-Fold Millimeter-Wave Signal Based on Mach-Zehnder Modulator

This paper proposes a 32-tupling frequency millimeter-wave (MMW) filter-free system based on four Mach-Zehnder Modulators (MZM) connected in parallel and cascaded with a simple radio-fiber (RoF) link structure. The four MZMs are all at the maximum transmission point (MATP), and the radio frequency (RF) driving voltage phase difference between MZMs is π /2. The center carrier is suppressed by using an optical attenuator (OATT) and an optical phase shifter (OPS). Two parallel MZMs can generate ±8th order and ±12th order optical sidebands, and the ±4th order optical sidebands can be suppressed by adjusting the modulation index m of the MZM, using cascaded two dual-parallel MZMS(DPMZM) and the phase difference of the RF signal source is π/4 to generate ±16th order optical sidebands. The theoretical analysis and simulation experiments are performed for the scheme proposed in this paper. The results show that the simulated and theoretical values of the optical sideband suppression ratio (OSSR) for ±16th order optical sideband signals are 60.02 and 59.96 dB, respectively, and the simulated and theoretical values of the RF sideband suppression ratio (RFSSR) for the 32-tupling MMW signal are 56.34 and 53.94 dB, respectively.     

Simulative investigation on the impact of laser-spectral width in single-tone radio-over-fiber transmission system using optical single side-band technique

In this paper, we analyzed the impact of laser-spectral width incorporating dual-electrode Mach–Zehnder modulator (DEMZM) in single-tone radio-over-fiber (RoF) transmission system by simulation setup. It is shown that an improvement in the measurement of received radio frequency (RF) power is achieved by reducing the laser line width from 100 MHz to 100 kHz, which further improves the BER rate and optical link by transmitting the information with low power. The results are calculated for 20 and 50 km optical single sideband (OSSB)–RoF transmission system by varying the chirp from 0 to −3 as it requires less bandwidth than optical dual sideband (ODSB)–RoF system and is tolerable for power degradation due to a chromatic fiber-dispersion, through a standard single-mode fiber (SSMF) carried by a continuous wave (CW) laser at 1550 nm of laser-spectral width varying from 100 MHz to 100 kHz with CW power of 10 mW that modulates a single RF channel of 20 GHz. Further, deployment of such lasers with OSSB scheme helps the telecom industry to reduce the designing cost of RoF communication systems.     

Generation of optical carrier suppression millimeter-wave signal using one dual-parallel MZM to overcome chromatic dispersion

In this paper, we have proposed a novel approach to generate optical carrier suppression (OCS) mm-wave with signal only carried by one first-order sideband using a dual-parallel MZM in radio-over-fiber (RoF) system, and the transmission performance was also investigated. As the optical mm-wave signal is transmitted along the fiber, there is no time shift of the data symbols resulting from the group velocity dispersion in the fiber because the signal is only modulated on one sideband. The simulation results showed that the eye diagram keeps open and clear even when the optical mm-wave signals are transmitted over 96-km and the power penalty is about 1-dB after fiber transmission distance of 60-km, which is quite consistent with our theoretical analysis. Furthermore, the proposed OCS optical mm-wave generation approach is also used in a full-duplex RoF link based on wavelength reuse at the base station for the uplink due to another pure sideband without carrying data. The bidirectional 2.5-Gbit/s data is successfully transmitted over 40-km standard single mode fiber with less than 0.5-dB power penalty in the simulation. Both the unidirectional RoF downlink and the full-duplex RoF system have good performance.     

The influence of fiber dispersion on the code form of the optical mm-wave signal generated by single sideband intensity-modulation

We have theoretically investigated the transmission performance of the optical mm-wave generation by using an external modulator based on single sideband (SSB) intensity modulation. Though the SSB millimeter (mm)-wave can immune the fading effect, the baseband signals with a high bit rate are degraded greatly after transmission along fiber. The main reason is that the fiber dispersion causes the time shift of the code edges; therefore the maximum transmission distance of the baseband signals is limited. The experimental and simulation results agree well with our theoretical analysis. We also propose a novel scheme to extend the transmission distance. In this novel scheme, the data signals are modulated only onto one of the two optical carriers; hence the shift of the code edges in the down-converted signals after transmission is eliminated.     

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。     

Bidirectional radio-over-fiber systems with SSB modulation and wavelength reuse based on injection-locked semiconductor lasers

A 60-GHz bidirectional radio-over-fiber （RoF） system using two-carrier-injected distributed feedback （DFB） laser is proposed and demonstrated to realize optical single sideband （SSB） modulation for downlink.An injection-locked Fabry-P＇erot laser is also carried out to realize wavelength reuse in uplink.Transmission of 2.5 Gb/s on a 60-GHz carrier for downlink and 622-Mb/s baseband signal for uplink are both successfully demonstrated over 50-km single mode fiber without chromatic dispersion compensation.     

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.     

