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Over the past years, light detection and ranging (lidar) technologies have been investigated and commercialized for various applications such as autonomous vehicles, terrestrial mappings, and precision measurements. Currently, the frequently used ranging methods are the pulsed time of flight (PToF) and frequency modulated continuous wave (FMCW) lidars that relies on frequency sweeping to capture range and velocity information. We have previously developed and demonstrated the multi-tone continuous wave (MTCW) that operates by employing amplitude modulation via multiple radio frequencies (RF) and coherent detection. Here, we present a theoretical and experimental study on phase-based MTCW lidar that can detect the range and velocity of objects with arbitrary velocities. The experiments demonstrate that the phase and frequency of the Doppler-shifted fixed RF tones can be used to extract the range and velocity information in a single shot measurement. We show that a

Atom-based sensors have generated a lot of attention in the past several years because of their many possible advantages over other conventional technologies. NIST and other groups have made great progress in the development of Rydberg atom-based radio-frequency (RF) E-field sensors/receivers. These sensors have the capability of measuring amplitude, polarization, and phase of the RF field. As such, various applications are beginning to emerge: SI-traceable E-field probes, power-sensors, voltage standards, receivers for communication signals (AM/FM modulated and digital phase modulation signals), and even recording musical instruments. In fact, this new atom-based technology has allowed for interesting and unforeseen applications. In this talk, I will summarize this work and discuss various applications.

Dielectric metasurfaces have recently attracted much attention due to their ability to efficiently control light propagation, that is, its amplitude, phase and polarization, on micro- and macro- levels. Such metasurfaces also naturally allow for integration in compact optical setups due to their small sizes. An important issue of energy losses is also addressed by employing all-dielectric platform. Advancements in nanofabrication have enabled realization of metasurface-based high-resolution wavefront engineering devices, which have been employed in different imaging applications, for example, as metalenses, polarization filters, metaholograms, etc. Quantitative phase imaging is a powerful tool for the optical inspection of transparent samples in connection with biological and technical applications. By measuring thickness and/or refractive index profiles, phase imaging facilitates, for example, the observation of dynamic events in unstained cells. As such, it has become indispensable in biological imaging, wavefront correction and metrology. However, conventional cameras and photodetectors are inherently not sensitive to the phase of an incident lightwave. As a consequence, direct phase detection is challenging. Only by multiple intensity measurements or application of specialized interferometric schemes, the phase profile of an object can be in principle reconstructed. In this paper, we report on the ability of metasurfaces to contribute to quantitative phase imaging by independent control of the phase profiles in two orthogonal polarization states of an incident beam.

We report on a single-shot phase detection method for holographic data storage systems using polychromatic reconstruction (PCR). In PCR, the multi-step interferometric measurements cannot be applied for signal phase detection, because the reconstructed image consists of the broad spectral components spatially distributed within the page. Our proposed method utilizes inter-pixel crosstalk caused by an aperture inserted in the Fourier plane of the input image, and does not require any interferometric measurements, like a four-step phase-shifting method. We have numerically investigated pixel error rates of phase-encoded signals in PCR, and confirm the validity of our proposed method.

Quantitative phase imaging technology has become an important technology for imaging phase objects such as cells in virtue of the advantages of non-destructive, non-invasive and high accuracy. More importantly, the phase of a cell is closely related to its internal structure and component. In this paper, according to the morphological and optical characteristics of typical leukocytes, the approximate models of different kinds of cells were firstly established to obtain the corresponding phases. Then, digital image edge operators such as gradient, gradient module and Laplace were used to detect the phase maps. Subsequently with the phase detection images of the cell, its feature information, such as the morphology and the refractive index change can be analyzed. Simulation results suggested that the edge operators are sensitive to the morphology, the interface of each medium and component of the cell. Therefore, the edge detection method of phase image can be used for cell’s classification recognition and preliminary determination of internal structure

The detection of ultrasound via optical resonators is conventionally performed by tuning a continuous-wave (CW) laser to the linear slope of the resonance and monitoring the intensity modulation at the resonator output. In this work, we develop an alternative CW technique that can significantly reduce the measurement noise by monitoring variations in the phase, rather than intensity, at the resonator output. In our current implementation, which is based on a balanced Mach-Zehnder interferometer for phase detection, we demonstrate a 24-fold increase in the signal-to-noise ratio of the detected ultrasound signal over the conventional, intensity-monitoring approach.

Phase-locked loop (PLL) is a circuit that can synchronize the output signal with the input signal in frequency and phase. Generally, it consists of three parts: Phase Detector (PD), Loop Filter (LF) and Voltage Controlled Oscillator (VCO). In modern technology, it is widely used in various fields, such as modulation and demodulation, frequency synthesis, power system, laser ranging, image processing and so on. According to the number of zero and pole in open loop transfer function, PLL can be divided into two types: TYPE I and TYPE II (Charge Pump). In TYPE I PLL, there is only one zero and pole produced by VCO. Therefore, when the loop is locked, there is always a phase error between input and output. However, in TYPE II phase-locked loop, not only does it contain a zero and a pole generated by VCO, but it also introduces a charge pump into the phase-locked loop and provides another pole for the whole loop together with a phase detector, thus making the phase error zero when the loop is locked. Charge Pump Phase-Locked Loop (CPPLL) has a large phase-locked range. Charge pump phase-locked loop (CPPLL) is widely used because of its large capture range and relatively simple structure. In this paper, the principle of charge pump phase locked loop (CPPLL) in phase laser ranging is analyzed, the linear model is built, and the performance of speed conversion is studied. The frequency-locked, phase-locked precision and conversion speed of the loop are analyzed, and the charge pump phase-locked loop circuit is designed. Experiments show that the circuit effectively prevents the charge sharing effect and improves the accuracy and speed of the system.

