We have been developing the optical waveguide for the multimode using the photo-bleaching property of polysilane.
The refractive index of polysilane can be easily changed by exposing to UV light as photobleaching. Using this property,
we can make waveguide with simple processes as spin coating, exposing and annealing. We found that this waveguide
has thermal adhesive property with glass substrate. And we applied this feature to fabricate multilayered optical
waveguides that have three-dimensional structure and can change the optical light at right angle.
In the field of optical interconnect technology, many works are in progress for polymer material that is more inexpensive in terms of material and processes than conventional quartz optical waveguides. We had developed a novel type of material for optical waveguides consisting polysilane, silicone and photosensitizer. This material named "GlasiaWG (TM) can decrease its refractive index by UV irradiation. Using this photobleaching phenomenon, we can fabricate optical waveguides that have flat surfaces by simple process without chemical etching. In this work, we have developed multilayered optical waveguides that enable to make two-dimensional multichannel connectors for multimode optical interconnects.
To fabricate multilayered optical waveguides, we prepare glass substrates whose thickness are 150μm and two kinds of GlasiaWG (TM) having different refractive indexes respectively. At first GlasiaWG (TM) having a higher refractive index is coated on the glass substrate, and then the coated film is irradiated by UV-light with a photomask to create core and side cladding parts. After baking the core layer at 250 degrees C another GlasiaWG(TM) with a lower refractive index is coated on the core layer and baked at 250 degrees C. One-layer optical waveguide is completed for one unit. After accuracy alignment, four units of optical waveguides are laminated by heating at 80 degrees C and pressing with 50kg/cm2, and diced to proper size pieces. Eventually four-layered optical waveguides are fabricated. Flat surfaces made by photobleachig process and adhesive properties with glass enable to fabricate multilayered optical waveguides. This fabrication is a feature of GlasiaWG<sup>TM</sup>.
We have tried to develop the technology for selective bleaching of core patterns of waveguides on polysilane films by UV light irradiation without wet development and RIE process. Furthermore, we have examined heat treatment of films in order to make transmission loss low instead of introducing fluorine groups in the polymer structure which conventional polymeric material are applied. As a waveguide device, evaluation of low loss straight-line waveguides and multilayered laminating type waveguides at 850nm for MM, and splitter of 8 branches (1×8) at 1550nm for SM was carried out. This new technology is expected to establish the low-cost manufacturing process of optical waveguides which are important components of passive optical devices for PON (passive optical network) system and optical interconnects.