Linearized analog photonic links based on a dual-parallel polarization modulator

A linearized analog photonic link (APL) is proposed based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of two polarization beam splitters and two polarization modulators (PolMs). Theoretical analysis shows that the APL is potentially free from the third-order nonlinear distortion if a polarization controller placed before the DPPolM is carefully adjusted. A proof-of-concept experiment is carried out. A reduction of the third-order intermodulation components as high as 40 dB and an improvement of the spurious-free dynamic range as large as 15.5 dB is achieved as compared with a single PolM-based link. The DPPolM-based APL is simple, compact, and power efficient since it requires only one laser, one modulator, and one photodetector.     

基于谐波拟合产生周期性三角形光脉冲串的实验研究

实验研究了一种基于谐波拟合产生周期性三角形光脉冲串的方法,方案首先利用马赫曾德调制器的载波抑制调制,获得具有周期性起伏的连续光强度信号,然后利用光纤色散所致的射频功率衰落效应,对光强度表达式中四次谐波分量进行抑制,调节调制深度后,光强度表达式将向理想三角形傅里叶展开式的前三项进行逼近,最后以谐波拟合的方式获得重复频率为射频调制频率二倍的周期性三角形光脉冲串.结合实验,在9.862 GHz和7.678 GHz射频调制频率下,获得了脉冲重复频率19.724 Gb/s(脉冲全宽约50.7 ps)和15.356Gb/s(脉冲全宽约65.1 ps)的稳定三角形光脉冲串输出,改变色散量并反向调节调制频率,可进一步改变脉冲的重复频率,所获得的实验结果与理论预期基本符合.     

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。     

Photonic instantaneous microwave frequency measurement based on two different phase modulation to intensity modulation conversions

A novel photonic technique for instantaneous frequency measurement of microwave signal based on phase modulation to intensity modulation conversion is proposed and demonstrated. In the proposed system, an optical carrier is modulated by a microwave signal with its frequency to be measured through a phase modulator. The phase-modulated optical signal is then converted to intensity-modulated signals in two independent paths using a dispersive media and a frequency discriminator respectively. Since the dependence of the received microwave power on the input microwave frequency in the two paths differs, the microwave power ratio between the two paths can be used to uniquely determine the microwave frequency. The major advantages of the approach lie in that only one laser source and the bias-free phase modulator is employed in the system, which improves the stability of the system. Experimental demonstrations of the frequency measurement based on the proposed approach are presented.     

Linearization and dispersion tolerable technique for remote access unit in uplink RoF system based on gain-saturated RSOA cascaded EAM

A novel scheme of a remote access unit which is based on an electroabsorption modulator cascaded by a gain-saturated reflective semiconductor optical amplifier is proposed to improve a transmission performance of uplink signal. The cascaded gain-saturated reflective semiconductor optical amplifier plays a role in enhancing linearity of the electroabsorption modulator as well as suppressing dispersion-induced carrier suppression in the uplink transmission using its nonlinear gain property. In the proposed scheme, carrier-to-interference ratio of transmitted 10-GHz band uplink signal was improved by 10.7 dB and the dispersion-induced carrier suppression of 5.65-GHz RF carrier was greatly mitigated by 33.4 dB through the 75.6-km optical link.     

星间微波光子链路调制方式的优化

针对外调制星间微波光子链路输出信噪比优化问题,建立了基于双电极马赫 曾德尔调制器的强度调制直接探测星间微波光子链路模型,通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比,利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明:相同输入射频信号功率和发射光功率情况下,双边带调制输出信噪比比单边带调制高3 dB,低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm,输出信噪比为17.3 dB时,所需最小光放大器增益为43.9 dB,对应的直流偏置相位为0.87。     

I/Q intensity-demodulation analog photonic link based on polarization modulator

We experimentally investigate a high-linearity analog photonic link based on polarization-modulation in-phase/quadrature (I/Q) intensity-demodulation. In the proposed system, a light wave with its polarization direction oriented at an angle of 45° with respect to the principal axis of the polarization modulator (PolM) is polarization modulated by a drive signal. In the receiver, the polarization-modulated signal is split into two paths using a 50:50 optical coupler (OC). In each path, a polarization beam splitter (PBS) is connected to the PolM via a polarization controller (PC) to realize the in-phase and quadrature signal, respectively. Thanks to the polarization-modulation to intensity-modulation conversion, the fluctuation of the optical phase noise has no impact on the coherent signals. In addition, the use of a single PolM allows the link avoids the matching requirements of dual modulator schemes. The linearization leads to suppression of the third-order intermodulation (IMD3) by more than 40 dB, compared to the quadrature signal. Experimental results show that the link gain is -11.5 dB, noise figure is 26.5 dB, and the third-order limited spurious free dynamic range (SFDR) is 124 dB in a 1 Hz bandwidth.     