An optical fiber temperature and strain sensing system based on phase-derived optical fiber time delay (OFTD) measurement is proposed. By detecting the phase different between probe and intrinsic microwave signals, high accuracy delay measurement can be obtained. As the OFTD in single mode fiber (SMF) changes linearly with the strain or temperature in a certain range, strain and temperature sensing can be achieved by measuring the change of OFTD with high accuracy. In the experiments, the delay measurement accuracy can reach 0.06 ps when the accuracy of phase detector is ±0.1 degree while the detecting frequency is 4.5 GHz. In addition, an accuracy of ±11 μe for strain sensing with 1.5 m fiber and a resolution better than 0.24 °C for temperature sensing with 10.66 m fiber are achieved.

The use of terahertz waves for imaging has been studied intensively from the scientific, medical, and industrial viewpoints. Phase information is important for terahertz imaging and thus several kinds of phase detection methods for terahertz waves have been reported. Phase imaging using continuous wave terahertz interferometry has the advantage of having a high signal-to-noise ratio. Phase-shifting interferometry by using a liquid crystal (LC) phase shifter is a possible candidate for terahertz phase imaging. Accordingly, it has several advantages, such as a simple experimental setup and a low drive voltage. In our previous research, we confirmed that hydrogen-bonded LCs do not exhibit dichroism at 2.5 THz. Furthermore, hydrogen-bonded LCs exhibit higher birefringence in the terahertz range than in the visible range. Recently, we studied phase-shifting interferometry by using a hydrogen-bonded LC device. Since the hydrogen-bonded LC do not exhibit dichroism at 2.5 THz, the birefringence of the sample could be successfully obtained. To improve repeatability of this measurement, it is important to monitor the operational state of the LC phase shifter while making phase measurements. To simultaneously measure the phase of the sample and the degree of the phase shift of an LC device, we introduced a beam splitter and an additional detector into the phase-shifting interferometry technique. We report an improved measurement method for phase-shifting interferometry by using the LC phase shifter.

Focusing difficulty has become a critical issue in 8K ultra-high definition television (UHDTV) production. Especially in 8K high-speed shooting, defocus blur significantly degrades a user's experience of slow-motion playback video. For this reason, incorporating a sensor-based phase detection autofocus (PDAF) system that can adjust the focus of a lens quickly into an 8K UHDTV camera has been strongly desired. Although conventional sensor-based PDAF systems have been designed for single-chip cameras capable of using optional color filters, the application of phase detection (PD) in professional broadcasting cameras with three-chip imaging has not been studied, in which incident light separates into three color components (red, green, and blue) by a separation prism. This paper presents an investigation into the PD property among the color channels using a newly prototyped 1.25-inch 8K 240-fps complementary metal-oxide-semiconductor (CMOS) image sensor with two types of horizontal PD pixels (left- and right-phase). Our experiment showed that crosstalk over angler responses of the PD sensor became larger as the wavelength of light increased, and that the crosstalk in each color component reduced the accuracy of the PD amount between a set of stereo images. Consequently, these results demonstrated that utilizing the phase-differential information from the blue component enables a high-precision sensor-based PDAF operation in three-CMOS imaging when shooting black and white objects

Optical waveguide phased array can realize high-speed beam scanning without mechanical deflection, which is a research hotspot of new system LiDAR. Limited by the manufacturing error of the device, the theoretical value of the modulation phase cannot achieve precise beam steering. The most commonly used SPGD algorithm achieves accurate beam deflection without pre-wavefront phase detection by optimizing the phase modulation voltages of the array elements, avoiding cumbersome parameter error calibration. However, in some cases, the SPGD algorithm converges slowly and is prone to local extremum. To achieve fast adaptive phase correction, a chaotic stochastic parallel gradient descent (CSPGD) algorithm combining chaos theory and SPGD is proposed in this paper. The neighborhood chaotic search is centered on the wave control voltages obtained by SPGD optimization. The ergodicity of chaotic sequences is employed to improve the fine search performance of the algorithm, thereby speeding up the correction and improving the correction accuracy. Plus, a phase-correcting optical system is built using a one-dimentional eight-element (1×8) lithium niobate (LiNbO3) optical waveguide phased array to verify the convergence performance of the new algorithm. The random phase modulation OPA is used to simulate a large phase error scenario. Simulation and experimental results show that the CSPGD phase correction algorithm can deflect the beam to the target direction more quickly and improve the beam quality effectively within the same iteration scale, compared with the classical SPGD algorithm.

