Kiyotaka Sasagawa

Ultrafast all-optical switching by cross-absorption modulation in silicon wire waveguides

We describe the use of two-photon absorption in submicron silicon wire waveguides for all-optical switching by cross-absorption modulation. Optical pulses of 3.2 ps were successfully converted from high power pump to low power continuous-wave signal with a fast recovery time. High speed operation was based on the induced optical absorption from non-degenerate two-photon absorption inside the waveguides.

Implantable CMOS Biomedical Devices

The results of recent research on our implantable CMOS biomedical devices are reviewed. Topics include retinal prosthesis devices and deep-brain implantation devices for small animals. Fundamental device structures and characteristics as well as in vivo experiments are presented.

CMOS-Based Multichip Networked Flexible Retinal Stimulator Designed for Image-Based Retinal Prosthesis

We propose and characterize a CMOS LSI-based neural stimulator for retinal prosthesis technology. The stimulator is based upon a multichip architecture in which small-sized CMOS stimulators named ldquounit chipsrdquo are organized on a flexible substrate. We designed a unit chip with an on-chip stimulator and light-sensing circuitry. We verified that all the functions implemented on the unit chip worked correctly and that an organized unit chip can be used as a retinal stimulator with multisite image-based patterned stimulation. We also demonstrated light-controlled retinal stimulation for the first time in an in vivo animal experiment on a rabbits retina.

Live Electrooptic Imaging System Based on Ultraparallel Photonic Heterodyne for Microwave Near-Fields

We report on 100 x 100 pixel live electrooptic imaging (LEI), which is real-time imaging of electrical signals on a microwave circuit. The circuits electric near-fields can be depicted in real time on a display screen at video frame rates as high as 30 frames/s. This system is based on photonics technology in which electric near-fields are applied to an electrooptic crystal plate and a sensing light beam is modulated there. The frequency of modulation is down-converted by using a photonic heterodyne of large-scale parallelism, and the spatial pattern of the electrooptic modulation is detected with a high-speed image sensor. A digital signal processor is used to extract the frequency component of interest and to animate it on the display screen. As examples, we present live pictures of electric field pattern data acquired by the LEI system in a real-time manner.

Highly Efficient Third Harmonic Generation in a Periodically Poled MgO:LiNbO3 Disk Resonator

High-efficiency generation of the third harmonic of 1.55 µm light is observed in a periodically poled MgO-doped LiNbO3 disk resonator. The second harmonic is simultaneously generated. The blue-green emission arises from cascaded parametric processes of second-harmonic and sum-frequency generation by whispering gallery modes. An external conversion efficiency of 1.5%/W2 is obtained.

Real-time monitoring system of RF near-field distribution images on the basis of 64-channel parallel electro-optic data acquisition

Described in this paper is a system for the real-time image monitoring of electromagnetic near-field distributions over devices and circuits at a specific radio frequency (RF), which is the first to the best of our knowledge. It is based on a 64-channel parallel electro-optic heterodyne detection scheme, in which arrays of photodiodes and mixers allow simultaneous acquisition of 8 × 8pixel data. Its highest frame rate of 10Hz enables even a motion picture display of RF near-field images. It has been applied to a patch antenna and a moving RF emitter for performance demonstration.

Development of Complementary Metal Oxide Semiconductor Imaging Devices for Detecting Green Fluorescent Protein in the Deep Brain of a Freely Moving Mouse

We have developed to observe neural activities in the deep brain of a freely moving mouse with green fluorescent protein (GFP). We implanted a dedicated complementary metal oxide semiconductor (CMOS) imaging device into the hippocampus or the basal ganglion of an anesthetized mouse to confirm the effectiveness of the CMOS imaging device for the detection of GFP generated in the deep brain of the anesthetized mouse. Moreover, we conducted an experiment to demonstrate the capability of the CMOS imaging device to detect GFP in the deep brain of a freely-moving mouse. As a result of the in vivo experiments with two methods of GFP expression, we successfully detected the light intensity of GFP in the hippocampus or the basal ganglion of the anesthetized mouse. Furthermore, we demonstrated that the implanted CMOS imaging device operated well in the freely moving mouse after one week from implantation. We demonstrated the basic technology to realize the observation of neural activities in the deep brain of a freely moving mouse.

S-band Tm3+-doped tellurite glass microsphere laser via a cascade process

We present a Tm3+-doped tellurite glass microsphere laser operating in the S band via a cascade process. The microsphere is fabricated by melting the end of a tellurite glass wire, and the microsphere laser is pumped at 800nm using a tapered optical fiber. Laser oscillation is observed simultaneously in the S band and the 1.9μm band. The threshold of lasing in the 1.9μm band is lower than in the S band, and the quantum efficiency in the 1.9μm band increases with pump power above the lasing threshold of the S band.

Novel implantable imaging system for enabling simultaneous multiplanar and multipoint analysis for fluorescence potentiometry in the visual cortex

Techniques for fast, noninvasive measurement of neuronal excitability within a broad area will be of major importance for analyzing and understanding neuronal networks and animal behavior in neuroscience field. In this research, a novel implantable imaging system for fluorescence potentiometry was developed using a complementary metal-oxide semiconductor (CMOS) technology, and its application to the analysis of cultured brain slices and the brain of a living mouse is described. A CMOS image sensor, small enough to be implanted into the brain, with light-emitting diodes and an absorbing filter was developed to enable real-time fluorescence imaging. The sensor, in conjunction with a voltage-sensitive dye, was certainly able to visualize the potential statuses of neurons and obtain physiological responses in both right and left visual cortex simultaneously by using multiple sensors for the first time. This accomplished multiplanar and multipoint measurement provides multidimensional information from different aspects. The light microsensors do not disturb the animal behavior. This implies that the imaging system can combine functional fluorescence imaging in the brain with behavioral experiments in a freely moving animal.

Polarization-Analyzing CMOS Image Sensor With Monolithically Embedded Polarizer for Microchemistry Systems

This paper proposes and demonstrates a polarization-analyzing CMOS sensor based on image sensor architecture. The sensor was designed targeting applications for chiral analysis in a microchemistry system. The sensor features a monolithically embedded polarizer. Embedded polarizers with different angles were implemented to realize a real-time absolute measurement of the incident polarization angle. Although the pixel-level performance was confirmed to be limited, estimation schemes based on the variation of the polarizer angle provided a promising performance for real-time polarization measurements. An estimation scheme using 180 pixels in a 1deg step provided an estimation accuracy of 0.04deg. Polarimetric measurements of chiral solutions were also successfully performed to demonstrate the applicability of the sensor to optical chiral analysis.