Thermo-Optical Tuning of Whispering Gallery Modes in Er:Yb Doped Glass Microspheres to Arbitrary Probe Wavelengths

TL;DR

This paper demonstrates an all-optical, thermally-assisted method to tune whispering gallery modes in Er:Yb doped glass microspheres across a broad range, enabling precise alignment with arbitrary probe wavelengths for applications in quantum optics and photonics.

Contribution

The study introduces a robust thermo-optical tuning technique that decouples pump and probe, allowing fine and broad-range resonance tuning in microsphere cavities, including specific alignment with atomic transitions.

Findings

Successful tuning to the 85Rb laser cooling transition

Broad tuning range achieved for various probe wavelengths

Decoupled pump and probe for precise control

Abstract

We present experimental results on an all-optical, thermally-assisted technique for broad range tuning of microsphere cavity resonance modes to arbitrary probe wavelengths. An Er:Yb co-doped phosphate glass (Schott IOG-2) microsphere is pumped at 978 nm via the supporting stem and the heat generated by absorption of the pump light expands the cavity and changes the refractive index. This is a robust tuning method that decouples the pump from the probe and allows fine tuning of the microsphere's whispering gallery modes. Pump/probe experiments were performed to demonstrate thermo-optical tuning to specific probe wavelengths, including the 5S1/2 F = 3 to 5P3/2 F' = 4 laser cooling transition of 85Rb. This is of particular interest for cavity QED-type experiments, while the broad tuning range achievable is useful for integrated photonic devices, including sensors and modulators.