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.     

Switchable instantaneous frequency measurement by optical power monitoring based on DP-QPSK modulator

We propose and analyze an instantaneous frequency measurement system by using optical power monitoring technique with improved resolution. The primary component adopted in the proposal is a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which is used to modulate the microwave signal that has a designed time delay and phase shifting. The generated optical signal is sent to polarization beam splitter (PBS) in DP-QPSK modulator. Owing to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted into the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal can be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the direct current (DC) biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range, and the influence of imperfection devices. The proposed scheme is wavelength-independent and its measurement range is switchable, which can avoid the laser wavelength drifting problem and thus greatly increasing the system flexibility.     

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.     

基于双音外差的电光相位调制器半波电压自校准测量方法

电光相位调制器是光纤通信系统、微波光子系统和相干光通信系统中的关键器件之一. 作为器件本征参数, 电光相位调制器的半波电压通常利用光谱方法和电谱方法进行测量. 光谱方法受到光源线宽和光谱仪分辨率限制, 测量的分辨率较低; 电谱方法则需要光电检测之前将相位调制转换成强度调制, 电谱方法的主要困难在于需要对探测器的不平坦响应进行额外校准. 提出了利用双音外差实现电光相位调制器半波电压自校准测量新方法, 该方法利用双音电光相位调制的边带与移频光载波的外差拍频, 对外差拍频信号进行频谱分析, 获得电光相位调制器的半波电压; 通过设定双音调制信号的频率关系, 克服了探测器光电转换中的不平坦频率响应, 实现了自校准测量. 该方法可扩展探测器和频谱仪的测试频率两倍以上, 节省至少一半的带宽需求. 与光谱测量方法相比, 该方法测试分辨率大幅提高且避免了光源线宽的影响; 与传统电域测量方法相比, 该方法无须额外校准, 无驱动功率和工作波长限制, 且对测试仪器带宽需求降低一半以上. 实验证实了所提方法获得的电光相位调制器半波电压的测量结果与光谱分析法获得的结果一致, 且大幅度地提高了测量范围和分辨率. 该方法提供了非常简单的电光相位调制器微波特性化分析方法, 对其他光电子器件分析也提供了参考.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

Magic Wavelength Measurement of the ~(87)Sr Optical Lattice Clock at NIM

We report on the magic wavelength measurement of our optical lattice clock based on fermion strontium atoms at the National Institute of Metrology(NIM).A Ti:sapphire solid state laser locked to a reference cavity inside a temperature-stabilized vacuum chamber is employed to generate the optical lattice.The laser frequency is measured by an erbium fiber frequency comb.The trap depth is modulated by varying the lattice laser power via an acousto-optic modulator.We obtain the frequency shift coefficient at this lattice wavelength by measuring the differential frequency shift of the clock transition of the strontium atoms at different trap depths,and the frequency shift coefficient at this lattice wavelength is obtained.We measure the frequency shift coefficients at different lattice frequencies around the magic wavelength and linearly fit the measurement data,and the magic wavelength is calculated to be 368554672(44) MHz.     

Microwave Photonic Up- and Down-Converter with Tunable Phase Shift Based on an Integrated Dual-Polarization Dual-Parallel Mach–Zehnder Modulator without Optically Filtering

ABSTRACT

In this paper, we propose and numerically simulate a microwave photonic phase-tunable frequency converter (MPPTFC) without optically filtering to realize both frequency up- and down-conversion and a full 360° phase-shift for the microwave signal based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In the proposed scheme, both microwave RF signal and frequency-tunable local oscillator (LO) are modulated on the lightwave by single-sideband carrier suppression (SSB-CS) modulation to generate optical orthogonally polarized optical tones carrying RF signal with up- or down-converted frequency. A PolM that can support lightwave modulation with opposite modulation indices in transverse electric (TE) and transverse magnetic (TM) modes is used to introduce a phase difference between the two modes. Then the orthogonally polarized optical tones are aligned into a single polarized state by a polarizer (Pol) and detected by a photodiode (PD), a frequency-converted and phase-shifted microwave signal can be obtained. Simulation results demonstrate that the proposed MPPTFC can up-/down-convert the microwave signal with a tunable frequency shift of LO frequency and realize a 360° continuously tunable phase shift via the DC bias voltage of the PolM simultaneously.     

