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.     

基于重采样技术的调频连续波激光绝对测距高精度及快速测量方法研究

调频连续波激光测距方法可以实现高精度的大尺寸绝对距离测量, 且测量过程无需合作目标, 在大空间坐标精密测量领域有很高的研究价值. 而如何提高测量分辨率和实用化一直是近年来调频连续波激光绝对测距研究的热点. 本文研究了调频连续波激光测距的原理, 基于双光路调频连续波激光测距系统, 提出了通过信号拼接提高测量分辨率的信号处理优化方案, 该方案可以提高测距分辨率, 且可以降低对激光器的性能要求; 提出了可实现高速测量的简易测量方法. 设计加工了双光路光纤调频连续波激光测距系统, 利用该系统进行了测距分辨率及测距误差标定实验, 实验结果表明: 优化方案可以有效地提高测量分辨率和测量效率, 在26 m测量范围内, 测距分辨率达到了50 μm, 测距误差不超过100 μm; 快速测量方案有较高实用价值.     

超稳光生微波源研究进展

随着科技的进步以及精密测量应用技术的不断提高,超稳微波源的稳定度和噪声水平等技术要求不断提高,应用范围愈加广泛,包括高性能频标研究、网络雷达研制、深空导航系统等方面.基于超稳激光和飞秒光梳的超稳光生微波源是目前频率稳定度最高的微波频率源,相对频率稳定度可达10~(16)@1 s量级.该装置也是未来频率标准(光频标)推广应用的基础,无论是时间的产生还是绝大多数的精密测量,都需要将光频标的输出激光变换为超稳的基带频率信号后才能够实现.本文介绍了超稳光生微波源技术的发展、现状和应用需求.以国家授时中心研制的国内首套超稳微波频率源技术为主线,介绍了超稳光生微波源的原理和结构以及各组成部分的技术发展情况:超稳激光方面,着重介绍超稳光学腔研究和研制的进展以及Pound-Drever-Hall锁频技术、剩余幅度调制等噪声抑制技术;飞秒光梳方面,着重介绍目前最常用的掺铒光纤光梳系统的激光锁模、频率控制等技术发展;低噪声光电探测方面,着重介绍宽带光电探测噪声抑制技术和激光幅度噪声引起微波相位噪声的抑制技术.最后对光生超稳微波技术进行了总结和展望.     

Broad-spectrum frequency comb generation and carrier-envelope offset frequency measurement by second-harmonic generation of a mode-locked fiber laser

A frequency comb spanning more than one octave has been achieved by injecting the second-harmonic generation (780 nm) of a mode-locked fiber laser (1.56 microm) into a photonic crystal fiber. We propose and realize a novel interferometric scheme for observing the carrier-envelope offset frequency of the frequency comb. Frequency noise has been observed on the measured carrier-envelope offset frequency, which has been confirmed to be generated in the photonic crystal fiber by comparing the measured beat frequencies between cw lasers and frequency combs before and after the photonic crystal fiber. The mode-locked fiber laser is considered to be an important candidate for the light source used in realizing a compact optical frequency measurement system including applications in the telecommunication bands.     

Photonic-based instantaneous microwave frequency measurement with extended range

A novel approach to extend the frequency range and improve the resolution of photonic techniques for microwave frequency measurements based on frequency-to-power mapping is demonstrated. The simultaneous use of several amplitude comparison functions allows the extension of the measurement beyond a single monotonic region. Experimental results between 7 and 19 GHz with a resolution better than 100 MHz are presented.     

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.     

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.     

Time-resolved chirp measurement for 100GBaud test systems using an ideal frequency discriminator

In this paper we present multi-channel chirp measurements of wide-band sources, using a programmable Fourier-domain optical processor (FDOP) as a near-perfect linear frequency discriminator element followed by a fast photodiode and electrical sampling oscilloscope. The electric field of a 10.7 Gbit/s phase-encoded data source and a directly modulated laser diode are simultaneously interrogated with this measurement system. The constellation diagram of the phase-encoded data source is demonstrated, and a comparison with another phase-sensitive measurement technique is performed. Additionally, an extension to this technique is demonstrated in which the time-resolved chirp of a picosecond-duration mode-locked laser diode with a 260 GHz spectral bandwidth is characterised using the FDOP and a high-bandwidth optical sampling oscilloscope. This measurement ensemble has sufficient temporal resolution to characterise random or repetitive data signals up to 100GBaud.     

