Optical bistability of waveguide consisting of poly(3-hexylthiophene)/polymethylmethacrylate composite film

Abstract

In the optical materials, the remarkable change of refractive index due to optical intensity is important for making photo-devices such as optical switching, memory and logic circuits. The optical waveguide consisted of poly (3-hexylthiophene)/polymethylmethacrylate (P3HT/PMMA) composite film and a prism was fabricated to find out its optical bistable characteristics. The refractive index of P3HT/PMMA composite film measured by ellipsometry was 1.48. Moreover, the refractive indexes of the atmosphere and the prism were 1.00 and 1.52 respectively. Therefore, the fabricated waveguide satisfied the condition of the quasi-waveguide. For improving the nonlinear optical characteristic of the composite film, P3HT/PMMA composite film was exposed to organic gas for 25 hrs. As the laser light source, Nd:YAG laser (wavelength: 1064 nm, pulse width: 5 ns, repetition frequency: 10 Hz) was adopted for optical bistability and third-harmonic intensity measurement. The input light intensity dependences of the optical bistable characteristics of the quasi-waveguide consisting of the P3HT/PMMA composite thin film, which was exposed to organic gas for 25 hrs were investigated. The measured optical bistability displaced excellent stability and hysteresis characteristics. It suggests that the composite film exposed to organic gas has larger grain size, better molecular orientation, homogeneous bulk and smooth surface than that of before organic gas treatment.