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In-line digital holography using a random phase modulation is proposed. Owing to the random phase modulation, twin-image problem inherent to the in-line optical setup is relieved. Furthermore, because no multiplexed recording is required, dynamic phenomena can be recorded. This idea is inspired by double-random phase- encryption. The difference between the proposed method and the double-random phase-encryption is brie y described. Preliminary experimental results confirm the feasibility of the proposed method. The difference of coherence of a light source is also discussed.

Computational ghost imaging (CGI) is expected to be applied to noninvasive biomedical imaging because of its characteristic which allows us to obtain the object's image under a low signal to noise ratio (SNR) condition. However only an amplitude distribution can be obtained by the CGI. Therefore the imaging of the pure phase objects is difficult. Although the phase shifting digital holography has been used for reconstruction of the complex amplitude in the CGI, its experimental setup is cumbersome and sensitive to vibrations. Furthermore four holograms are required for the reconstruction of the complex amplitude because of the phase shifting algorithm, rendering the acquisition time of the phase image slow. Therefore the method is difficult to be applied to the biomedical imaging. An alternative non-interferometric method is proposed in this study. The proposed method uses the transport of intensity equation for the phase retrieval of the pure phase objects, termed transport-of-intensity CGI (TI-CGI). In the TI-CGI, the phase distribution is retrieved from a single defocused image obtained by a modulated optical setup of the CGI, achieving the fast and robust imaging compared with the conventional phase shifting method. Therefore the TI-CGI may be more suitable for the biomedical imaging than the phase shifting method. The TI-CGI is demonstrated by an optical experiment under the low SNR condition generated by the neutral density filters with 1% and 0.1% transmittance. The experimental results conform the effectiveness of the TI-CGI.

Three-dimensional imaging is very attractive for biomedical fields, industrial inspecting, and so on. Computational optical sensing and imaging is widely studied due to the recent development of imaging device, computational power, and so on. It is also used for three-dimensional sensing and imaging. In this area, random amplitude or phase modulation is introduced to improve its performance. In this paper, computational ghost imaging using a designed random amplitude modulation is presented. Owing to the designed random amplitude modulation, the number of measurements can be reduced. A phase modulation for twin image reduction of in-line digital holography is also presented. Owing to the random phase modulation, the overlapping an object image and its conjugate image can be reduced.

In-line digital holography is conventional but still attractive because of its simple optical setup. In general, sequential phase-shifting technique is mandatory to remove twin-image which makes the reconstructed image quality low. However, sequential phase-shifting technique requires multiple recording. Multiple recording means that it is not suitable for a dynamic phenomenon. In this paper, two kinds of a single-shot in-line digital holography without twin-image using a diffused illumination are presented. One is a generalized phase-shifting digital holography and the other is a computational removal of twin-image. The ideas and their experimental results are given to confirm the feasibility.

The possibility of incoherent digital holography has been widely studied because it is free from coherent light sources. Here spatially incoherent Fourier digital holography is described. The incoherent hologram is obtained by a rotational shearing interferometer. The hologram obtained by the interferometer is a cosine transform of a spatially incoherent object. After describing the principle of a rotational shearing interferometer, methods to obtain Fourier transform of an object presented.

Shift multiplexing method using a spherical wave is proposed for a holographic memory system based on a computer-generated hologram (CGH). In the proposed method, a propagated signal beam along an optical axis is generated by a CGH. The zero order beam of the CGH is obtained as a point source in the Fourier plane. This point source becomes a spherical reference beam on a recording medium by displacing a Fourier transform lens. The use of the spherical reference beam allows us to implement shift multiplexing in the holographic memory based on a CGH. Shift selectivity of the proposed method is numerically evaluated. In addition, shift multiplexing with the proposed method is numerically demonstrated.

Two methods to apply the generalized phase-shifting digital holography to color digital holography are proposed. One is wave-splitting generalized phase-shifting color digital holography. This is realized by using a color Bayer camera. Another is multiple exposure generalized phase-shifting color digital holography. This is realized by the wavelength-dependent phase-shifting devices. Experimental results for both generalized phase-shifting color digital holography are presented to confirm the proposed methods.

The modified Michelson type interferometer with lenses for a radial shear to record incoherent holograms is proposed. It enables us to record a hologram by self-interference without coherent illumination such as a laser. The interferometer has two wave plates which can realize phase-shifting incoherent holography. The feature can avoid a very large bias term and the twin image, which are the inherent problem of incoherent holography by self-interference. The advantages of the proposed method using lenses and wave plates are easy adjustment of the zone plate and simplification of the optical system. A preliminary experiment using an LED as an incoherent object was performed to confirm the four step phase-shifting by wave plates.

A holographic storage system based on digital holography is proposed for recording and retrieving a phase data page in a compact and simple optical setup. In the proposed recording system, complex amplitude distribution can be modulated using a single phase-only spatial light modulator. The complex amplitude distribution of a retrieved phase data page is detected with the Fourier fringe analysis. The use of digital holographic techniques enables realizing a compact and simple holographic recording system, which is independent of misalignment problem in conventional holographic storage systems. The capability of the proposed recording system is numerically and experimentally evaluated.

