Depth-added computer-generated holographic stereogram (DA-CGHS) is applied to generate a high-definition (HD) CGH. We have developed a new look-up table (LUT) based technique to compute the diffraction field. In the optimized circumstance, the computing speed of LUT can be twenty-six times faster than that of pixelwise computing. To display the HD-CGH, we have built a hologram printer to fabricate the HD-CGH on a silver halide holographic plate. The size of the printed hologram is about 5 cm square, and the pixel pitch is 0.832 micrometer. Therefore, a hologram with 6×10<sup>4</sup> by 6×10<sup>4</sup> pixels can be fabricated by our printer.
Computational ghost imaging (CGI) is a single-pixel imaging technique by illuminating the object with structuredlight. The image of the object can be retrieved by the correlation of numerous power measurements and the corresponding illumination patterns. Although CGI owns many unique merits, its shortcoming is apparent. The demand of numerous measurements is time-consuming, and the reconstructed image always suffers from speckle-like noise. In this paper we proposed to use complementary illumination patterns to perform CGI. In addition, we applied Gerchberg-Saxton-like algorithm to optimize the reconstructed image. By this way, the time of reconstruction is reduced. In addition, the signalto-noise ratio (SNR) significantly increases in comparison with that by using complete random illumination patterns.
Optical scanning holography (OSH) is a scanning-type digital holographic technique. In OSH, a heterodyne interference pattern is generated to raster scan the object. OSH can be operated in the incoherent mode and thus is able to record a fluorescence hologram. In addition, resolution of the OSH is proportional to the density of the interference pattern. Here we use a high-NA microscope objective to generate a dynamic Fresnel zone plate to record a hologram of micro-specimen. The achieved transverse resolution and longitudinal resolution are 0.78μm and 3.1μm, respectively.
Optical Scanning Holography (OSH) is a scanning-type digital holographic recording technique. One of OSH’s most important properties is that the OSH can record an incoherent hologram, which is free of speckle and thus is suitable for the applications of holographic display. The recording time of a scanning hologram is proportional to the sampling resolution. Hence the viewing angle as well as the resolution of a scanning hologram is limited for avoid too long recording. As a result, the viewing angle is not large enough for optical display. To solve this problem, we recorded two scanning holograms at different viewing angles. The two holograms are synthesized to a single stereoscopic hologram with two main viewing angles. In displaying, two views at the two main viewing angles are reconstructed. Because both views contain full-depth-resolved 3D scenes, the problem of accommodation conflict in conventional stereogram is avoided.
Owing to the resolution of the recording device, digital holograms are generally fabricated with in-line configurations. However, holograms obtained in this way are plagued by the annoying problems of zero-order noise and the twin images. Here, we investigate methods to suppress the zero-order noise. We compare the suppression ability of each method with different ratio factors. The ratio factor is defined as the ratio between the reference light amplitude and the object light amplitude. We also introduce a new parameter, the normalized correlation peak value, to evaluate the fidelities of holograms obtained under various ratio factors. Results show that the suppression abilities and the hologram fidelities strongly depend on the ratio factor.
We recorded a hologram in a photorefractive LiNbO3:Fe crystal with a two-color recording technique in transmission geometry. The holographic recording involves a light with wavelength 633 nm for interference, and a light with wavelength 532 nm for exciting. The short wavelength light excites more charges so that the holographic recording is affected, and the storage capacity (M-number) and the sensitivity vary accordingly. We found that the optimized intensity ratio of the interference lights and the exciting light is between 50 and 60. In the optimized conditions, the M number and the sensitivity are enhanced by 43 and 35%, respectively. Because the crystal we used is a typical iron-doped LiNbO3 crystal and the short wavelength exciting light source is inexpensive now, the proposed method is easy to be achieved in most holographic systems.
The feasibility of conventional polarization-selective substrate-mode holograms is usually limited by the finite refractive index modulation strength. Therefore, in this study, a novel design of polarization selective element with a large diffraction angle is proposed based on the coupled-wave theory. The polarization selective element for 632.8nm is fabricated with VRP-M silver-halide recording material. The diffraction efficiencies of s- and p- components are 83% and 5%, and the calculated extinction ratios are 5.58 and 275, respectively. Polarization selective elements fabricated by the proposed method have all the merits of conventional substrate-mode hologram but not limited by the finite refractive index modulation of common recording materials.
