Quadrature Phase Detection Research Articles

Quadrature phase detection based on a laser self-mixing interferometer with a wedge for displacement measurement

We report a novel and simple method to generate a pair of self-mixing signals with quadrature phase difference in He-Ne laser by introducing a wedge into the external cavity. A wedge phase-shift laser self-mixing effect theory is developed to explain the phase-shift phenomenon, and the relationship between the phase difference and the distance from the center of the iris diaphragm to the center of the spot is given. Then a simple and effective wedge-quadrature laser self-mixing interferometer is established for displacement measurement by the quadrature phase detection method. Experimental results show that the max error is 182 nm for a target displacement of 20 μm. This structure provides a useful exploration for phase-shift signal generation and simplifies the self-mixing signal demodulation process with only a single four-quadrant inverse tangent operation, which has potential application in real-time displacement measurement.

Quadrature Phase Detection Based on a Laser Self-Mixing Interferometer with a Wedge for Displacement Measurement

Quadrature Phase Detection Based on a Laser Self-Mixing Interferometer with a Wedge for Displacement Measurement

Quadrature phase detection based on phase shift of self-mixing interferometer for real-time displacement measurement

A real-time displacement reconstruction technique based on a phase retardation method is proposed. By introducing a waveplate and a polarization beam splitter into the external cavity, two self-mixing signals with a phase shift of π∕2 can be obtained. Then the displacement of the external object can be reconstructed by a quadrature demodulation algorithm, which significantly simplifies the data processing and meets the requirements of real-time displacement reconstruction techniques. The results show that the absolute errors of the reconstructed displacements are less than 75 nm.

Гомодинный квадратурный интерферометр перемещений. Моделирование

In this paper, based on the Jones matrix formalism, we describe the optical scheme of a single-pass homodyne displacement interferometer with a quadrature phase detection principle. The interferometer is built according to the Michelson scheme, and polarizing optical elements are used to obtain quadrature signals with a phase shift of 90°. The interferometer is supposed to be used as part of a new Russian standard of the kilogram based on watt balance for precision measurements of the displacement and speed of the coil in the vertical direction. The results of modeling the optical scheme of the interferometer are considered in order to assess the effect on the measurement accuracy of the imperfection of the polarizing elements and their alignment. An algorithm for correction of nonlinearity arising in the quadratic detection of interference signals is also considered. The results of experimental testing of a homodyne displacement interferometer with a quadrature principle of phase registration are carried out.

Quadrature phase detection based on an extrinsic Fabry-Pérot interferometer for vibration measurement.

A novel vibration measurement system based on a fiber-optic extrinsic Fabry-Pérot interferometer is established. Two quadrature interferometry signals are obtained in accordance with the 90° phase shift between two output arms of a 2×2 fiber coupler. This outcome drastically simplifies the processing of collected data because only a single arctangent operation is needed to calculate the wrapped phase. Repetitive test results show that the relative micro-vibration reconstruction error of this method is less than 0.12%. This structure simplifies the extrinsic Fabry-Pérot signal demodulation process, which has guiding significance for the online measurement of high-precision physical quantities.

Multiport atom interferometry for inertial sensing

We present new techniques for inertial-sensing atom interferometers which produce multiple phase measurements per experimental cycle. With these techniques, we realize two types of multiport measurements, namely quadrature phase detection and real-time systematic phase cancellation, which address challenges in operating high-sensitivity cold-atom sensors in mobile and field applications. We confirm experimentally the increase in sensitivity due to quadrature phase detection in the presence of large phase uncertainty, and demonstrate suppression of systematic phases on a single shot basis.

A Compact X-Band Vector Network Analyzer for Microwave Image Sensing

This paper develops a compact and portable X-band vector network analyzer (VNA) for the low-cost microwave image sensing applications. Since significant local oscillator (LO) injection pulling and poor LO phase noise performance may reduce the accuracy of measurement, the developed VNA uses the single-conversion technique and the phase noise cancellation technique to suppress the injection pulling effect and the LO phase noise, respectively. A hybrid phase detection algorithm that includes arctangent, arcsine, and arccosine functions is proposed to overcome the bottleneck of the distortion of conventional quadrature phase detection in some phase regions. The experimental results demonstrate that the X-band microwave image sensing system that uses the developed VNA, which is highly compact and portable, can effectively yield a contour image of bones in a chicken wing and pork ribs.

