Fiber to chip coupling is a critical aspect of any integrated photonic circuit. In terms of ease of fabrication as well as wafer-scale testability, surface grating couplers are by far the most preferred scheme of the coupling to integrated circuits. In the past decade, considerable effort has been made for designing efficient grating couplers on Silicon-on-Insulator (SOI) and other allied photonic platforms. Highly efficient grating couplers with sub-dB coupling performance have now been demonstrated. In this article, we review the recent advances made to develop grating coupler designs for a variety of applications on SOI platform. We begin with a basic overview of design methodology involving both shallow etched gratings and the emerging field of subwavelength gratings. The feasibility of reducing footprint by way of incorporating compact tapers is also explored. We also discuss novel grating designs like polarization diversity as well as dual band couplers. Lastly, a brief description of various packaging and wafer-scale testing schemes available for fiber-chip couplers is elaborated.
Silicon Nitride (SiN) is emerging as a promising material for a variety of integrated photonic applications. Given its low index contrast however, a key challenge remains to design efficient couplers for the numerous platforms in SiN photonics portfolio. Using a combination of bottom reflector and a chirp generating algorithm, we propose and demonstrate high efficiency, grating couplers on two distinct SiN platforms. For a partially etched grating on 500 nm thick SiN, a calculated peak efficiency of −0.5 dB/coupler is predicted, while for a fully etched grating on 400 nm thick SiN, an efficiency of −0.4 dB/coupler is predicted. Experimentally measured coupling efficiencies are observed to be −1.17 and −1.24 dB/coupler for the partial and fully etched grating couplers respectively in the C-L band region. Furthermore, through numerical simulations, it is shown that the chirping algorithm can be implemented in eight additional combinations comprising SiN film thickness between 300–700 nm as well as alternate claddings, to achieve a per coupler loss between −0.33 to −0.65 dB.
We report the experimental realization of a compact, efficient coupler between silicon waveguides and vertical metal-insulator-silicon-metal (MISM) plasmonic waveguides. Devices were fabricated using complementary metal-oxide-silicon technology processes, with copper layers that support low-loss plasmonic modes in the MISM structures at a wavelength of 1550 nm. By implementing a short (0.5 μm) optimized metal-insulator-silicon-insulator structure inserted between the photonic and plasmonic waveguide sections, we demonstrate experimental coupling loss of 2.5 dB, despite the high optical confinement of the MISM mode and mismatch with the silicon waveguide mode.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.