To measure object wave in digital holography, the phase-shifting technique is popular by changing the phase of the reference wave. A piezo actuator (PZT) is usually used as a device to shift the phase. In a case to obtain the phase information of color object with multiple wavelengths, four-step phase-shifting algorithm with quarter wavelength shift is not convenient since the amount of the phase shift is difference according to each wavelength. In this paper, the generalized four-step phase-shifting method is proposed and experimentally verified to obtain color digital hologram using an image sensor with a Bayer pattern for capturing interference pattern shifted phase by one PZT.
Recently the technology of hologram receives a lot of interest owing to its advantages and many researches on hologram recordings have been actively studied. In some studies, digital hologram printing methods have lots of applications because of the ability to record large area hologram based on the technique of holographic stereogram. The holographic stereogram printing method records the hologram composed of hogels which are the unit of the hologram recorded at once. This method has advantages in flexibility of the size since it records the hologram hogel by hogel. In addition, the hologram printer records not only wavefront of real objects captured by charge coupled device (CCD) but also hologram patterns of virtual objects calculated by computer-generated hologram (CGH) algorithm. In previous systems, it is difficult to implement the hologram in high resolution because of the low numerical aperture of hogels. In this paper, we suggest the method of recording high-resolution hologram using binary wavefront pattern and discuss the optical modulation properties of the printed binary pattern.
Depth extraction and recovery from the recorded image have been studied and applied in many fields such as biology, robotics, and computer vision. In some researches, the aperture in the imaging system is coded as a particular function in order to distinguish relative distances from the focal plane or recognize sampled points from the recorded image and the image captured through this coded aperture is useful to retrieve blurred images or acquire depth maps. These studies are associated with the shape of point spread function (PSF). In some approaches, diffraction-based engineered PSFs such as double-helix and cubic phase are applied to extract the depth information. In this paper, we propose a depth measurement method based on the optical analysis of the pupil function. It is well known that the PSF is represented as a Fourier transform of the product of pupil function and spherical phase in a coherent imaging system. Also, it is possible to estimate the intensity of the PSF corresponding to the distance of the object in an incoherent imaging system. Then the depth information is extracted from a snapshot image by inverse transform of the image.
Hologram is a recording in a two or three-dimensional medium. It is a form of interference pattern between welldefined coherence reference beam and the light with same wavelength arriving from an object. When the hologram is illuminated by the reference beam, the hologram reconstructs desirable wave-fronts by modulation of reference beam. The coherence of reference beam is important for recording the hologram since it determines if the diffraction pattern is made or not. Incoherent light source does not form an interference pattern. For this reason, most of the holograms are reconstructed with coherent light like a laser. However, coherent light also derives speckle noise that makes the reconstruction image unclear. So, it is meaningful to find the suitable amount of partial coherence for hologram reconstruction and receives lots of interests for a long time. But, up to my knowledge, there is no experiment that adjusts spatial coherence quantitatively. In this paper, we invent an optical method to control the amount of spatial coherence of the light source by using a digital micro mirror device (DMD). Here, the DMD takes a role of an adjustable spatial filter because the number of on-state pixels of DMD changes the amount of spatial coherence. As a result, we verify the relation between the spatial coherence and the expressible depth of reconstruction image and find the optimal amount of coherence of LED for our holographic reconstruction experiment.
Recently, three-dimensional (3D) display technologies actively have been researched for improving the quality of 3D display and for reducing 3D sickness such as the vergence-accommodation conflict. One of approaches is super multiview (SMV) display in which more than two views enter the pupil of the eye. We invented a time-sequential SMV theater system which is able to change the number of views entering the pupil. The SMV display consists of the projection part and the observation part. The projection part contains a light engine to realize full-color images by using three digital micro-mirror devices (DMDs). The image projected at the screen is observed through the observation part. The optical system functions as defining the direction of the optical rays acquired by the eyes according to the position of the opening. We implement this opening by using a DMD and the movement of the opening is realized by changing the slit patterns on the DMD. Two DMDs are synchronized to each other and the projection image is selectively observed by the predetermined position of the opening sequentially. In our system, the observation part is designed the observer to wear the device and this system is expected to have a potential to provide SMV to the audience in the theater.
