Self-organized Lightwave Network Research Articles

Micro/nanoscale self-aligned optical couplings of the self-organized lightwave network (SOLNET) formed by excitation lights from outside

The self-organized lightwave network (SOLNET) provides “optical solder,” which enables self-aligned optical couplings between misaligned optical devices with different core sizes. We propose a low-cost SOLNET formation method, in which write beams are generated within optical devices by excitation lights from outside. Simulations based on the finite-difference time-domain method reveal that the two-photon processes enhance optical-solder capabilities. In couplings between 600-nm-wide waveguides opposed with 32-μm distance a wide lateral misalignment tolerance of ~2µm to maintain <1dB loss at 650nm in wavelength is obtained. The coupling loss at 1-μm lateral misalignment is 0.4dB. In couplings between 3-μm-wide and 600-nm-wide waveguides, losses at 650nm are 0.1dB for no misalignments and 0.9dB for 1-μm misalignment. These results suggest that SOLNETs provide optical solder with mode size converting functions.

Polymer waveguides self-organized by two-photon photochemistry for self-aligned optical couplings with wide misalignment tolerances

Self-organized optical waveguides formed in a photopolymer using two-photon photochemistry is proposed for self-aligned optical couplings involving nano-scale optical devices with wide tolerances in lateral misalignments. Simulations based on the finite-difference time-domain method revealed that on introducing a 400-nm write beam and a 780-nm write beam into the two-photon photopolymer respectively from two 600-nm-wide waveguides facing each other with 32μm gap a self-aligned coupling waveguide called a two-photon self-organized lightwave network (SOLNET) is formed between the two waveguides. The lateral misalignment tolerance was found to be 3000nm, which is five times larger than the misalignment limit of ~600nm in waveguides formed by conventional one-photon photochemistry. Preliminary experiments demonstrated that the two-photon SOLNETs are formed between multimode optical fibers by introducing a 448-nm write beam and a 780-nm (or 856-nm) write beam from the fibers into a photosensitive organic/inorganic hybrid material, SUNCONNECT®, with doped camphorquinone (or biacetyl).

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.

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.

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.

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.

Simulation of micro/nanometer-scale self-organized lightwave network (SOLNET) using the finite difference time domain method

A simulator for self-organized lightwave network (SOLNET) is developed. The simulator is based on the finite difference time domain method. SOLNET enables us to construct self-aligned coupling waveguides between misaligned micro/nanometer-scale optical devices by self-focusing, which arises from an increase in refractive index induced by write beams in photo-refractive materials. The SOLNET simulator reveals that an L-shaped nanometer-scale optical waveguide of SOLNET is grown from a 0.5-μm-wide optical waveguide when write beams are introduced from the optical waveguide into photo-refractive materials, where a wavelength filter is embedded. The SOLNET simulator also reproduces coupling path construction between a 2-μm-wide optical waveguide and a 0.5-μm-wide optical waveguide having a wavelength filter on the core edge. The optical waveguides are placed with misalignment of 0.5-μm offset. By introducing write beams from the 2-μm-wide optical waveguide, the incident write beams and reflected write beams from the wavelength filter merge into one optical waveguide in the photo-refractive materials, constructing a self-aligned coupling waveguide.

Optical Waveguide Films With Two-Layer Skirt-Type Core Structures for Beam Leakage/Scattering Reduction at Tapered Mirrors

Using the self-organized lightwave network (SOLNET) technique, we observed guided beam leakage and scattering at tapered mirrors of core end facets in optical waveguide Alms. The leakage/scattering are caused by the tunneling of guided beams into the cladding film and pattern imperfection of core edge corners. To reduce them, we proposed the two-layer skirt-type core structure, where a core has a layered structure of low-index (LI) part and high-index (HI) part. The LI part located between the HI part and the cladding film prevents guided beams from tunneling into the cladding film. The skirt-type shape of core end facets puts core edge corners away from the guided beam paths. The beam propagation method and the finite-difference time-domain method revealed that the leakage/scattering are reduced in the proposed core structure. Optical waveguide films with the two-layer skirt-type core structure were fabricated by the built-in mask method. Appropriate skirt lengths were found to be around core widths. Guided beams were confined into the HI part to reduce the tunneling into the cladding film.

