Replication-based fabrication for an optical device that incorporates vertically curved structures

Abstract

The replication process is a good method to fabricate passive optical devices. Silicon-based fabrication technology provides an efficient way to fabricate a replication master with an optically smooth surface roughness. As silicon-based technologies are often two-dimensional processes, the replication requires sophisticated fabrication steps for a master structure. For this, a vertically curved structure, which is essential for a passive optical device, is hard to fabricate. Special processes, such as x-ray lithography, laser ablation, and gray-scale lithography, can overcome the conventional two-dimensional fabrication process challenges. But these processes need additional steps, machines, and masks. This study demonstrates an easy way for fabricating a silicon master structure for vertically curved mirrors. This fabrication method is roughly divided into two steps. During the first step, a silicon wafer is etched using an inductively coupled plasma system to form optical waveguide structures in the master structure (45μm depth and ∼5nm surface roughness). During the second step, the vertically curved mirror structures at each end of the waveguides are formed by using photoresist reflow process. After the master fabrication, the master shape was transferred to a PDMS mold. The replication process was carried out by using UV curable polymers, and a successful vertical redirection of light by the curved structure was observed with a charge-coupled device. The measured propagation loss of the fabricated waveguide structure was 0.13dB∕cm, and the curved mirror loss was 0.35dB.