Design, simulation, and fabrication of a 90° SOI optical hybrid based on the self-imaging principle

Abstract

This paper introduces a compact 90º optical hybrid, built on small size SOI waveguide technology .This optical hybrid is a critical component of a potentially low-cost coherent optical receiver design developed within the frame of our Optical Coherent Transmission for Access Network Extensions (OCTANE) project. In previous recent work, 90º optical hybrids were realized in SOI rib waveguide technology with 4 µm top silicon and a rib height of approximately 2 µm. In this paper, we introduce a compact 90º optical hybrid, built on small size SOI waveguide technology (1.5 µm SOI -based rib waveguide, with 0.8µm rib height). The proposed device consists of multimode interferometers (MMIs) connected in such a way that four different vector additions of a reference signal (local oscillator) and the signal to be detected are obtained. At the outputs, the hybrid provides four linear combination of the signal with the reference which differs by a relative phase shift of the reference of 90º. The four output signals are detected by a pair of balanced receivers to provide in-phase and quadrature (I&Q) channels. The phase differences arise naturally from the self imaging property of a MMI.The key elements of the 90º optical hybrid, including a 2×2 MMI, a 4×4 MMI, and polarization diversity configuration have been designed and simulated, using the numerical mode solving tool FIMMPROB. The 2×2 and 4×4 MMI had overall lengths of 701μm and 3712.5μm lengths respectively. Tapers are used to couple adiabatically single mode waveguides to the entrance and exit ports of the MMI to assure correct operation by avoiding coupling to the higher order transverse modes allowed at the entrance and exit ports of the MMI. The simulation results at 1550nm show polarization independence and phase errors between the ports of less than 0.03 degrees. Currently the design is in fabrication at the Canadian Photonics Fabrication Center with the support of CMC Microsystems and experimental results will be subject to a further report.

Design, simulation, and fabrication of nano-scale silicon-on-insulator (SOI) integrated photonic phased array switch elements (IPPAS) utilizing nanoelectromechanical systems (NEMS)

“…Glance literature survey shows that application examples for utilizing MMI couplers include electro-optic switches [3,4], MZI-based switches [5,6], passive MZI polarization splitters and convertors [7], microring resonators [8], optical 90° hybrids [9] and phased array wavelength division multiplexers (WDMs) [10]. Tapers are usually used to adapt the width of the interconnecting single mode waveguides to the wider width of the I/O access ports interfacing with the MMI coupler.…”