Rui Shogenji

Reconstruction of a high-resolution image on a compound-eye image-capturing system.

The authors have proposed an architecture for a compact image-capturing system called TOMBO (thin observation module by bound optics), which uses compound-eye imaging for a compact hardware configuration [Appl. Opt. 40, 1806 (2001)]. The captured compound image is decomposed into a set of unit images, then the pixels in the unit images are processed with digital processing to retrieve the target image. A new method for high-resolution image reconstruction, called a pixel rearrange method, is proposed. The relation between the target object and the captured signals is estimated and utilized to rearrange the original pixel information. Experimental results show the effectiveness of the proposed method. In the experimental TOMBO system, the resolution obtained is four times higher than that of the unit image that did not undergo reconstruction processing.

Image reconstruction for thin observation module by bound optics by using the iterative backprojection method

A method for reconstructing high-spatial-resolution images in an imaging system known as thin observation module by bound optics (TOMBO) is reported. We investigate a novel procedure combining a pixel-rearrangement method and iterative backprojection (IBP). Pixel rearrangement has been used until now in TOMBO, and IBP is a digital superresolution technique. We verify the effectiveness of the combined procedure with simulated and experimental results.

Multispectral imaging using compact compound optics

A very thin image capturing system called TOMBO (thin observation module by bound optics) is developed with compound-eye imaging and digital post-processing. As an application of TOMBO, a multispectral imaging system is proposed. With a specific arrangement of the optical system, spatial points can be observed by multiple photodetectors simultaneously. A filter array inserted in front of the image sensor enables observation of the spectrum of the target. The captured image is reconstructed by a modified pixel rearranging method extended to treat multi-channel spectral data, in which pixels in the captured image are geometrically rearranged onto a multi-channel virtual image plane. Experimental results of the image reconstruction show the effectiveness of the proposed system.

Color imaging with an integrated compound imaging system

Color-imaging methods with an integrated compound imaging system called TOMBO (Thin observation module by bound optics) are presented. The TOMBO is a compact optoelectronic imaging system for image capturing based on compound-eye imaging and post digital processing. First, a general description of the TOMBO system is given, and then two configurations for color imaging are described. Experimental comparison of these configurations is made by use of an experimental TOMBO system. The characteristics and the performance on the proposed methods are briefly discussed.

Bimodal fingerprint capturing system based on compound-eye imaging module

A compact imaging system called TOMBO (Thin Observation Module by Bound Optics) is proposed in which a microlens array is used for thin hardware configuration. This paper describes a fingerprint-capturing module as an application of the TOMBO. Experimental results by the TOMBO prototype system are shown to clarify the applicability of the TOMBO to the fingerprint capturing. Different types of biometrics, i.e., fingerprint and face images, are captured by the same hardware, which shows the extendability of the system for multimodal identification.

Control of Spatio-Temporal Dynamics of Broad-Area Semiconductor Lasers by Strong Optical Injection

Control of spatio-temporal dynamics in broad-area semiconductor lasers is investigated numerically under the condition of strong optical injection. Irregular filamentation of the laser emissions are considerably suppressed as the optical injection ratio is increased. At high optical injections ratios, the laser oscillates with a regular structure in the time-resolved near-field pattern. At the same time, the time-averaged near-field pattern at the exit facet exhibits a good top-hat distribution.

Chaotic dynamics in semiconductor lasers subjected to polarization-rotated optical feedback

In-phase or synchronized oscillations between transverse electric (TE) and transverse magnetic (TM) modes with a loop delay are common phenomena in the numerical studies of semiconductor lasers subjected to polarization-rotated optical feedback. However, we experimentally find antiphase oscillations of laser output powers with zero time lag under appropriate conditions of orthogonal polarization optical feedback. Antiphase oscillations are well reproduced by the numerical simulations for the experimental model taking into account the frequency detuning between the two modes.

Dynamics of Broad-Area Semiconductor Lasers With Short Optical Feedback

The dynamics of filamentations in broad-area semiconductor lasers with short optical feedback were numerically studied. Regular pulse packages similar to those observed in narrow-stripe edge-emitting semiconductor lasers were found as the feedback reflectivity is increased. However, the regular pulse packages consisted of a periodic envelope of the external cavity frequency and fine pulse trains of periodic filaments, which is different from the regular pulse packages observed in narrow-stripe edge-emitting semiconductor lasers. From the analysis for spatio-temporal near-field patterns, we found periodic undulations of the spatial and temporal filament sizes as the external mirror reflectivity was changed. We also investigated filtered optical feedback, where a part of the emitted beam is fed back into the laser cavity. The time-averaged near-field pattern was found to have a strong dependence on the feedback level in the case of spatial filtered optical feedback.

Thin observation module by bound optics (TOMBO) with color filters

This paper demonstrates, for the first time, TOMBO color imaging system that employs color-splitting filters on each lens. A red, green, or blue color filter is allocated to each microlens instead of each pixel in conventional single-sensor color imaging system. Thus the microlens array here also makes up a color filter array of Bayer geometry. For the imaging device, a CMOS image sensor with 1040 x 960 pixels whose size is 6.25 um square was used. 8 x 8 microlens array with 750 um pitch was employed as a taking lens. Excellent color images were obtained by rearrangement, interpolation, and postdigital processing.

Variable field-of-view visible and near-infrared polarization compound-eye endoscope

A multi-functional compound-eye endoscope enabling variable field-of-view and polarization imaging as well as extremely deep focus is presented, which is based on a compact compound-eye camera called TOMBO (thin observation module by bound optics). Fixed and movable mirrors are introduced to control the field of view. Metal-wire-grid polarizer thin film applicable to both of visible and near-infrared lights is attached to the lenses in TOMBO and light sources. Control of the field-of-view, polarization and wavelength of the illumination realizes several observation modes such as three-dimensional shape measurement, wide field-of-view, and close-up observation of the superficial tissues and structures beneath the skin.