Laser-transmission-induced Raman emission masked by progressive transparency in polymer waveguides

Laser-transmission-induced Raman emission (LTIR) in polymer waveguides is observed and analyzed in this work. When injected with a 532-nm continuous-wave laser of 10 mW, the waveguide shows a distinct line of orange-to-red emission, which is quickly masked by the green light in the waveguide due to the laser-transmission-induced transparency (LTIT) at the source wavelength. However, when a filter is applied to remove the emission below 600 nm, a clear red line is shown in the waveguide, which stays constant over time. Detailed spectral measurements show that the polymer material can generate broadband fluorescence when illuminated with the 532-nm laser. However, a distinct Raman peak at 632 nm only appears when the laser is injected into the waveguide with much higher intensity. The LTIT effect is fitted based on experimental data to describe the generation and fast masking of the inherent fluorescence and LTIR effect empirically. The principle is analyzed through the material compositions. This discovery may trigger novel on-chip wavelength-converting devices using low-cost polymer materials and compact waveguide structures.