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, 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.
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.
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.