Yasuhiro Kuwana

Synthesis and optical properties of polyimides

Polyimides are important industrial materials because of their excellent properties. They are extensively used in the electronics industry and have great potential in the field of optical communications. In this article, we discuss the effect of the polyimide structure and the processing conditions on the optical properties. Both commercially available fluorinated polyimides and polyimides synthesized in our laboratory were used in this study. The relationship between the extent of fluorination and the refractive index was studied, and it was found that fluorination reduced the refractive index as expected. Studies conducted on the structure–property relationship revealed that with the use of more rigid monomers for the polyimides, the polyimides could be modified to show a large birefringence. The extent of birefringence depended on the composition of the polymer. In addition, the processing conditions directly controlled the residual stress in the polymer films. The residual stress was an important factor in inducing light scattering, which resulted in higher optical loss.

Signal Propagation Characteristics in Polyimide Optical Wave-guide with Micro-Mirrors for Optical Multichip Module

In order to develop key technologies for a multichip module with optical interconnection, a test module using polyimide optical waveguides (POWs) with micro-mirrors and a photodiode array was successfully fabricated. Through the fabrication of this test module, we developed such basic technologies as POW formation, vertical optical coupling with micro-mirrors buried in POWs, chip bonding with copper bumps, and so on. The signal propagation in POWs was characterized by the detection of vertical output signals at micro-mirrors. From these characteristics, the transmission loss caused by passing a mirror was evaluated to be 0.16 dB.

Polyimide optical waveguide with multi-fan-out for multichip module system

We have been developing a special purpose parallel processor system with a compact size and a high performance specific for the scientific computation. A multichip module (MCM) with a high speed bus is indispensable to achieve such parallel processor system. We have developed a high speed bus for such MCM using a polyimide optical waveguide with micro-mirrors. We can easily obtain many output signals from one input signal in this optical waveguide. Such polyimide optical waveguide with micro-mirrors is formed on a MCM substrate which is called an optical plate. An optical coupling between the polyimide optical waveguide and the laser diode or the photodetector on LSI chips is performed through the micro-mirror. We observed twenty output signals for the photodetectors from one input signal in the polyimide waveguide of fabricated test module. We have also evaluated the performance of parallel processor system using such MCM with the polyimide optical waveguide by computer simulation.