Three-Dimensional Optical Circuits Consisting of Waveguide Films and Optical Z-Connections

Two types of three-dimensional (3-D) optical circuits based on waveguide films are proposed and experimentally demonstrated. Type 1 is Stacked waveguide films with 45deg mirrors. films with 70-mum-thick undercladding layers and 32-mum-wide cores with air cladding are fabricated by the built-in mask method using photo-definable materials. The films are stacked by contacting their undercladding layers. Optical Z-connections are formed by aligning the 45deg mirrors in upper and lower films. The mirror-to-mirror distance is ~170 mum. When a probe beam of 650 nm or 1.3 mum in wavelength is introduced into input in the first film, it is transmitted to the second film through optical Z-connection and is observed at output. Loss at the optical Z-connection for 1.3-mum wavelength is ~14 dB, which might be due to leakage of probe beams reflected from the mirror with large diverging angles. Type 2 is Waveguide films with vertical waveguides. After coating a photo-refractive layer of 500-mum thickness on the back of a cladding layer of a waveguide film, a 405-nm wavelength write beam is introduced into input. Then, a vertical waveguide of 3-D self-organized lightwave network (3-D SOLNET) is grown in the photo-refractive layer above a 45deg mirror. A probe beam guided in the vertical waveguide is observed with a beam size close to that in the core of the waveguide film. Loss reduction at the optical Z-connection is expected by combining optical circuits of Types 1 and 2 to insert the 3-D SOLNET between waveguide films as well as by decreasing cladding layer thicknesses

Coupling efficiencies in reflective self-organized lightwave network (R-SOLNET) simulated by the beam propagation method

The reflective self-organized lightwave network (R-SOLNET) enables the formation of self-aligned waveguides in the photorefractive (PR) material between misaligned optical devices by introducing a write beam. The incident write beam from one device and the reflected write beam from the second device induce self-focusing in the PR material and construct a coupling waveguide. A wavelength filter on the waveguide edge is used to facilitate the reflected beam. The beam propagation method reveals that R-SOLNET exhibits higher coupling efficiencies and better tolerances than the one-beam-writing SOLNET and the free-space coupling. The apparent usefulness of R-SOLNET is remarkable for gaps wider than 100 /spl mu/m in 8-/spl mu/m-wide waveguide circuits. For 240-/spl mu/m gap, coupling efficiency better than 50% can be achieved even when the lateral misalignment is as large as 4 /spl mu/m. The results indicate that R-SOLNET may be useful for vertical waveguide constructions of optical z-connections in three-dimensional intrachip optical interconnects and switching systems, as well as for self-aligned optical couplings with devices that cannot emit write beams such as vertical-cavity surface-emitting lasers, photodetectors, and electrooptic switches.

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.

Predicted Insertion Loss Reductions Achieved by Implementing Three-Dimensional Microoptical Network in Chip-Scale Optical Interconnects

We simulate insertion loss reductions achieved by implementing three-dimensional (3-D) microoptical network in chip-scale optical interconnects using a model structure of 3-D microoptical switching system (3-D MOSS). 3-D MOSS for a 1024/spl times/1024 Banyan network consisting of stacked layers with embedded microoptical switches minimizes the insertion loss at a layer count of 16. The optimum is determined by balance of in-plane and vertical optical connections, whose losses change oppositely with the layer count, causing a tradeoff relationship. Loss induced by 25% waveguide misalignment is decreased to a level comparable to that for no misalignment by introducing self-organized lightwave network in the 3-D optical wiring. The remaining major losses arise from microoptical switches and microreflectors.

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.