Parallel Phase-shifting Research Articles

Parallel Phase-Shifting Digital Holographic Phase Imaging of Micro-Optical Elements with a Polarization Camera

In this paper, we propose a measurement method of micro-optical elements with parallel phase-shifting digital holographic phase imaging. This method can record four phase-shifting holograms with a phase difference of π/2 in a single shot and correct the pixel mismatch error of the polarization camera using a bilinear interpolation algorithm, thereby producing high-resolution four-step phase-shifting holograms. This method reconstructs the real phase information of the object to be measured through a four-step phase-shifting algorithm. The reproduced image eliminates the interference of zero-order images and conjugate images, overcoming the problem that traditional phase-shifting digital holography cannot be measured in real time. A simulation analysis showed that the relative error of this measurement method could reach 0.0051%. The accurate surface topography information of the object was reconstructed from an experimental measurement through a microlens array. Multiple measurements yielded a mean absolute error and a mean relative error for the vertical height of the microlens array down to 5.9500 nm and 0.0461%, respectively.

Single-Pixel Compressive Digital Holographic Encryption System Based on Circular Harmonic Key and Parallel Phase Shifting Digital Holography

An encryption system that combines compressive sensing (CS) and two-step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two-step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two-step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single-pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two-step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single-pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.

Pixel Resolution Imaging in Parallel Phase-Shifting Digital Holography

Parallel phase-shifting digital holography (PPSDH) employing a polarization image sensor can suppress zero-order and twin-image noise through a single exposure, achieve instantaneous measurement of complex-valued dynamic objects, and have broad applications in the areas of biomedicine, etc. To improve the imaging resolution of PPSDH, we propose an oversampled super-pixel image reconstruction method, which can be expressed as the implementation of nearest-neighbor interpolation to replace blank pixels in sparse sub-phase-shift holograms. We found experimentally that the maximum spatial lateral resolution of the reconstructed image based on the existing super-pixel method, B-spline, bicubic, bilinear, and the proposed nearest-neighbor interpolation was 12.4 µm, 11.4 µm, 9.8 µm, 8.8 µm, and 7.8 µm, respectively. The main reason for not reaching the ideal value of 6.9 µm was the inherent residual zero-order and twin-image noise, which needs to be removed in the future.

Simultaneous Measurement of Vibration and Temperature Using Frequency-Scanned Parallel Phase-Shifting Interferometry

In order to simultaneously detect high-frequency dynamic parameters and low-frequency quasi-static parameters through spectrum acquisition, a novel frequency-scanned parallel phase-shifting interferometry is proposed in this work. A Michelson interferometer (MI) composed of a 3 × 3 coupler is used for high-frequency vibration measurement. Different from conventional 3 × 3 fiber coupler based demodulation methods, a frequency swept laser source with flat intensity output is used. The time-varying vibrations will be encoded on the phase shifted spectra measured at two return ports of the coupler. Using a modified phase shifting algorithm, the optical path difference (OPD) changes along optical frequency can be retrieved, thereby significantly improving the sampling rate of the dynamic MI. Thanks to the full-spectrum scanning, the asymmetric parameters of non-ideal 3 × 3 couplers can be directly measured. Moreover, it provides the possibility of spectral demodulation of multiple quasi-static parameters. Another sensing channel containing multiple fiber Bragg grating (FBG) sensors is used to achieve quasi-distributed temperature measurement. Experimental results demonstrate its effectiveness in dynamic/static multi-parameter measurement.

Development of the Single-Shot Imaging System for the Detection of Transparent Defects through the Use of Parallel Phase-Shifting Digital Holography

Development of the Single-Shot Imaging System for the Detection of Transparent Defects through the Use of Parallel Phase-Shifting Digital Holography

Single-shot wavelength-selective quantitative phase microscopy by partial aperture imaging and polarization-phase-division multiplexing.

We propose a single-shot wavelength-selective quantitative phase microscopy by annular white-light illumination, polarization-phase-division, and parallel phase-shifting. Compared to conventional multi-wavelength incoherence digital holography, the proposed microscopy presents the following merits: no switching of illumination or mechanical scanning, high spatiotemporal phase sensitivity, and single-shot reconstruction at each wavelength. Experiments validate these characteristics by quantitative phase imaging of gratings, cells, and tissues.

Parallel phase shifting radial shear interferometry with complex fringes and unknown phase shift.