The phase detection method of Light-addressable potentiometric sensor (LAPS) can realize accurate detection under the weak light intensity. Now available phase detection method has high algorithm complexity and is difficult to achieve. Aiming at this practical problem, a phase detection method based on orthogonal detection is proposed. This method takes the modulation signal of light source and its orthogonal signal as the reference, multiply with the LAPS signal, respectively. After that extracts the dc component through low-pass filtering and divide. Then could be able to obtain the phase information of the LAPS signal. In this paper, the sensitivity and linearity of H+ detection and the influence of the modulated light intensity on the LAPS detection system are analyzed by orthogonal detection phase detection method. The results show that at the frequency of 4KHz and the detection pH units of 4.00~10.01, with a sensitivity of 60.08 mV/pH and non-linear error of 0.013%, and the modulated light intensity has slight effect on LAPS phase detection. This method has low complexity, high accuracy and excellent sensitivity and linearity for LAPS detection.

This contribution considers the application of pulsed LED illumination, synchronized with the exposure gap of a CMOS Bayer camera and an oscillating reference mirror, to record two π/2 phase shifted interferograms for quadrature based phase retrieval. Measurements of a superfine roughness standard in lateral motion are presented, demonstrating the capability of the setup to record the surface topography of moving objects. The application of the interferometric measurement data to calibrate a topography measuring wave front sensor, which is employed to support surface unwrapping is also discussed.

We describe a full field heterodyne interferometry system where the object beam is shifted by a high frequency with respect to the reference beam. The optical path difference between the object and reference beam is encoded in the phase of the envelope of the interference signal which is at the difference frequency. Conventionally, high frequency heterodyne interferometry is restricted to measurement of a single (or a few) point(s) as is the case in displacement measuring interferometers for precision machine tool axis feedback. This is because of the problem of demodulating the signal phase simultaneously for many pixels comprising a full-field image. This problem is overcome here by exploiting the capability of the special pixel structure employed in a Time of Flight (ToF) camera. This structure enables the measurement of the envelope phase of an optical signal at every pixel with respect to an electronic reference at the same frequency. ToF cameras are designed to measure the distance to an object in its field of view by detecting the phase delay, due to time of flight, of reflected light from a modulated source synchronized to the camera. In the described experimental interferometer, a Twyman-Green architecture is used with an acousto-optic modulator to produce interfering beams with a difference frequency of 20MHz. The image detector is a modified ToF camera based on a Texas Instruments OPT8241 sensor. The interferometer directly outputs a wrapped optical phase map with 12-bit resolution (equivalent OPD resolution 0.15 nm) at greater than 50 frames per second with no post-processing. The phase reconstruction is highly insensitive to the reference/object beam intensity ratio or to environmental noise.

The LDDM system is a measurement system mainly used for medium and short-range precision displacement data, especially in the field of practical engineering. In the LDDM system, the accuracy and speed of measurement system depend directly on the design of phase discriminator system. This article introduces a new high-precision digital phase detector based on FPGA hardware platform. It uses improved CIC filter and CORDIC function to design the module. Firstly two orthogonal local oscillator signals are generated, and multiply the two signals separately by the signal to be measured. After the modified CIC filter, the phase difference between the local oscillator signal and the signal containing only DC information is calculated by the CORDIC algorithm solving module. Finally, the phase difference of the signal to be measured is obtained by subtracting the phase difference between the two channels. The results of Matlab and Modelsim simulation and hardware platform experiments show that the high-precision digital phase detector designed in this article achieves a good level of measurement speed and measurement accuracy. The experimental phase error is only 1.03×10-4 rad, and the accuracy reached 0.0515%.With the addition of 30dB noise, the average phase discrimination error of 20 times is 1.02×10-4 rad, which achieve a high accuracy. It is important to achieve a higher accuracy displacement measurement for the LDDM system.

The angular displacement sensor based on time-grating is a novel kind of displacement sensor, but there is a limitation in some applications with harsh environment owing to extracting angular information uses the analog phase detector. To reduce the error comes from solution and improve the static stability of sensor, a novel signal process system is presented. In comparison to the traditional method using analog electrical technology to obtain angular displacement, the proposed method uses the All phase Fast Fourier transform (AP-FFT), that has a perfect performance on suppressing the spectrum leakage and the property of phase invariant, to obtain the phase angle. In the paper, we design the core system for data sampling and processing. Firstly, it utilizes AP-FFT to transform the sensing signal from time domain to frequency domain; in addition, the angle is calculated in the phase spectrum. Finally, the experimental platform is designed to verify the performance of the proposed technique. The error of the novel method is compared to that of the traditional method, it can be concluded that the proposed method is very effective in suppressing noise and enhances the stability in a static condition.

This paper discusses the use of double-sideband suppressed-carrier (DSB-SC) modulation and radio frequency mixer as phase detector to extract phase information for methane detection in chirped laser dispersion spectroscopy (CLaDS). The 1.66 μm light from narrow-linewidth laser was modulated by electro-optic modulator (EOM) working on DSB-SC mode. These two sidebands passed through gas chamber and formed interference on photodetector. The phase change from gas absorption in beating signal can be extracted by using passive RF mixer with another input as reference signal which is achieved by doubling RF drive signal of EOM. In RF mixer, two inputs with identical frequency but various phase shift corresponds to DC bias voltage variation of output. The phase change is proportional to refractive index change and can be referred to gas concentration by using Kramers-Kronig relations. The advantage of phase sensitive CLaDS is wide dynamic range for gas detection. It compensates the deficiency of wavelength modulation spectroscopy (WMS) on high concentration circumstances. And the passive scheme pushes the system requirement to the lowest level.

