Cascaded Multimode Interference-Based 1x2 Light Splitter for Photonic Integrated Circuits

Abstract

Multimode interference (MMI)-based devices have become important components within photonic and optoelectronic integrated circuits, due to their simple structure, low excess loss, large optical bandwidth and low polarization dependence. Their main function is to provide N×N power splitting [1,2] in Mach Zehnder interferometers, ring lasers and optical switches, 3-dB power couplers [3], and 1×2 light splitters and combiners. MMI devices are based on the principle of self-imaging. An input field profile in a multimode waveguide is reproduced in single or multiple images at periodic intervals along the propagation direction of the waveguide, as a result of beating of different modes in the waveguide. Since the beat length in a multimode waveguide is proportional to the square of the width of the waveguide, using a combination - cascade of two stages of multimode waveguides with smaller widths yields a splitter whose overall length is shorter than that of a single 1×2 MMI splitter, for a given output waveguide spacing. This work develops and demonstrates the methodology for designing optimum novel light splitters. These splitters are well suited for use in Michelson and Mach Zehnder interferometric modulators and wavelength converters [4], as well as biosensors [5].