Ya-Lun TSAI, Hsiao-Chin LAN, Sheng Fu LIN, Chia-Chi CHANG, Hsu-Liang HSIAO, Yun-Chih LEE, Jenq-Yang CHANG, and Mount-Learn WU^*

Department of Optics and Photonics, National Central University, Jhongli 32001, Taiwan, R.O.C.

(Received May 26, 2010; Accepted September 21, 2010)

In this paper, the design of low-loss tapered waveguides by applying photonic-crystal-based microlenses is presented. The microlenses are realized by using two-dimensional photonic crystal (PhC) structures with a hexagonal periodic lattice of air-holes. In order to make the PhC structures behave as homogeneous and isotropic microlenses, the PhC structures are designed to operate in the low-frequency domain with light wavelength sufficiently larger than the PhC lattice constant. The effective indices of the PhC are calculated and the structures are properly arranged in microlens-like shapes. By monolithically integrating the effective microlenses in the tapered area between the two optical waveguides with different core dimensions, the wavefront of the eigenmode can be coupled from the larger core to the smaller core effectively and also the radiation loss in the tapered area between the two connected optical waveguides can be effectively suppressed. The results show that the PhC-based microlens in the telescopic structure can serve as an optical element in the tapered waveguide with the advantages of low loss, high efficiency and compactness.

Key words: integrated optics, photonic crystal, taper

^*E-mail address: mlwu@dop.ncu.edu.tw