Phase-Shifting Digital Holography

We propose a parallel two-step phase-shifting digital holography technique capable of instantaneous measurement of three-dimensional objects, with a view toward measurement of dynamically moving objects. The technique is based on phase-shifting interferometry. The proposed technique carries out the two-step phase-shifting method at one time and can be optically implemented by using a phase-shifting array device located in the reference beam. The array device has a periodic two-step phase distribution, and its configuration is simplified compared with that required for three-step and four-step parallel phase-shifting digital holographies. Therefore the optical system of the proposed technique is more suitable for the realization of a parallel phase-shifting digital holography system. We conduct both a numerical simulation and a preliminary experiment in the proposed technique. The results of the simulation and the experiment agree well with those of sequential phase-shifting digital holography, and results are superior to those obtained by conventional digital holography using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.

We propose a phase-shifting interferometry technique using only two in-line phase-shifted self-interference holograms. There is no requirement for additional recording or estimation in the measurement. The proposed technique adopts a mathematical model for self-interference digital holography. The effectiveness of the proposed technique is demonstrated by experiments on incoherent digital holographic microscopy and color-multiplexed fluorescence digital holography with computational coherent superposition. Two-color-multiplexed four-step phase-shifting incoherent digital holography is realized for the first time, to the best of our knowledge, using the proposed technique.

Phase based imaging and sensing have been for decades effective optical methodologies for high resolution surface profiling. Several techniques for acquiring the phase information encoding the surface topography have been developed; the most prominent is phase shift interferometry (PSI) in which several phase shifted interference images are usually acquired in a sequence and are algebraically combined to extract the phase information. However, phase imaging is limited both by the 2π phase modulo limiting the ability to map structures with heights only up to half the source's wavelength i.e. several hundreds of nm, and also by error induced by the movements of the sample between the acquisitions of phase shifted interference images. Several approached for dealing with these limitations have been developed that provided only a limited solution, e.g. using a beat wavelength interferogram by a two wavelength illumination but that is more sensitive to phase noise and thus less accurate and parallel PSI in which all phase shifted images are acquired simultaneously but that does not resolve the height limitation. We have developed a combined and improved technique for parallel PSI and three wavelength illumination enabling overcoming both limitations without elevating phase noise sensitivity and have set up two prototypes: the first allowing video rate 3D imaging of moving samples such as biological live samples or high throughput scanning of metrology samples with nm scale resolution, and the second allowing single point very high speed axial motion tracking and vibrometry with sub-nm scale resolution and max step height of 30µm.

An investigation was made into the feasibility of compressing complex Synthetic Aperture Radar (SAR) images using MatrixViewTM compression technology to achieve higher compression ratios than previously achieved. Complex SAR images contain both amplitude and phase information that are severely degraded with traditional compression techniques. This phase and amplitude information allows interferometric analysis to detect minute changes between pairs of SAR images, but is highly sensitive to any degradation in image quality. This sensitivity provides a measure to compare capabilities of different compression technologies. The interferometric process of Coherent Change Detection (CCD) is acutely sensitive to any quality loss and, therefore, is a good measure by which to compare compression capabilities of different technologies. The best compression that could be achieved by block adaptive quantization (a classical compression approach) applied to a set of I and Q phased-history samples, was a Compression Ratio (CR) of 2x. Work by Novak and Frost [3] increased this CR to 3-4x using a more complex wavelet-based Set Partitioning In Hierarchical Trees (SPIHT) algorithm (similar in its core to JPEG 2000). In each evaluation as the CR increased, degradation occurred in the reconstituted image measured by the CCD image coherence. The maximum compression was determined at the point the CCD image coherence remained g 0.9. The same investigation approach using equivalent sample data sets was performed using an emerging technology and product called MatrixViewTM. This paper documents preliminary results of MatrixView's compression of an equivalent data set to demonstrate a CR of 10-12x with an equivalent CCD coherence level of g0.9: a 300-400% improvement over SPIHT.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

A multistage single-sideband generator consisting of a cascade of binary periodically switched phase shifters, e.g. with values of 180 degrees , 90 degrees , and 45 degrees for a double stage unit is described. With a special order of phase shift values, any degree of suppression of the image sideband may be obtained even with imperfect phase shifters merely by increasing the number of stages. This means that any degree of accuracy in the homodyne measurement of amplitude and phase values of a device under test can be obtained using the concept described. The phase and amplitude information is retrieved from a bandpass-filtered low-frequency signal at the mixer output. The receiver seems to be particularly suited for industrial applications of microwaves, where accurate amplitude and phase information is needed and where simplicity and robustness are of prime importance. >

Phase-shifting digital holography has been used for the study of vibrating objects. The time-averaged complex amplitude of Fresnel diffracted field due to a vibrating object was obtained by using a three-step phase-shifting algorithm. Taking the inverse Fresnel transform of the complex amplitude resulted in an image of the object superimposed with Bessel fringes. The Bessel fringes are contour map of the vibration amplitude. By sinusoidally modulating the phase of the reference beam at the vibration frequency, the brightest fringe could be shifted to points of interest, thus extending the measurable range of vibration amplitude.