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。     

Dynamic model of slow light in a tensile-strained semiconductor optical amplifier

The slow light effect in semiconductor optical amplifiers has many potential applications in microwave photonics such as phase shifting and filtering. Models are needed to predict the slow light effect in SOAs and its dependence on the bias current, wavelength, and power and modulation index. In this paper we predict the slow light characteristics of a tensile-strained SOA by using a detailed time-domain model. The model includes full band-structure based calculations of the material gain, bimolecular recombination and spontaneous emission, a detailed carrier density rate equation and travelling-wave equations for the amplitude modulated signal and amplified spontaneous emission. The slow light parameters of interest include the beat signal phase shift and amplitude response. The model predictions show good agreement with experimental trends reported in the literature.     

Linear and nonlinear distortion effects in direct detection 40 Gb/s MSK modulation formats multi-span optically amplified transmission

The generation of minimum shift keying (MSK) requires a linear variation of the phase, hence a constant frequency of the optical carrier. However, the generation of the optical phase may be preferred by driving an optical modulator using sinusoidal signal for practical implementation. Thus a nonlinear variation of the carrier phase, hence some distortion effects are produced. In this paper, we investigate the use of linear and nonlinear phase shaping filtering and their impacts on MSK modulated optical signals transmission over optically amplified long haul communications system. The evolution of the phasor of the in-phase and quadrature components is illustrated for lightwave-modulated signal transmission. The distinct features of three different MSK modulation formats: linear MSK, weakly nonlinear MSK and strongly nonlinear MSK and their transmission are simulated. Transmission performance obtained indicates the resilience of the MSK signals in transmission over multi-optically amplified multi-spans.     

基于布里渊载波相移的宽带可调谐二倍频微波信号生成

本文提出并实验验证了一种基于光纤中受激布里渊散射效应的光子二倍频微波信号生成技术.利用布里渊增益谱内的强色散特性,对光强度调制器产生的双边带调制信号的载波进行π/2相移,可实现载波与±1阶边带拍频仅生成二倍频微波信号.由于光纤中受激布里渊散射的窄带特性以及仅对双边带调制信号的载波进行相移,不影响调制信号两个边带的幅值和相位,因而生成的二倍频微波信号可实现宽带调谐,调谐范围仅受其他光器件的工作带宽限制.此外,信号光和产生受激布里渊散射的抽运光均来自同一光源,因而不受波长漂移的影响,系统具良好的稳定性.     

电光调制在被动综合孔径成像探测中的应用

介绍了一种新型被动综合孔径成像探测方法:视场辐射信号被接收和放大后,通过电光幅度调制将其幅度和相位信息加载到光波上,经光纤传输在末端形成阵列,通过光学系统直接成像,将视场实时恢复出来.该方法可实现工作在微波、毫米波和太赫兹波段的高分辨力实时成像探测的目的.深入分析了电光调制器在综合孔径成像探测中的应用,建立电光调制模型,讨论了在小信号调制下的电光幅度调制近似理论.通过数值计算与仿真分析,得到综合孔径成像探测中电光调制器的调制信号强度限制的有关结论.结果表明,利用上变频电光调制技术和光信息处理,所得到的成像仿真图的半峰全宽和信噪比性能都优于传统的基于下变频技术的成像仿真结果.     

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.     