A Shack-Hartmann wavefront sensor (SHWFS) which consists of a microlens array and an image sensor has been used to measure the wavefront aberrations in various fields owing to its advantages such as simple configuration. However, a conventional SHWFS has the finite dynamic range. The dynamic range cannot be expanded without sacrificing the spatial resolution and the sensitivity in a conventional SHWFS. In this study, the SHWFS using a dual microlens array to solve the problem is proposed. In the proposed method, an astigmatic microlens is arranged at the center of a group of 2 x 2 spherical microlenses. A pattern image including spots and linear patterns is obtained at the focal plane by the dual microlens array. The pattern image can be separated into two images as if two microlens array with different diameter were used by discriminating spots from linear patterns with the pattern matching technique. The proposed method enables to expand the dynamic range of an SHWFS by using the separated two images. The performance of the proposed method is confirmed by the numerical simulation for measuring a spherical wave.

The system to record incoherent holograms using a rotational shearing interferometer is proposed. It enables us to record a hologram without coherent illumination such as a laser. The systems can record an incoherent hologram by self-interference. A rotational shearing interferometer to record incoherent cosine hologram is described. Furthermore, a rotational shearing interferometer with lenses to record incoherent hologram is described. It has the advantage of obtaining depth information by the reconstruction owing to lenses for the shear which is parallel to the optical axis. The preliminary experiments were performed. An LED and a liquid crystal display with an LED backlight were used as incoherent objects. The incoherent holograms were recorded. The object images were reconstructed numerically. The experimental results confirm the proposed incoherent holography using a rotational shearing interferometer.

Digital holography is a useful technique for recording the fully complex field of a wavefront. However, the quality of a reconstructed image of a digital hologram is not good, because it is suffering from speckles. To improve the image quality, a speckle reduction method in digital holography using various rectangular apertures is proposed. Different-sized rectangular apertures are applied for the hologram. Furthermore, the position of the aperture is arbitrary. Owing to the various size and position, the generated speckles have the various sizes and patterns. By averaging the speckle, the speckle noise can be reduced. Some reconstructed images based on the experimental results are shown to confirm the proposed method. For quantitative evaluation, the speckle contrast is also shown.

A multilayer recording using a varifocal lens generated with a phase-only spatial light modulator (SLM) is proposed. A phase-only SLM is used for not only improving interference efficiency between signal and reference beams but also shifting a focus plane along an optical axis. A focus plane can be shifted by adding a spherical phase to a phase modulation pattern displayed on a phase-only SLM. A focal shift with adding a spherical phase was numerically confirmed. In addition, shift selectivity and recording performance of the proposed multilayer recording method were numerically evaluated in coaxial holographic data storage.

A Mueller matrix imaging method by use of the characteristics of digital holography is proposed. In the proposed method, only two exposures are required to obtain the Mueller matrix. The Mueller matrix can be calculated from Stokes vectors. Stokes vectors can be obtained from two fully-complex amplitude distributions. Fully complex amplitude distributions can be obtained by digital holography. The optical experiments by using two kinds of specimens which are four linear polarizers and a quarter wave plate are shown to demonstrate the proposed method.

Single exposure phase-shifting digital holography is mandatory for recording/analyzing dynamic phenomena. As one of the candidate for the single exposure phase-shifting digital holography is the wave-splitting phase-shifting digital holography. We have proposed generalized phase-shifting digital holography as one of the wave-splitting phase-shifting digital holography. In the digital holography, the phase-shift quantity, which corresponds to the difference between the phase quantities of the reference wave on the adjacent pixels is generalized different from ordinal wave-splitting methods. Owing to the generalized phase-shifting, we can use a random-phase wave as the reference wave. The proposed phase-shifting digital holography enables us to record a fully-complex field of a dynamic phenomena without dc and conjugate terms using a commercially available optical devices. The relation between the property of the reference wave and the quality of the reconstructed images are discussed. Experimental results are given to confirm the proposed phase-shifting digital holography.

A lensless digital holographic tomography using not a filtered back projection method but a light back propagation method is proposed. In the proposed method, the phase distribution on the detector is used for a light propagation. On the contrary, in the conventional method, the phase information is used for a back projection. Owing to the propagation, the deflection from a true optical path is reduced in the proposed method. For the measurement of a specimen with a huge refraction angle, it is shown that our proposed method improves on measurement accuracy compared with a conventional filtered back projection method. Numerical simulations are given to confirm the feasibility of the proposed method.

A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented. Pattern recognition by use of polarimetric phase-shifting digital holography is also presented. Using holography, the amplitude and phase difference distributions between two orthogonal polarizations of 3D phase objects are obtained. This information contains both complex amplitude and polarimetric characteristics of the object, and it can be used for improving the discrimination capability of object recognition. Preliminary experimental results are presented to demonstrate the idea.

