Opto-mechanical-thermal integration analysis of Doppler asymmetric spatial heterodyne interferometer

In order to improve the detection accuracy of Doppler asymmetric spatial heterodyne(DASH)interferometer in harsh temperatures,an opto-mechanical-thermal integration analysis is carried out.Firstly,the correlation between the interference phase and temperature is established according to the working principle and the phase algorithm of the interferometer.Secondly,the optical mechanical thermal analysis model and thermal deformation data acquisition model are designed.The deformation data of the interference module and the imaging optical system at different temperatures are given by temperature load simulation analysis,and the phase error caused by thermal deformation is obtained by fitting.Finally,based on the wind speed error caused by thermal deformation of each component,a reasonable temperature control scheme is proposed.The results show that the interference module occupies the main cause,the temperature must be controlled within(20±0.05)℃,and the temperature control should be carried out for the temperature sensitive parts,and the wind speed error caused by the part is 3.8 m/s.The thermal drift between the magnification of the imaging optical system and the thermal drift of the relative position between the imaging optical system and the detector should occupy the secondary cause,which should be controlled within(20±2)℃,and the wind speed error caused by the part is 3.05 m/s.In summary,the wind measurement error caused by interference module,imaging optical system,and the relative position between the imaging optical system and the detector can be controlled within 6.85 m/s.The analysis and temperature control schemes presented in this paper can provide theoretical basis for DASH interferometer engineering applications.

A Low-Voltage,Low-Power CMOS High Dynamic Range dB-Linear VGA for Super Heterodyne Receivers

This paper presents a low-voltage low-power variable gain amplifier,which is applied in the automatic gain control loop of a super heterodyne receiver. Six stages are cascaded to provide an 81dB digitally controlled gain range in a 3dB step. The gain step error is less than 0.5dB. It operates at an intermediate frequency of 300kHz, and the power consumption is 1.35mW from a 1.8V supply. The prototype chip is implemented in a TSMC＇s 0.18μm 1P6M CMOS process and occupies approximately 0.24mm^2 . It is very suitable for portable wire- less communication systems. The measurement results agree well with the system requirements.

A method of measuring micro-impulse with torsion pendulum based on multi-beam laser heterodyne

In this paper, we propose a novel method of multi-beam laser heterodyne measurement for micro-impulse. The measurement of the micro-impulse, which is converted into the measurement of the small tuning angle of the torsion pendulum, is realized by considering the interaction between pulse laser and working medium. Based on Doppler effect and heterodyne technology, the information regarding the small tuning angle is loaded to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, thereby obtaining many values of the small tuning angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, the small tuning angle can be obtained accurately and the value of the micro-impulse can eventually be calculated. Using Polyvinylchlorid＋2%C as a working medium, this novel method is used to simulate the value of the micro-impulse by MATLAB which is generated by considering the interaction between the pulse laser and the working medium, the obtained result shows that the relative error of this method is just 0.5%.

An improved arctangent algorithm based on phase-locked loop for heterodyne detection system

We present an ameliorated arctangent algorithm based on phase-locked loop for digital Doppler signal processing,utilized within the heterodyne detection system. We define the error gain factor given by the approximation of Taylor expansion by means of a comparison of the measured values and true values. Exact expressions are derived for the amplitude error of two in-phase & quadrature signals and the frequency error of the acousto-optic modulator. Numerical simulation results and experimental results make it clear that the dynamic instability of the intermediate frequency signals leads to cumulative errors, which will spiral upward. An improved arctangent algorithm for the heterodyne detection is proposed to eliminate the cumulative errors and harmonic components. Depending on the narrow-band filter, our experiments were performed to realize the detectable displacement of 20 nm at a detection distance of 20 m. The aim of this paper is the demonstration of the optimized arctangent algorithm as a powerful approach to the demodulation algorithm, which will advance the signal-to-noise ratio and measurement accuracy of the heterodyne detection system.

Dependence of interferogram phase on incident wavenumber and phase stability of Doppler asymmetric spatial heterodyne spectroscopy

Instrument drifts introduce additional phase errors into atmospheric wind measurement of Doppler asymmetric spatial heterodyne spectroscopy (DASH). Aiming at the phase sensitivity of DASH to instrument drifts, in this paper we calculate the optical path difference (OPD) and present an accurate formula of DASH interferogram. By controlling variables in computational ray-tracing simulations and laboratory experiments, it is indicated that initial phase is directly determined by incident wavenumber, OPD offset and field of view (FOV). Accordingly, it is indicated that retrieved phase of DASH is sensitive to slight structural change caused by instrument drift, which provides the proof of necessary-to-track and -correct phase errors from instrument drifts.

