Microcavity-based parallel measurements of optical power and wavelength

Abstract

Accurate determination of light power and wavelength is fundamental to nearly all optical and laser applications. However, simultaneous and precise measurements of these two parameters remain a critical challenge due to intrinsic cross-sensitivity in conventional devices. Here, we propose and demonstrate a dual-parameter decoupling strategy based on photothermal whispering gallery mode (WGM) microcavities, enabling parallel measurements of both optical power and wavelength without cross-sensitivity. Optical absorption of the pump light by the composite microcavity produces increased temperatures that are proportional to the pump power and wavelength of the light, resulting in a wavelength shift in the WGM resonance of the microcavity. We demonstrate a record-high photothermal tuning sensitivity of ∼−4 nm/mW and an ultralow detection limit of thermal power down to 4 μW, both of which surpass all previous schemes by more than an order of magnitude. With a linear response to the pump wavelength, the designed microcavity allows for near-infrared wavelength measurement over a broad bandwidth from 780 to 1064 nm. Importantly, by introducing the decoupling strategy that employs spectral changes of two microcavities with asymmetric responses, we demonstrate parallel measurements of both optical power and wavelength with high accuracy. As the first proof-of-principle demonstration of a single optical power–wavelength measurer using optical microcavities, our work could advance various applications relying on miniaturized and precise optical metrology devices.