We present an interferometric method to analyze transparent samples using complex fringes generated by a parallel phase shifting radial shear interferometer using two coupled interferometers. Parallel interferograms are generated using two interferometers: the first one generates the polarized base pattern, and the second system is used to generate parallel interferograms allowing the adjustment of the x-y positions of the parallel interferograms. To obtain the optical phase map, parallel phase shift is generated by collocating polarizing filters at the output of the system; the polarizers are placed at arbitrary angles since they do not require adjustment because of the phase-recovery algorithm. The optical phase was processed using a two-step algorithm based on a modified Gram-Schmidt orthogonalization method. Such an algorithm has the advantage of not being iterative and is robust to amplitude modulation. The proposed method reduces the number of captures needed in phase-shifting interferometry. We applied the developed system to examine static and dynamics phase objects.

High-Speed Imaging of a Laser Ablation Process Using Parallel Phase-Shifting Interferometry

High-Speed Imaging of a Laser Ablation Process Using Parallel Phase-Shifting Interferometry

Single-shot phase-shifting incoherent digital holography

We propose single-shot incoherent digital holography in which a single-path in-line configuration and phase-shifting interferometry are adopted. Space-division multiplexing and polarization states of the waves are utilized to implement parallel phase-shifting holography. A single-path setup in parallel phase-shifting is constructed to capture an incoherent hologram easily with a compact system. An instantaneous and three-dimensional (3D) object image is obtained without undesired diffraction waves using parallel phase-shifting. The validity of the proposed technique is experimentally demonstrated for both transparent and reflective objects.

並列位相シフトディジタルホログラフィを用いた高速透明物体の動画像定量可視化

並列位相シフトディジタルホログラフィを用いた高速透明物体の動画像定量可視化

Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter

We present a digital holography microscopy technique based on a parallel-quadrature phase-shifting method. Two π/2 phase-shifted holograms are recorded simultaneously using polarization phase-shifting principle, slightly off-axis recording geometry, and two identical CCD sensors. The parallel phase-shifting is realized by combining circularly polarized object beam with a 45° degree polarized reference beam through a polarizing beam splitter. DC term is eliminated by subtracting the two holograms from each other and the object information is reconstructed after selecting the frequency spectrum of the real image. Both amplitude and phase object reconstruction results are presented. Simultaneous recording eliminates phase errors caused by mechanical vibrations and air turbulences. The slightly off-axis recording geometry with phase-shifting allows a much larger dimension of the spatial filter for reconstruction of the object information. This leads to better reconstruction capability than traditional off-axis holography.

High-Speed Three-Dimensional Microscope for Dynamically Moving Biological Objects Based on Parallel Phase-Shifting Digital Holographic Microscopy

We succeeded in 3-D motion-picture imaging for dynamic motion of biological objects swimming at different depths by parallel phase-shifting digital holographic microscopy (PPSDHM). PPSDHM is a technique for high-quality instantaneous 3-D imaging of specimens in the microscopic field of view by single-shot recording of multiple phase-shifted holograms. We constructed a PPSDHM for recording high-speed dynamic phenomena and then motions of biological objects in water were recorded at 20 000 and 150 000 frames/s, respectively, which is the fastest among the previous reports on 3-D imaging of biological objects.

Parallel Phase-Shifting Digital Holography Capable of Simultaneously Capturing Visible and Invisible Three-Dimensional Information

We propose a parallel phase-shifting digital holography capable of simultaneously capturing both outside three-dimensional (3D) information of the object such as a surface of an object which human being can perceive (visible information) and internal 3D information of the object (invisible information) using a visible laser light and an invisible laser light. This technique can carry out phase-shifting interferometry for each light with a single-shot exposure, because an interference fringe image in which the information of each light and each phase-shift is spatially multiplexed is recorded by a phase-shifting array device and a wavelength-filter array. We numerically simulated the proposed technique, and the effectiveness of the proposed technique was shown by evaluating the simulation results using a correlation coefficient. Also we conducted a preliminary experiment using a red filter and a near-infrared filter placed 8 cm apart from each other as objects containing both visible and invisible 3D information. A He-Ne laser operated at 633 nm and a diode laser operated at 830 nm were used as a visible light source and an invisible light source, respectively. The 3D imaging capability of the proposed technique was successfully demonstrated by the preliminary experiment, and the validity of the technique was also confirmed by evaluating root mean square errors of the reconstructed images. Also the capability for simultaneously 3D capturing of outside (visible) information and internal (invisible) information was demonstrated by a preliminary experiment.