Optical Property of Electro-Tunable Defect Mode in 1D Periodic Structure with Light Crystal Defect Layer Ryotaro Ozaki, Tatsunosuke Matsui, Masanori Ozaki, and Katsumi Yoshino Graduate School of Engineering, Osaka University, Suita, 565-0871 Japan SUMMARY A liquid crystal defect layer is introduced into a one-dimensional photonic crystal and its optical distance is varied by an electric field so that the defect mode can be controlled. An optical propagation simulation is carried out for study of optical characteristics in a model in which nematic liquid crystal is introduced as a liquid crystal defect layer in a dielectric multilayer as a one-dimensional pho- tonic crystal. We investigate whether the defect mode can be controlled by varying the optical length by way of change in orientation of the liquid crystal molecules. Based on the simulation results, a device is fabricated with a nematic defect layer introduced within a SiO 2 /TiO 2 lami- nated periodic structure. The defect mode of the one-dimen- sional photonic crystal is measured. It is confirmed that the experimental results and the simulation results agree well. Further, it is successful in shifting the defect mode wave- length by applying a voltage. Hence, it is clear that the defect mode can be modulated by changing the optical length of the defect layer by means of control of the orien- tation of the liquid crystal molecules by an applied voltage. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(5): 2431, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10167 Key words: photonic crystal; liquid crystal; defect mode. 1. Introduction Photonic crystals are materials with a completely new concept that have a photonic bandgap in which the exist- ence of light is forbidden when the medium has a periodic structure on the order of the optical wavelength. If a defect disturbing the periodicity is introduced into this photonic crystal, localization of light is generated and a defect mode appears within the photonic bandgap [1, 2]. This defect mode can be applied to infinitesimal optical circuit devices and lasers without thresholds. This technique is expected to be important for the next-generation optoelectronics. Ex- tensive research has been carried out worldwide both theo- retically and experimentally [37]. On the other hand, liquid crystals are widely used for display at present due to their characteristics of optical anisotropy and dielectric anisotropy based on the orienta- tion order. The present authors have proposed the use of optical anisotropy caused by control of orientation of the liquid crystal by temperature and electric field in the appli- cation of photonic crystals [812]. Liquid crystals are in- troduced into a three-dimensional photonic crystal using self-assembly of colloidal particles such as opal and in- verted opal. A tunable photonic crystal is realized in which the photonic bandgap is shifted. It was demonstrated that control of the photonic band is possible by electric fields and temperature. However, in these three-dimensional sys- tems, introduction of a defect is a problem. On the other © 2004 Wiley Periodicals, Inc. Electronics and Communications in Japan, Part 2, Vol. 87, No. 5, 2004 Translated from Denshi Joho Tsushin Gakkai Ronbunshi, Vol. J86-C, No. 5, May 2003, pp. 511517 Contract grant sponsor: Supported in part by a Scientific Research Grant [Basic Research B(2) 14350165] from the Ministry of Education and Science. 24