Parallel Phase-shifting Digital Holography Research Articles

Selective Interpolation Method for Two-Step Parallel Phase-Shifting Digital Holography

We propose the reconstruction algorithm for two-step parallel phase-shifting digital holography. Parallel phase-shifting digital holography records a single hologram and numerically extracts the multiple images needed for obtaining the complex amplitude in phase-shifting technique. During the reconstruction process, phase error and degradation of image occur due to the calculation error. The proposed algorithm interpolates into two steps that include the subpixel data to reduce the error, so the quality that a reconstructed image can be enhanced. Both numerical simulation and experiment are conducted to verify the effectiveness of the proposed algorithm.

Single-shot dual-wavelength phase unwrapping in parallel phase-shifting digital holography.

We propose a single-shot phase-unwrapping method using two wavelengths in parallel phase-shifting digital holography (PPSDH). The proposed method enables one to solve the phase ambiguity problem in PPSDH. We conducted an experiment of the proposed method using two lasers whose wavelengths are 473 and 532nm. An object having about 1.9μm step, which is 7.1 times larger than the half wavelength of one of the lasers (266nm), was fabricated by using vapor deposition of aluminum. Single-shot measurement of the height of the object was successfully demonstrated, and the validity of the proposed method was verified.

Superresolution of interference fringes in parallel four-step phase-shifting digital holography

A superresolution method for interference fringes obtained by parallel four-step phase-shifting digital holography is proposed. A complex amplitude distribution of an object wave is derived from a recorded hologram by parallel phase-shifting interferometry using two pixels without any interpolation procedures. Multiple distributions are derived by changing one of the two pixels when conducting phase-shifting interferometry. The angular spectrum distribution of the object wave is obtained by both the Fourier transforms and synthesis of the spectrum distribution from the Fourier-transformed images in the spatial frequency domain. Available space bandwidth is extended to half of that of an image sensor.

A4-Sized Parallel Phase-Shifting Digital Holography System

An A4-sized parallel phase-shifting digital holography system was constructed and experimentally demonstrated. Parallel phase-shifting digital holography is a technique being capable of instantaneous recording of three-dimensional (3-D) image of moving object. Aiming at a 3-D motion picture measurement of moving object system that can be carried on sites where the measurement system is needed, we improved a previous portable parallel phase-shifting digital holography system. The size and weight of the improved portable system are 300 mm × 210 mm × 160 mm and 6 kg, respectively. Also, we experimentally recorded a series of holograms of a moving object and reconstructed motion pictures, which show the same event but are focused at each depth, from the holograms. Thus, the 3-D motion picture recording and reconstruction capability of the constructed system were successfully demonstrated. A 3-D motion picture at 10 frames/s was obtained by the system.

Effect of intensity quantization level in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) enables the instantaneous recording of three-dimensional fields. The three-dimensional field can be reconstructed using a computer by numerical scalar wave propagation. In PPSDH, we record a space-division multiplexed hologram that includes the required phase retardation in the spatial distribution of the reference wave and then interpolate the data at blanked pixels for each phase retardation to obtain the complex amplitude distribution of an object wave. The recorded quality of the multiplexed hologram influences the reconstruction quality. In this study, we investigate the effect of the intensity quantization of a multiplexed hologram on the reconstruction quality. We compare the influence of intensity quantization in PPSDH with that in the conventional phase-shifting method. Random noise is also added to the multiplexed hologram. The required intensity quantization level is helpful for selecting a digital image sensor.

Space-bandwidth extension in parallel phase-shifting digital holography using a four-channel polarization-imaging camera

We propose a method for extending the space bandwidth (SBW) available for recording an object wave in parallel phase-shifting digital holography using a four-channel polarization-imaging camera. A linear spatial carrier of the reference wave is introduced to an optical setup of parallel four-step phase-shifting interferometry using a commercially available polarization-imaging camera that has four polarization-detection channels. Then a hologram required for parallel two-step phase shifting, which is a technique capable of recording the widest SBW in parallel phase shifting, can be obtained. The effectiveness of the proposed method was numerically and experimentally verified.

Performance comparison of bilinear interpolation, bicubic interpolation, and B-spline interpolation in parallel phase-shifting digital holography

To improve the quality of reconstructed images, we apply bicubic interpolation and B-spline interpolation to parallel phase-shifting digital holography for the first time. The effectiveness of bilinear interpolation, bicubic interpolation, and B-spline interpolation in parallel phase-shifting digital holography is shown by a numerical simulation. In the simulation result, the application of bicubic interpolation and B-spline interpolation succeeded in decreasing the rootmean- square error of the reconstructed image by 12.6 and 11.9%, respectively.

Removal of residual images in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) is a technique of single-shot phase-shifting digital holography. We found that there are two problems with this technique. (1) Some extraneous noises caused by the intensity unevenness of the reference wave become slightly superimposed on the object image. (2) The conjugate image cannot be completely removed. This is because the object wave causes the phase-shift error by illuminating an image sensor with a large incident angle. To solve these problems, we propose an algorithm for removing residual 0th-order diffraction and conjugate images in PPSDH. In the proposed algorithm, we modified phase-shifting interferometry in order to work through the unevenness of the intensity distribution and applied the Fourier transform technique to PPSDH to remove the residual conjugate image. The effectiveness of the proposed algorithm was experimentally verified.

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

Image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography [Invited

We propose an image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography. The proposed algorithm applies three kinds of interpolations and generates three different kinds of object waves. A Fourier transform is applied to each object wave, and the spatial-frequency domain is divided into 3×3 segments for each Fourier-transformed object wave. After that the segment in which interpolation error is the least among the segments having the same address of the segment in the spatial-frequency domain is extracted. The extracted segments are combined to generate an information-enhanced spatial-frequency spectrum of the object wave, and after that the formed spatial-frequency spectrum is inversely Fourier transformed. Then the high-frequency information of the reconstructed image is recovered. The effectiveness of the proposed algorithm was verified by a numerical simulation and an experiment.