A growing number of applications are calling for the compact high energy laser sources. In the last decade, significant progress has been made in the area of solid state lasers especially fiber lasers. The solid state laser is widely used in the processing industry, telecommunication systems at present. However, thermal effect, nonlinear effect and the damage of optical components limits the output power. We present a laser coherent combining technique based on heterodyne method in all-fiber feedback format. In this technique the feedback signals are coupled and transferred by fiber to simplify the system, while all factors of the signals such as the wavefront distribution, polarization state, power ratio of the sub-beams and the reference beam need to be considered and strictly controlled. Compared with the previous system, this technique brings another important advantage: Only the coupling side should meet stringent tolerance toward collimation. Phase detection for laser interferometry, phase control of sub-lasers is theoretically analysis and simulated to reveal the system control bandwidth, phase precision. A high speed phase detection circuit and a phase control circuit are developed. Proof of concept of this technique is experimentally demonstrated at 1.06μm. The experiment setup is shown. Stable results are obtained. The peak power rises up while the theoretical result is 2. Experiments reveal the validity of the technique in nanosecond pulse laser coherent combining.

A mathematic model based on surface plasmon resonance (SPR) effect is presented to measure the nano metallic film thickness with the coupling device of Kretschmann configuration composed of K9 prism-gold film-air. Four modulation modes of SPR method, such as intensity, phase, wavelength and angle, are numerically analyzed. Their detection principles, the measurement range and sensitivity of different modulation type sensors are discussed. The simulation results show that the SPR intensity detection method has the highest measurement range and the SPR phase detection method has the highest sensitivity. In practical applications, not only the measurement range and sensitivity, but the optical signal processing mode, experiment devices, the complexity of the algorithm and cost factors should be considered to research and develop the appropriate thin metallic film's thickness measurement SPR sensor with higher sensitivity and stability.

A great number of design concepts of surface acoustic wave (SAW)-based gyroscopes was proposed through the last decade mainly due to their unique robustness and ability to survive extremely high shocks. At the same time, these devices are small, cheap and easy to produce. Later publications offered a novel idea of constructing a fully passive and wireless gyroscope using SAW-based elements. Although this idea is very attractive, proposed design concepts rise a number of questions. This paper is dedicated to give a short overview of existing design concepts, focusing on details of its operation. Moreover, a new design concept utilizing a single delay line and a phase detector is proposed.

In this paper we demonstrated a coherent raster-scan imaging system that can acquire phase information based on continuous terahertz imaging. It mixes the terahertz with a Fs-laser by a electro-optic crystal of ZnTe to make a hybrid modulation on the crystal to achieve continuous terahertz detection. In this way, it can not only propagate for a long distance but also achieve phase detection for continuous terahertz imaging. The surface images of objects that are under test can be obtained by the Backward-Wave Oscillator, which the output power is 10mW at 205.994GHz. With the repetition frequency of 80MHz, the output power of the MaiTai is 1.65W and 100fs pulse light at 800nm. The images can achieve diffraction-limited resolution approximately. And the simulated results show that the system can obtain phase imaging of test objects based on continuous terahertz source. The way to get the phase of the signal has significant meaning for coherent detection of continuous terahertz source.

In this paper we proposed a method of phase extraction for continuous terahertz wave. Firstly, we study the mathematical relationship of phase between the electro-optic sampling signal and terahertz wave in the theory, and then build the platform of continuous terahertz wave, using BWO as the source of terahertz radiation and Fs-laser as the detection of pulse. After using differential circuit and the principle of electro-optic sampling, we detect the polarization properties of optical signal and transform it into electric signal. With the filter amplifying circuit for signal processing, we obtain the phase of continuous THz wave at 0.2 THz. This method of phase extraction provides a potential way to the continuous THz wave coherent imaging, which is of great significance to the further study on continuous THz wave coherent imaging.

In this paper, we demonstrate the feasibility of microwave holographic imaging application based on spintronic microwave sensors. By adapting the rapid phase detection technique, a magnetic tunnel junction can achieve a real-time measurement of both the amplitude and phase of the scattered microwave using a lock-in amplifier. The built system has a capability to detect not only the existence of the concealed objects but also their shapes, allowing the concealed threat to be distinguished along with other hidden objects. The system is also able to estimate the distance of target by a broadband measurement. Anticipating the phase-detection of the dielectric function of the targets, we have also carried out extensive density functional theory calculations for a number of condensed phase energetic materials to determine their dielectric response in the microwave range.

Coherent beam combining (CBC) by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters like OPOs. However, a phase modulator operating at the frequency-converted wavelength is needed, which is non standard component. Fortunately, nonlinear conversion processes rely on a phase-matching condition correlating, not only the wave vectors of the coupled waves, but also their phases. This paper demonstrates that, using this phase correlation for indirect control of the phase, coherent combining of optical frequency converters is feasible using standard all-fibered electro-optic modulators. For the sake of demonstration, this new technique is experimentally applied twice for continuous wave second-harmonic-generator (SHG) combination: i) combining 2 SHG of 1.55-μm erbium-doped fiber amplifiers in PPLN crystals generating 775-nm beams; ii) combining 2 SHG of 1.064-μm ytterbium-doped fiber amplifiers in LBO crystals generating 532-nm beams. Excellent CBC efficiency is achieved on the harmonic waves in both these experiments, with λ/20 and λ/30 residual phase error respectively. In the second experiment, I/Q phase detection is added on fundamental and harmonic waves to measure their phase variations simultaneously. These measurements confirm the theoretical expectations and formulae of correlation between the phases of the fundamental and harmonic waves. Unexpectedly, in both experiments, when harmonic waves are phase-locked, a residual phase difference remains between the fundamen tal waves. Measurements of the spectrum of these residual phase differences locate them above 50 Hz, revealing that they most probably originate in fast-varying optical path differences induced by turbulence and acoustic-waves on the experimental breadboard.

