Compact Transverse Electric Silicon-on-Insulator Mode Converter for Mode-Division Multiplexer

Abstract

On-chip optical-interconnect technology emerges as an attractive approach due to its ultra-large bandwidth and ultra-low power consumption. Silicon-on-insulator (SOI) wire waveguides, on the other hand, have been identified to potentially replace copper wires for intra-chip communication. To take advantage of the wide bandwidth of SOI waveguides, wavelength-division multiplexing (WDM) has been implemented. However, WDM have inherent drawbacks, as it requires the operation and alignment of many individual laser sources. Mode-division multiplexing (MDM) is a viable alternative to WDM in MIMO photonic circuits on SOI as it requires only one carrier wavelength to operate. In this vein, mode converters are key components in on-chip MDM systems. The goal of this paper is to introduce a transverse electric mode converter where its characteristics are theoretically studied. The suggested device can convert fundamental transverse electric modes to first-order transverse electric ones and vice versa. It is based on small material perturbation which introduces gradual coupling between different modes. This device is very simple and highly compact; the size of which is 3µm². A theoretical analysis of the proposed mode converter is developed using perturbative coupled-mode theory. Mathematical expressions for both the insertion loss and crosstalk are derived and optimized for best performance. In addition, three-dimensional finite-difference time-domain (3D-FDTD) simulations are performed in order to verify the mathematical model of the device. Our numerical results reveal that the proposed device has an insertion loss of 1.2dB and a crosstalk of 10.1dB. The device's insertion loss can be decreased to 0.95dB by adding tapers to its material perturbation.