The forked grating coupler (FGC) is a novel low-profile device compatible with silicon photonics that is capable of sensitive detection or efficient radiation of Optical Vortex (OV) light beams conveying orbital optical angular momentum (OAM). The FGC device combines the idea of a Bragg coupler with the forked hologram to create an integrated optics device that can selectively and efficiently couple selected optical vortex modes at near-normal incidence into planar confined dielectric waveguide modes of a photonic IC. FGCs retain many of the advantages of Bragg couplers, including convenience of placement and fabrication, reasonable bandwidth, small size, and CMOS process compatibility. In this work, prototype designs of FGC structures for 1550 nm wavelength have been developed for implementation on silicon on insulator (SOI) substrate. Fully vectorial three-dimensional (3D) electromagnetic simulation has allowed performance to be optimized over a range of structural parameters. Results have been evaluated against optical performance metrics including overall efficiency, mode match efficiency, and crosstalk between OV modes. Candidate FGC devices have been fabricated on SOI with e-beam lithography and tested optically. Tolerance to etch depth error has been evaluated.
Christopher T. Nadovich, Derek J. Kosciolek, William D. Jemison, and David T. Crouse, "Forked grating coupler optical vortex beam interface for silicon photonics," Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 99181J (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 16 September 2016); https://doi.org/10.1117/12.2236708.
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