The down-looking synthetic aperture imaging ladar (SAIL) with electro-optic modulation was proposed. The measurement uses electrically controlled scanner to produce beams with spatial parabolic phase difference, which consists of electro-optic crystal and cylindrical lens. Due to the high modulation rate without mechanical scanning, this technique has a great potential for applications in extensive synthetic aperture imaging ladar fields. The phase mapping of electrically controlled scanner under the different applied voltage is achieved and measured by the polarized digital holographic interferometry. The phase mappings of the scanner in the down-looking SAIL with the o-polarized light and e-polarized light are obtained. The linear phase distribution and the parabolic phase distribution are observed after applying the external electric field. The corresponding analyses and discussions are proposed to explain the phenomena.

The existence of phase error influences the imaging performance of optical synthetic aperture system and limits the resolution of the imaging system. The relationship between point spread function of binocular system and piston error is analyzed and the conclusion that the relation between point spread function and piston error is irrational with coordinates along the perpendicular bisector of baseline has been deduced and proved. Therefore the effect of position accuracy to error detection is avoided. The distribution characteristic of point spread function on baseline determines the range of piston error and by which a unique value of piston error is obtained. Finally, the piston error detection method of binocular system is extended to the common optical synthetic aperture system. Simulation experiment demonstrates that this method can conquer effect of various noises and the detection accuracy is better than 0.004 times of wavelength.

We develop a new technology, which is referred to as progressive phase conjugation (PPC), in which phase conjugation is electrically performed without requiring a coherent reference beam by fusion using a reference-free spatial phase detection and spatial phase modulation. This method enables remote setting of a phase detector from the signal transmitter without an additional transmission line for the reference beam. It also enables realization of high-speed and dynamic wavefront compensation owing to its open-loop architecture using the single-shot phase detection method. Therefore, the PPC is applicable to a wide range of optical communication technologies, including the reconfigurable spatial-mode extraction and conversion of mode transmission in a multi-mode fiber (MMF). In our experiment, spatial modes are generated by directing a laser beam into a MMF with a 50-micron core diameter. At the output side of the optical fiber, the phase distributions of the spatial modes are detected using the reference-free phase detector constructed by combining a spatial filtering method with holographic diversity interferometry using two CCD imagers. Then, the phase conjugate distribution of the detected phase pattern is displayed on a LCOS-type SLM. We confirm that the PPC system can extract a specific mode pattern with a considerably low crosstalk of less than 1% by displaying the corresponding phase-conjugation pattern on the SLM. In addition, we demonstrated a reconfigurable spatial-mode conversion by the phase control technology using the SLM. By applying the spatial phase modulation to an optical beam incident on the SLM, the spatial mode of the output beam is flexibly changed.

The reliability of nanometer track writing in the large scale chip manufacturing process depends mainly on a precise positioning of the e-beam writer moving stage. The laser interferometers are usually employed to control this positioning, but their complicated optical scheme leads to an expensive instrument which increases the e-beam writer's manufacturing costs. We present a new design of an interferometric system useful in a currently developed cost effective e-beam writers. Our approach simplifies the optical scheme of known industrial interferometers and shifts the interference phase detection complexity from optical domain to the digital signal processing part. Besides the effective cost, the low number of optical components minimizes the total uncertainty of this measuring instrument. The scheme consists of a single wavelength DFB laser working at 1530 nm, one beam splitter, measuring and reference reflectors and one photo-detector at the interferometer output. The DFB laser is frequency modulated by slight changes of injection current while the interference intensity signal is processed synchronously. Our algorithm quantifies the phase as two sinusoidal waveforms with a phase offset equal to the quarter of the DFB laser wavelength. Besides the computation of these quadrature signals, the scale linearization techniques are used for an additional suppression of optical setup imperfections, noise and the residual amplitude modulation caused by the laser modulation. The stage position is calculated on basis of the DFB laser wavelength and the processed interference phase. To validate the precision and accuracy we have carried out a pilot experimental comparison with a reference interferometer over the 100 mm measurement range. The first tests promise only ±2 nm deviation between simplified and the reference interferometer.

In this paper, a new approach is presented for solving the problem of spatial shift wrapping associated with Spatial Shift Estimation (SSE)-based Fringe Pattern Profilometry (FPP). The problem arises as the result of fringe reuse (that is, fringes periodic light intensity variance), and the spatial shift can only be identified without ambiguity with the range of a fringe width. It is demonstrated that the problem is similar to the phase unwrapping problem associated with the phase detection based FPP, and the proposed method is inspired by the existing ideas of using multiple images with different wavelengths proposed for phase unwrapping. The effectiveness of the proposed method is verified by experimental results on an object with complex surface shape.