Recently, various light-field displays with special structures have been suggested. Among them, the cylinder-shaped display has distinct advantages in providing 360-degree field of view. In this paper, we propose a cylindrical light-field display which consists of panoramic projection optics and a cylindrical screen with several long vertical narrow openings. The projected scene is imaged on the inner surface of the cylinder and the contents are watched through the slit on the side of the cylinder during it rotates. Therefore, horizontal-parallax-only light field is formed to display threedimensional contents inside of the cylinder.
Three-dimensional (3D) displays have various shapes such as plate, pyramid, cylinder, sphere and etc. Every shape has its characters. One of them, the spherical shape is totally symmetric around the center. We design our system in order to display the image inside of the crystal ball. Even though the spherical crystal ball has perfect symmetry, there are some significant difficulties in designing optics since the crystal ball has severe spherical aberration. To display 3D contents, we generate many views by digital micromirror device in high speed and change the propagation direction of each view by 2-axis scanning mirrors and relay lenses. Theses plural images correspond to views of 3D object inside of the crystal ball.
Recently, super multi-view technology has been considered as one of the most popular research topic and many studies
have been done to improve the quality of such super multi-view display. In this paper, we present specific experiments
for human cognition. We designed our system for the special purpose that the human cognition of 3D contents is
examined. In comparison of the previous super multi-view displays, the number of views in our system can be
controlled. Our system has a great advantage that the effect of the number of views can be evaluated at the common
system. We can change the number of views, by changing the synchronization ratio which determines the speed of the
opening of the optical chopper and the refresh time of the DMD. We expect that this system will be useful for
understanding the principle of the human cognition for 3D display.
Holography has been regarded as one of the most ideal technique for three-dimensional (3D) display because it records and reconstructs both amplitude and phase of object wave simultaneously. Nevertheless, many people think that this technique is not suitable for commercialization due to some significant problems. In this paper, we propose an electronic holographic 3D display based on macro-pixel with local coherence. Here, the incident wave within each macro-pixel is coherent but the wave in one macro-pixel is not mutually coherent with the wave in the other macro-pixel. This concept provides amazing freedom in distribution of the pixels in modulator. The relative distance between two macro-pixels results in negligible change of interference pattern in observation space. Also it is possible to make the sub-pixels in a macro-pixel in order to enlarge the field of view (FOV). The idea has amazing effects to reduce the data capacity of the holographic display. Moreover, the dimension of the system is can be remarkably downsized by micro-optics. As a result, the holographic display will be designed to have full parallax with large FOV and screen size. We think that the macro-pixel idea is a practical solution in electronic holography since it can provide reasonable FOV and large screen size with relatively small amount of data.
Three-dimensional (3D) display usually provides binocular disparity to observer. To construct 360degree table-top display, lots of views are required. In order to display a large amount of views to observer, time-multiplexing technique is applied. We suggest a new structure for view-sequential 360-degree table-top display system. In my system, a transmissive screen is used and digital micromirror device (DMD) image is projected on it. This system defines the direction of bundle of rays to configure the sequential view. It has some advantages resulting from the transmissive flat screen. When the transmissive screen is used instead of the reflective one, the light power efficiency is improved. Moreover, the arrangement of the pixel is more uniform when the screen is flat instead of a static conic screen. We construct a table-top display with about 288views around 360degree and its feasibilities are confirmed.
In general, digital holography means a technology to measure an object wave by using a focal plane array (FPA) sensor. Since the limitation of the dimension of the FPA sensor, the field of view obtained by the FPA sensor is usually very narrow. Many methods have been proposed to increase the field of view of measurement. One simple solution is the synthesis of the holograms with small apertures, where each of them is measured by the FPA sensor respectively. If we imagine specific applications such as 360-degree table-top digital holographic display, the large field of view of the object is required to present the three-dimensional contents to the observer who may change his position dynamically. In this paper, we use two-axis rotation stage for acquisition of the object wave with large field of view. In our system, the optics including a laser and a CCD sensor are fixed and the object is mounted on the rotation stage. During the rotation of the object, the holograms are taken sequentially and the object wave over the hemispherical surface in k-space is obtained. The increase of solid angle of the measured hologram means the increase of acquired angular spectrum of interested objects. The resolution of the measurement is closely related with the numerical aperture and the data with fine resolution is expectable. But since it is not easy to match the relative phases of the each hologram, unfortunately the enhancement of the resolution in the reconstructed object wave is negligible.