Compensation of dispersion-induced power fading for highly linear radio-over-fiber link using carrier phase-shifted double sideband modulation

A carrier phase-shifted (CPS) double sideband (DSB) modulation technique in radio-over-fiber (RoF) system is proposed and experimentally demonstrated. By tuning the biases in a single-drive dual parallel Mach-Zehnder modulator (SD-DPMZM), the optical carrier in the DSB spectrum acquires additional phase shift. The transmittance response of a dispersive RoF link is thus being controlled and shifted in the frequency domain. Experiments successfully turned the maximum transmission frequency to 10?GHz and 15?GHz for both 25 and 39?km fiber links. This is also a highly linear scheme, of which a spurious-free dynamic range (SFDR) of 111.3?dB·Hz^2/3 is experimentally obtained.     

High carrier suppression double sideband modulation using polarization state rotation filter and optical external modulator

We propose a high carrier suppression double sideband modulation technique using a Mach-Zehnder modulator (MZM) and an integrated polarization state rotation filter (PSRF), which is designed to improve the carrier suppression ratio. With the functions of MZM and PSRF, about 30 dB carrier suppression ratio relative to first-order sidebands is demonstrated. Moreover, we demonstrate the optical generation of microwave/millimeter-wave signals by beating the carrier suppressed double sideband (DSB-SC) lightwave signals. The experimental results show that the improvement of carrier suppression ratio with PSRF can effectively cancel the modulating RF frequency component. A tunable and high purity microwave signal, which is limited by the bandwidth of MZM and photodetector (PD), is obtained, and it does not suffer from obvious phase noise degradation with 25 km transmission.     

TUNABLE FIBER FABRY-PEROT FILTER FOR OPTICAL CARRIER-SUPPRESSION AND SINGLE-SIDEBAND MODULATION IN RADIO OVER FIBER LINKS

A novel method of simultaneous realization of optical carrier-suppression and single-sideband modulation using fiber Fabry-Perot tunable filter is presented. In order to enhance transmission performance of radio over fiber links, we use a fiber Fabry-Perot tunable filter to filter out one sideband as well as suppress the optical carrier power. The results demonstrate 20.5dB and 14.2dB improvement in the signal noise ratios when 18GHz and 10GHz microwave signals carrying 5Mbit/s quadrature-phase-shift-keyed (QPSK) format data is transmitted over 35 km single mode fiber, respectively.     

面向天基引力波探测的时间延迟干涉技术

时间延迟干涉技术(Time-delay Interferometry,TDI)对中国引力波探测项目及其它天基激光精密测量任务具有重要的参考价值。在天基引力波探测任务中,需利用激光干涉仪对无拖曳检验质量块间实现十皮米量级的位移测量精度。其中,激光源频率噪声和时钟频率噪声是两项主要噪声。在欧洲主导的LISA(Laser Interferometer Space Antenna)引力波探测项目中,利用TDI对三星上的十二组相位测量值进行延迟和线性组合,构造出臂长相等的干涉仪,从而消除了激光源噪声以及光学平台位移噪声。为了消除时钟噪声,将时钟信号倍频到GHz,再通过相位调制的方式加载到星间激光链路上,最终从时钟边带拍频信号中提取出时钟噪声,并在TDI的数据组合中将时钟噪声项消除。为了实现TDI的时间延迟处理,要求对星间绝对距离进行精确测量。因此,在TDI机制中,星间激光链路需要同时实现位移测量、时钟边带调制和绝对距离测量3个功能。其中,后两个功能分别大约消耗10%和1%的载波激光功率。LISA项目针对TDI技术的地面论证结果表明,TDI技术对激光源和时钟的噪声抑制分别达到了109和5.8×104倍。     

A generalized time-domain model for nonlinear inter-satellite microwave photonics links under dual-tone modulation

A generalized time-domain model is presented for the evaluation of nonlinear distortion effects in inter-satellite microwave photonics links using a dual-drive Mach-Zehnder modulator (DD-MZM) under dual-tone modulation. The model results in simple exact expressions for any harmonic and inter-modulation components at the output of the detector which can be applied to almost all operating conditions of DD-MZM, providing useful information to select system parameters for the performance optimization. Two special cases, double sideband and single sideband modulation, are studied in detail. Numerical results for the third-order inter-modulation distortion ratio (IMR3) are well matched with the analysis ones.     

Characterization of Rayleigh backscattering performance of CS-SSB signal in carrier distributed passive optical network

Rayleigh backscattering (RB) is an intrinsic phenomenon when light propagating in fiber and its level is fixed by the fiber type and the network configuration used. Thus, RB noise would be one of the major impairments in a carrier distributed passive optical network (PON). Previously demonstrated carrier suppressed subcarrier-amplitude modulated phase shift keying (CSS-AMPSK) modulation may be useful to effectively mitigate the RB noise. However, this modulation is basically a carrier suppressed double sidebands modulation (CS-DSB) format, in which the same information is carried by the two sidebands with equal magnitude. This is not very power-efficient for PON. Here, we further extend our RB studies by using carrier suppressed single sideband non-return-to-zero (CS-SSB-NRZ) modulation. We experimentally characterize the CS-SSB-NRZ modulation when subjected to both contributions of RB: Carrier-RB and Signal-RB. Then, numerical simulations are performed, and the results are in good match with the experiment. Finally, upstream transmission experiment is performed showing the feasibility of using the CS-SSB-NRZ signal for the carrier distributed PON. The RB performance of the SSB-NRZ signals transmitted at different distances and driven at different radio-frequency (RF) f_s is also investigated.