Near-infrared luminescent polymer waveguides and microlasers

ABSTRACT We have fabricated and characterized polymeric slab asymmetric waveguides doped with a near-infrared-emitting dye, 2-(6-(p-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-ethylbenzothiazolium perchlorate. Upon nanosecond photopumping, the waveguides have shown a small-signal gain coefficient of 37.2 ± 2.1 cm -1 at 820 nm for a pump fluence of 1.57 mJ/cm 2 (314 kW/cm 2 ). The loss coefficient and transparency fluence have been found to be 7.3 ± 1.0 cm -1 at 820 nm and 0.14 mJ/cm 2 (28 kW/cm 2 ), respectively. It is shown that a small-signal gain of 19.7 ± 2.3 dB is achievable in a 1.2-mm-long waveguide. Furthermore, near-infrared laser emission from self-assembled luminescent polymer microcavities has been demonstrated. The microrings are formed around silica optical fibers of varying diameters (80, 125, and 200 µm) and the larger microresonators have an overall quality factor of ~2 × 10 3 , which is limited by surface roughness and scattering. We illustrate how the laser threshold varies inversely with both the quality factor and the inner diameter of the microrings. The free spectral range and the intensity variation of the laser output are also presented. Keywords: Amplified spontaneous emission, microcavities, near-infrared region, organic dye, optical gain, polymer lasers, waveguide amplifiers