# Low threshold anti-Stokes Raman laser on-chip

## TL;DR

This paper demonstrates on-chip ultra-high Q silica microcavities doped with metal, achieving low-threshold anti-Stokes Raman lasing with significantly improved efficiency and enabling SARS at sub-milliwatt power levels.

## Contribution

Introduction of metal doping in ultra-high Q silica microcavities to enhance Raman gain and circulating intensity, enabling efficient on-chip anti-Stokes Raman lasing at low power thresholds.

## Key findings

- SARS generated with sub-mW input powers.
- Raman lasing efficiencies over 10x higher than conventional silica microcavities.
- Low lasing thresholds achieved for anti-Stokes Raman lasing.

## Abstract

Raman lasers based on integrated silica whispering gallery mode resonant cavities have enabled numerous applications from telecommunications to biodetection. To overcome the intrinsically low Raman gain value of silica, these devices leverage their ultra-high quality factors (Q), allowing sub-mW stimulated Raman scattering (SRS) lasing thresholds to be achieved. A closely related nonlinear behavior to SRS is stimulated anti-Stokes Raman scattering (SARS). This nonlinear optical process combines the pump photon with the SRS photon to generate an upconverted photon. Therefore, in order to achieve SARS, the efficiency of the SRS process must be high. As a result, achieving SARS in on-chip resonant cavities has been challenging due to the low lasing efficiencies of these devices. In the present work, metal-doped ultra-high Q (Q>107) silica microcavity arrays are fabricated on-chip. The metal-dopant plays multiple roles in improving the device performance. It increases the Raman gain of the cavity material, and it decreases the optical mode area, thus increasing the circulating intensity. As a result, these devices have SRS lasing efficiencies that are over 10x larger than conventional silica microcavities while maintaining low lasing thresholds. This combination enables SARS to be generated with sub-mW input powers and significantly improved anti-Stokes Raman lasing efficiency.

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Source: https://tomesphere.com/paper/1907.02448