Thermally resettable laser transmission induced transparency in polymer waveguides at 635 nm

Laser transmission induced transparency (LTIT) has been observed in a polymer waveguide using commercial perfluorinated acrylate-based materials when a continuous-wave laser at 635 nm is injected. The transmitted optical power increases continuously and follows a non-linear curve with respect to the laser injection time. Loss reduction over 13 dB is observed within 60 min at a moderate laser power of 5 mW. While higher injection power leads to a quicker change of the waveguide transparency, this loss reduction tends to saturate at a level irrelevant to the injection power. Further experiments demonstrate that a laser injection at 635 nm can also slightly improve the transparency at near-infrared wavelengths from 1500 nm to 1600 nm which is also the target wavelength range for this material. The state after a certain laser injection dose of 635 nm proves to be stable and the transmission characteristics of the polymer waveguide can be maintained and will continue after being stored at room temperature over a long period of time. By baking the waveguide at 200 °C for 20 min, the transparency property can be reset and the waveguide will return to the original high-loss state of 635 nm. These unique properties can be attributed to the photo-induced generation and thermally induced recombination of free radicals in the organic material. Our discovery may trigger interesting applications of polymer waveguides in the development of optical memory, clock, and encryption devices, beyond their target applications in optical communication.