A 32-Channel Hybrid Wavelength-/Mode-Division (de)Multiplexer on Silicon

Abstract

A monolithically integrated 32-channel hybrid (de)multiplexer on silicon is proposed and experimentally demonstrated to enable wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) simultaneously for a large capacity of optical interconnect links. The proposed (de)multiplexer consists of a four-channel mode (de)multiplexer based on cascaded asymmetric directional couplers and eight-channel wavelength-division-(de)multiplexers based on two microring resonator (MRR) arrays with a channel spacing of 2 nm. These MRRs are realized with a bending radius of as small as $4~\mu \text{m}$ by introducing a multimode microring waveguide so that a large free spectral range (~24 nm) is enabled for transverse magnetic polarization. Furthermore, each MRR works bi-directionally and provides two drop ports from which the same wavelength-channel from two of the mode-channels is dropped separately. For the fabricated 32-channel hybrid MDM-WDM (de)multiplexer, the excess loss is <−4.5 dB, the inter-mode crosstalk is <−18 dB, and the crosstalks between the adjacent and non-adjacent wavelength-channels are ~−20 and <−25 dB, respectively.