On-chip multidimensional (de)multiplexer utilizing adiabatic structure-connected micro-ring resonators

Abstract

On-chip multidimensional multiplexing has shown considerable potential for enhancing transmission capacity and developing communication networks in integrated optical systems. Micro-ring resonators, which utilize the wavelength-dependent whispering gallery resonance mechanism and feature customizable cavity lengths, offer inherent advantages for accurate wavelength filtering. These characteristics make them promising candidates for wavelength multiplexers. However, a significant challenge arises from the mismatch in the effective refractive index between orthogonal linear polarizations, which introduces complexities to polarization channel multiplexing and impedes progress in on-chip multidimensional multiplexing that integrates both wavelength and polarization channels. In this work, we propose a double-layer adiabatic structure-connected micro-ring resonator (AMRR) with vertical refractive index asymmetry, demonstrating its utility in multidimensional (de)multiplexers. Our approach enables polarization division multiplexing (PDM) by facilitating polarization rotation between transverse electric and transverse magnetic polarizations through polarization hybridization. The (de)multiplexing of both wavelength and polarization channels is achieved by controlling the incident light direction and filtering the resonance wavelength within the micro-ring resonator. As a proof of concept, we successfully transmitted 144 Gbit/s QPSK-OFDM signals and achieved bit error rates below the forward error correction threshold at −19 dBm using the proposed multidimensional (de)multiplexer, which accommodates 3 wavelengths and 2 polarizations. Our design, which leverages the AMRR for simultaneous (de)multiplexing of wavelength and polarization channels, not only overcomes the limitation of traditional micro-ring resonators in implementing PDM, but also reduces the footprint of the multidimensional (de)multiplexer to 27 µm × 219 µm, an order of magnitude smaller compared to conventional designs.