In this paper, we propose a tunable optical filter with a high Q factor based on photonic crystal technology, achieving a Q factor of 442.85 using thin film lithium niobate technology. By proportionally adjusting the dimensions of the unit structure, this filter enables coarse tuning across the 1520–1570 nm range (C band). Furthermore, by utilizing the thermo-optic effect of lithium niobate, we can achieve fine-tuning of the optical filter within a temperature range of 300 K to 600 K, allowing for a center wavelength tuning capability of up to 3.7 nm. This design not only enhances the filter’s performance but also broadens its potential applications in optical communication and optical signal processing.

A 90° optical hybrid employing an MMI coupler was fabricated on a thin-film lithium niobate (TFLN) platform that can be used for integrated coherent transceivers. The fabricated 90° optical hybrid exhibited a CMRR greater than 20 dB, a phase error below ±7.5°, and an excess loss less than 1.8 dB (including contributions from the 90° hybrid, a 1 × 2 MMI coupler, and an optical delay line, after subtracting the losses from the coupler and delay line, the 90° optical hybrid introduced less than 0.9 dB of loss) over the C-band with a compact footprint of 13.8 × 250 μm², facilitating the future development of high-bandwidth optical coherent transceivers heterogeneously integrated on TFLN.