The one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. Using a CCD camera with pixelated polarizers, three images for phase analysis can be obtained simultaneously. The proposed method can be applied to a moving object, because a complex field of the wavefront of a 3D object can be obtained in a single exposure.

The quasi one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with distributions of a reference wave and an object wave, the complex field of the wavefront of a 3D object can be obtained. As two phase-shifted holograms can be obtained simultaneously in the proposed method, even a moving object can be recorded.

We present a fusion method for multi-wavelengths holographic images using Discrete Wavelet transform (DWT). The advantage of DWT is more control on high as well as low frequencies to get better quality. Fusion results include monochromatic fused images and color fused images from holographic images reconstructed from holograms recorded with multiple wavelengths from 567nm to 613nm.

To improve the image quality of the decrypted image through the double-random phase-encoding optical encryption, the design method of the input phase mask is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask matches to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of the phase levels of the designed input phase mask.

Deformation measurement of a cantilever based on digital holographic interferometry is presented. The digital holograms of the cantilever before and after deformation are obtained by use of phase-shifting technique. By using the phase-shifting digital holography, the object wave information without zeroth order diffraction wave can be extracted. The phase difference of the reconstructed cantilever before and after deformation is obtained numerically using discrete Fresnel diffraction integral. Owing to the numerical analysis, the deformation of the cantilever can be obtained with high resolution of nanometer dimensions. The optical experimental results are shown to confirm our proposed method. Furthermore, we propose a mechanical movement free double-exposure method in phase-shifting digital holography using a laser diode.

An encrypted optical storage based on a joint transform correlator architecture by using a photorefractive material is presented. A key code designed by optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a random phase distribution is introduced. Original two-dimensional data and the key code are placed side by side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in a same crystal by angular multiplexing. Furthermore we can record by key code multiplexing because another designed key code can produce another independent phase distribution. We demonstrate the concept of the optical data storage system by computer simulations.

A digital holographic data reconstruction method with data compression is proposed. We show the number of quantization level of a digital hologram can be reduced. By computer simulations it is confirmed that the method is especially useful for binary images. For gray scale images, we propose a bit plane decomposition method. By this method, we show both high reconstructed image quality and a high compression ratio can be achieved. This method is applicable to both a normal digital hologram and an encrypted digital hologram.

To analyze fringe patterns, frequency and phase analysis of fringes becomes popular. It provides accurate results and automated processing. In this paper, the theories of the frequency and phase domain methods such as the Fourier transform method, the wavelet transform method and the phase-shifting method are proposed for photoelastic fringe pattern analysis. The applications of these methods are described.

A double random phase optical encryption system that uses a binary key code is proposed. The key code is generatedas a binary computer generated hologram. The binary key code can be displayed on a binary spatial light modulatorsuch as a ferroelectric liquid crystal display. The use of a binary spatial light modulator enables us to renew thekey at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used toperform shift invariant encryption and decryption. Computer simulations of the effects of using a binary encodedkey code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presentedto demonstrate the effectiveness of the proposed system.Keywords: optical encryption , computer generated hologram, joint transform correlator 1. INTRODUCTION Information security is an increasingly important problem. Several optical information processing methods have been proposed for information security''°. In one approach, the data is encrypted by double random phase encoding

We propose a data security system that combines the optical encryption and a digital holographic technique. The proposed system enables us to store, transmit, and decrypt the encrypted data digitally. The data is encrypted optically using the double random phase encryption and is recorded as a digital hologram. The optical key, that is, the Fourier phase mask is also recorded as a digital hologram. The encrypted data is decrypted digitally by using the hologram of the optical key. Figure 1 (a) shows the input images used in the experiments to be decrypted. The electrically reconstructed image is obtained with an input phase mask without the Fourier phase mask. The digitally reconstructed encrypted images are shown in Fig. 1 (b). The image is obtained by inverse Fourier transforming the digital hologram of the encrypted data. The original image cannot be recognized. The digitally reconstructed decrypted images using the hologram of the Fourier phase mask are shown in Fig. 1 (c). Here one can see the original images. The experimental results demonstrate the feasibility of the proposed method.

An idea for security verification of identification such as passports, credit cards, and others in terms of difficulty of reproduction is proposed. The polarization information is used for security verification. As the state of the polarization encoded cannot be seen by an ordinary intensity sensitive device such as a CCD camera, it cannot be copied. For optical validation system, a joint transform correlator is used. Computer simulations and optical experimental results are shown to confirm our proposed method.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A novel architecture for the double random phase encoding optical encryption system using a joint transform correlator is proposed. In the proposed method, the joint power spectrum of the image to be encrypted and the key code is recorded as the encrypted power spectrum. Owing to the joint transform architecture, the alignment of the image and the key code is robust. Computer simulations using a computer generated hologram is presented to confirm our proposed system.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The application of a phase-encoded joint transform correlator to decryption of an optical image encryption system by a double-random phase encoding is described.

We present the principle and implementations of high-speed pattern matching with the incoherent holographic technique along with its experimental results.

We demonstrate a flexible high-speed correlator that consists of an incoherent-optical system and a fast electronic digital-image-processor.