论文链接： https://ieeexplore.ieee.org/document/10336842

Polarization controlling devices on thin-film lithium niobate (TFLN) are critical components for photonic integrated circuits (PICs) on the platform because the birefringence of lithium niobate intrinsically determines its polarization-dependent property. Polarization beam splitter (PSR) is the most important polarization controlling device on TFLN, because it can simultaneously split and rotate the TM polarization into TE polarization. So far, a few PSRs on TFLN have been reported, but the lengths of these devices are longer than 400 μm, some even reaching the millimeter level, which is not favorable in dense integration. And due to the excessive long footprint of the devices, the insertion loss increases inevitably.

Here, we demonstrated a compact PSR on TFLN based on two adiabatic tapers and an asymmetric DC. The device is fabricated via a one-step electron beam lithography (EBL) and inductively coupled plasma (ICP) etching process. The total length of the device is only 240 µm, and the TE and TM polarization modes have high extinction ratios within the entire telecom-C band. The experimentally measured polarization extinction ratios (PERs) of TE and TM modes exceed 26.6 dB and 10.6 dB respectively in the wavelength range of 1520-1570 nm. At the same time, the PER of the two orthogonal modes both exceed 30 dB at the wavelength of 1544 nm. The device is readily applicable for efficient polarization multiplexing and polarization modulating, which will become an indispensable component of the PICs on TFLN in the future.

Fig. 1. (a) Schematic illustration of the PSR on TFLN. (b) Cross section and (c) top view of the PSR (not to scale).

Fig.2. Light propagation in the PSR at 1550 nm.

Fig. 3. (a) Optical microscope and (b) SEM images of the fabricated PSR, the cross section of the input waveguide and a straight waveguide.

Fig. 4. (a) Output intensity distribution and mode profiles at different input polarization states, i.e., TE, 45◦, TM mode input. (b) Experimental transmission at through and cross ports for TE and TM mode input.

This research is published by “Yinan Wu, Xuerui Sun, Xiaotian Xue, Hao Li, Shijie Liu, Yuanlin Zheng, and Xianfeng Chen, Compact Adiabatic Polarization Splitter-Rotator on Thin-Film Lithium Niobate, Journal of Lightwave Technology, 42(7), 2429-2435 (2024)”.

Link: https://ieeexplore.ieee.org/document/10336842