End-Facet Polishing of Surface Plasmon Waveguides in Lithium Niobate

This paper describes a custom polishing procedure developed to produce high quality end-facets on die having a rather unique cross section. The dies comprise two thin lithium niobate claddings on either side of a thin narrow gold stripe, supported by a silicon substrate. This heterogeneous structure operates as an optical waveguide supporting a long-range surface plasmon-polariton mode, and is fabricated via wafer-bonding and thinning. Optical insertion loss measurements were obtained on a set of diced waveguides before and after end-facet polishing. Polishing reduced the insertion loss of the waveguides by 4.7-9.1 dB, indicating that one as-diced end-facet contributes a scattering loss of 2.35-4.55 dB.