Viewing sub-regions which are working as basic image cells in the viewing zone of electro-holographic display based on
a stereo hologram are defined and the composition of images viewed at these regions are found. Each of these subregions
can work as a basic image cell which provides a distinct image different from those of other sub-regions, though
each of them can be divided into pieces of different compositions. When the numbers of pixels in each pixel cell and
pixel cells in a panel, increase, most of these pieces will disappear because their sizes are smaller than the blurring caused
by diffraction effect. Furthermore, more than two sub-regions will within the pupil size of viewers’ each eye. This might
induce a continuous parallax to viewers to create the supermultiview condition.
Even though digital holography was invented a number of decades ago, many people think there are still several
problems for holographic display to be commercialized. The main problem results from the small space-bandwidth
product of the spatial light modulators, since the holographic displays generally need enormous data capacity in
comparison with other traditional display. But, if we define our target as a holographic display for a single user, it is
feasible to build a holographic display with a reasonable screen size. In this paper, we introduce two kinds of digital
holographic displays recently studied.
The DARPA MOSAIC program applies multiscale optical design (shared objective lens and parallel array of microcameras)
to the acquisition of high pixel count images. Interestingly, these images present as many challenges
as opportunities. The imagery is acquired over many slightly overlapping fields with diverse focal, exposure and
temporal parameters. Estimation of a consensus image, display of imagery at human-comprehensible resolutions,
automated anomaly detection to guide viewer attention, and power management in a distributed electronic environment
are just a few of the novel challenges that arise. This talk describes some of these challenges and
presents progress to date.
Three-dimensional (3D) display has attracted considerable attention in recent years because of development in display
technology. Various methods for realizing 3D display have been proposed; among them, multi-view display could be
practical to implement before aspiring 3D display. The term of multi-view display system based on autostereoscopic
display has the meaning of view splitting; the view images are projected to the pre-defined positions from the same
display device. Therefore the users located at the correct positions can see corresponding images. Although the multi-view
display technique has been studied by many research groups, the fundamental importance of the sound with display
has not, so far, been noticed nor has been examined in detail. The purpose of this paper is to realize a multi-view display
system with directional sound, which allows the individual observer to experience directional sound in multi-view
display environment. The explanation and experimental results of the proposed system are provided.
In this paper, we discussed the method for optimization of
fiber-optic surface plasmon resonance (SPR) sensor and the
effect of optimized parameters by analysis of the transmission spectrum of waveguide-based SPR sensors. Because of
their high sensitivity, the SPR sensors can be used in a lot of chemical and biological studies, but it is difficult to perform
a theoretical analysis of an SPR fiber sensor. Therefore, for the design and analysis of the sensor responses, a fiber-optic
SPR sensor can be optimized numerically by adjusting parameters such as the thickness of metal layers and the grating
period, etc. We simulated and optimized parameters by employing the method of the rigorous coupled wave analysis and
the genetic algorithm. Also we discussed the methods for improving sensing capability.
In this paper, a high-definition integral floating display is implemented. Integral floating display is composed of an
integral imaging system and a floating lens. The integral imaging system consists of a two-dimensional (2D) display and
a lens array. In this paper, we substituted multiple spatial light modulators (SLMs) for a 2D display to acquire higher definition. Unlike conventional integral floating display, there is space between displaying regions of SLMs. Therefore, SLMs should be carefully aligned to provide continuous viewing region and seamless image. The implementation of the system is explained and three-dimensional (3D) image displayed by the system is represented.
We present a variable-focusing surface plasmon dielectric lens using the air-gap modulation. Based on the modal
analysis of the planar slab waveguide consisting of the dielectric slab over the metal substrate, we examine the
transmission characteristics of the single air-metal surface plasmon polariton (SPP) mode through the planar slab
waveguide. Our simulation results reveal that the 2π modulation of the phase of the transmitted SPP mode can be
realized. By using the lens with parabolic shape, the SPP mode converges and focuses to one point. It is shown that the
dynamic modulation of the air-gap width gives rise to the dynamic change in the focal length.
