Efficient and Broadband Trident Spot-Size Convertor for Thin-Film Lithium Niobate Integrated Device

Thin-film lithium niobate on insulator (LNOI) has recently emerged as a promising platform for high-speed optical communication devices. For practical applications, an efficient, polarization-insensitive, misalignment-tolerant and broadband fiber-to-chip coupler is necessary. In this letter, we present edge based trident spot-size convertor (SSC). Experiment shows 1.18/1.10 dB per facet low loss at 1550 nm TE/TM polarization respectively. A relatively large alignment tolerance (AT) also been demonstrated. Over wavelength range from 1490 ~ 1640 nm, the exhibits maximum of 1.30 dB, dependent (WDL) 0.23 TE mode (PDL) 0.33 when coupled to single fiber (SMF) with field diameter (MFD) $6~\mu \text{m}$ .