Intermodal Group Delay in Multimode Waveguides on LNOI and SOI for Optical Interconnects

Abstract

Mode division multiplexing (MDM) is one of the recent technologies to circumvent the capacity-crunch in single-mode waveguides for on-chip communication [1]. MDM uses orthogonal modes of multimode waveguides as independent carriers, that can be employed in optical interconnects for on-chip communication between multiple cores. Intermodal group delay (Δτ g ) that causes pulse broadening, limits the data rate in such digital communication systems. Δτ g arises because of differences in the group velocities of various modes propagating in multimode waveguides. This paper numerically evaluates group delay (τ g ) for four-mode wide waveguides supporting four quasi transverse electric (qTE) modes on buried, strip and rib configurations as well as tall waveguides supporting four quasi transverse magnetic (qTM) modes. Waveguides are designed on lithium niobate on insulator (LNOI) with X-cut, Z-cut orientation and silicon on insulator (SOI) high-contrast integrated photonic platforms at a wavelength (λ) of 1550 nm. The dimensions are tailored to have good power confinement in the core (> 75%) along with a TE polarization fraction > 92% for qTE and g per unit length of the waveguide is evaluated from equation (1). The group delay difference between the fastest and the slowest mode is considered as the overall intermodal group delay of the waveguide (10 mm long).