Integrated optical orbital angular momentum multiplexing device using 3-D waveguides and a silica PLC

We demonstrate a low-loss hybrid-integrated device based on a silica planar lightwave circuit (PLC) coupled to a 3-D photonic circuit that efficiently generates and multiplexes 15 optical orbital angular momentum (OAM) modes in free space.

There is significant interest in utilizing space-division multiplexing (SDM), like time-division multiplexing and wavelength-division multiplexing, to increase the photon efficiency or spectral efficiency of free-space and fiber-optic links. SDM includes using optical orbital angular momentum (OAM) modes [1] (e.g., beams with azimuthally varying optical phase) to provide orthogonal information channels. Practical applications require integrated devices that multiplex and demultiplex OAM modes onto/from multi-mode fibers or free-space and also interface with single-mode fiber (SMF) components such as modulators and coherent receivers. Previously, our group and others have demonstrated OAM multiplexing using silicon photonic integrated circuits (PICs) [2], [3] that generate OAM beams with a single polarization from a waveguide grating structure. Here, we demonstrate an integratable OAM multiplexer based on hybrid integration of a silica planar lightwave circuit (PLC) with a silica 3-D PIC that supports up to 15 OAM modes, both TE and TM polarizations, and shows relatively low optical loss at , Fig. 1.

(A) Device concept. (b) illustration of the silica plc coupled to the 3-d pic. (c) detail of output face of 3-d waveguides. (d) photo of fabricated silica plc. (e) photo of 3-d pic output face before polishing.