Tetsuzo Yoshimura

Self-organized lightwave network based on waveguide films for three-dimensional optical wiring within boxes

This paper presents core technologies for a self-organized microoptical system (SELMOS) within optoelectronic computers; mass-productive fabrication processes of waveguide films and new types of self-organized lightwave networks (SOLNETs) for three-dimensional (3-D) optical wiring with optical Z-connections. Waveguide films are fabricated by the built-in mask method, which is reusable and can construct surface-normal mirrors/filters at one time within photolithographic accuracy. Beveled core edge walls are made by the tilted ultraviolet (UV) exposure through the built-in mask using a photodefinable material. Near- and far-field patterns reveal that the walls act as micromirrors for optical Z-connections. SOLNET is a network consisting of self-organized coupling waveguides between misaligned optical devices. The self-organization is generated in a photorefractive material by self-focusing of the two write beams from the two devices. Direct SOLNET, where wavelengths of the write beam and the signal beam are the same, is demonstrated using a laser diode. Reflective SOLNET, where one of the two write beams is replaced with a reflected write beam from the edge of the coupled device, realizes two-beam-writing SOLNET in a one-beam-writing configuration. It is especially effective when the coupled device cannot transmit write beams. The proof-of-concept is demonstrated both theoretically and experimentally. These results indicate a possibility to form 3-D optical wiring simply in SELMOS.

Three-dimensional self-organized microoptoelectronic systems for board-level reconfigurable optical interconnects-performance modeling and simulation

Self-organized microoptoelectronic system (SELMOS) built from three concepts - scalable film optical link multichip-module (S-FOLM), three-dimensional (3-D) microoptical switching system (3D-MOSS), and self-organized lightwave network (SOLNET)-is proposed. The feasibility of SELMOS for board-level reconfigurable optical interconnects is studied by the beam propagation method/finite difference time domain simulation focusing on three key issues; reducing size/cost of electrical to optical (E-O) and optical to electrical (O-E) signal conversion devices, tolerating alignment accuracy for optical coupling, and miniaturizing high-speed massive optical switching. S-FOLM, which consists of film-waveguide-based 3-D structures with embedded optoelectronic active elements and optical Z-connections for interplane links, enables drastic size/cost reduction of E-O and O-E conversion devices. 3D-MOSS, which is an S-FOLM with embedded microoptical switches, has a potentiality of 1024 /spl times/ 1024 switching with a system size of /spl sim/1.4 /spl times/ 0.6 cm/sup 2/ and an insertion loss of 29 dB. The switching rate of the 3D-MOSS is determined by the heat releasing speed to be /spl sim/2 /spl times/ 10/sup 5/ 1/s when PLZT waveguide-prism-deflector microoptical switches are used. By using advanced electrooptic materials, rates higher than 10/sup 8/ 1/s are expected. Twenty-five percent misalignment in waveguide assembly raises the insertion loss of the 3D-MOSS to 73 dB. The loss is reduced to 32 dB in SELMOS-based 3D-MOSS, where a self-organized 3-D microoptical network is implemented using SOLNET. Further loss reduction is expected by structural optimization of loss-inducing parts. Thus, SELMOS is found to be a solution of the three key issues for board-level reconfigurable optical interconnects. In addition, photolithographic packaging with selectively occupied repeated transfer (PL-Pack with SORT), which integrates different types of active elements into one substrate in desired arrangements using an all-photolithographic process, can contribute to cost and the coefficient of thermal expansion-mismatching reduction.

Effects of the deposition sequence on amorphous silicon thin-film transistors

We examined the effects of the deposition sequence on the threshold voltage and field-effect mobility in amorphous silicon thin-film transistors. When the nitrides are deposited after the a-Si:H(normal), the threshold voltages become more positive, and the field-effect mobilities are lower than with the inverted sequence. Photoluminescence measurements reveal that the tail states in the a-Si:H near the a-Si:H/a-SiNx interface for the normal sequence are wider than for the inverted sequence.

Directional-Coupled Optical Switch between Stacked Waveguide Layers Using Electro-Optic Polymer

A vertical optical switch consisting of an electro-optic polymer is described. Two-layer stacked slab waveguides were fabricated with para-nitroaniline-bonded epoxy polymer as the core layer and polyvinylalcohol as the cladding layer. After poling treatment, a He-Ne laser beam was coupled to the waveguides, and guided-wave switching was observed between the two waveguide layers with application of voltage to the electrodes.

Self-aligned optical couplings by self-organized waveguides toward luminescent targets in organic/inorganic hybrid materials

Self-organization of optical waveguides is observed between two opposed optical fibers placed in a photosensitive organic/inorganic hybrid material, Sunconnect. A luminescent target containing coumarin 481 was deposited onto the edge of one of the two fibers at the core. When a 448-nm write beam was introduced from the other fiber, the write beam and the luminescence from the photoexcited target increased the refractive index of Sunconnect to induce self-focusing. Traces of waveguides were seen to grow from the cores of both fibers and merged into a single self-aligned optical coupling between the fibers. This optical solder functionality enabled increases in both coupling efficiency and tolerance to lateral misalignment of the fibers.

