Topology optimized design of a transverse electric higher order mode converter

The investigation of methods to support the ever increasing demand for data transfer has continued for years; one such method suggested within the field of optical communication, is space division multiplexing (SDM) [1]. Simultaneously the field of photonic integrated circuits (PICs) is being investigated due to attractive features such as high device density and low operating power [2]. For PICs it is necessary with a toolbox of devices and one such of importance to the processing of on chip SDM is the mode converter. Several schemes have been used to realize such devices [3] [4]. In this paper we present the possibility of employing topology optimization (TO) to design a device that allows for reversible conversion between the transverse electric fundamental even (TE0) mode and the second higher order odd mode (TE2). Topology optimization is an iterative inverse design process, where repeated finite-difference time-domain (FDTD) calculations are made in accordance with a sensitivity analysis. This is done using a software package which has been developed in house, and which has shown to deliver low loss designs with a controllable bandwidth in addition to small device footprints [5]. The design is made for fabrication in silicon-on-insulator (SOI) and previous work has shown excellent concordance between simulations and experimental results when employing 3D TO [6].