Gain lifetime characterization through time-resolved stimulated emission in a whispering-gallery mode microresonator

TL;DR

This paper introduces a novel method to measure gain lifetime in photonic microresonators by analyzing linewidth changes in the optical mode, offering advantages over traditional photoluminescence techniques.

Contribution

The authors demonstrate a new approach using linewidth measurements in a whispering-gallery microresonator to determine gain lifetime, applicable to various materials and nanostructures.

Findings

Gain lifetime estimated at 5.1 ms in erbium-doped microresonator

Linewidth transitions from Lorentz peak to dip indicate gain decay

Method enhances efficiency with taper fiber coupling

Abstract

The precise measurement of the gain lifetime at a specific wavelength holds significant importance for understanding the properties of photonic devices and further improving their performances. Here, we show that the evolution of gains can be well characterized by measuring linewidth changes of an optical mode in a microresonator; this method cannot be achieved using time-resolved photoluminescence (PL) spectroscopy. We use an erbium-doped high-Q whispering-gallery microresonator to show the feasibility of this method. With the increase of time after the pump laser is turned off, the transmission spectrum of a probe signal exhibits transitions from a Lorentz peak to a dip; this indicates a decay of optical gains, and the corresponding lifetime is estimated to be 5.1 ms. Moreover, taper fiber coupling is used to increase the pump and collection efficiency. This method can be extended to other materials and nanostructures.