Highly-efficient thin film LiNbO3 surface couplers connected by ridge-waveguide subwavelength gratings

Abstract

The ridge waveguide integrated grating couplers (GCs) in lithium niobate on insulator (LiNbO 3 , LNOI) were designed, fabricated and characterized. Two ends of the gratings structures were connected through the middle photonic rib-waveguide of a sub-micrometric-diameter, which was nanostructured with the geometry of side-wall corrugated subwavelength gratings structure. A high coupling efficiency of -5.1 dB for the best thin film LiNbO 3 (TFLN) grating coupler was measured at the telecommunication wavelength of 1561 nm for quasi-transverse-electric (TE) polarized signals, with a broad 3-dB optical bandwidth of wider than 95 nm. All the devices structure patterns for the integrated LNOI GCs could be simultaneously defined by one step of electron-beam lithography, and then easily fabricated by the dry-etching processes. This compact component exhibited magnificent performance, and might show the potential functionalities for the TFLN-based integrated optical waveguide devices.

Integrated Subwavelength Gratings on a Lithium Niobate on Insulator Platform for Mode and Polarization Manipulation

“…Moreover, the etching techniques developed for lithium niobate thin film are still specialized, resulting in limited reproducibility compared with other platforms, e.g., SOI. [20] In this contribution, we propose and demonstrate compact SWG waveguides on a LNOI platform. To overcome the aforementioned challenges, a silicon nitride thin film is deposited onto the surface of the LNOI chip, where the SWGs are designed and formed using mature CMOS-compatible etching processes developed by microelectronics industry.…”

“…Moreover, the etching techniques developed for lithium niobate thin film are still specialized, resulting in limited reproducibility compared with other platforms, e.g., SOI. [ 20 ]…”