Optical gain at 650 nm from a polymer waveguide with dye-doped cladding

Signal amplification at the polymer optical fiber low-loss window of 650 nm is reported in an SU8 rib waveguide coated with Rhodamine-640 doped poly(methyl methacrylate). A signal beam is end-fired into the facet of a $7\times 100\mu \mathrm{m}$ waveguide and amplified by top pumping of the $2\text{‐}\mu \mathrm{m}$ -thick cladding region with a pulsed pump source focused into a 9-mm-long stripe. A gain of 14dB and a minimum signal-to-noise ratio of around 2 dB are achieved in a 15-mm-long device with a low threshold pump intensity of $0.25\mu \mathrm{J}∕{\mathrm{mm}}^2$ , which is an order of magnitude lower than previously reported.