基于高双折射光子晶体光纤与光纤环的超宽带可调谐微波光子滤波器

提出一种基于高双折射光子晶体光纤与光纤环的超宽带可调谐微波光子滤波器.以多波长光纤激光器作为光源,向高双折射光子晶体光纤内填充温敏液体,通过改变填充温敏液体的温度,高双折射光子晶体光纤可具有不同的双折射,得到不同波长间隔的激光,从而使微波光子滤波器具有不同的自由频谱范围.当温度的变化范围为20~80℃时,仿真测得微波光子滤波器自由频谱的变化范围为2.49~39.9GHz.引入光纤环构建级联型微波光子滤波器,滤波器的主旁瓣抑制比可提高到33.6dB,Q值可达到499,提高了滤波器的频率选择性.     

基于双平行调制器光毫米的产生与测试

提出了一种光载毫米波产生新方案,采用双平行马赫曾德调制器（DPMZM）,基于线性的光相干技术,产生四倍频的毫米波信号。该技术不需要复杂的电信号处理,以及射频信号的锁相技术,便可产生稳定的毫米波信号。该方法产生的毫米波信号具有频率稳定、抖动小、信噪比高等优点,可以广泛应用于光电器件测试与校准。     

Dual-polarization fiber grating laser-based laser Doppler velocimeter

A dual-frequency laser Doppler velocimeter implemented by a dual-polarization fiber grating laser is proposed,with the two laser frequencies produced by the two orthogonally polarized laser outputs of the fiber grating laser.The reflected laser outputs from a moving target experience the Doppler frequency shift,which is shown to be linearly related to the velocity and the beat note frequency difference between the laser outputs and the reflected light. With a digital frequency demodulation scheme,a high sensitivity of 0.64 MHz/(m/s) and a velocity resolution of less than 0.5% of the velocity for velocity measurement are demonstrated,which shows that the proposed laser Doppler velocimeter is capable of measurement of wide range of velocity.     

基于椭圆偏振光注入垂直腔表面发射激光器的正交偏振模式单周期振荡产生两路光子微波

提出了基于椭圆偏振光注入下垂直腔表面发射激光器(VCSEL)输出的正交偏振模式单周期(P1)振荡来同时获取两路光子微波的实现方案, 并进行了相关仿真研究. 结果表明: 在合适的参数条件下, 一个自由运行的VCSEL(定义为主VCSEL, M-VCSEL)可输出椭圆偏振光, 其X偏振分量和Y 偏振分量具有相同的激射频率; 将M-VCSEL输出的椭圆偏振光注入到另外一个VCSEL(定义为副VCSEL, S-VCSEL), 在给定主副VCSEL间频率失谐的条件下, 通过选择合适的注入强度可使S-VCSEL 中两个偏振分量均呈现单周期(P1)振荡, 从而可获得两正交的光子微波信号; 随着注入强度的增加, 光子微波的频率以及功率均呈现增加的趋势; 结合微波频率、功率以及输出光谱中第一边带和第二边带的幅度差在由注入强度和频率失谐所构成参数空间下的分布图, 可确定获取高品质微波信号的优化注入参数范围.     

High-resolution spectroscopy using interleaved 100 GHz optical frequency comb scanned by phase modulator

A high-resolution spectroscopy technique is proposed with an optical phase modulator combined with an interleaved optical frequency comb. The optical phase modulator and a frequency-locked laser light guarantee a spectral resolution less than 1 MHz on an absolute frequency axis. A wide measurement frequency range was realized using a 25 GHz optical frequency comb lying over a 4 THz frequency region. An extraction of single tooth intensity from the comb was realized by a heterodyne technique with a frequency-tunable laser used as a local oscillator. Also, the 25 GHz optical frequency comb was interleaved to generate four 100-GHz combs for removing the crosstalk from the 25 GHz neighboring sidebands in the teeth. This proposed spectroscopy technique was experimentally demonstrated with a resonator of less than 1 MHz linewidth and a H¹³C¹⁴N gas cell. Thus, a measurement frequency range higher than 4 THz (1530 nm-1560 nm) was confirmed with an effective spectral resolution 100 kHz order. In addition, the characteristics of the proposed system were compared with those of the previous system with a single-sideband (SSB) optical modulator.     

基于光注入半导体激光器单周期振荡的光子微波产生及全光线宽窄化

本文对基于光注入半导体激光器的单周期动力学态产生光子微波并利用光反馈压缩其线宽进行了实验研究. 研究结果表明: 通过适当调节注入参数, 能对该方法产生的光子微波频率在数十GHz范围内进行连续、大范围地调节; 通过引入光反馈并精细调节反馈强度, 光子微波的线宽能够从40—100 MHz的范围被压缩约两个数量级至300—900 kHz范围;反馈长度对光子微波的线宽几乎没有影响, 但当反馈长度精细变化时, 光子微波频率会出现一定范围内的周期性漂移.     

