Improving binary phase correlation filters using iterative techniques

An iterative technique has been used to improve the design and performance of the binary phase version of a tandem-component correlation filter. The results are compared to a regular matched filter, a phase-only filter (POF), and a binary phase POF, in terms of optical efficiency, SNR, and peak correlation intensity.     

High precision phase measurement using adaptive sampling

The conventional phase measurement techniques introduce error in the phase when the input signals are distorted by harmonics. A novel technique, known as adaptive sampling, for high-precision phase measurement is introduced. A digital signal-processing approach is used in this technique. The maximum sampling rate required for this technique is h+2 samples/cycle of the input signals, i.e. (h+2) f sampless, where h, is the highest harmonic present in the signals and f is the fundamental frequency of the signals. This sampling rate is way below the Nyquist sampling rate (more than 2hf samples/s) when h is a large number. In the adaptive sampling technique the sampling rate is started from three samples/cycle and then is gradually increased until the phase is correctly measured. This phase measurement technique has been verified using synthesized signals     

Partial-pressure measurement of atmospheric-pressure binary gas using two pressure gauges

We investigated a new method to measure the partial pressure of a binary gas system at near-atmospheric pressure conditions. The method utilizes two types of vacuum gauges, a capacitance manometer and a quartz friction pressure gauge. The partial pressure of the binary gas can be estimated by measuring the impedance change with a quartz friction pressure gauge, which depends on both viscosity and total pressure of a binary gas, and considering the total pressure change as measured by a capacitance manometer. We applied this method to measure the partial pressure of ozone in an ozone-oxygen gas mixture. The results suggested that the new method allows a partial-pressure measurement of ozone with an accuracy of , close to atmospheric pressure. The advantages of the new method include compact size, high safety standards when measuring highly reactive gases, and the allowance for in-line monitoring.     

Large in-plane displacement measurement in dual-beam speckle interferometry using temporal phase measurement

Abstract

Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object is displaced in its plane continuously. A high-speed camera is used to acquire a number of frames of the image of the object motion sequentially. Through Fourier transformation and inverse Fourier transformation of the frames stacked together, the total phase is determined. Finally, the magnitude of the in-plane displacement of the object motion is extracted. The range of displacement that can be measured using this novel method lies between few microns and over 100 μm on the upper end. Theory together with experimental results are presented in this paper.     

High precision phase measurement using reduced sine and cosinetables

A high-precision phase measurement technique, which can accurately determine the phase even when the signals are distorted by harmonics, was presented previously by the author (ibid., vol.38, p.954-60, Oct. 1989). He proposes a microprocessor-based hardware implementation of the technique. The hardware implementation requires two reduced tables: a sine table and a cosine table. If each table has i(i+5)/2 entries, then the phase can be accurately determined even if the signals are distorted by any number of harmonics in the range of second through ith harmonics     

Three-dimensional shape measurement using improved binary spatio-temporal encoded illumination and voting algorithm

Some regions of objects will be measured incorrectly or cannot be measured in optical three-dimensional (3D) measurement system based on coded structured light, due to occlusion, shadow, transfer function of measurement system, and noise. To obtain 3D data as much as possible and as correctly as possible, we proposed a method using improved binary spatio-temporal encoded illumination and voting algorithm. Firstly, the binary spatio-temporal encoded (BSE) pattern is improved with a redundancy encoding method. One code is assigned to two adjacent sections and distinguished with their temporal coordinates. The redundancy encoding method provides more cues for code correcting and retrieving. Secondly, symbols are estimated according to four coding cues--code redundancy, continuity of stripes, intensity variation in temporal direction, and neighbor symbols in sequence. Finally, a voting algorithm is adopted to obtain final symbols. A plaster model of a human head was measured to validate the method. The experimental results reveal that more valid points can be obtained and the reliability of the decoding results is improved.     