Assessment of weak light condition in parallel four-step phase-shifting digital holography

Minimum optical energy required for four-step parallel phase-shifting digital holography (PPSDH) is evaluated numerically by using photon-counting analysis. PPSDH enables us to develop instantaneous three-dimensional (3D) measurement by single-shot measurement. In fast measurement of dynamic 3D events, detected optical power at an image sensor will be decreased. For biomedical sensing, maximum light intensity exists for preventing the damage of the tissue. In the numerical evaluation, a photon-counting approach is used for the evaluation of minimum detected energy by comparing the reconstructed images. Numerical results indicate that hundreds of photons at each pixel in the image sensor are enough for the reconstruction and total detected energy in a multiplexed hologram is about 1 pJ.

Single-shot femtosecond-pulsed phase-shifting digital holography

Parallel phase-shifting digital holography is capable of three-dimensional measurement of a dynamically moving object with a single-shot recording. In this letter, we demonstrated a parallel phase-shifting digital holography using a single femtosecond light pulse whose central wavelength and temporal duration were 800 nm and 96 fs, respectively. As an object, we set spark discharge in atmospheric pressure air induced by applying a high voltage to between two electrodes. The instantaneous change in phase caused by the spark discharge was clearly reconstructed. The reconstructed phase image shows the change of refractive index of air was -3.7 × 10(-4).

Algorithm for reconstructing wide space-bandwidth information in parallel two-step phase-shifting digital holography

We propose an image-reconstruction algorithm of parallel phase-shifting digital holography (PPSDH) which is a technique of single-shot phase-shifting interferometry. In the conventional algorithms in PPSDH, the residual 0th-order diffraction wave and the conjugate images cannot be removed completely and a part of space-bandwidth information is discarded. The proposed algorithm can remove these residual images by modifying the calculation of phase-shifting interferometry and by using Fourier transform technique, respectively. Then, several types of complex amplitudes are derived from a recorded hologram according to the directions in which the neighboring pixels used for carrying out the spatial phase-shifting interferometry are aligned. Several distributions are Fourier-transformed and wide space-bandwidth information of the object wave is obtained by selecting the spectrum among the Fourier-transformed images in each region of the spatial frequency domain and synthesizing a Fourier-transformed image from the spectrum.

Parallel phase-shifting digital holography with adaptive function using phase-mode spatial light modulator

Parallel phase-shifting digital holography using a phase-mode spatial light modulator (SLM) is proposed. The phase-mode SLM implements spatial distribution of phase retardation required in the parallel phase-shifting digital holography. This SLM can also compensate dynamically the phase distortion caused by optical elements such as beam splitters, lenses, and air fluctuation. Experimental demonstration using a static object is presented.

High-speed phase imaging by parallel phase-shifting digital holography

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second.

Construction of a portable parallel phase-shifting digital holography system

We propose a portable parallel phase-shifting digital holography system. Parallel phase-shifting digital holography is a technique capable of instantaneous and three-dimensional measurement of objects. This technique has been verified by an experiment on anti-vibration optical tables, but had not been realized as a system for practical use yet. Then, we designed a portable system of parallel phase-shifting digital holography for the purpose of practical use. The size and weight of the system are 450 mm (L)×250 mm (W)×200 mm (H) and less than 7 kg, respectively. We designed the configuration of the system in a way which can be easily changed to implement two types of parallel phase-shifting digital holographies. The system was constructed by the use of ready-made optical components. To confirm the validity of the system, the capability of the three-dimensional imaging free from the superimposition of the unwanted images, which was the problem accompanied with conventional in-line digital holography, with a single-shot exposure was successfully demonstrated.

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.

Experimental demonstration of parallel two-step phase-shifting digital holography

Parallel two-step phase-shifting digital holography is a technique for single-shot implementation of phase-shifting interferometry and requires only the intensity distribution of the reference wave and spatial two phase-shifted holograms. We constructed a system of parallel two-step phase-shifting digital holography and experimentally demonstrated the technique, for the first time. The system uses an originally fabricated image sensor having an array of 2 × 1 micro polarizers. Each micro polarizer was attached on pixel by pixel. In the experiment, the unwanted images, the zero-order diffraction wave and the conjugate image, are removed from the reconstructed image of objects by the system, while the images superimpose on the image of objects reconstructed by Fresnel transform alone. Also the capability of single-shot and three-dimensional imaging is demonstrated by the system.

Parallel two-step phase-shifting digital holography using polarization

We propose an optical implementation of a parallel two-step phase-shifting digital holography that utilizes a polarization technique. The implementation uses a phase-shifting array device consisting of a retarder array attached to an image sensor, and does not require the optical system to image the phase-shifting array device onto the image sensor required for the previously reported optical implementation of the parallel two-step phase-shifting digital holography. Then, the proposed implementation is essentially simple to align and compose. A preliminary experiment showed that the parallel two-step phase-shifting digital holography based on the proposed implementation can remove the conjugate image clinging to the image reconstructed by Fresnel transform alone with DC term suppression. Also, when the reconstruction distance was changed, the qualities of the reconstructed images were quantitatively evaluated by using normalized root-mean-square error. It was clarified that the proposed implementation was superior to other parallel phase-shifting digital holographies and Fresnel transform alone. Thus, the validity of the proposed implementation was confirmed.

Image quality improvement of parallel four-step phase-shifting digital holography by using the algorithm of parallel two-step phase-shifting digital holography

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.