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.     

一种基于电光调制光频梳光谱干涉的绝对测距方法

提出了一种基于电光调制光学频率梳的光谱干涉测距方法.理论分析了电光调制光学频率梳的数学模型和光谱扩展原理,并分析得出了光谱干涉测距方法的非模糊范围和分辨力的影响因素.在实验中,使用三只级联的电光相位调制器调制单频连续波激光生成了40多阶高功率梳齿状边带,并通过单模光纤和高非线性光纤对电光调制器输出的激光进行光谱扩展,得到重复频率为10 GHz,光谱宽度达30 nm的光学频率梳.将该光频梳作为光谱干涉测距装置的光源,可以实现无"死区"的绝对距离测量.另外,使用等频率间隔重采样和二次方程脉冲峰值拟合算法对测量结果进行数据处理,可以修正系统误差,提升测距精度.实验结果表明,在1 m的测量范围内,使用该装置可以在任意位置达到±15μm以内的绝对测距精度.     

Compact interrogator for fiber optic Bragg sensors based on an acousto-optic filter formed by photonic crystal rows of air holes

Fiber optic sensors are typically used with expensive tunable lasers or optical spectrum analyzers for wavelength interrogation. We propose to replace the tunable laser by a broadband optical source incorporated with a novel thin linewidth acousto-optic tunable filter. It utilizes optical beam expanders constituted by photonic crystal rows of air holes in LiNbO(3) waveguide. A new design is numerically studied for a short structure (with 32 photonic crystal rows) by a two-dimensional finite-difference time-domain method. Extrapolation of these results to larger structure sizes (about 1 cm) demonstrates the possibility to develop compact interrogators with 0.4 pm wavelength resolution and 40 nm tunable range around 1550 nm.     

基于光纤色散相位补偿的高分辨率激光频率扫描干涉测量研究

为了实现更高分辨率的激光频率扫描干涉测量, 增大光源的扫频范围以及减小扫描频率的非线性成为关键. 采用外腔式大带宽扫频光源结合光纤辅助干涉仪构建的外部时钟频率采样非线性校正是目前较为常用的方法. 本研究发现随着扫频带宽和测量范围的增加, 光纤辅助干涉仪与测量光路中存在的色散失配导致频谱出现严重展宽, 极大的降低了测量的分辨率. 本文建立了辅助干涉仪和测量干涉仪色散失配影响的理论模型, 利用该模型分析了扫频带宽和测量范围与测量分辨率的变化关系, 与实验结果相一致, 并进而提出了基于峰值演化消畸变的色散相位补偿方法, 有效地提高了测量的分辨率, 在2.53 m 处实现了接近理论值的64.5 μm的测量分辨率. 该色散失配模型及补偿方法为提高大尺寸激光频率扫描干涉仪的测量分辨率及测距范围提供了参考.     

Photonic generation of millimeter-wave ultra-wideband signal using microfiber ring resonator

The photonic generation of millimeter-wave (MMW) ultra-wideband (UWB) signal using microfiber ring resonator (MRR) is proposed. The central frequency and 10-dB bandwidth of generated MMW-UWB signal varying with Q factor of MRR are analyzed. We successfully demonstrate a generation of 24-GHz MMW-UWB signal by utilizing a microfiber ring resonator with free spectrum range of 20 GHz and Q factor of 19,000. The generated MMW-UWB signal has a power spectrum density complying with Federal Communication Committee requirements.     

基于超连续光谱激发的时间分辨相干反斯托克斯拉曼散射方法与实验研究

采用钛宝石飞秒激光器输出的一部分光抽运光子晶体光纤以产生超连续光谱,作为抽运光和斯托克斯光,另一部分飞秒激光作为探测光,并结合时间延迟方法,建立超连续光谱激发时间分辨相干反斯托克斯拉曼散射(CARS)实验系统,测试了具有较宽拉曼光谱的二甲基亚砜样品.实验结果表明,所建立的实验系统能有效抑制非共振背景噪声,并且通过一次测量,即可获得二甲基亚砜在690—3200cm-1范围内的CARS光谱信息,获得的二甲基亚砜CARS光谱范围达到2500cm-1.同时给出了所采用的光子晶体光纤光谱展宽的实验结果.