Integrated Electro-Optic Isolator on Thin Film Lithium Niobate

TL;DR

This paper demonstrates a fully integrated electro-optic isolator on thin-film lithium niobate, achieving high isolation, low insertion loss, and broad tunability, advancing chip-scale optical system integration.

Contribution

It presents the first realization of a low-loss, high-isolation, broadband EO-based optical isolator on thin-film lithium niobate with practical on-chip integration.

Findings

Maximum optical isolation of 48 dB achieved.

On-chip insertion loss of 0.5 dB demonstrated.

Isolation ratio exceeds 37 dB across 1510-1630 nm wavelength range.

Abstract

Optical isolator is an indispensable component of almost any optical system and is used to protect a laser from unwanted reflections for phase-stable coherent operation. The development of chip-scale optical systems, powered by semiconductor lasers integrated on the same chip, has resulted in a need for a fully integrated optical isolator. However, conventional approaches based on application of magneto-optic materials to break the reciprocity and provide required isolation have significant challenges in terms of material processing and insertion loss. As a result, many magnetic-free approaches have been explored, including acousto-optics, optical nonlinearity, and electro-optics. However, to date, the realization of an integrated isolator with low insertion loss, high isolation ratio, broad bandwidth, and low power consumption on a monolithic material platform is still absent. Here we realize non-reciprocal traveling-wave EO-based isolator on thin-film LN, enabling maximum optical isolation of 48 dB and an on-chip insertion loss of 0.5 dB using a single-frequency microwave drive at 21-dBm RF power. The isolation ratio is verified to be larger than 37 dB across a tunable optical wavelength range from 1510 to 1630 nm. We verify that our hybrid DFB laser - LN isolator module successfully protects the single-mode operation and the linewidth of the DFB laser from reflection. Our result is a significant step towards a practical high-performance optical isolator on chip.