Compact waveguide crossings with a cascaded multimode tapered structure

Abstract

A compact waveguide crossing constructed by a cascaded multimode tapered structure is numerically presented. By using an eigenmode expansion method, we observe that the phase difference between the two lowest guided modes can be changed after a multimode waveguide junction because of the coupling between these two guided modes. Accordingly, we propose a fourfold symmetric waveguide crossing composed of three cascaded tapered structures with Gaussian profiles on each branch. Analyzed by the finite difference time domain method, this waveguide crossing has the size of 4160 nm x 4160 nm, insertion loss of 0.13 dB, cross talk of -43.5 dB, and backreflection of -33.6 dB at the wavelength of 1550 nm and broad transmission spectrum at the wavelength range of 1500-1600 nm. (C) 2015 Optical Society of America