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.

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.

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.

Ultrafast optical phase-sensitive ultrasonic detection via dual-comb multiheterodyne interferometry

Highly sensitive and broadband ultrasound detection is important for photoacoustic imaging,biomedical ultrasound,and ultrasonic nondestructive testing.The elasto-optical refractive index modulation induced by ultrasound arouses a transient phase shift of a probe beam.Highly sensitive phase detection with a high Q factor resonator is desirable to visualize the ultraweak transient ultrasonic field.However,current phase-sensitive ultrasonic detectors suffer from limited bandwidth,mutual interference between intensity and phase,and significant phase noise,which become key to limiting further improvement of detection performance.We report a phase-sensitive detector with a bandwidth of up to 100 MHz based on dual-comb multiheterodyne interferometry(DCMHI).By sensing the phase shift induced by the ultrasound without any resonators in the medium,the DCMHI boosted the phase sensitivity by coherent accumulation without any magnitude averaging and extra radio frequency amplification.DCMHI offers high sensitivity and broad bandwidth as the noise-equivalent pressure reaches 31 mPa∕pHz under 70 MHz acoustic responses.With a large repetition rate difference of up to 200 MHz of dual comb,DCMHI can achieve broadband acoustic responses up to 100 MHz and a maximum possible imaging acquisition rate of 200 MHz.It is expected that DCMHI can offer a new perspective on the new generation of optical ultrasound detectors.

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.

A novel phase-sensitive scanning near-field optical microscope

Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton （SPP） devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field opti- cal microscope （SNOM） with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.

Optical Surface Tilt Measurement with Sub-Second Accuracy

This paper presents a coherent resolved heterodyne interferometer used for recognition of surfaces of optical systems with resort to a short coherence length light source and a position sensitive detection(PSD), and its special features of surface sensitivity, high resolution and short measuring time.

Simulation Analysis of Balance Detection Technique in Coherent Optical Receiver

This paper introduces the working principle of the balanced heterodyne detection system, establishes the corresponding mathematical model, deduces the signal to noise ratio (SNR) formula of the balanced heterodyne detection. By comparing balance heterodyne detection with general coherent detection with MATLAB numerical simulation, the superiority of balance heterodyne detection system is proved theoretically. Finally, the simulation models of ordinary heterodyne detection, balance detection and double balance detection system are built by OptiSystem. The simulation results are consistent with the conclusions derived from the mathematical analysis, which provides a new method for the research of weak laser detection technology.

Simple real-time high-sensitivity heterodyne coherent optical transceiver at intraplane satellite communication

In this paper,we demonstrate a high-sensitivity and real-time heterodyne coherent optical transceiver for intraplane satellite communication,without digital-to-analog converter(DAC)devices and an optical phase lock loop(OPLL).Based on the scheme,a real-time sensitivity of-49 dBm is achieved at 5 Gbps QPSK.Because DAC is not needed at the transmitter,as well as OPLL at the receiver,this reduces the system cost.Furthermore,the least required Rx ADC bit-width is also discussed.Through theoretical analysis and experimental results,our cost-effective transceiver satisfies the scenario and could be a promising component for future application.

Developing an Advanced Prototype of the Acousto-Optical Radio-Wave Spectrometer for Studying Star Formation in the Milky Way

The designed practically prototype of an advanced acousto-optical radio-wave spectrometer is presented in a view of its application to investigating the Milky Way star formation problems. The potential areas for observations of the cold interstellar medium, wherein such a spectrometer can be exploited successfully at different approximations, are: 1) comparison of the Milky Way case with extragalactic ones at scale of the complete galactic disk;2) global studies of the Galactic spiral arms;and 3) characterization of specific regions like molecular clouds or star clusters. These aspects allow us to suggest that similar instrument will be really useful. The developed prototype of spectrometer is able to realize multi-channel wideband parallel spectrum analysis of very-high-frequency radio-wave signals with an improved resolution power exceeding 103. It includes the 1D-acousto-optic wide-aperture cell as the input device for real-time scale data processing. Here, the current state of developing this acousto-optical spectrometer in frames of the astrophysical instrumentation is briefly discussed, and the data obtained experimentally with a tellurium dioxide crystalline acousto-optical cell are presented. Then, we describe a new technique for more precise spectrum analysis within an algorithm of the collinear wave heterodyning. It implies a two-stage integrated processing, namely, the wave heterodyning of a signal in an acoustically square-law nonlinear medium and then the optical processing in the same solid-state cell. Technical advantage of this approach lies in providing a direct multi-channel parallel processing of ultra-high-frequency radio-wave signals with the resolution power exceeding 104. This algorithm can be realized on a basis of exploiting a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The general concept and basic conclusions here are confirmed by proof-of-principle experiments with the specially designed cell of a new type based on a lead molybdate crystal.

Novel high-sensitivity coherent transceiver for optical DPSK/DQPSK signals based on heterodyne detection and electrical delay interferometer

We present a novel coherent transceiver for optical differential phase-shift keying/differential quadrature phase-shift keying （DPSK/DQPSK） signals based on heterodyne detection and electrical delay interferometer. A simulation framework is provided to predict a theoretical sensitivity level for the reported scheme. High sensitivity of –45.18 dBm is achieved for 2.5-Gb/s return-to-zero （RZ）-DPSK signal, and high sensitivities of –36.83 dBm （I tributary） and –35.90 dBm （Q tributary） are observed for 2.5-GBaud/s RZ-DQPSK signal in back-to-back configuration. Transmission for both signals over 100 km is also investigated. Experimental results are discussed and analyzed.

