Optofluidic laser array based on stable high-Q Fabry–Pérot microcavities

Abstract

We report the development of an optofluidic laser array fabricated on a chip using stable plano-concave Fabry–Pérot (FP) microcavities, which are far less susceptible to optical misalignment during device assembly than the commonly used plano-plano FP microcavities. The concave mirrors in our FP microcavities were created by first generating an array of microwells of a few micrometers in depth and a few tens of micrometers in diameter on a fused silica chip using a CO₂ laser, followed by coating of distributed Bragg reflection (DBR) layers. The plano-concave FP microcavity had a Q-factor of 5.6 × 10⁵ and finesse of 4 × 10³, over 100 times higher than those for the FP microcavities in existing optofluidic lasers. 1 mM R6G dye in ethanol was used to test the plano-concave FP microcavities, showing an ultralow lasing threshold of only 90 nJ mm⁻², over 10 times lower than that in the corresponding unstable plano-plano FP microcavities formed by the same DBR coatings on the same chip. Simultaneous laser emission from the optofluidic laser array on the chip and single-mode lasing operation were also demonstrated. Our work will lead to the development of optofluidic laser-based biochemical sensors and novel on-chip photonic devices with extremely low lasing thresholds (nJ mm⁻²) and mode volumes (fL).