“In this paper, we provide an overview and comparison of devices used for optical waveguide-to-waveguide coupling including inter-chip edge couplers, grating couplers, free form couplers, evanescent couplers, cantilever couplers, and optical wirebonds. The objective of this paper is to provide a review of the theory, techniques, and applications of optical couplers. Coupling at optical frequencies presents challenges to achieving high efficiency, compactness, high fabrication tolerance, and ease of integration in photonic integrated circuits. Especially, the light coupling between optical fibers and integrated waveguide structures provides essential input-output interfaces for photonic integrated. A new technical paper titled “Advances in waveguide to waveguide couplers for 3D integrated photonic packaging” was published by researchers at MIT and Bridgewater State University. The coupler, called the universal impedance matching coupler, using this method has the shortest subwavelength coupling length, a 99.
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