Optofluidic distributed feedback lasers with evanescent pumping : reduced threshold and angular dispersion analysis

Abstract

We demonstrate an evanescently pumped water-based optofluidic DFB laser with a record low pump threshold of ETH = 520 nJ. The low threshold results from an optimized mode shape, which is achieved by a low refractive index substrate, and from the use of a mixed-order DFB grating. Investigating the photonic band structure via angular dispersion analysis both above and below lasing threshold allows us to measure the refractive index of the liquid gain layer and to determine device parameters such as the waveguide core layer thickness. We show that it is possible to tailor the divergence of the lasing emission by varying the number of second order grating periods used for outcoupling.