Keiichiro Kagawa

Irregular Lens Arrangement Design to Improve Imaging Performance of Compound-Eye Imaging Systems

Typical compound-eye imaging systems consist of multiple lenslets arranged regularly because of the advantages of these arrangements, such as simplicity in design, fabrication, and data processing. Such a regular arrangement, however, exhibits strong fluctuation of the imaging performance over the object distance. To solve this problem, irregularity is introduced, and this approach is applied to a compound-eye imaging system called thin observation module by bound optics (TOMBO). An efficient design method for improving the imaging performance is presented. Simulation results, including the peak signal-to-noise ratio of the super-resolved images, confirm the effectiveness of the proposed method.

A compound-eye imaging system with irregular lens-array arrangement

TOMBO (Thin Observation Module by Bound Optics) is a compound-eye imaging system inspired by a visual organ of insects. TOMBO has various advantages over conventional imaging systems. However, to demonstrate applicability of TOMBO as an imaging system, high-resolution imaging is significant and unavoidable. In this study, a TOMBO system with irregular lens-array arrangement is proposed and a high-resolution imaging method integrating a super-resolution process with depth acquisition of three-dimensional objects is presented. The proposed TOMBO system improves image resolution for far objects, because it can alleviate degeneration of the sampling points on the far objects caused by the regular arrangement of the lens array in the conventional TOMBO system. An experimental TOMBO has 1.3 mm focal length of lens, 0.5 mm pitch of lenses, 0.5 mm diameter of aperture, 3 × 3 of units, 160 × 160 pixels per unit, and 3.125 μm pitch of pixel. The target planar object is located at 5 m from the TOMBO system. The simulation result shows that the coverage ratio of the sampling points, PSNR of the super-resolved image, and the error of the depth estimation for the object are improved by 50%, 3 dB, and 56%, respectively. The experimental result shows that the error of depth estimation for the planar object located at 3.2 m is 18% and that the contrast of 123 lp/mm at the center of a unit is improved by 0.38 with the super-resolution processing.

An Active Intraoral Shape Measurement Scheme Using a Compact Compound-Eye Camera with Integrated Pattern Projectors

We propose an active intraoral shape measurement scheme to realize a compact intraoral diagnostic system for measuring the three-dimensional shapes of gums and teeth. To measure intraoral surfaces with little texture, compact pattern projectors based on diffractive optical elements are integrated in lens gaps of a compact compound-eye camera called a thin observation module by bound optics (TOMBO). The three-dimensional shape is reproduced on the basis of triangulation using the amount of pattern distortion. A scaled-up prototype system is constructed to verify the measurement scheme using the TOMBO camera and a spatial light modulator. The prototype system demonstrates an rms distance accuracy of 0.46 mm. A temporal change of the shape is quantitatively evaluated with a reference surface based on teeth positions.

Discrete correlation processor as a building core of a digital optical computing system : architecture and optoelectronic embodiment

In this paper we present a general-purpose discrete correlation nprocessor (DCP) expected to be the building core block of a digital noptical computing system. The DCP-1 is embodied by noptoelectronic devices such as a VCSEL and a complementary metal-oxide nsilicon photodetector. The application targets of the DCP-1 are noptical interconnection and various types of digital optical ncomputing. It is expected that digital optical computing techniques ncoupled with the optoelectronic technology will provide large ncapability and flexibility in information processing. Introduction nof a processing scheme of optical array logic enlarges the applicable nfield of the DCP-1 as well as its processing capability. With the nexperimental DCP-1 a bit error rate smaller than 10-9 was nobtained for A · B operation nunder a 500-kHz clock rate.

Dynamic Reconfiguration of Differential Pixel Output for CMOS Imager Dedicated to WDM-SDM Indoor Optical Wireless LAN

A dedicated complementary metal-oxide-semiconductor (CMOS) imager with parallel photoreceivers has been deployed for new indoor wireless local area network systems where images and communications are mixed to offer location awareness and an extended data transfer bandwidth with wavelength- and space-division multiplexing for the downlink and uplink, respectively. To realize data acquisition while capturing images, dynamic reconfiguration of differential pixel output with a small area overhead is proposed for suppressing signal contamination at the sensitive photoreceiver circuitry by common mode noise from the image readout digital circuitry. A prototype CMOS imager with 64 times 64 pixels and four parallel photoreceiver channels was fabricated in a standard 0.35-mum CMOS process, and concurrent scene image capturing and multipoint data acquisition at 10-Mb/s/channel were demonstrated. The measured signal-to-crosstalk ratio was around 18 dB.

