Influence of Refractive Index on Lasing Coupling Efficiency and Emission Spectrum

An optical fiber with a diameter of 125 μm is integrated in a polydimethylsiloxane (PDMS) microfluidic channel. The lasing gain medium is consisted of a lower refractive index (RI) rhodamine 6G (Rh6G) dye solution. With this configuration, we have presented the study on the lasing coupling efficiency and lasing emission spectrum affected by the RI of the dye solution under different polarization states of the pump light. When the fiber is pumped by a linearly s- or p-polarized light, the intensity of the emitted whispering gallery modes (WGMs) lasing, i.e., transverse magnetic (TM) or transverse electric (TE) mode, decreases by approximately two-fold as the RI of the dye solution increases from 1.325 to 1.419, meaning a significant difference on the lasing coupling efficiency is achieved under different RI of the dye solution. When the fiber is excited by a s- and p-mixed polarized light, the mode separation between the adjacent TM and TE mode decreases with the increase of the RI of the dye solution, providing a simple and effective method for applications, such as RI sensing.