Integrated fiber grating couplers in silicon photonics [article]

Benjamin Wohlfeil, Klaus Petermann, Technische Universität Berlin, Technische Universität Berlin
To satisfy the ever increasing demand in bandwidth in modern communication systems, optical transmission is replacing the increasingly insufficient electronic communication devices. Although primarily employed for large distances, much research has been focused recently on the application of optical communication on much smaller ranges, such as chip to chip or even on-chip transmission. Integrating photonic components enables the conception of high speed transceivers, that are necessary for the
more » ... e necessary for the multi-level transmission systems, which will provide the necessary bandwidth in years to come. The Silicon-on-Insulator platform is the prime candidate for this as it provides excellent properties for silicon photonic components and also enables the co-integration of optical functionality alongside with electronic devices, thus complementing the shortcomings of either technology. Due to the high refractive index in the near-infrared region of the electromagnetic spectrum, silicon provides for very compact waveguides of only a few hundred nanometers in size. However, this otherwise beneficial property states a problem when trying to connect a compact silicon waveguide with the external world: Coupling light between an optical fiber of several microns in size and a much smaller integrated waveguide is potentially a very lossy endeavor. This thesis addresses the problem of fiber-chip-coupling by means of silicon photonic grating couplers and describes solutions to varying problems and technological constraints. Starting with a very basic grating coupler designed for the vacuum wavelength λ=1310nm and offering a measured coupling efficiency of -3.8dB more complex and better performing gratings for the wavelength region around λ=1550nm are presented. With a locally grown epitaxial silicon layer on top of the grating coupler 1.7dB coupling loss were achieved, which was shown by simulations could be further improved by making use of a second grating etch step to the otherwise uniform grating. Following this line of thought, the q [...]
doi:10.14279/depositonce-4521 fatcat:yproflqzeffevpvjat54qguxhu