Photorefractive and pyroelectric photonic memory and long-term stability in thin-film lithium niobate microresonators

TL;DR

This paper investigates the long-term stability and photorefractive and pyroelectric effects in thin-film lithium niobate microresonators, revealing a long-lived optical index change useful for photonic memory and device tuning.

Contribution

It uncovers the long-term stability issues and memory effects in TFLN microresonators, demonstrating optical trimming based on these effects, which was previously unexplored.

Findings

Long-lived change in optical refractive index over 10 hours.

Strong dependence of instability on crystal orientation.

Successful optical resonance frequency trimming using photonic memory.

Abstract

The stability of the integrated photonic circuits is of critical importance for many applications that require high frequency precision or robust operation over time, such as optomechanical sensing, frequency conversion, optical communication, and quantum optics. Photonic memory is useful for low-energy optical computing and interconnects. Thin film lithium niobate (TFLN), as an emerging photonic platform, exhibits complex material properties including pyroelectric (PE) and photorefractive (PR) effects which could lead to intra-device drift and excess noise under different environmental or operating conditions as well as be utilized for building photonic memory. However, the long-term stability and memory effect of its optical properties has not been explored. In this paper, we discovered a long-lived change of optical refractive index as a result of light excitation and temporal temperature variation using Z-cut TFLN microresonators and reveal a strong dependence of the instability with the crystal orientation of the thin film form. The recovery time are measured to be over 10 hours. Leveraging the photonic memory with a long relaxation time, we realize optical trimming of the cavity resonance frequencies. Our result offers insights towards understanding the fundamental noise properties and dynamic behavior of the integrated TFLN material and devices.