A characterization of Rhodamine 640 for optical amplification: Collinear pump and signal gain properties in solutions, thin-film polymer dispersions, and waveguides

We report a study of the optical signal amplification properties of Rhodamine 640 in solution, in thin-film format dispersed within a poly(methyl methacrylate) (PMMA) polymer matrix, and in a waveguiding structure created by coating polymer-dispersed Rhodamine 640 onto a patterned quartz substrate. The optical signal amplification experiments were carried out using a collinear pump and signal setup. Depending on both pump and signal energies, gains of up to 41 dB were achieved in solution, while 1% by weight dye-doped PMMA films showed net gains of $54{\mathrm{cm}}^{-1}$ , and associated losses of $16{\mathrm{cm}}^{-1}$ . Using the same concentration dye/PMMA dispersions, waveguide structures were fabricated with a $120\times 1{\mu \mathrm{m}}^2$ cross section and a length of 1.2 cm. The internal optical gain values measured at 625 and 650 nm were found to be as high as 26 and 8 dB, respectively. The corresponding signal-to-noise ratio was in the 7–21-dB range at 625 nm and in the 3–21-dB range at 650 nm. Both in solution and in the waveguide structures we found that amplified spontaneous emission had a detrimental effect on the optical gain characteristics through a decrease in the signal-to-noise ratio.