Microwave Photonic Phase Shifter Based on an Integrated Dual-polarization Dual-parallel Mach-Zehnder Modulator without Optical Filter

ABSTRACT

A frequency-doubled microwave photonic phase shifter (MPPS) without optical filter is proposed. The MPPS is based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM with a 90° polarization rotator in one arm is used to generate an optical carrier suppressed double sideband (OCS-DSB) signal with orthogonal polarization, and the PolM with two modes opposite phase modulation is used to introduce the optical phase shift between the two orthogonally polarized tones. Simulations show that the MPPS can realize a continuously tunable phase shift of 360° with only one DC bias voltage, and is not sensitive to the optical carrier wavelength and microwave signal frequency since no optical filter is used.     

A MZI-based photonic instantaneous microwave frequency measurement simplified by an optical polarizer

A novel photonic scheme of microwave signal frequency measurement with adjustable measurement range and resolution is proposed and experimentally demonstrated. The proposed scheme is based on simultaneous optical phase modulation and intensity modulation with interferometric detection. A low-pass frequency response is achieved by a Mach–Zehnder interferometer (MZI) while a bandpass frequency response is produced by a polarizer placed on the back instead of in front of the MZI. The microwave frequency can be estimated by the measured amplitude comparison function (ACF) obtained from the ratio of the two frequency responses. This scheme is simple, cost-effective as it requires no extra laser sources or modulators in the basic analog modulation link. The measurement errors as shown in experimental results can be kept in 0.1 GHz over a frequency range of 0.1–8.5 GHz.     

Optoelectronic Oscillator Based on Polarization Modulation

Abstract

A polarization modulator together with a polarizer can implement phase modulation, intensity modulation with tunable chirp, and frequency-doubling intensity modulation. If an optical filter is incorporated, frequency-quadrupling and frequency-sextupling intensity modulations and a microwave photonic phase shifter can also be realized. By using a polarization modulator to replace the intensity modulator in an optoelectronic oscillator, various new features are enabled. In this article, an analytical model for the polarization modulator-based systems is established. The recent development in employing polarization modulators for constructing optoelectronic oscillators is discussed. The emerging applications enabled by the polarization modulator-based optoelectronic oscillators and the possible future development are also discussed.     

Optimization of an Externally Modulated RF Photonic Link

The noise figure and sub-octave spurious-free dynamic range of a carrier-suppressed analog RF photonic link are examined. Expressions for noise figure and dynamic range are derived as a function of the modulator bias angle. A closed form expression for the bias angle that optimizes link noise figure and spurious-free dynamic range is also derived. Experimental results are presented and shown to agree with calculations. These experimental results include some of the lowest noise figure and highest dynamic range results published to date for an RF photonic link incorporating a standard Mach-Zehnder modulator: 6 dB and 122 dB·Hz^2/3, respectively.     

基于双通道马赫曾德尔调制器调制边带滤波的微波光子移相器

提出了一种基于双通道马赫曾德尔调制器(DPMZM)调制边带滤波的微波光子移相器。在双通道马赫曾德尔调制器的结构中,在一路马赫曾德尔干涉仪上实现抑制光载波的双边带调制输出,而在另一路马赫曾德尔的相位调节臂上通过调节偏置电压实现光载波信号的光学移相,两路光信号经过干涉合路后由光纤布拉格光栅(FBG)滤除其中一个一阶边带,最后输入到光电探测器(PD)进行光电转换得到移相的微波信号。实验结果表明,基于DPMZM调制边带滤波的微波光子移相器具有传输特性稳定、输出幅度波动小的优点。该结构还具有相移调节响应速度快、应用频带宽以及移相范围大于360°等特点。     

Terahertz modulator using photonic crystals

In this letter, a novel terahertz wave modulator based on a silicon oxide/polyaniline photonic crystal is proposed. The modulation mechanism of the novel modulator is based on a dynamic shift of the photonic band gap by the applied external electric field. Its performances were investigated with the finite-difference time-domain method. The novel modulator has 3 dB modulation bandwidth of 10 kHz, a size as small as 20 mm and its extinction ratio larger than 30 dB at the frequency of 1 THz.     

基于受激布里渊散射的宽带宽和高精度的微波频率瞬时测量

提出了一种基于受激布里渊散射效应的瞬时频率测量方法.未知信号经过强度调制作为泵浦光,矢量网络分析仪产生的信号经过相位调制作为扫描信号光,当泵浦光和扫描信号光之间满足相位匹配条件时,受激布里渊散射效应发生并实现相位调制到强度调制的转换,未知信号的频率被测量.实验验证可以测量0.5 GHz-27 GHz的微波信号的频率,最大误差小于20 MHz.     

