Silicon Multimode Waveguide Crossing Based on Anisotropic Subwavelength Gratings

Abstract

Multimode waveguide crossings (MWCs) are becoming more and more important as one of the key elements for on-chip optical routing and cross-connection. However, it is still very challenging to achieve scalable MWCs with compact footprints, low excess losses (ELs), and low intermode cross-talks (CTs). This work demonstrates an unprecedented silicon MWC with high performances by using the anisotropy of one-/two-dimensional (1D/2D) subwavelength grating (SWG) structures. For the proposed silicon MWC, the 2D-SWG crossing region at the center has a higher refractive index than the 1D-SWG regions at both sides for the guided-modes of TE polarization, due to the anisotropy of the 1D/2D SWGs. As a result, the crossing region can be equivalent to a straight waveguide, and the launched TE modes can transmit through the crossing region with negligible ELs and low intermode CTs. Such an MWC can be scaled very flexibly and easily according to the new principle. The fabricated three-mode MWC with a footprint of 14.8 × 14.8 µm 2 shows ELs of <0.26 dB and intermode CTs of <−20 dB in the wavelength range of 1525-1605 nm.

Ultra‐Broadband Multimode Waveguide Crossing via Subwavelength Transmitarray with Bound State

“…2D SWG [34] 3 (TE 0 -TE have ELs less than 0.98 dB and CTs less than −23 dB in the wavelength range of 1400-2100 nm for TE-type design. And for the TM-type design supporting TM 0 -TM 9 , the numerical simulation results show that all ten modes have ELs less than 1.08 dB and CTs less than −19 dB within the wavelength range of 1400-1700 nm.…”

“…However, constraints exist on their optical bandwidth and footprint since most of the lenses are dispersive and large. Here, we propose a simple asymmetric SWTA structure as an alternative of subwavelength grating (SWG) [34,42] to provide a bound state within the crossing region. The bound state of the crossings that behave like waveguide bulges can always be found if the wavefunction vanishes on the boundary.…”

“…More recently, Zhao et al demonstrated a promising technique using sophisticatedly designed subwavelength grating, which is able to provide anisotropic index profile for orthogonal directions. [34] The device has a broadbandwidth of 80 nm, while it occupies a chip area of 14.8 µm × 14.8 µm for three modes. Hence, the difficulty is associated with constructing a delicate refractive index profile for wavefront shaping and dispersion engineering without occupying too much chip area.…”

High-Speed Optical Mode Switch in Lithium Niobate on Insulator

“…Furthermore, MDM can easily be combined with other multiplexing technologies to realize larger-scale parallelism for data communication. 7,8 Due to the inherent advantages of the MDM technology, various optical multimode building blocks have been demonstrated on the silicon-oninsulator (SOI) platform, such as optical mode (de)multiplexers, 9,10 multimode waveguide bends, 11,12 multimode waveguide crossings, 13,14 optical mode exchangers, 15,16 and optical mode switches. 17−19 Among them, optical mode switches play a key role in the high-speed MDM networks to switch signals on and off.…”

High‐Performance Mode‐Multiplexing Device with Anisotropic Lithium‐Niobate‐on‐Insulator Waveguides

“…[16][17][18] Note that multimode photonics is enormously attractive because the introduction of higher-order modes greatly enhances the link capacity with the mode-division multiplexing (MDM) technology [19,20] as well as improves the design flexibility of on-chip photonic devices. [21] Currently multimode photonics has been investigated extensively on silicon, and various multimode silicon photonic devices have been developed successfully, including mode (de)multiplexers, [22,23] multimode waveguide bends (MWBs), [24][25][26][27][28] and multimode waveguide crossings, [29,30] etc. Furthermore, multimode photonics also shows great potential for some applications such as enhanced electro-optic and thermo-optic modulations, [31,32] phasematching for nonlinear photonics, [33,34] and high-Q ringresonators, [35,36] etc.…”