重复频率可调谐的超低抖动光窄脉冲源的研究

提出了一种新型的基于光电振荡器的重复频率可调谐的超低抖动光窄脉冲源. 光电振荡器系统可以产生超低相位噪声的微波信号; 被该信号调制的直调光经过两次相位调制之后, 使光脉冲的啁啾增强; 再通过一段色散补偿光纤, 光脉冲被进一步压窄. 实验中使用YIG可调滤波器, 可以得到8–12 GHz内步进为200 MHz的可调谐微波信号, 因此光脉冲的重复频率具有可调谐性. 当微波信号即脉冲重复频率为9.6 GHz时, 测得脉冲宽度为3.7 ps, 相位噪声为-130.1 dBc/Hz@10 kHz. 由此得出光脉冲的瞬时抖动为60.1 fs (100 Hz–1 MHz), 因此该方案产生的光窄脉冲源具有超低的抖动.     

基于注入半导体激光器的微波副载波相位调制信号产生

光载无线技术是解决终端超宽带无线通信的重要方法,光信号与微波/毫米波信号的融合处理技术在光-无线的数据格式转换中至关重要.提出了一种基于相位调制信号光注入Fabry-Perot型半导体激光器实现微波副载波相位调制信号产生的方法.光学注入半导体激光器的输出光场会产生一周期(P1)振荡效应, P1振荡产生的边带实现了相位调制信号光的调制分量的放大,被放大的调制分量与注入光载波在激光器腔内拍频形成微波副载波.注入光相位的变化导致新产生的微波副载波相位变化, 实现了注入信号光相位信息转化为微波副载波相位信息.本系统完成1.3 Gb/s, 2.7 Gb/s, 2 Gb/s光相位调制信号到微波副载波相位调制信号的转换,并测量了微波的单边带相位噪声. 通过光电转换和电域混频将还原出的光基带信号与原信号进行逻辑对比,证明了数据信息转换的正确性.     

基于微波频差转换的光学拍频研究

光学拍频是大学物理和光学实验教学中的重要内容.由于激光器存在中心波长漂移问题,实验中不易产生可观测的拍频信号.受到微波光子技术中微波波段和光波波段相互作用机理的启发,提出了基于微波频差转换的光学拍频方法.借助强度调制和相位调制将两个频差较小的微波信号调制到同一光载波上,结合光学滤波器获得了两个频差极小的稳定光信号,利用...     

Measurement of modulation index and half-wave voltage of an electro-optical phase modulator with a dispersion-based phase filter

In this paper, a novel method based on the use of an optical phase filter is proposed to evaluate the modulation index, as well as the half-wave voltage of an optical phase modulator. When a phase modulated signal propagates along the length of a dispersive fiber, the fiber dispersion acts as an optical phase filter and spectrally alters the relative phasing of the phase modulated signal, causing the phase modulation to become intensity modulation, which allows the swept frequency measurement of phase modulators by using a vector network analyzer. The modulation index and half-wave voltage as a function of the modulation frequency are experimentally measured for a commercial phase modulator, which agree well with the results obtained using the widely accepted optical spectrum analysis method. The proposed method requires only a length of dispersive fiber and works without any small-signal approximation, which is applicable for different driving levels and operating wavelengths with the same setup.     

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。     

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.     

相敏式激光啁啾色散光谱技术在高吸收度情况下的应用

研究了相敏式激光啁啾色散光谱法在高吸收度情况下的应用.用窄频半导体激光器作为光源,利用一工作于载波抑制模式的铌酸锂电光强度调制器调制单频激光,在单频激光两侧产生两个边频分量,并通过两边频分量产生外差干涉信号.利用外差干涉的相位波动来测量甲烷气体位于1653.7 nm附近的折射率波动,通过气体折射率与吸收系数之间的Kramers-Kronig关系计算甲烷气体浓度.传统的波长调制光谱法受限于郎伯-比尔定律,在应用于高吸收度的情况时,存在灵敏度下降的问题,甚至出现随气体浓度上升输出信号反而下降的现象.实验结果显示,相同实验条件下,波长调制光谱法的线性测量范围为38.1—1500 ppm·m,线性测量的动态范围仅为16 d B;而相敏式激光啁啾色散光谱法在很大的吸收度范围内均具有线性输出,检出限低至47.3 ppm·m,线性测量范围上限为174825 ppm·m,具有超过35 d B的动态范围.