Wavelength tuning of amplified spontaneous emission through onchip control of the droplet size

Abstract Wavelength tunable amplified spontaneous emission (ASE) based on dye-doped ‘unconventional microdroplets’ which do not support the whispering gallery modes is demonstrated using a microfluidic chip. A tunability of around 18 nm in the wavelength of ASE is achieved by tweaking the size and shape of the droplets through controlling the pressure given to the chip, thus by modifying the flow rate of the liquid through the channel. The shift in ASE peak wavelength observed upon changing the droplet configuration is attributed to the concentration-dependent redshift exhibited by the dye molecules. This assumption is confirmed by observing a blueshift in emission peak after reducing the region of illumination of the chip, thereby reducing the number of dye molecules under the illumination region. Also, the droplet configuration consisting of the largest droplets have shown around 270 times enhancement in the peak intensity at 3 mJ pump energy, and around 20% reduction in threshold compared to the stream of smallest possible droplets.