Probing material absorption and optical nonlinearity of integrated photonic materials

TL;DR

This study measures the fundamental material absorption limits of high-Q microresonators made from various photonic materials, revealing how material nonlinearity and absorption jointly influence device performance.

Contribution

It introduces a cavity-enhanced photothermal spectroscopy method to determine the material-limited Q factors and Kerr nonlinearities across multiple photonic materials.

Findings

Material-limited Q factors vary among different materials.

Kerr nonlinearity correlates with material absorption.

Results guide future microresonator design and material development.

Abstract

Optical microresonators with high quality ($Q$) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator $Q$ factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of $Q$, the ultimate attainable $Q$, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited $Q$ factors in several photonic material platforms. High-$Q$ microresonators are fabricated from thin films of SiO$_2$, Si$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. By using cavity-enhanced photothermal spectroscopy, the material-limited $Q$ is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate $Q$ vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.