Optical phase-locked loop (OPLL) is used to improve the linearity of an optical link for transmission of analog signals. The finite loop delay and the presence of a low-pass filter, required for stable loop operation, lead to a nontrivial frequency response. Here, the linearity improvement in OPLL is investigated, and simple relation among the loop delay, the open-loop gain, and the loop-filter bandwidth that must be satisfied for stable operation of the OPLL is found. This relation is used to determine the fundamental limit on spur-free dynamic range (SFDR) improvement that OPLL can offer over a conventional Mach-Zehnder (MZ)-type detector.

According to the principle of centroid measurement, position-sensitive detectors (PSD) are commonly used for micro displacement detection. However, single-beam detection method cannot satisfy such tasks as multi-dimension position measurement, three dimension vision reconstruction, and robot precision positioning, which require synchronous measurement of multiple light beams. Consequently, we designed PSD phase detection method using frequency-domain multiplexing for synchronous detection of multiple modulated light beams. Compared to previous PSD amplitude detection method, the phase detection method using FDM has advantages of simplified measuring system, low cost, high capability of resistance to light interference as well as improved resolution. The feasibility of multi-beam synchronous measurement based on PSD phase detection using FDM was validated by multi-beam measuring experiments. The maximum non-linearity error of the multi-beam synchronous measurement is 6.62%.

Mass stranding of live whales has been explained by proposing many natural or human-related causes. Recent necropsy reports suggest a link between the mass stranding of beaked whales and the use of naval mid-frequency sonar. Surprisingly, whales have experienced symptoms similar to those caused by inert gas bubbles in human divers. Our goal is to develop a compact optical sensor to monitor the consumption of the oxygen stores in the muscle of freely diving whales. To this end we have proposed the use of a near-infrared phase-modulated frequency-domain spectrophotometer, in reflectance mode, to probe tissue oxygenation. Our probe consists of three main components: radiofrequency (RF) modulated light sources, a high-bandwidth avalanche photodiode with transimpedance amplifier, and a RF gain and phase detector. In this work, we concentrate on the design and performance of the light sensor, and its corresponding amplifier unit. We compare three state-of-the-art avalanche photodiodes: one through-hole device and two surface-mount detectors. We demonstrate that the gain due to the avalanche effect differs between sensors. The avalanche gain near maximum bias of the through-hole device exceeds by a factor of 2.5 and 8.3 that of the surface-mount detectors. We present the behavior of our assembled through-hole detector plus high-bandwidth transimpedance amplifier, and compare its performance to that of a commercially available module. The assembled unit enables variable gain, its phase noise is qualitatively lower, and the form factor is significantly smaller. Having a detecting unit that is compact, flexible, and functional is a milestone in the development of our tissue oxygenation tag.

A roll angle interferometer with high sensitivity is designed in this paper. Two sets of centrosymmetric beams are used to travel through the measurement and reference arms of the roll angle interferometer which contains two specific optical devices: wedge prism assembly and wedge mirror assembly. The optical path change in both arms caused by roll is converted into phase shift which can be measured by interferometer. Because of the adoption of the centrosymmetric measurement structure, the straightness errors, yaw error and pitch error can be avoided and the dead path is minimized, so that the stability and the accuracy of the measurement can be greatly enhanced. The resolution for the roll measurement is about 0.006″ with the measurement range of ±1°.

The pH value has been one of the keen parameters in the cell culture. And the optical measurement method especially the optical method using optical fiber has been widely used due to its small volume and high accuracy. In this work we design a phase detection system to detect the phase difference between the signal and reference signal in the Dual Lifetime Referencing Method. The modulation frequency of the DLR method ranges from 10 kHz to 60 kHz and the system we designed can detect phase difference from the frequency of 1 kHz to 100 kHz. The error can be as small as 0.2%.

Determination of the interference phase, i.e. the mutual phase shift between interfering waves is a principal issue in the interferometric measurement, especially on the nanometre scale. Our goal was to develop a novel interference phase detection technique that employs a computational approach and a frequency modulation of the laser source to achieve comparable performance with a homodyne detection with an optical phase shift generation. We have used a Michelson setup with polarizing optics that allowed to compare both the homodyne detection method and our novel method side by side while both methods shared the optical setup. Our method also comprises error compensation that deals e.g. with residual amplitude modulation and the scale non-linearities. The experiments revealed that the novel method achieves a periodic error less than 0.16 angular degrees and a standard deviation of less than 1.5 degrees, compared against the reference. The operational distance was 600mm. The method had proven it is suitable replacement for traditional homodyne detection techniques since it has comparable performance and significantly lower demands on the optical setup.

In view of the difficulties of testing the range accuracy of infrared phase range finder under field conditions, this paper establishes a simulated testing model. This model receives the infrared wave emitted by the phase range finder, and then makes spectrum analysis on the sampled received wave to obtain its initial phase. Therefore the initial phase of the local oscillation source in the phase range finder can be estimated. According to the preset simulated range value the initial phase of the simulated echo can be calculated and set. By examining the response after the phase range finder receiving the simulated echo, it is possible to judge whether its range accuracy is up to the technical specification. This paper presents functional simulation experiments, and the results confirm the feasibility of the simulated testing system model.

