Enhancement of Amplified Spontaneous Emission and Laser Performance of Rhodamine 6G/Cellulose Acetate DFB and DBR Waveguide Devices: A Role of Thermally Annealed P(VDF-TrFE) Intermediate Layer

Inserting a crystalline P(VDF-TrFE) intermediate layer under rhodamine 6G (R6G) laser active waveguide layer preserved the emissive R6G molecules in the matrix, which increases the intensity of fluorescence of R6G dye in the matrix and thus enhances the laser performance, including the optical gain of amplified spontaneous emission (ASE). The thermal annealing of the intermediate layer of P(VDF-TrFE) affects the optical gain of ASE and the laser performance in terms of slope efficiency and the threshold for the R6G/CA waveguide laser devices with DFB and DBR structures. With a higher annealing temperature, the crystallinity, crystallite size, and thus surface roughness of the P(VDF-TrFE) layer were increased; simultaneously, the fluorescence intensity, the optical gain of ASE, and the slope efficiency were increased, and the threshold for lasing was reduced. Thermal annealing of P(VDF-TrFE) at 120 °C gave a higher crystallinity, larger crystallite size, and thus deeper surface roughness. A DBR laser device with m = 2 mode number gave a slope efficiency of 4.6% and the optical gain of ASE of 13.0 cm–1. The deeper roughness of the surface due to the larger polar β-crystallites of P(VDF-TrFE) was significantly related to the increased intensity of fluorescence, optical gain of ASE, and slope efficiency for laser emission and the reduced threshold for lasing. The present approach is the easier way to enhance the lasing performances for ionic laser dyes in industrial applications.