Theoretical limit evaluation of ranging accuracy and power for LiDAR systems in autonomous cars

With the development of autonomous cars, the demand for accurate light detection and ranging (LiDAR) systems is increasing. Previous evaluations of LiDAR were mainly based on experiments and lacked theoretical significance. We theoretically evaluate the accuracy and optical output power of LiDAR systems in autonomous cars. We focus on two ranging schemes: the time-of-flight (TOF) method and the quadrature phase detection (QPD) method. Considering the special requirements of autonomous driving, the theoretical limits of ranging accuracy are calculated by deriving the Cramer–Rao bound (CRB). The influence of reflectivity as well as distance on accuracy are discussed. We also determine the relationship between optical output power and essential parameters, and make comparisons between TOF and QPD. It can be concluded that TOF is more efficient under most circumstances. When designing autonomous cars, such theoretical evaluation provides guidance for choosing laser emitters and receivers, justifying the significance of our work to LiDAR development.

Demonstration for a two-axis interferometric tilt sensor in KAGRA

Recently, a folded Mach–Zehnder interferometer with homodyne in- and quadrature-phase detection was proposed as a high-precision, wide-dynamic range tilt sensor. By way of a practical application and to validate actual performance, two-axis tilt sensors were developed and installed for one mirror of the input mode cleaner cavity in KAGRA, the large-scale cryogenic gravitational-wave telescope in Kamioka, Gifu, Japan. Building on previous work, we have demonstrated that the two-axis tilt sensor has properly sensed the tilt angle changes of the mirror motion with high precision and without calibration. Compared with our initial angular sensor, an optical lever, which is calibrated by using the interferometer tilt sensor, we found that both sensors showed actual tilt motions of the mirror at low frequencies, and the two-axis interferometer sensor has a better sensitivity at higher frequencies.

NMR measurement system including two synchronized ring buffers, with 128 rf coils for in situ water monitoring in a polymer electrolyte fuel cell.

A small radio-frequency (rf) coil inserted into a polymer electrolyte fuel cell (PEFC) can be used to acquire nuclear magnetic resonance (NMR) signals from the water in a membrane electrode assembly (MEA) or in oxygen gas channels in the PEFC. Measuring the spatial distribution of the water in a large PEFC requires using many rf probes, so an NMR measurement system which acquires NMR signals from 128 rf probes at intervals of 0.5 s was manufactured. The system has eight rf transceiver units with a field-programmable gate array (FPGA) for modulation of the excitation pulse and quadrature phase detection of the NMR signal, and one control unit with two ring buffers for data control. The sequence data required for the NMR measurement were written into one ring buffer. The acquired NMR signal data were then written temporarily into the other ring buffer and then were transmitted to a personal computer (PC). A total of 98 rf probes were inserted into the PEFC that had an electrical generation area of 16 cm × 14 cm, and the water generated in the PEFC was measured when the PEFC operated at 100 A. As a result, time-dependent changes in the spatial distribution of the water content in the MEA and the water in the oxygen gas channels were obtained.

Multichannel Microwave Interferometer for Simultaneous Measurement of Electron Density and its Fluctuation on HL-2A Tokamak**supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB104002, 2013GB107002, 2014GB107001) and National Natural Science Foundation of China (Nos. 11475058, 11475057, 11261140326, 11405049)

A multichannel microwave interferometer system has been developed on the HL-2A tokomak. Its working frequency is well designed to avoid the fringe jump effect. Taking the structure of HL-2A into account, its antennas are installed in the horizontal direction, i.e. one launcher in high field side (HFS) and four receivers in low field side (LFS). The fan-shaped measurement area covers those regions where the magnetohydrodynamics (MHD) instabilities are active. The heterodyne technique contributes to its high temporal resolution (1 μs). It is possible for the multichannel system to realize simultaneous measurements of density and its fluctuation. The quadrature phase detection based on the zero-crossing method is introduced to density measurement. With this system, reliable line-averaged densities and density profiles are obtained. The location of the saturated internal kink mode can be figured out from the mode showing different intensities on four channels, and the result agrees well with that measured by electron cyclotron emission imaging (ECEI).

