Nanometer-Scale SOI Based Y-Branch Couplers for High Density Optical Integrated Circuits

SOI Ridge nanowire waveguide (RNW) has advantages of strong confinement of optical mode, low propagation loss, small bend radius and fully compatible with CMOS technique, etc. An ultra-compact Y-branch coupler based on SOI RNW was designed and fabricated. Based on the finite-difference beam propagation method (FD-BPM), key parameters of the coupler were analyzed. Then the device was fabricated by electron beam lithography (EBL) and inductively coupled plasma (ICP) reactive ion etching. Results showed that the propagation loss of RNW was 1.89 dB/mm, and the radiation loss of the coupler with branch angle of 30° was only 0.66 dB. Compared with traditional Y-branch coupler, the proposed structure were more promising for high density optical integrated circuits.