Triangulation sensors have been in wide use for many years. Most point sensors use a laser spot, which is detected using either a lateral effect photodiode or a linear detector array. The centroid of the spot is used to determine the range using triangulation. On many engineered surfaces, this spot image may suffer from speckle, surface texture, or other issues that limit the ability to repeatably measure the centroid. Many analysis means, such as fitting of the spot, zero crossing, and averaging methods have been tried to make the sensor more robust to surface influenced noise. This paper will present a system using a split image and phase detection to obtain the range. The speed of the sensor is gained by using simple point photodiodes and a moire effect to obtain the phase measurement. The paper will discuss the pros and cons of this approach, and show results on untreated metal parts.ear)

Lidar system often use pulse range method, phase detection (PD) range method and linear frequency modulation continues wave (LFM/CW) range method. Each method has its limit between range resolution and no fuzzy range. In this paper, a Lidar system with high range resolution in a long distance is designed by using LFM/CW range method cooperating with PD range method. A MCU is used to control the system working on LFM/CW range mode and PD range mode alternately. In which LFM/CW range mode is used to obtain an approximate target range with low resolution in long distance, and PD range mode is used to obtain a high resolution range value within one resolution of LFM/CW range mode. Then use the PD mode's range value to amend the range from LFM/CW method, and achieve high range resolution in long distance. This paper describes the system's principle. The simulation and experiment results in typical object situation prove the system could achieve high range resolution effectively.

The traditional technique of phase laser range finder is mixing high frequency signals with analog circuits and filtering them to obtain the useful signal with low frequency. But the analog mixing circuits are susceptible to interference and will bring amplitude attenuation, phase jitter and offset and this way has difficulties in achieving high precision ranging and fast speed ranging at the same time. The method of this paper is based on under-sampling technique with digital synchronous detection and referring to Digital down converter technique of digital IF receiver in radar system. This method not only reduces the complexity of data processing, improves the speed and accuracy of phase detection at the same time, but also reduces requirements for ADC devices and DSP chips in the ladar system by a lower sampling rate. At the same time, the structure of electronic system is global simplified compared with traditional analog ladar system and the anti-jamming is greatly enhanced. So this method has important research value.

In this report, error estimation method of phase detection in phase shift method is proposed. Phase detection algorithm extracts phase of modulated signal from several numbers of interferogram that acquired during phase shifting. The fourier domain expression of phase detection algorithms show frequency response for sine and cosine components. And it shows behavior for phase detection in the case that phase shifting error exists. However, these two response functions, those are response function for sine component and that for cosine component, do not directly show frequency response of phase detection itself. On the contrary, newly developed frequency response function, which is derived from these two frequency response function, directly shows frequency response of phase detection. And it clearly shows the behavior of phase detection algorithm when phase tuning error exists. The newly developed frequency response function is similar to the Bode plot. The magnitude plot shows sensitivity for frequency components. And the phase plot can be used for error estimation of phase detection. There is good agreement between the developed frequency response function and calculated error value. These results of comparison between error estimation using developed frequency response function and calculated error value are shown in this report.

Frequency up-conversion technology can be used to increase detection efficiency for near infrared photons, as has been demonstrated in fiber-based quantum communication systems. In a continuous wave pumped up-conversion detector, the temporal resolution is limited by the timing jitter of the detector in the visible range, which limits the maximum clock rate of a quantum communication system. In this paper we describe a scheme to improve the temporal resolution of an up-conversion single-photon detector using multi-wavelength optical-sampling techniques, allowing for increased transmission rates in single-photon communications systems. We experimentally demonstrate our approach with an up-conversion detector using two spectrally and temporally distinct pump pulses, and show that it allows for high-fidelity single-photon detection at twice the rate supported by a conventional single-pump up-conversion detector.

A novel surface plasmon resonance (SPR) sensor based on differential spectral phase interferometry is introduced. Our scheme incorporates a broadband white-light emitting diode (WLED) with double-pass Michelson interferometer for highly sensitive Kretschmann SPR phase detection over the visible spectrum. Superior to laser based SPR interferometer which is vulnerable to nonlinear phase saturation and conventional spectroscopic SPR sensor which only measures the spectral intensity, the proposed spectral phase interferometer directly acquires the optimal SPR phase response of every spectral component which is equivalent to having infinitely many SPR laser interferometers operating simultaneously at fixed angle of incidence. Therefore the inherent phase saturation problem due to monochromatic laser source could be readily addressed. As the result, our system prevail over existing phase detection schemes by (1) achieving comparable ultimate detection limit as good as 10-7 refractive index unit (RIU), (2) extending the phase measurement range as far as 10-2 RIU, (3) simplifying the phase modulation scheme by directly acquiring the spectral oscillation instead of adding a temporal carrier. Experimental verification with BSA-aBSA interaction demonstrates that our system is capable of achieving ultimate sensitivity of 0.5ng·ml-1 (3.3pM) for ultra-sensitive aBSA detection which is among the best reported in literature. Yet such sensitivity is extended over a wide range of measurement as each wavelength specific SPR phase jump is monitored over the entire visible spectrum. Further biosensing application such as detection of cytochrome-c with aptamer immobilized on the SPR sensing surface is currently under investigation. We believe that by combination of high sensitivity, wide dynamic range and simplicity of operation, our SPR system would be truly applicable to complicated real-life biosensing.