SNR improvement in self-heterodyne detection Brillouin optical time domain reflectometer using Golay pulse codes

The application of Golay pulse coding technique in spontaneous Brillouin-based distributed temperature sensor based on self-heterodyne detection of Rayleigh and Brillouin scattering is theoretically and experimentally analyzed. The enhancement of system signal to noise ratio(SNR) and reduction of temperature measurement error provided by coding are characterized. By using 16-bit Golay coding, SNR can be improved by about 2.77 d B, and temperature measurement error of the 100 m heated fiber is reduced from 1.4 °C to 0.5 °C with a spatial resolution of 13 m. The results are believed to be beneficial for the performance improvement of self-heterodyne detection Brillouin optical time domain reflectometer.

Optical heterodyne-Zeeman modulation magnetic rotation spectroscopic technique

Optical heterodyne detection using 500 MHz phase modulation was combined with the Zeeman modulation-magnetic rotation spectroscopy (ZM-MRS) to form a new spectroscopic technique, which effectively reduced the amplitude fluctuation from laser source and greatly improved the signal-to-noise ratio in the detection of transient molecules.

The Study on Heterodyne and Phase Diversity Coherent Optical Fiber Communication Systems and Their Components

The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.

Optical heterodyne detected velocity modulation molecular ionic spectroscopy

Optical heterodyne detected velocity modula- tion molecular ionic spectroscopy is presented and employed to observe the rovibrantional spectra of O+2 and O-2. That the lineshape of OH-VMS is of the second derivative of Gaussian profile and its sensitivity is 3.5×10?8 are theoreti- cally analyzed, and they are both in good agreement with our experimental results.

光纤超声传感器的射频域自相干解调技术

在光纤光声成像技术中,检测灵敏度是决定光纤超声传感器成像质量的关键性因素之一。以小型化正交双频光纤激光器为超声敏感元件,建立更好的信号解调技术对声致相位变化进行检测,以实现高灵敏度超声检测和光声成像。引入射频域自相干解调技术对超声波引起的激光频率变化进行读取,实验结果表明,该技术具有超声响应信号放大效果,传感器的灵敏度在8~32 MHz的超声频率内获得了显著提升,将最小可检测声压从9.0 Pa降低到5.7 Pa。进一步地,将该超声检测技术应用于活体光声显微成像,发现在同等光强的激发条件下,图像信噪比获得逾4 dB的提升。该技术为光纤光声成像技术的应用拓展奠定了坚实的技术基础。

基于SOA光纤环形激光器的分布式声传感系统

为了降低传统分布式声学传感器(DAS)系统复杂度并提高信噪比(SNR),提出了一种基于半导体光放大器的光纤环形激光器(SOA-FRL)的DAS系统。该系统用SOA-FRL取代了传统的DAS系统中的窄线宽激光器和脉冲调制器,实现了高稳定的光脉冲输出;采用双脉冲外差探测方法,实现了精确的声信号探测和声源定位。实验结果表明:在频率为1 kHz、幅值为1.14 rad的声信号作用下,所提系统的解调SNR高达38.25 dB,空间分辨率为12 m。

采用激光光源线宽展宽的光纤陀螺标度因数性能提升技术

光纤陀螺中使用激光光源代替传统宽谱光源有利于提升性能和降低成本,但激光光源作为一种窄线宽的高相干光源,将其用于光纤陀螺又会引入瑞利散射、克尔效应和偏振交叉耦合等干扰,因此有必要对激光光源进行线宽展宽。首先对基于高斯白噪声外部相位调制的激光光源线宽展宽方法进行理论分析,建立光谱展宽卷积模型。其次采用延迟自相关测量方法验证了高斯白噪声外部相位调制对激光光源线宽的展宽效果。最后基于仿真分析结论,搭建了激光器线宽展宽光源装置,将激光光源的光谱展宽成线宽20 GHz的光谱,应用于光纤陀螺并验证了标度因数性能,为激光光源在光纤陀螺中的应用提供了理论基础,具有一定的工程应用价值。

基于光相干外差检测的布里渊散射DOFS的研究

对布里渊散射分布式光纤传感器(DOFS)检测原理进行了分析,针对布里渊散射光信号的特点,应用光相干和外差技术来检测布里渊散射光信号 具体采用微波电光调制产生频率可调的参考光,和布里渊散射光进行相干检测,根据布里渊频移特性取出布里渊散射光信号,从而得到分布式传感信号 分别实现了 25km光纤的分布式温度和应变传感,达到 3℃的温度分辨率、100με的应变分辨率和 10m的空间分辨率.

干涉型光纤传感器信号检测技术的研究

光纤传感器是一种高灵敏度传感器,而信号检测技术是它的关键技术之一。介绍了干涉型光纤传感器的信号检测方法。首先简单分析了干涉型光纤传感器相位衰落现象产生的物理机制,然后分别介绍了各种抗相位衰落信号检测方法的基本工作原理和特点,着重讨论了其中几种主要的方法,详细分析了它们的优缺点、应用场合以及技术难点。最后对各种检测方法的主要性能进行了比较,并对它们的发展前景做了展望。