The phase-shifting errors mainly result from the imprecise movement of phase-shifter and the vibration of system. These
geometric errors are classified into the positional inaccuracy and tilting of optics. And they can be represented as the
longitudinal and transversal displacements of interferograms on the hologram plane. In this paper, we propose adaptive
phase-shifting digital holography compensating these two displacements and this proposed method is based on genetic
algorithm for finding optimized variables corresponding to real system. By computer simulations, the deteriorations in
reconstruction image are modeled and the chromosomes are constituted. We find the fittest solution compensating the
longitudinal and transversal displacements experimentally and present the reconstruction images by encoding the
resultant holograms on a spatial light modulator.
We propose an optical implementation of iterative Fourier transform algorithm using a spatial light modulator and phaseshifting
digital holography technique. It is shown that the optically implemented iterative Fourier transform system can
improve quality of target diffraction images in real time by the same way the numerical iterative Fourier transform algorithm
does in the numerical simulation. In the proposed implementation, the wave front of diffraction field is directly measured by
the phase shifting digital holography technique and the phase modulation of light field is performed by a phase-type spatial
light modulator. The feasibility and more general applicability of the proposed implementation of the iterative Fourier
transform algorithm for digital holography techniques are discussed.
In this paper, our recent works on dynamic light field synthesis engineering using spatial light modulators are presented. The combination of optimization techniques in theoretical design methods and experimental methods with spatial light modulators is a main motivation of our study. The firstly discussed system is the genetic feedback tuning loop for the optimal system tuning and aberration compensation. The genetic algorithm is embedded into the light field synthesis system and the iterative system tuning procedure is devised for optimizing and tuning the real system. The secondly introduced topic is the experimental implementation of the iterative fractional Fourier transform algorithm for designing the phase profiles of phase holograms. The ath fractional Fourier transform and its inverse transform is optically implemented. The light field synthesis systems with optically implemented iterative fractional Fourier transform are proposed. In the proposed systems, using the phase-shifting digital holography technique, the phase profile of real light field is measured, and with phase spatial light modulator the light field is generated. It is shown that the diffraction image measured at each iteration step evolves to the optimal goal. Some experimental results validating the proposed schemes are presented.
For large viewing-angle enhancement in three-dimensional (3D) display, a dynamic computer-generated holographic display system combined with integral imaging is proposed and implemented using a single phase-type spatial light modulator and an elemental lens array. For viewing-angle enhanced colorized 3D integral image display the computer-generated holograms have been synthesized and scaled for minimizing the color dispersion error in the hologram plane. Using the integral imaging and synthetic phase holography, we can get 3D images with full parallax and continuously varying viewing-angle range of +/-6 degree. Finally we show some experimental results that verify our concept.
Optical waveguiding using nano-strip embedded photonic crystal (NEPC) is proposed and analyzed with theoretical modeling and numerical analysis. The underlying physical origin of the wave propagation is elucidated to be a photonic version of orbital hybridization, i.e., multiple period s- and p-state cavity mode hybridization. Theoretical description of the phenomena is made by using ab initio tight binding approach in comparison with plane wave expansion method (PWE). This extends understanding of the wave propagation in the photonic crystal (PC) waveguide made by one-dimensional defect. As a practical application of the NEPC and its waveguiding characteristics, low group velocity and low dispersion propagation in the NEPC is explained in relation to other waveguides and PC slab waveguide structures. The NEPC case of low group velocity and low dispersion can provide very broad bandwidth for the wave guiding compared to the other waveguides. By exploiting the hybridization in the NEPC, a useful understanding and modeling for such unique wave propagation can be made, which is expected to be applicable for the development of a new design theory and optical structure for novel dispersion devices.
Several issues on the optimal diffractive beam shaping with a dynamic phase spatial light modulator are addressed. As for design theories, the optimal design method of the phase holograms considering the functional relationship between phase and amplitude modulations of the phase spatial light modulator is described. To achieve the optimal trade-off between diffraction efficiency and smoothness of the obtained diffraction images, the iterative Fourier transform algorithm with adaptive regularization parameter distribution is devised. Regarding experimental issues, we propose a beam shaping system configuration with the genetic feedback tuning loop in which the simplified genetic algorithm is employed to finely compensate the internal aberration of the optics in the beam shaping system. It is shown that the real-time tuning of the phase holograms for accurate beam shaping is possible using the dynamic behavior of the spatial light modulator.