Path difference measurement using phase stepping with white light

Phase stepping algorithms are commonly used with narrow bandwidth sources for fast accurate measurement of interferometer phase differences. We show that path difference can also be measured using phase stepping with a wide bandwidth source. The errors resulting from the spectral characteristics of the source are discussed and shown to be relatively small, allowing measurement of path difference to typically 0.1 μm or better. White-light phase stepping is demonstrated experimentally with results which closely match those predicted theoretically.     

Self-adjusting dynamic binary phase holograms

An optical system constructed around a dynamic diffractive optic element, a ferroelectric liquid-crystal spatial light modulator in binary phase-only modulation mode, is investigated. The spatial light modulator is successively adjusted according to the direct binary search technique to diffract an incoming laser light beam into a predecided intensity distribution by use of feed back from the diffracted light. It was found that the feedback signal was noisy and that vibrations and limited bistability in the spatial light modulator's pixels were the main noise sources. The final diffraction efficiency depends on the degree of noise in the feedback signal, but even under fairly noisy conditions the iterations were found to converge properly.     

Superluminescent diode interferometer using sinusoidal phase modulation for step-profile measurement

We propose an interferometer in which the relationship between the degree of coherence (DCH) and the optical path difference (OPD) is utilized for determining an OPD longer than a wavelength. A superluminescent diode is employed as the source of the interferometer, and sinusoidal phase-modulating interferometry is used to detect the DCH and the phase of the interference signal. The combination of the OPD determined from the DCH and the phase of an interference signal enables us to measure an OPD longer than a wavelength with a high accuracy of a few nanometers. Experimental results show clearly the usefulness of the interferometer for a step-profile measurement.     

Simultaneous wavenumber measurement and coherence detection using temporal phase unwrapping

Wavelength scanning interferometry and swept-source optical coherence tomography require accurate measurement of time-varying laser wavenumber changes. We describe here a method based on recording interferograms of multiple wedges to provide simultaneously high wavenumber resolution and immunity to the ambiguities caused by large wavenumber jumps. All the data required to compute a wavenumber shift are provided in a single image, thereby allowing dynamic wavenumber monitoring. In addition, loss of coherence of the laser light is detected automatically. The paper gives details of the analysis algorithms that are based on phase detection by a two-dimensional Fourier transform method followed by temporal phase unwrapping and correction for optical dispersion in the wedges. A simple but robust method to determine the wedge thicknesses, which allows the use of low-cost optical components, is also described. The method is illustrated with experimental data from a Ti:sapphire tunable laser, including independent wavenumber measurements with a commercial wavemeter. A root mean square (rms) difference in measured wavenumber shift between the two of ~4 m?1 has been achieved, equivalent to an rms wavelength shift error of ~0.4 pm.     

The measurement of thin film stress using phase shifting interferometry

Abstract

A new technique for determining the stress of thin films is described. This technique combines digital phase shifting interferometry with image-processing software. A circular disc polished on one side is used as the coated substrate during film deposition. The average stress in thin films can be derived by comparing the deflection of the substrate before and after film deposition. The deflection of the substrate by the deposited film is obtained by the phase map. Using the Zernike polynomial fitting algorithm, a three-dimensional contour map is generated from the polynomial coefficients to visualize the deformation of the thin film and to examine the tensile or compressive stress after film deposition. Four oxide films prepared by ionbeam sputter deposition are investigated for their film stresses. The experimental results show that the stress values are concordant with measurements using other methods.     

