Ultracompact polarization-insensitive power splitter using subwavelength-grating-based MMI couplers on an SOI platform.

Abstract

An ultracompact and polarization-insensitive power splitter using a subwavelength-grating-based multimode interference (MMI) coupler on an SOI platform is proposed and analyzed in detail. By properly tailoring the structural parameters of the subwavelength gratings embedded in the center of the MMI coupler, the effective reflective indices for TE and TM modes supported by this MMI coupler can be engineered, leading to equal coupling lengths for the two polarizations and an efficient reduction in length for the used MMI coupler. As a result, an ultracompact polarization-insensitive power splitter can be realized. Moreover, to effectively minimize the loss, tapered waveguides are used, and two right angles are cut at both corners of the used MMI coupler. Results show that a footprint of ${2}.{2}\;\unicode{x00B5} {\rm m} \times {3}.{8}\;\unicode{x00B5} {\rm m}$2.2µm×3.8µm for the MMI region is achieved with an insertion loss of 0.07 dB for both TE and TM modes (polarization dependent loss ${\sim\;{0}\;{\rm dB} }$∼0dB) and a reflection loss of $ - {28}.{29}\;{\rm dB}$-28.29dB ($ - {31}.{25}\;{\rm dB}$-31.25dB) for TE mode at the wavelength of 1.55 µm. Insertion loss below 0.3 dB is obtained over the bandwidth of 200 nm, covering the C-band. In addition, fabrication tolerances to the structural parameters are analyzed, and the injected light propagating through the power splitter is also presented.