Metal detector is widely used in food security and industrial manufacture. In order to solve the product effect problem which used only amplitude feature, the dual channel digital detecting algorithm was put forward, based on amplitude and phase information. Also, the balance coil mathematical model was built, and the metal signal feature was deeply analyzed. Through the coordinate orientating, the amplitude and phase information of metal could be exactly extracted, product learning and clustering algorithm could efficiently separate the metal signal and product effect signal. The experiment results showed that the phase information could separate different material metal effectively, cooperated with the amplitude information, the dual channel digital detecting algorithm could extract the metal information accurately and detect the metal with strong product effect.

We propose an algorithm that can improve the quality of the reconstructed image from the single hologram recorded by the optical system of the parallel four-step phase-shifting digital holography. The proposed algorithm applies the image-reconstruction algorithm of parallel two-step phase-shifting digital holography to the hologram so as to reduce errors in the reconstructed image and eliminate ghosts. We numerically and experimentally confirmed that the proposed algorithm decreased 25% in terms of root mean square error in amplitude, and eliminated the ghosts, respectively.

该文提出了一种新的非相干分布源的DOA和角度扩展估计算法。根据空间频率模型下的非相干分布源协方差矩阵的结构特点，可将协方差矩阵分离成两个分别由相位信息和幅度信息重建的矩阵。对矩阵的各主次对角线元素均进行平滑，可得到包含相位信息和幅度信息的平滑向量。利用最小均方拟合方法，可从相位信息中估计得到方位角；估计得到的方位角信息代入到幅度信息中即可获得角度扩展信息的估计，实现非相干分布源的DOA和角度扩展去耦估计。计算机仿真验证了算法的性能。

Aiming at the problem that security of digital watermarking is imperfect, a new digital watermarking algorithm based on holography is put forward. In embedment watermarking stage, first, original watermarking information is divided into two parts: amplitude and phase information. Then, a hologram which will be used as new watermarking information is generated by interference of the phase information light and the reference beam, and the amplitude information will be the key when original watermarking is extracted. At last, host image is transformed by the multilevel structures wavelet transform, and the new watermarking information is embedded into its suitable wavelet domain. In extraction watermarking information stage, the original watermarking information is obtained by the extracted watermarking information combined with the amplitude information. The theory and simulation show our algorithm has excellent performance in security, shear resistance and anti interference of white noise.

Recently, it has become necessary to detect cracks in structures such as buildings and bridges. Phase-shifting digital holography is one valuable method that can be used to measure the strain distribution on the surface of an object. However, to simplify the optical measurement setup, more compact equipment is required. An interferometric trigger method with dual piezo actuators for phase shifting is proposed. This method is useful for designing a head discrete-type measurement system that uses phase-shifting digital holography with multiple imaging sensors. The ability to phase shift using the proposed trigger method was confirmed with the reconstruction of an object and an experiment that was performed to measure the displacement distribution.

State of drying paint is monitored from the dynamic behaviors of images reconstructed by phase-shifting digital holography. For quantitative analysis cross-correlation coefficient of complex amplitude, named here, coherence factor, between successive frames with an interval of 20 s. Its modulus shows variation indicating the random dynamic behavior of the paint surface, while its phase is apparently related with the change of paint thickness. In the dried state they reach stationary values. The modulus has been shown to relate to the degree of speckle correlation in the model of Gaussian random process.

We propose the use of the binary amplitude of a diffracted field to obtain complex-amplitude encoding of a phase-only hologram. Although the complex amplitude in the hologram plane consists of an amplitude and phase, a phase-only hologram retains only the phase information of the complex amplitude, which degrades the quality of the holographic reconstruction. The proposed method approximates the amplitude in the hologram plane by a binary amplitude, which allows us to record the complex amplitude of the original optical field in a phase-only hologram. We verified the effectiveness of the method by applying it to two examples: a hologram reconstruction and the generation of Hermite–Gaussian beams.

Three-dimensional object recognition using joint fractional Fourier transform correlators with the help of digital Fresnel holography

Double Encryption of Image Based on Scramble Operation and Phase-Shifting Digital Holography