Photonic crystal waveguide - fabrication of the periodic arrays by visible light holographic technique coupled with electron beam-induced deposition

摘要

In recent years a lot of interest has been directed towards waveguide-based two dimensional photonic crystals. The reason behind this interest is a possibility of employing them in future photonic integrated circuits (PIC). With the photonic-crystal-based PIC it will be possible, for the first time, to realize compact in size, multicomponent optical integrated circuits. In this article we present a simple fabrication method for large arrays of holes of arbitrary shape and size. Later, a method of local modification of the structure (defect creation) is also given. Fabrication of the periodic array in photoresist is made through the multiple exposition of thin photoresist film with two interfering laser beams (holographic method). Exposition has been done with a pulsed Nd-YAG laser. The setup has been adapted from the existing one, previously used to fabricate diffraction gratings in positive photoresist films (the gratings served as grating couplers for planar waveguides). An idea of periodic pattern fabrication with the setup similar to ours was first proposed in 1975, but no further consideration for any application was given then. In this paper we present two examples of periodic structures obtained with double expose, with substrates rotated by the angles of 75/spl deg/ and 90/spl deg/. The one dimensional period of the structures was equal to 1.26 /spl mu/m. Two different shapes of holes were obtained in photoresist. In the second exposition setup (90/spl deg/) nearly circular openings with diameter of 780 nm were achieved. The commonly known problem with fabrication of photonic crystals by the holographic method is difficulty in defect creation. Here, we propose the use of three-dimensional additive nanolithography with electron beam-induced deposition (EBID) for this task. Both a point defect (local resonator) and a line defect (channel waveguide) have been fabricated and documented.