Spatial heterodyne spectroscopy for space-based measurements of atmospheric CO_2

To reduce the error from measurement and retrieval process, a new technology of spatial heterodyne spectroscopy is proposed. The principle of this technology and the instrument spatial het- erodyne spectrometer （SHS） are introduced. The first application of this technology will be for CO2 measurements from space on a high spectral observation satellite. The outstanding measurement principle and the priority of combination of retrieval algorithm and three channels （ O2 A-band, CO2 1.58 μm and 2.06 μm bands） are theoretically analyzed and numerically simulated. Experiments u- sing SHS prototype with low spectral resolution of 0. 4 cm -1are carried out for preliminary valida- tion. The measurements show clear CO2 absorption lines and follow the expected signature with the- ory spectrum, and the retrievals agreed well with GOSAT CO2 products, except a small bias of about 4 × 10 ^-6. The results show that the ability of spatial heterodyne spectroscopy for CO2 detecting is ob- vious, and SHS is a competent sensor.

A Novel Scheme for Hundred-Hertz Linewidth Measurements with the Self-Heterodyne Method

We propose a novel scheme to accurately determine the hundred-hertz linewidth using the delayed self-heterodyne method,in which the delay time is far less than the coherence time of the laser.This exceeds the former understanding of the delayed self-heterodyne technique,which requires a prohibitively long fiber.The self-heterodyne autocorrelation function and power spectrum are evaluated,and by numerical analysis we ensure that-3 dB of the power spectrum is applied to the self-heterodyne linewidth measurements.For a laser linewidth of less than 100 Hz,the linewidth can be measured directly by a 10 km fiber,and in a more general case,the linewidth can be deduced from-20 dB or-40 dB of the fitting Lorentzian curve.

Numerical investigation of multi-beam laser heterodyne measurement with ultra-precision for linear expansion coefficient of metal based on oscillating mirror modulation

This paper proposes a novel method of multi-beam laser heterodyne measurement for metal linear expansion coefficient. Based on the Doppler effect and heterodyne technology, the information is loaded of length variation to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, this method can obtain many values of length variation caused by temperature variation after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain length variation accurately, and eventually obtain the value of linear expansion coefficient of metal by the calculation. This novel method is used to simulate measurement for linear expansion coefficient of metal rod under different temperatures by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.4%.

Robust and high-speed rotation control in optical tweezers by using polarization synthesis based on heterodyne interference

The rotation control of particles in optical tweezers is often subject to the spin or orbit angular momentum induced optical torque,which is susceptible to the mechanical and morphological properties of individual particle.Here we report on a robust and high-speed rotation control in optical tweezers by using a novel linear polarization synthesis based on optical heterodyne interference between two circularly polarized lights with opposite handedness.The synthesized linear polarization can be rotated in a hopping-free scheme at arbitrary speed determined electronically by the heterodyne frequency between two laser fields.The experimental demonstration of a trapped vaterite particle in water shows that the precisely controlled rotation frequency of 300 Hz can be achieved.The proposed method will find promising applications in optically driven micro-gears,fluidic pumps and rotational micro-rheology.

Performance Analysis of Temperature and Strain Simultaneous Measurement System Based on Heterodyne Detection of Brillouin Scattering

Microwave heterodyne detection can be used to measure the temperature and strain distribution along a fiber with high accuracy in a Brillouin optical time domain reflectometry （BOTDR） system. This method involves simultaneous measurement of Brillouin scattering and Rayleigh scattering in fiber, and scanning of Brillouin spectrum to obtain the desired information. This paper presents a simultaneous measurement system of temperature and strain based on microwave detection and analyzed the system performances such as measurement accuracy, dynamic range, and spatial resolution theoretically. The analysis shows that the system can achieve a temperature resolution of 1°C and a strain resolution of 100 μs.