Design and Simulation of Quadrature Phase Detection in Electrical Capacitance Volume Tomography

Capacitance measurement accuracy is affected by phase conformity between signal and reference. This work describes phase detection scheme which is necessary for phase synchronization in tomography application. Core processing for calculating phase and amplitude of the detected signal was built on FPGA (Field-Programmable Gate-Array) platform. Phase shift demodulation algorithm employs IP core provided by Xilinx FPGA. Direct digital synthesizer (DDS), multiplier, accumulator, and CORDIC (coordinate rotation digital computer) modules were used as excitation-reference signal generator, signal multiplication, accumulation, and conversion to polar coordinate in order to conduct trigonometric operation respectively. Hardware design was emulated on MATLAB-Xilinx System Generator to observe its performance. Phase detection range 0-114.58 o and mean absolute error 0.58 o have been achieved. Data processing rate solely at digital signal stage was approximately 100data/s suitable for 32-channel electrical capacitance volume tomography (ECVT) system.

Hardware Design for Quadrature Phase Detection Algorithm in ECVT

Hardware Design for Quadrature Phase Detection Algorithm in ECVT

Double-modulation reflection-type terahertz ellipsometer for measuring the thickness of a thin paint coating.

We constructed a double-modulation, reflection-type terahertz (THz) ellipsometer for precise measurement of the thickness of a paint film which is coated on a metal surface and which is not transparent to visible or mid-infrared light. The double-modulation technique enabled us to directly obtain two ellipsometric parameters, Δ(ω) and Ψ(ω), as a function of angular frequency, ω, with a single measurement while reducing flicker noise due to a pump laser. The bias voltage of a photoconductive antenna (PCA) used as a THz pulse emitter was modulated at 100 kHz, and a first lock-in amplifier (LA1) was connected to the output of an electro-optic (EO) signal-sampling unit. In addition, a wire-grid polarizer (WGP) was rotated at 100 Hz to conduct polarization modulation with a frequency of 200 Hz. The output signal from LA1 was fed into a second lock-in amplifier (LA2) that worked in synchronization with the rotating WGP (RWGP). By operating LA2 in a quadrature phase-detection mode, we were able to obtain in-phase and out-of-phase signals simultaneously, from which the two ellipsometric parameters for an isotropic sample could be derived at the same time while cancelling common-mode noise. The lower detection limit of the thickness measurement and the relative standard deviation (RSD) of a black paint film coated on an aluminum substrate were 4.3 µm and 1.4%, respectively. The possibility of determining all elements of the Jones matrix for an anisotropic material is also discussed.

Photoacoustic tomography using a Michelson interferometer with quadrature phase detection

We present a pressure sensor based on a Michelson interferometer, for use in photoacoustic tomography. Quadrature phase detection is employed allowing measurement at any point on the mirror surface without having to retune the interferometer, as is typically required by Fabry-Perot type detectors. This opens the door to rapid full surface detection, which is necessary for clinical applications. Theory relating acoustic pressure to detected acoustic particle displacements is used to calculate the detector sensitivity, which is validated with measurement. Proof-of-concept tomographic images of blood vessel phantoms have been taken with sub-millimeter resolution at depths of several millimeters.

