Kenji Miyao

Novel Optical/Electrical Printed Circuit Board with Polynorbornene Optical Waveguide

An optical interconnection with a new optically transparent polymer called polynorbornene (PNB) was investigated for short-distance and high-speed data transmission on printed circuit boards (PCBs). PNB waveguides were formed by simple photoirradiation followed by heating without development and reactive ion etching (RIE) processes. The PNB waveguides exhibit a high-heat resistance of more than 270 °C and an extremely low optical loss of 0.029 dB/cm at 830 nm. We successfully integrated PNB waveguides into a multilayer PCB, which we call a optical/electrical printed circuit board (O/E-PCB), and confirmed a basic data transmission rate of 10 Gbps.

Low-Loss Optical Interposer with Recessed Vertical-Cavity Surface-Emitting Laser Diode and Photodiode Chips into Si Substrate

A new interposer with an optical interconnection called optical interposer has been proposed for a high-performance parallel processor system. The optical interposer is composed of polynorbornene (PNB) optical waveguides with 45° micromirrors and a Si substrate having chip-sized through-Si holes of 150 µm depth. The polymeric waveguides are formed on the Si substrate before forming the through-Si holes by deep reactive ion etching (DRIE). Vertical-cavity surface-emitting laser diode (VCSEL) and photodiode (PD) chips are placed onto the photolithographically defined hole patterns that are 15 µm larger than the size of the chips. In addition, the chips can be precisely aligned and recessed into the holes by passive alignment of self-assembly driven by the surface tension of a lead-free solder. We can fabricate the low-loss optical interposer with an insertion loss of below 0.2 dB measured at the waveguide length of 5 cm and a coupling loss of 0.5 dB measured with a 45° micromirror.

High Performance Polynorbornene Optical Waveguide for Opto-Electric Interconnections

We have newly developed a multi-mode polymer optical waveguide with polynorbornene (PNB). The PNB waveguide has extremely low optical loss of 0.03 dB/cm at wavelength of 830-nm and high glass transition temperature (Tg) of 270degC. The PNB waveguide can be formed by only UV irradiation step without both etching and developing processes. By using this method, the waveguide can be easily patterned with various shapes such as Y-branch, bend, taper, and so on. In addition, we can fabricate the minimum waveguide pitch less than 75 mum with the 50-mum-width core. We can also easily fabricate a stacked waveguide because the core layer with flat surface can be formed without an etching and a developing process. In the PNB waveguide, 45deg mirror was formed by an excimer laser. This method provides a small mirror (100 mum times 200 mum) with smooth surface in respective waveguides. From the result of insertion loss measurements, total optical loss was less than 2 dB in an 8-cm-length waveguide with two 45deg mirrors. Furthermore, new opto-electric (O-E) interconnection with PNB optical waveguide was proposed. This PNB waveguide has high flexibility and high adaptability to reflow soldering process because of its high Tg. Therefore, the PNB waveguide can be formed in flexible printed circuit boards (PCBs) without particular process, as compared to the conventional PCB fabrication process, which leads to low cost O-E interconnection.