Calibration of the Width of Micro－Step with Two－Mode Laser Heterodyne Interferometer

A computer-aided heterodyne interferometer which can achieve high precision measurement for the shape of micrograph is introduced. Laser common-path heterodyne interferometer and precise phase measuring techniques are used-Besides, in lateral positioning, the mathematical expression of interference signal at the edge of the micrograph is derived on considering that the laser beam has certain radius and its distribution conforms to Gaussian distribution. Because the method of least squares is used, the system can measure with high precision not only the height but also the width. The precision of height measurement is of the order of nm.The precision of width measurement is better than 0.1μm.

Doppler radial velocity detection based on Doppler asymmetric spatial heterodyne spectroscopy technique for absorption lines

Doppler asymmetric spatial heterodyne spectroscopy(DASH)technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade.With the advantages of high phase shift sensitivity,compact,and rugged structure,DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work.Unlike atmospheric emission lines,almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars,so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established.According to the analysis of the components of the interferogram received by the detector array,we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines.In the end,numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out.The simulation results show that the relative errors of the retrieved speeds are less than 0.7%under ideal conditions,proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.

Millimeter-Wave Heterodyne Six-Port Receiver:New Implementation and Demodulation Results

This paper presents a new implementation of a millimeter-wave heterodyne receiver based on six-port technology. The six-port model is implemented in Advanced Design System （ADS） using S-parameter measurements for realistic advanced simulation of a short-range 60 GHz wireless link. Millimeter-wave frequency conversion is performed using a six-port down-converter. The second frequency conversion is performed using conventional means because of low IF. A comparison between the proposed receiver and a conventional balanced millimeter-wave mixer shows that the proposed receiver improves conversion loss and I/Q phase stability over the local oscillator （LO） and RF power ranges. The results of demodulating a V-band quadrature phase-shift keying （QPSK） signal at a high data rate of 100 Mb/s-1 Gb/s are discussed. The results of a bit error rate （BER） and error vector magnitude （EVM） analysis prove that the proposed architecture can be successfully used for wireless link transmission up to 10 m.

Practical security analysis of continuous-variable quantum key distribution with an unbalanced heterodyne detector

When developing a practical continuous-variable quantum key distribution(CVQKD),the detector is necessary at the receiver's side.We investigate the practical security of the CVQKD system with an unbalanced heterodyne detector.The results show that unbalanced heterodyne detector introduces extra excess noise into the system and decreases the lower bound of the secret key rate without awareness of the legitimate communicators,which leaves loopholes for Eve to attack the system.In addition,we find that the secret key rate decreases more severely with the increase in the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of the local oscillator(LO)under the same degree of imbalance.Finally,a countermeasure is proposed to resist these kinds of effects.

Design Consideration and Reconstruction Method for Double-source Double-multislice Spiral CT

To accelerate the scan speed and improve the image quality, a new type of CT configuration, "double-source double-multislice spiral CT" (DSDMS-CT), which is based on two sets of single-source multislice spiral CT was proposed with a special reconstruction algorithm. Simulation results using the fan-beam filtered backprojection algorithm with a special interpolation method were presented for both single-source multislice spiral CT and DSDMS-CT. The results of new CT model show that it scans faster than the traditional spiral CT and has a better slice sensitivity profile (SSP) with larger pitch value.

Dynamic Free-Spectral-Range Measurement for Fiber Resonator Based on Digital-Heterodyne Optical Phase-Locked Loop

We propose a novel scheme, based on digital-heterodyne optical phase-locked loop with whole-fiber circuit, to dynamically measure the free-spectral-range of a fiber resonator. The optical phase-locked loop is established with a differential frequency-modulation module consists of a pair of acousto-optic modulators. The resonance-tracking loop is derived with the Pound-Drever-Hall technique for locking the heterodyne frequency of the OPLL on the frequency difference between adjacent resonance modes. A stable locking accuracy of about 7 × 10?9 and a dynamic locking accuracy of about 5 × 10?8 are achieved with the FSR of 8.155 MHz, indicating a bias stability of the resonator fiber optic gyro of about 0.1?/h with 10 Hz bandwidth. In addition, the thermal drift coefficient of the FSR is measured as 0.1 Hz/?C. This shows remarkable potential for realizing advanced optical measurement systems, such as the resonant fiber optic gyro, and so on.

