[OPTICAL REVIEW Vol. 12, No. 2 (2005) 97-100]
© 2005 The Optical Society of Japan

A New Method for Accurately Measuring Temperature Dependence of Refractive Index

Masahiro TOMIKI, Naohiro KURIHARA, Okihiro SUGIHARA1 and Naomichi OKAMOTO

Department of Electrical and Electronic Engineering, Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
1Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan

(Received September 30, 2004; Accepted January 21, 2005)

A new high-accuracy method for measuring temperature dependence of refractive index is proposed and applied to some polymer waveguides. The method uses 3 m-lines from a grating coupler on the waveguide surface, and has an accuracy of better than 1× 10-5 (1/°C). The grating period dependent on the temperature does not affect the accuracy. The measurement thermo-optic (TO) coefficients of polycarbonate (PC) and polymethyl methacrylate (PMMA) are strongly dependent on the waveguide structure in contrast with the previously reported value. It is found that the TM-mode refractive index of UV-curing polymer (J-91) increases with the increase in temperature, contrary to common expectations for polymers. A highly efficient TO switch is expected using the J-91 polymer waveguide.

Key words: thermo-optic coefficient, polymeric waveguide, grating coupler, m-line, embossing