Quantitative density fluctuation measurements utilizing quadrature reflectometers on DIII-D

Fixed-frequency reflectometers utilizing quadrature phase detection are employed on DIII-D to study both coherent and turbulent density fluctuations. For coherent fluctuations, the reconstructed phase information successfully identifies MHD/coherent mode activity, e.g. tearing modes, compressional Alfvén eigenmodes, etc. For an m = 3/n = 2 tearing mode, a basic 1D phase screen model is applied to infer fluctuation levels, and the result is consistent with the beam emission spectroscopy (BES) measurement. For turbulent fluctuation studies, a 2D full-wave code (Valeo E.J., Kramer G.J. and Nazikian R. 2002 Plasma Phys. Control. Fusion 44 L1) is applied to interpret reflectometry data obtained in the H-mode edge pedestal region to deduce density fluctuation levels. The measurement is simulated using realistic geometry, plasma conditions and antenna patterns. Comparison of the fluctuation level deduced from the 2D code with BES measurement shows reasonable agreement.

A Robust Quadrature Decoding Logic and its FPGA Implementation for Measurement of Angular Motion using a Ring Laser Gyroscope

A ring laser gyroscope outputs an interference pattern that rotates at a rate proportional to the rotation rate of the body on which the gyroscope is strapped. The standard measurement setup for similar such systems consists of a pair of photo-detectors followed by wave shapers that convert the'rotating interference pattern into a pair of pulse trains in quadrature. The phase relation between the two pulse trains indicates the direction of rotation, and counting anyone of the pulse trains over a period of time gives a measure of the incremental motion. Commercially available optical encoder assemblies using similar quadrature-output sensors implement a sequence of noise filtering, quadrature phase detection and counting to measure incremental motion. Such designs have certain limitations in so far as their applicability is concerned. This paper documents these limitations briefly and proposes a novel design and its FPGA implementation of an improved digital noise filter and a high-resolution quadrature phase decoder for measurement of incremental motion based on the processing of the output of a ring laser gyroscope.

Phase error correction method for a vibration compensated interferometer

In order to compensate for vibrations while simultaneously measuring plasma line-averaged density, the existing real-time interferometer on DIII-D uses both a HeNe and CO2 laser operating at 10.59 and 0.632 μm, respectively. The line density resolution is 1018 m−2 which is predominantly determined by the measurement electronics. In particular, errors resulting from detection of the CO2 phase shift and finite bit size in the processing electronics are the major limiting factors. This article describes a method for postshot error correction generally applicable to two-color interferometers that utilize analog quadrature phase detection. The error correction scheme exploits the facts that error introduced by the phase comparator is periodic and that measurements can be made while the density is zero and only the errors are recorded. Application of this method will reduce unphysical density oscillations which are purely a result of vibration induced phase shifts. Application to DIII-D data shows a 25% reduction in noise amplitude on line density measurements.

80 Gbit∕s optical clock recovery with automatic lock acquisition using electrical phase-locked loop

A novel electrical phase-locked loop architecture for optical clock recovery using an input mixer mixing down to the intermediate frequency is presented. Phase detectors of the phase-locked loop operate on an intermediate frequency. The architecture allows the use of the quadrature phase detection enabling automatic lock acquisition.

Long dual‐cavity fiber optic Fabry‐Perot strain sensor with rugate mirrors

An all-fiber Fabry-Perot interferometer using coherence demultiplexing and rugate mirror reflectors grown with electron cyclotron resonance, plasma-enhanced chemical vapor deposition (ECR–PECVD) on the fiber ends is proposed. The interferometer consists of a laser diode source, two optical fiber cavities, three rugate mirrors, an optical phase modulator, and a quadrature phase detection system. Coherence demultiplexing allowed the use of fiber cavities of several meters in length with a partially coherent illuminating light source. Truly inhomogeneous refractive index mirrors were designed, taking into account dispersion and losses of SiOxNy at the required wavelength of 1.3 µm. The reflectance/transmittance ratios during growth were adjustable from 0.05/0.95 to 0.95/0.05 and mirrors used in the experimental interferometer had nominal reflectances of 40, 68, and 40%, respectively. Design and fabrication procedures permitted implementation of window functions and matching layers for flexible control over transmittance and reflectance characteristics. The long-cavity Fabry-Perot sensor was demonstrated for use as a strain gauge. Good agreement was shown with the results obtained by a conventional strain gauge.