超低频激光干涉法振动幅相特性测量技术的研究

基于对结构动力学、地球物理和地震物探等研究领域中超低频振动计量器具量值溯源迫切需求的分析,对超低频（低至0.002Hz）、大振幅（1m（p-p））激光绝对法振动幅值和相位测量技术进行了研究。针对激光干涉仪在动态超低频、大振幅情况下,跟踪测量性能变差的问题,研制了具有直流输出特性的大光程零差正交激光干涉仪;采用自主提出的自适应动态分解算法,解决了超低频数据量庞大、数据采集处理困难的技术难题.。给出了在超低频振动台上对石英挠性加速度计进行校准的实验数据。结果表明,该系统可实现动态光程大于1m、频率范围0.002Hz~2kHz的加速度幅值和相位的激光绝对法精确测量。     

基于目标模拟器的测量雷达相位一致性测试方法

相位一致性直接影响测量雷达的测角精度,因此在重大任务前必须对一致性进行测试,而常用测试方法如注入法安装架设复杂、使用条件要求高,标定法又过度依赖于标校塔或标校架,在地形受限时无法使用。该文中提出一种利用雷达自带的目标模拟器进行"注入式"相位一致性测试的方法,可对除馈源和天线以外的部分进行相位一致性测试,并在某型精密跟踪测量雷达上进行验证。结果表明:该方法操作简便,精度与常规注入法相当,可应用于基层雷达站进行相位一致性自检及野外临时阵地等不具备常规测试方法的场合。     

Real-time measurement of corner position in binary images

The design and testing of an efficient method for measurement of the location of corners of binary regions in digital images is described. From a single perspective image, the image coordinates of corner points are obtained from moments and intersection points accumulated within specified windows. Corner-point coordinates may then be used in further processing such as inverse photogrammetric solutions to determine 3D position. A video-processing board based on a TMS 320C25 DSP chip has been developed to process the image windows. Together with an 80386-based single-board computer, object corner location is achieved at the standard RS-170 television field rate of 60 Hz     

Precise measurement of optical phase retardation of a wave plate using modulated-polarized light

We propose a new method for precisely measuring the optical phase retardation of a wave plate using modulated-polarized light. Modulated-polarized light is used such that the zeros of the system can be accurately determined. A Babinet-Soleil compensator is employed to measure the optical phase retardation. A cross-wavelength measurement is also proposed for determining the phase retardation at a wavelength, which is not the measuring wavelength.     

Analysis of phase sensitivity for binary computer-generated holograms

A binary diffraction model is introduced to study the sensitivity of the wavefront phase of binary computer-generated holograms on groove depth and duty-cycle variations. Analytical solutions to diffraction efficiency, diffracted wavefront phase functions, and wavefront sensitivity functions are derived. The derivation of these relationships is obtained by using the Fourier method. Results from experimental data confirm the analysis. Several phase anomalies were discovered, and a simple graphical model of the complex fields is applied to explain these phenomena.     

On pseudorandom sequences of k symbols constructed using finite fields

A family of pseudorandom sequences of \(k\) symbols are constructed by using finite fields of prime-power order. The construction is an extension of certain construction of Sárközy and Winterhof on binary sequences using the quadratic character with polynomial arguments over any finite fields, and of certain construction of Ahlswede, Mauduit and Sárközy on sequences of \(k\) symbols using multiplicative characters with polynomial arguments over finite prime fields. Certain pseudorandom measures of the resulting sequences are considered.     

Displacement vector measurement using instantaneous ultrasound signal phase - multidimensional autocorrelation and doppler methods

Two new methods of measuring a multidimensional displacement vector using an instantaneous ultrasound signal phase are described, i.e., the multidimensional autocorrelation method (MAM) and multidimensional Doppler method (MDM). A high measurement accuracy is achieved by combining either method with the lateral Gaussian envelope cosine modulation method (LGECMM) or multidirectional synthetic aperture method (MDSAM). Measurement accuracy is evaluated using simulated noisy echo data. Both methods yield accurate measurements comparable to that of our previously developed cross-spectrum phase gradient method (MCSPGM); however, they require less computational time (the order, MDM < MAM approximate, equals MCSPGM) and would provide realtime measurements. Moreover, comparisons of LGECMM and MDSAM performed by geometrical evaluations clarifies that LGECMM has potentials to yield more accurate measurements with less computational time. Both MAM and MDM can be applied to the measurement of tissue strain, blood flow, sonar data, and other target motions.