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.

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.

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.

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.

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.

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%.

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.

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.

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.

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.

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.

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.

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.

Heterodyne detection enhanced by quantum correlation

Heterodyne detectors as phase-insensitive(PI) devices have found important applications in precision measurements such as space-based gravitational-wave(GW) observation.However, the output signal of a PI heterodyne detector is supposed to suffer from signal-to-noise ratio(SNR) degradation due to image band vacuum and imperfect quantum efficiency.Here, we show that the SNR degradation can be overcome when the image band vacuum is quantum correlated with the input signal.We calculate the noise figure of the detector and prove the feasibility of heterodyne detection with enhanced noise performance through quantum correlation.This work should be of great interest to ongoing space-borne GW signal searching experiments.

High accuracy amplitude and phase measurements based on a double heterodyne architecture

In the digital low level RF （LLRF） system of a circular （particle） accelerator, the RF field signal is usually down converted to a fixed intermediate frequency （IF）. The ratio of IF and sampling frequency determines the processing required, and differs in various LLRF systems. It is generally desirable to design a universally compatible architecture for different IFs with no change to the sampling frequency and algorithm. A new RF detection method based on a double heterodyne architecture for wide IF range has been developed, which achieves the high accuracy requirement of modern LLRF. In this paper, the relation of IF and phase error is systematically analyzed for the first time and verified by experiments. The effects of temperature drift for 16 h IF detection are inhibited by the amplitude and phase calibrations.

A Heterodyne Interferometer with Separated Beam Paths for High-Precision Displacement and Angular Measurements

As standard concepts for precision positioning within a machine reach their limits with increasing measurement volumes,inverse concepts are a promising approach for addressing this problem.The inverse principle entails other limitations,as for high-precision positioning of a sensor head within a large measurement volume,three four-beam interferometers are required in order to measure all necessary translations and rotations of the sensor head and reconstruct the topography of the reference system consisting of fixed mirrors in the x-,y-,and z-directions.We present the principle of a passive heterodyne laser interferometer with consequently separated beam paths for the individual heterodyne frequencies.The beam path design is illustrated and described,as well as the design of the signal-processing and evaluation algorithm,which is implemented using a System-On-a-Chip with an integrated FPGA,CPU,and A/D converters.A streamlined bench-top optical assembly was set up and measurements were carried out to investigate the remaining non-linearities.Additionally,reference measurements with a commercial homodyne interferometer were executed.

Heterodyne Standing-Wave Interferometer with Improved Phase Stability

This paper describes a standing-wave interferometer with two laser sources of different wavelengths,diametrically opposed and emitting towards each other.The resulting standing wave has an intensity profile which is moving with a constant velocity,and is directly detected inside the laser beam by two thin and transparent photo sensors.The first sensor is at a fixed position,serving as a phase reference for the second one which is moved along the optical axis,resulting in a frequency shift,proportional to the velocity.The phase difference between both sensors is evaluated for the purpose of interferometric length measurements.

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.