Byoungho Lee

We propose an enhanced three-dimensional (3D) integral imaging system using multiple display devices. Experimental results with double devices prove the improvement in the image depth for a given image quality. We present experiments on an enhanced 3D integral imaging system using double display devices, in which two 3D subimages that cover different depth ranges are separately generated in each device, and then they are combined with a beam splitter to reconstruct the whole 3D image with an enhanced depth of view. In a similar manner, the double-device system can also be used to obtain a wider viewing angle by combining two images with different viewing angle ranges. We discuss the possibility of 3D integral imaging systems using multiple display devices as extensions of the system with double display devices.

An etched long-period fiber grating with an outer liquid-crystal cladding capable of polarization-isolated electrical modulation, is described. A 5-dB transmission-dip modulation with 4-dB polarization isolation can be obtained at 225 V. The reduction in fiber diameter by a chemical etching process leads to an improvement in the long-range ordering of liquid-crystal molecules and a reduction in the controlling voltage. In addition, the experimental results are supported by numerical simulation. © 2003 Society of Photo-Optical Instrumentation Engineers.

Integral imaging (II) is one of the promising techniques in the field of autostereoscopic three-dimensional display. Despite of its many advantages, the narrow viewing angle has been a drawback. We propose a technique that enhances the viewing angle of II by resizing the elemental images taken by the pickup process and switching the elemental lenses in the display process. We explain the principle of the proposed technique, analyze the effect on the resolution of the integrated image, and show the experimental results.

Viewing-angle-enhanced integral 3-D imaging using double display devices with masks is proposed. In this approach, the total system consists of two integral imaging systems with masks, and the integrated images from each system are combined spatially. By using double display devices with masks instead of time-multiplexed images, this scheme does not require the after-image effect or mechanical moving parts. The viewing area where an observer can see the 3-D image without elemental image overlapping is remarkably enhanced by this method. © 2002 Society of Photo-Optical Instrumentation Engineers.

By adoption of double-device systems, integral imaging can be enhanced in image depth, viewing angle, or image size. Theoretical analyses are done for the double-image-plane integral imaging systems. Both ray optics analysis and wave optics analysis confirm that the double-device integral imaging systems can pick up and display images at two separate image planes. The analysis results are also valuable in the understanding of the conventional integral imaging systems for image positions off the central depth plane.

We propose a way of single-beam photorefractive recording of subwavelength-size binary optical data using near-field scanning optical microscopy (NSOM). Data are recorded in the form of pure (without any change in the topography of the surface) refractive index changes induced near the surface of photorefractive crystal by the light intensity distribution from the subwavelength-size fiber tip of the NSOM. This change in the refractive index can modify the transmission characteristics of the NSOM. Therefore, the characteristics of the reading beam depend on whether the light from the tapered fiber tip was previously exposed (recorded) or not, and thus can be regarded as on-off (binary) data. © 2002 Society of Photo-Optical Instrumentation Engineers.

The characteristics of the use of a hollow-core splice scheme for macrobend measurements are discussed both theoretically and experimentally. A perturbation theory for the modes of a bent hollow-core fiber and its loss characterization are developed so as to better understand the characteristics of the scheme. The maximal detection range of fabricated sensors with the proposed scheme is experimentally determined to be as large as a few hundred millimeters relative to the radius of curvature. In addition, the numerical estimation of the loss characteristics using the scheme shows modal trends which are in good agreement with experimental data. © 2002 Society of Photo-Optical Instrumentation Engineers.

We investigate a general scheme of frequency-hopping optical orthogonal codes with a specified distance between adjacent frequency symbols and propose a novel code that allows time blanks between adjacent frequency symbols in code sequences. A time blank represents the absence of frequency symbols in code sequences and makes no interference with frequency components. The insertion of time-blank patterns can provide ample scope to generate much more code sequences than the conventional codes lacking in time-blank patterns, and we show this by constructing an algorithm to generate the proposed code. The performance analysis demonstrates that its performance is superior to that of the conventional codes in terms of the bit error rate. We also derive the upper bound on the proposed code set.

We demonstrate a multimode-fiber bundle reference scheme in a photorefractive volume hologram and discuss its angular/spatial selectivity both experimentally and theoretically. We measure the angular/spatial selectivity, changing distances between the photorefractive crystal and the output facet of the multimode-fiber bundle. The distance variation leads to a beam-size change in the reference beam, however, the object-beam size was fixed in all cases. The dependence of the angular/spatial selectivity for random-pattern (RP) referencing on a hologram dimension was examined and the characteristics compared with those derived from Gaussian referencing. Experimental results show that the RP referencing makes little contribution to the enhancement in angular selectivity, even though it leads to a considerable enhancement in spatial selectivity. The angular selectivity is mainly dependent on the dimension of a volume hologram, even with RP referencing. It is also noteworthy that the use of an RP beam can cause some high-frequency noise in the angular-multiplexing regime, which should be avoided in a hologram memory system. Nonetheless, the spatial selectivity of the RP referencing shows nearly no dependence on hologram dimension, and is mainly dependent on the transversal speckle size of the random-pattern beam. These characteristics can also be verified by the numerical results presented here, which are in good agreement with the experimental results.

In spite of the many advantages of integral imaging, its narrow viewing angle has been a disadvantage. We propose a method to enhance the viewing angle of integral imaging by opening and shutting each lens in the array (i.e., the elemental lenses) sequentially. We prove our idea by using a mask that has a pattern of an on–off vertical array of apertures. Moving the mask prevents the aliasing of a neighboring lens. Thus image overlap or image flipping is reduced and the viewing angle of the system is increased.