Position sensitive detector (PSD) is based on the lateral photoelectric effect (LPE) to produce an electrical. The photocurrents output from the electrodes, so the amplitude and phase of the output signal are related to the distance between the light spot and the electrodes. The information of the phase was detached from photocurrent signal. The diversification of phase along with the distance was analyzed, and phase difference between the corresponding electrode signal current as well as the associated difference with the change of PSD related parameters. The result of experiment on one-dimensional and two-dimensional PSD is shown that the position detection error and the linearity all can meet the test requirements.

Data and simulation results characterizing the capability of a DUV system to inspect EUV mask blanks and substrates are reported. Phase defects and particles on multilayer (ML) surfaces, ARC-coated absorber, and substrate material are considered. In addition to the previously reported results of inspecting phase defects on multilayer surfaces, phase defects on a quartz substrate surface are shown. The principle of phase detection is described. Simulations show that the 22-nm node requirement for phase defect detection should be met, assuming a reduction in the multilayer roughness. Initial inspections of deposited SiO2 spheres show sensitivities of at least 40 nm on ML and quartz; however, the availability of calibrated spheres of smaller diameters has limited testing below this value. Simulation results show relative sensitivities for detecting SiO2 spheres of different diameters on various EUV materials.

In biological samples the resonant CARS signal of less abundant constituents can be overwhelmed by the nonresonant background, preventing detection of those molecules. We demonstrate a method to obtain the phase of the oscillators in the focal volume that allows discrimination of those hidden molecules. The phase is measured with respect to the local excitation fields using a cascaded phase-preserving chain. It is measured point-bypoint and takes into account refractive index changes in the sample, phase curvature over the field-of-view and interferometric instabilities. The detection of the phase of the vibrational motion can be regarded as a vibrational extension of the linear (refractive index) phase contrast microscopy introduced by Zernike around 1933

Nonlinear effects induced by Kerr effect in optical fibers result in the severe inter-channel crosstalk and degrade WDM transmission system performances. The electrical post-compensation through backward propagation is demonstrated for nonlinear impairment compensation of FWM via phase diversity detection, whose required bandwidth is less than that of heterodyne detection. By 20-km transmission of dispersion-shifted fiber (DSF), the generated FWM components with both of the original optical signals whose wavelength are around 1550nm are detected by phase diversity detection with one local oscillator. The detected signals are compensated by off-line signal processing using backward propagation, and after compensation there is over 6dB improved for the power difference between signals and FWMs.

In the processing of fiber collimator packaging, the main factor that impacts the packaging quality is the optical coupling loss which aroused by the phase offset of optical fiber base pin inclined surface and grin lens inclined surface. Based on "detectable" and DFT, a new fiber collimator packaging method has been put forward. Using machine vision and digital image processing technology to make sure tips at correct phase, then the tips was inserted into the stainless steel sleeve and keep a feed motion to regulate the gap between the tips and grin lens. This way helps find the best packaging phase and makes sure the biggest output power. The system is composed of CCD camera, image acquisition card and VC++ image processing software. Experiments proved the effectiveness and practicality, the phase tolerance can be controlled in ± 3° and meet the fiber collimator packaging precision requirement. This packaging process have been used in practical production and it improved efficiency and qualified rate, it also has applied for the invent patent.

Phase object exists widely in nature, such as biological cells, optical components, atmospheric flow field and so on. The phase detection of objects has great significance in the basic research, nondestructive testing, aerospace, military weapons and other areas. The usual methods of phase object detection include interference method, grating method, schlieren method, and phase-contrast method etc. These methods have their own advantages, but they also have some disadvantages on detecting precision, environmental requirements, cost, detection rate, detection range, detection linearity in various applications, even the most sophisticated method-phase contrast method mainly used in microscopic structure, lacks quantitative analysis of the size of the phase of the object and the relationship between the image contrast and the optical system. In this paper, various phase detection means and the characteristics of different applications are analyzed based on the optical information processing, and a phase detection system based on optical filtering is formed. Firstly the frequency spectrum of the phase object is achieved by Fourier transform lens in the system, then the frequency spectrum is changed reasonably by the filter, at last the image which can represent the phase distribution through light intensity is achieved by the inverse Fourier transform. The advantages and disadvantages of the common used filters such as 1/4 wavelength phase filter, high-pass filter and edge filter are analyzed, and their phase resolution is analyzed in the same optical information processing system, and the factors impacting phase resolution are pointed out. The paper draws a conclusion that there exists an optimal filter which makes the detect accuracy best for any application. At last, we discussed how to design an optimal filter through which the ability of the phase testing of optical information processing system can be improved most.

Measurements of glucose concentration are important parts of biochemical analyses. Based on the principles of the common-path heterodyne interferometry, we develop a high sensitivity optical sensor for measuring glucose concentration. A heterodyne light beam after transmitted through a glucose solution passes through some polarization components for interference. The phase difference determined with heterodyne interferometric technique of the interference signal is greatly enhanced as a result of proper azimuth angles of some polarization components, and a high sensitivity measurement of glucose concentration can be achieved. The feasibility of the measuring method was demonstrated by our experimental results. This optical sensor should bear the merits of high accuracy, short sample medium length, and simpler operational endeavor.