空间外差遥感数据光谱-干涉图双向校正算法研究

空间外差光谱技术(SHS)作为新型高光谱分析技术,被广泛应用于大气检测、卫星遥感等领域,但由于空间外差光谱仪的制作不理想或工作环境的变化都会改变仪器参数而引入误差,使干涉图数据不准确,需要进行误差校正。在卫星平台下,由于与地面环境的巨大差异,导致地面测定的校正参数对空间外差干涉图数据不再适用,特别是调制项误差(相位误差和非均匀误差)的改变,极大影响了光谱的准确性。针对空间外差遥感数据的调制项误差,从光谱与干涉图两个方面入手,进行误差分离与原因分析,认为空间外差遥感数据误差主要来源于CCD尺寸伸缩导致的光谱频率变化和CCD响应改变导致的干涉图强度变化,提出了光谱-干涉图双向校正方法。校正测试数据选取高分五号搭载检测仪(GMI)实测的12条O 2吸收光谱。取其中一条作为标定光谱,以SCIATRAN仿真的无误差光谱为基准,与标定光谱进行对比,分析两者在光谱维的频率偏差,通过特征峰频率确定两者的频率变换关系。然后根据变换关系将仿真光谱进行频率拉伸,使拉伸后的仿真光谱与实测光谱谱峰重合,计算拉伸仿真光谱与实测光谱干涉图,将两者干涉图相比得到干涉图强度的变化关系。最后将干涉图强度变化关系用于其余11条光谱的校正,得到校正后光谱。为了衡量校正效果,以校正前后光谱的标准差、均方误差和信噪比作为评价指标。结果显示标准差、均方误差都明显降低,同时信噪比显著增大,且标准差基本都在0.07以下,信噪比基本能达到20以上。其中校正效果最好的实测光谱,标准差减少了0.3767,信噪比提高了25.1016,均方误差降低了0.1587,校正效果较差的实测光谱,标准差减少了0.2296,信噪比提高了9.6328,均方误差降低了0.1049。因此所提出的光谱-干涉图双向校正方法对空间外差遥感数据的误差校正起到较好的效果,且处理过程简单,为同类数据的处理提供了一种新思路。

激光测振多普勒信号仿真技术研究

JJF1219-2009《激光测振仪校准规范》提出用调频电信号校准外差式激光测振仪信号采集、处理电路的方法,该方法对产生标准调频信号的信号发生器提出了很高要求,目前还没有激光测振仪校准专用的调频信号发生器,而通用函数信号发生器,在最大频移、调制振动频率范围等方面不能完全满足要求。通过研究数字信号合成技术,设计基于PC、FPGA和高速数模转换器(DAC)的多普勒调频信号发生器,实现激光多普勒调频信号模拟的仿真信号输出,具有参数设置灵活,带宽高,频率稳定性好的优点,经测试,该仿真信号达到了校准需要的技术要求,可用来评价外差式激光测振仪的信号采集、信号处理电路相关参量的计量特性。

双目结构光视觉引导的螺栓自动装配系统设计

为解决螺栓自动化装配过程中存在的零件位姿快速获取和在弱纹理、反光等复杂场景中实现精确定位等难题,基于双目结构光视觉原理,研制了一套螺栓自动装配系统。首先,通过双目结构光视觉系统获取工件场景的三维信息,涉及光栅条纹图案的获取、双目标定、多频外差法求解绝对相位、相位校正、极线校正、立体匹配,接着采用欧式聚类对重建的点云数据进行分割,获取单个螺栓的三维点云聚类,然后利用迭代最近点(ICP)算法估计模板点云到目标点云的位姿变换矩阵,识别连接螺栓在空间中的位姿,最后结合机械臂末端进行自动装配拧紧。实验结果表明,整个装配过程可自动完成,单个螺栓拧紧装配时间约为10 s,系统测试平均轴孔对中误差不超过1.20 mm,误差标准差不超过0.11 mm。

基于保偏布喇格光栅的窄线宽半导体激光器

为了研制面向量子精密测量应用的近红外波段光纤光栅外腔半导体激光器,采用独立设计的高偏振依赖增益芯片和双折射光纤布喇格光栅,通过法布里-珀罗等效谐振腔模型,系统分析了光栅反射率、外腔和芯片长度对激光线宽的影响。结果表明,所研制激光器实现了54.46 mW的输出功率、58.88 dB的边模抑制比和24.46 dB的偏振消光比,利用延迟自外差拍频方法测得的洛伦兹线宽低至2.69 kHz。此研究为独立设计制备分立器件的单频窄线宽外腔半导体激光器提供参考,有望应用于雷达成像、陀螺仪、磁力仪和原子钟等量子精密测量领域。