1-4hit |
Keiichiro KAGAWA Tomohiro NISHIMURA Takao HIRAI Yasushi YAMASAKI Hiroaki ASAZU Tomoaki KAWAKAMI Jun OHTA Masahiro NUNOSHITA Kunihiro WATANABE
We propose a new scheme of indoor optical wireless LAN based on a special CMOS image sensor (CIS), which realizes a low-power compact communication module with large uplink capacity due to space division multiple access. In our scheme, all nodes and a hub utilize the CIS as a photoreceiver as well as a position-sensing device for finding the positions of the communication modules, while a single large photodiode is used in the conventional systems. Although conventional image sensors cannot detect modulated signals because they integrate photocurrents, our CIS has a high-speed readout function for receiving optical data from the specific pixels receiving optical signals. The advantages of the proposed scheme are 1) compact embodiment of the communication module due to no need of the bulky mechanical components for searching the other modules, 2) space division multiple access, which leads to 3) large capacity of uplink, and 4) applicability of simple modulation and coding schemes for optical signals. In our scheme, diffusive and narrow beam lights are complementally used for position detection and communication, respectively, which leads to the advantage 5) low power consumption of both light emitter and receiver circuits. To demonstrate two basic functional modes of our CIS: an IS (image sensor) mode and a COM (communication) mode, we fabricate an 88-pixel CIS by use of a 0.8µm BiCMOS technology. In the experiments, the image of a light source is successfully captured in the IS mode for integration time of 29.6msec and optical power of 1.1nW. After the functional mode of the pixel receiving the light is changed to the COM mode, the eye pattern of the modulated light is obtained from the pixel at frequency of 1MHz. We also fabricate a test pixel circuit with in-pixel amplifier, with which operation speed is improved to 100MHz.
Keiichiro KAGAWA Makoto SHOUHO Kazuo HASHIGUCHI Masahiro NUNOSHITA Jun OHTA
We demonstrate low-voltage operation of a CMOS imager with an in-pixel large-gain comparator without degradation of the dynamic range by using a pulse-width-modulation scheme in pixel readout. Experimental results showed a dynamic range of 57 dB with a 1.0 V power supply voltage at the pixel array block, which demonstrates the possibility of low-voltage, single-power-supply operation of imagers fabricated with deep-submicron CMOS technologies.
Masahiro NUNOSHITA Takashi NAKAYAMA
A narrow-bandwidth optical wave filter was constructed by a stacked directional coupler with two slab waveguides of different materials. The matched phase constant β0 defines the center wave-length of the filter, whereas the different dispersion relations and the inhomogeneity of the guides define the filter bandwidth. The narrowest 3 dB bandwidth was 0.2 nm at the center wavelength of 616.8 nm.
Kiyotaka SASAGAWA Kazushi KUSAWAKE Keiichiro KAGAWA Jun OHTA Masahiro NUNOSHITA
Self-pulsation of Nd3+-doped fluoride fiber laser is experimentally and theoretically demonstrated using a Tm3+-doped fluoride fiber pumped at 808 nm as a saturable absorber. Self-pulsation at finite pump power predicted by linear stability analysis is confirmed through experiments, achieving a pulse width and peak power of 4.5µs and 1.5mW when the Nd3+-doped fiber was pumped at 230mW.