Fabrication of Tapered Waveguide by Ashed Photoresist

초록

The objective of this paper is to present novel method that can be fabricated a tapered waveguide master using micro-loading dffect of photoresist ashing process. Integrated optics is a very promising solution to high data transmission rate with wide bandwidth by integrating many optical devices such as sources, modulators, detectors and other passive devices onto one substrate, where planar waveguides are used to interconnect those devices. However, there is a size mismatch between devices and components, for example, optical fiber and waveguide, and passive component and waveguide. It is necessary to have an optical component to interconnect optical devices with different sizes in large scale integrated optics. In order to make effective connection among the devices, prism coupling, tapered optical fiber and grating coupling have been proposed. Because connecting points of both sides are different in height and width, the coupling should be matched in both horizontal and vertical dimensions. It should be ideal to have a tapered structure for coupling and thus it is requied to control the tapered structure in three dimension[1]. Soft lithography has been known as a next generation patterning technology because of its possibility of low cost and mass production. General steps in soft lithography are preparation of a master, preparation of mold templates from the master and fabrication of final structure by imprinting with mold[2]. Therefore, it is the most important first step to design and prepare the master. In this work, we propose to make three dimensional master structure by plasma ashing process of photoresist. Isotropic etch mechanism is utilized to get different final sizes. Different sizes in width and height of a structure can be effective as a tapered adapter which connects two optical devices with different sizes. Fabrication of this tapered waveguide is difficult vecause height and width of the structure should be reduced at the same time. O2 plasma h