Optoelectronic parallel-matching architecture: architecture description, performance estimation, and prototype demonstration

We propose an optoelectronic parallel-matching architecture (PMA) that provides powerful processing capabilities in global processing compared with conventional parallel-computing architectures. The PMA is composed of a global processor called a parallel-matching (PM) module and multiple processing elements (PEs). The PM module is implemented by a large-fan-out free-space optical interconnection and a PM smart-pixel array (PM-SPA). In the proposed architecture, by means of the PM module each PE can monitor the other PEs by use of several kinds of global data matching as well as interprocessor communication. Theoretical evaluation of the performance shows that the proposed PMA provides tremendous improvement in global processing. A prototype demonstrator of the PM module is constructed on the basis of state-of-the-art optoelectronic devices and a diffractive optical element. The prototype is assumed for use in a multiple-processor system composed of 4 x 4 PEs that are completely connected through bit-serial optical communication channels. The PM-SPA is emulated by a complex programmable device and a complementary metal-oxide semiconductor photodetector array. On the prototype demonstrator the fundamental operations of the PM module were verified at 15 MHz.

A compact shape-measurement module based on a thin compound-eye camera with multiwavelength diffractive pattern projection for intraoral diagnosis

We have proposed a compact three-dimensional shape-measurement system for intraoral diagnosis, in which multiwavelength pattern projectors based on diffractive optical elements (DOEs) are integrated in the lens gaps of a compound-eye camera. We have built a prototype module with blue and green pattern projectors in both sides of the compound-eye camera to increase in-plane spatial resolution. With the two projectors, the stripe pitch was reduced to 0.73 mm in average from about 1.4 mm for one wavelength. Root-mean-square (rms) error of the measured depth map of a plane board was 0.27 mm at the distance of 40 mm. The rms errors for the measured results of the gums and teeth of a plaster figure and an examinee were 0.37 and 0.40 mm, respectively.

High-speed multispectral three-dimensional imaging with a compound-eye camera TOMBO

We propose a high-speed multispectral three-dimensional imaging system based on a compact and thin compound-eye camera called TOMBO. Wavelengths and times are assigned to the lenses in TOMBO. The time delays are introduced by the rolling shutter of CMOS image sensors, and wavelength decomposition is realized by attaching several kinds of wavelength filters to the lenses. A depth map is reproduced based on disparities in the unit images captured at the same timing. In reproducing the depth map, sum of sum of absolute differences (SSAD) is evaluated after average equalization to compare images for different wavelengths. A prototype of TOMBO is built with a SXGA monochrome CMOS image sensor with a rolling shutter, optical crosstalk barriers, a commercial 5x5-element microlens array, and commercial gelatin color filters. Enhancement of the frame rate and reproduction of a depth map and a 5-band deep-focus image are demonstrated.

A Computational Compound Imaging System Based on Irregular Array Optics

A computational imaging system using compound-eye optics with irregularity can improve imaging performance especially for long distance objects. The system characteristics are analyzed and an efficient algorithm is implemented using a graphic processing unit.

Free-space optical data transmission using wavelength-division-multiplexing with a dedicated CMOS image sensor for indoor optical wireless LAN

We have proposed a space- and wavelength-division-multiplexing (WDM) indoor optical wireless LAN system based on a custom CMOS image sensor to realize a compact, high-speed, and intelligent nodes and hub. The CMOS image sensor can detect multiple fast optical data concurrently as well as captures ordinary images from which positions of communication nodes or the hub is obtained. In this paper, with the CMOS image sensor, we demonstrate an application of WDM technique to downlinks. We fabricated a 64x64-pixel custom CMOS image sensor with 4-channel concurrent data acquisition function. Experimental results showed that the CMOS sensor received 10Mbps×3ch WDM data while capturing ordinary images.