Optofluidic Ring Resonator Dye Microlasers

We discuss versatile, miniaturized optofluidic ring resonator (OFRR) dye lasers that can be operated regardless of the refractive index of the liquid. The OFRR is a piece of a thin-walled fused silica capillary that integrates the photonic ring resonator with microfluidics. In an OFRR dye laser, the active lasing materials (such as dyes) are passed through the capillary whereas the circular cross section forms a ring resonator and supports whispering gallery modes that provide optical feedback for lasing. Because of the high Q-factors extremely low lasing threshold is achieved (25 nJ/mm²). The operation wavelength can conveniently be changed by using different dyes and fine-tuned with solvent. The OFRR laser is excited through direct excitation or through efficient energy transfer. The laser can be efficiently out-coupled through a fiber taper in contact with the capillary, thus providing easy guiding for the laser emission. Theoretical analysis and experimental results for OFRR lasers are presented.