In angle multiplexing, the angle between the reference light and the object light is slightly changed in different
recordings. In reconstruction, only the reference beam with an accurate angular position can retrieve the corresponding
object beam due to the characteristics of Bragg condition. Accordingly, a suitable angular separation of the reference
beam should be decided for angle multiplexing. A larger angular separation will decrease the storage density, and a
smaller angular separation will increase the cross-talk noise in small bi-angles. In general speaking, only one condition
of full angle of lights is involved to calculate the angular separation with coupled-mode theory or with experiment. Thus
the angular separation is fixed in the whole procedure of angle multiplexing. As a result, the angular separations of most
multiplexed holograms are either larger or smaller. Only one hologram is multiplexed in the critical angular condition. In
this paper, angle multiplexing with different angular separations were performed to quantitatively demonstrate the effect.
The possible method to deal with the issue was also proposed.
We proposed a novel optical geometry for holographic data storage in which a phase input pattern was involved. The
input phase pattern was derived from an amplitude pattern by iterative Fourier transform algorithm. Two important
parameters of reconstructed images, diffraction efficiency and image quality, were discussed and measured. Our
geometry exhibited uniform holographic recording as well as uniform erasing. Moreover, the loss of light due to
absorption in the input pattern was minimized. The little light loss also ensured a higher diffraction efficiency of the
In this paper we propose a novel method to perform multiplexing. In our setup, we use only one beam of light to illuminate and pass through the object pattern and to image it into a photorefractive lithium niobate crystal. Image information is recorded in the crystal in the form of gratings due to fanning effect. We can read the image information using another collimated or white-light reading beam. To record multi-images in the same crystal, the object beam of each recording should be tilted to the last object beam for avoiding crosstalk. As a result, we can record multi-images in a lithium niobate crystal, and read them separately without crosstalk.
Random-phase-multiplexing storage using photorefractive crystals is one of the most important topics in the field of photorefractive optics. To achieve random phase recording, we can use a diffuser to encrypt the reference light in a holographic recording setup. To decrypt the recorded pattern, the same diffuser used in encryption must be used in the reconstruction light, and it must be set in the original orientation. In this way, a number of 2-D patterns can be stored in a single photorefractive crystal with a single diffuser set at different orientations for different patterns. A merit in this recording method is that the encryption is virtually not possible to be decrypted if the original diffuser for encrypting is not available. In this paper, we proposed a way to decrypt the encrypted information in a photorefractive lithium niobate crystal without the possession of the original diffuser. In this method, we suppose somehow we know one of the patterns stored in the crystal, and then we retrieve the original diffuser with this pattern. And ultimately all the other patterns stored in the crystal are decrypted and retrieved with this retrieved diffuser.
We present a setup that transfers 2-D images between two ports. By using a photorefractive LiNbO3 crystal and a BaTiO3 crystal, we are able to transfer images either way without making any change in the experimental layout. The resolutions of the device are 10.1 and 6.4 lp/mm for the two transferring directions, respectively.
We propose and demonstrate a new way to image a coherent pattern through a thick dynamic phase distorting medium using a photorefractive LiNbO<sub>3</sub> crystal. The method involves only one beam of light- the object light. Making use of photorefractive fanning effect, gratings are formed in the LiNbO<sub>3</sub> crystal through the interference between the fanning light and the image light. In this way, the undistorted image is recorded in the crystal. The intensity distribution of the image can then be reconstructed at any time later. An undistorted image can be obtained under the condition that the period of the fluctuation time in the medium is much shorter than the response time of the crystal. Since this method uses only one beam of light, its layout is simpler and thus it avoids some aberrations due to the constraint in the layout in other methods, such as the aberration due to oblique incident light.
We demonstrate an optical setup being capable of transferring a two-dimensional picture in either way from one plane to another. The transferring takes place only when the receiving port sends a requesting signal. This setup consists of a LiNbO<sub>3</sub> crystal for the purpose of four-wave mixing, and a BaTiO<sub>3</sub> crystal for the purpose of producing self pumped phase conjugate wave. The characteristic of this setup is that it does not require any change in the experimental arrangement when the transferring direction of the picture is reversed. Finally, this setup can perform not only static but also dynamic image transferring.
Photorefractive phase conjugators are well known working with extraordinarily polarized light waves with respect to the crystal forming the conjugator. We demonstrate here experimentally a photorefractive phase conjugator, which works with an incident light beam predominantly polarized in ordinary state. The conjugate waves are, however, extraordinarily polarized. Good quality conjugate waves were still observed even when the intensity ratio f the o- component to the e-component in the incident beam is more than one thousand.