Monolithic optofluidic ring resonator lasers created by femtosecond laser nanofabrication

Abstract

We designed, fabricated, and characterized a monolithically integrated optofluidic ring resonator laser that is mechanically, thermally, and chemically robust. The entire device, including the ring resonator channel and sample delivery microfluidics, was created in a block of fused-silica glass using a 3-dimensional femtosecond laser writing process. The gain medium, composed of Rhodamine 6G (R6G) dissolved in quinoline, was flowed through the ring resonator. Lasing was achieved at a pump threshold of approximately 15 μJ mm⁻². Detailed analysis shows that the Q-factor of the optofluidic ring resonator is 3.3 × 10⁴, which is limited by both solvent absorption and scattering loss. In particular, a Q-factor resulting from the scattering loss can be as high as 4.2 × 10⁴, suggesting the feasibility of using a femtosecond laser to create high quality optical cavities.