Electro-optic tunable grating-assisted optical waveguide directional coupler in lithium niobate

Abstract

In this paper, a high-performance electro-optical tunable grating-assisted directional coupler (GADC) is proposed and demonstrated experimentally. Our proposed GADC consists of a two-mode waveguide (TMW) and a single-mode waveguide (SMW) formed with lithium niobite (LN). By introducing a longperiod waveguide grating into the side-wall of the TMW to compensate for the phase mismatch of the fundamental modes of the SMW and TMW, the fundamental modes of the two waveguides can be coupled e ciently each other at a speci c wavelength. Furthermore, push-pull electrode structure is introduced to achieve the electro-optic (EO) tuning function featuring high speed, low driving voltage, and large tuning range. The best LN GADC we fabricated on x-cut LN substrate using annealing proton exchange process shows a high isolation of ~ 34 dB at 1532.9 nm wavelength, quite large EO tuning e ciency of 1.195 nm/V (1526.4-1549.1 nm) or 1.736 nm/V (1576.1-1602.2 nm), and a thermo-optic tuning e ciency of 0.128 nm/°C (22 °C-60 °C). Our proposed LN GADC can nd applications in the elds of high-speed tunable wavelength ltering, mode ltering, and EO modulation.

Research on polarization beam splitter based on metamaterial subwavelength structure

“…Its main function is to decompose an incident beam of light into two mutually perpendicular beams of linearly polarised light [1-2], which plays a vital role in the fields of lasers, liquid crystal displays, optical storage， and polarised imaging. There are many types of PBS, such as Multiple Mode Interference (MMI) [3][4], Directional Coupler (DC) [5][6][7], Plasma Waveguide [8][9], etc. However, for all these structures, they suffer from a huge floor space and a poor extinction ratio.…”