Analysis of Reflective Self-Organized Lightwave Network (R-SOLNET) for Z-Connections in 3-D Optical Circuits by the Finite-Difference Time-Domain Method

Reflective self-organized lightwave network (R-SOLNET) is a novel optical waveguide formation method that utilizes an attractive force induced between light beams in photo-induced refractive index increase materials, in which the refractive index increases as a result of write-beam exposure. R-SOLNET forms self-aligned optical couplings between optical devices, which tolerate the mutual positional misalignment, and it also forms optical waveguides in a free space. We propose R-SOLNET in 3-D optical circuits for board/chip-level optical interconnects to reduce the amount of effort that is required for optical device assembly and vertical optical waveguide formation. We predicted by the finite-difference time-domain method that an optical Z-connection of R-SOLNET would vertically connect two 2-μm-core optical waveguide films stacked with a 10-μm gap. A self-aligned vertical waveguide is formed even when misalignment exists between the films. A coupling efficiency of >;40% is achievable with 25% misalignment in waveguide core assembly.

Cancer Therapy Utilizing Molecular Layer Deposition and Self-Organized Lightwave Network: Proposal and Theoretical Prediction

Cancer therapy utilizing the molecular layer deposition (MLD) and the self-organized lightwave network (SOLNET) is proposed. The MLD is a growth method, in which different kinds of molecules are sequentially provided to a substrate to synthesize organic tailored materials with designated molecular arrangements. The first proposal is the selective delivery of multifunctional materials, containing luminescent molecules for imaging, sensitizers for photodynamic therapy, paramagnetic agent, and so on, to cancer cells by the MLD. The second proposal is the in situ synthesis of drugs, especially, large and toxic ones, at cancer cell sites by the MLD to deliver the drugs efficiently deep inside the cancer without attacking normal cells. The third proposal is the SOLNET-assisted laser surgery. After luminescent molecules are adsorbed in cancer cells by the MLD, a write beam is introduced from an optical fiber into the area containing cancer cells through photoinduced refractive index increase materials to construct self-aligned optical waveguides of the SOLNET connecting the optical fiber to the cancer cells. Surgery laser beams are guided to cancer cells by the SOLNET. A proof-of-concept, which indicates that the surgery laser beams are guided toward cancer cell targets selectively, is presented by a simulation using the finite-difference time-domain method and a preliminary experimental observation.

Fabrication of Self-Organized Optical Waveguides in Photo-induced Refractive Index Variation Sol–Gel Materials With High-Index Contrast

Using photo-induced refractive index variation sol-gel materials, we fabricated a self-organized lightwave network (SOLNET), which is a concept of optical waveguides self-organized in photosensitive materials, whose refractive index increases by write beam exposure. The refractive index of the sol-gel materials increases from 1.65 to 1.85 when exposed to UV light/blue light and baking. When write beams with a wavelength of 405 nm are introduced into the sol-gel thin film under baking at 200degC, self-focusing is induced and a SOLNET is formed. In this study, we evaluated the light confinement effect and coupling efficiencies of the fabricated SOLNET. The half-width of the output beam spot decreases from 23.8 to 11.8 mum, and the coupling efficiencies increase as write beam intensity decreases from 1.0 to 0.1 mW. These results show that SOLNET widths become narrow when write beam intensity is reduced; thus, SOLNETs formed with a low write beam intensity produce a strong light confinement effect. Furthermore, during their formation, SOLNETs were found to be drawn toward reflective portions of the sol-gel thin film, such as defects or silver paste droplets, indicating that a reflective SOLNET is formed. We have shown that photo-induced refractive index variation sol-gel materials are promising materials for SOLNET fabrication. To create actual connections between nanoscale optical circuits, further work is necessary to optimize the baking temperature and write beam intensity required for nanoscale SOLNET formation.

Reflective self-organizing lightwave network using a phosphor

Self-organization of optical waveguides that connect two optical devices automatically through a reflective self-organized lightwave network (R-SOLNET) using a phosphor was simulated by the finite difference time domain method. The simulation showed that a R-SOLNET is constructed between a waveguide with a core width of 1.2 μm and a phosphor target, which is located a distance of 6.4 μm from the waveguide edge and guides the probe beam to the phosphor target. The optical coupling efficiency was 95% when the waveguide and phosphor target were fully aligned. Even when the misalignment was 800 nm, a coupling efficiency of 60% was obtained. The coupling efficiency for the SOLNET without the phosphor target was 16%. In addition, experiments to confirm the principle of a R-SOLNET using a phosphor were performed with an optical fiber and tris(8-hydroxyquinolinato) aluminum (Alq 3 ) phosphor target. The experiments revealed that the write beam is propagated toward the Alq 3 target, and consequently, a R-SOLNET connecting the fiber edge and Alq 3 target is formed to guide probe beams to the target. The R-SOLNET expanded from the diameter of the fiber core to the width of the Alq 3 target.

Simulation of Self-Aligned Optical Coupling Between Micro- and Nano-Scale Devices Using Self-Organized Waveguides

Using the finite-difference time-domain method, we simulated the growth of self-organized waveguides between a 3-μm-wide micro-scale waveguide and a 600-nm-wide nano-scale waveguide, which has a luminescent target on its core edge. The two waveguides are placed together, with gap sizes ranging from 16 to 64 μm, in a photo-induced refractive-index increase-type material. When a 400 nm wavelength write beam is introduced from the micro-scale waveguide, luminescence is generated by the luminescent target. A waveguide is then gradually self-organized between the two waveguides, even when a lateral misalignment of 600 nm exists between them, and provides a self-aligned optical coupling with a coupling loss of 1.5-1.8 dB. This indicates that the self-organized waveguide can be used as an optical solder to connect a micro-scale waveguide in a multi-chip module or printed circuit board to a nano-scale waveguide in a large-scale integrated circuit. The optimum writing time required to attain the minimum coupling loss increases with increasing lateral misalignment. The dependence of the optimum writing time on the misalignment is reduced with increasing gap distance, and the dependence almost vanishes when the gap distance is 64 μm, thus enabling unmonitored optical solder formation.