Linear and Nonlinear Optical Properties of Polydiacetylene Waveguides.

The linear and nonlinear optical properties of a spin-coated polydiacetylene, (5,7-dodecadiyn-1,12-diol -bis(n-butoxy-carbonyl-methyl-urethane)), or poly(4BCMU), were measured to predict its performance in all-optical devices at 1.319 mum. Material requirements for all-optical devices were identified and figures-of -merit noted. A two-photon absorption figure of merit was verified by numerical simulation of a waveguide device. The refractive index and waveguide loss in spin-coated poly(4BCMU) films were measured. A photo-induced bleaching was observed, and its effect on linear and nonlinear optical properties was quantified. Fabrication of integrated-optical structures using this photobleaching process was demonstrated. The nonlinear refractive index and absorption were measured at 1.319 μm with 60 picosecond laser pulses, using poly(4BCMU) strip-loaded channel waveguides. A novel pulse-modulated interferometer was developed for measuring the intensity-dependent refractive index. The fast electronic contribution was found to be n_2 = (4.8 +/- 2.7) times 10^{ -8} cm^2/MW, an a slower thermal contribution of n_{rm 2T} = -(7.9 +/- 4.5) times 10^{ -11} cm^2/MW was measured. The thermal index change was shown to limit the duty cycle of operation for a poly(4BCMU) device. The two-photon absorption coefficient was also measured, yielding gamma < 0.25 cm/GW. These values were used to estimate performance of a poly(4BCMU) all-optical device using standard figures -of-merit. For this specific waveguide, the figures-of -merit indicated poor performance. If waveguide losses were neglected, (by assuming improved fabrication for example), and assuming the nonlinearity does not saturate at intensities below the damage threshold, the figures-of-merit improve to useful levels. The limit on duty cycle imposed by thermal effects appears to restrict operation to GHz frequencies of slower.