Optimization of an Externally Modulated RF Photonic Link

Abstract

The noise figure and sub-octave spurious-free dynamic range of a carrier-suppressed analog RF photonic link are examined. Expressions for noise figure and dynamic range are derived as a function of the modulator bias angle. A closed form expression for the bias angle that optimizes link noise figure and spurious-free dynamic range is also derived. Experimental results are presented and shown to agree with calculations. These experimental results include some of the lowest noise figure and highest dynamic range results published to date for an RF photonic link incorporating a standard Mach-Zehnder modulator: 6 dB and 122 dB·Hz^2/3, respectively.     

Dispersion induced power fading for radio frequency signals and its application for fast online PMD and CD monitoring

We derive the expressions for the power fading including first-order polarization mode dispersion (PMD), chromatic dispersion, chirp parameter as well as polarization-dependent chromatic dispersion (PCD), which is dependent on the angle of precession of output state of polarization around the PMD vector. From the expression for radio frequency (RF) signals power fading, we get the average power fading for chromatic dispersion, chirp parameter, first-order PMD and PCD for both double sideband (DSB) modulation and single sideband (SSB) modulation. We also demonstrate a fast PMD and chromatic dispersion monitoring technology with reduced polarization-dependent gain. The measured results agree well with theoretical analysis. PACS 42.81.-i; 42.81.Gs; 42.30.Lr     

All optical microwave photonic filters with a round-trip configuration

We propose novel photonic microwave multi-tap filters using a section of Hi-Bi fiber in a round-trip configuration, together with their application in a 20 km single mode fiber (SMF) radio-over-fiber (RoF) link. We demonstrate for the first time that the effect of chromatic dispersion in these multi-tap filters can be reduced in an RoF link when a linearly chirped fiber Bragg grating (FBG) is adopted. This result can be used to combat radio frequency power fading in an RoF link. The configurations are free from optical coherent interference and phase noise. Measured results show 3-tap filters with notch rejections greater than 35 dB and suppression of the level of secondary sidelobes by adjusting a polarization controller. PACS 42.81.-I; 42.81.Gs; 07.50.Qx     

基于多波长激光器的带通微波光子滤波器设计

提出了一种基于多波长光纤激光器的可调谐的带通微波光子滤波器。它以可调谐多波长光纤激光器作为光源,将相位调制器和色散器件相结合,通过在普通单模光纤中相位调制到强度调制的转换效应消除了低频谐振峰实现了带通微波光子滤波器。利用双折射光纤环镜输出谱中的一个窗口对多波长激光信号频谱进行加窗处理,使微波光子滤波器的边瓣抑制比提高了约11dB。通过调节多波长光纤激光器中的偏振控制器可以使输出多波长激光信号的相邻波长间隔得到调节,从而结合普通单模光纤的色散延时作用可以使微波光子滤波器的通带中心频率在7.66GHz范围内调谐。     

Simulation of Third-Order Intermodulation Distortion Suppression Incorporating Dual-Parallel Mach–Zehnder Modulator in a CR-SSB Modulation

A novel scheme is proposed to enlarge the spurious free dynamic range (SFDR) of microwave photonic (MWP) link by using dual-parallel Mach–Zehnder modulator, which modifies the single sideband signal and replaces the optical carrier with an unmodulated one to remove the optical main sources of third-order intermodulation distortion (IMD3). Simulation results show that the IMD3 and fifth-order intermodulation distortion can be suppressed greatly even when the modulation depth increases to a high value, and the link is limited by seventh-order intermodulation distortion and the SFDR is improved by 34.2 dB Hz in a 1-Hz bandwidth. The error vector magnitude of the MWP link with the proposed scheme is improved significantly for the transmitted 1-Gbit/s 16- quadrature amplitude modulation (QAM) signal.     

Thermo-optically tunable silicon photonic crystal light modulator

We designed, fabricated, and characterized a thermo-optically tunable compact (10 μm × 10 μm) silicon photonic crystal (PhC) light modulator that operates at around 1.55 μm for TE polarization. The operational principle of the device is the modulation of the cutoff frequency in a silicon-based line defect PhC. The cutoff frequency is shifted because of the thermo-optic tuning of the silicon refractive index, which is realized by localized heating on the PhC. The modulator is formed by a triangular lattice array of cylindrical air holes on a silicon-on-insulator wafer. Optical characterization was carried out, and the result clearly showed thermo-optic tuning of the cutoff frequency at around 1.55 μm.