Bending-Induced Bidirectional Tuning of Whispering Gallery Mode Lasing from Flexible Polymer Fibers

Polymer microfibers with a circular cross-section are directly drawn from a solution. By encapsulating the dyedoped microfibers with polydimethylsiloxane (PDMS) elastomer, optically pumped lasing with enhanced photostability is achieved. The lasing characteristics as well as size-dependent lasing action are carefully analyzed, and the lasing phenomenon is ascribed to whispering gallery mode. The PDMS elastomer offers another degree of freedom to mechanically tune the lasing from microfibers. It is interesting to note that by different types of bending, bidirectional shifting of the laser wavelength is observed, which is due to strain-induced refractive index change of the fiber and PDMS matrix. Our studies not only show an effective method to passivate the microfibers, but also open up a new approach to manipulating the lasing, which allows for fine adjustment of laser emission to any desired wavelength within the tuning range.