Optical bistability of polythiophene derivative/polymethylmethacrylate composite thin films

Abstract

Polymer composite materials have considerable attention in the modern technology and are an object of numerous fundamental and scientific investigations. Polymer composite materials have advances in physical and optical properties over single materials. It is well known that the refractive index of the optical materials play an major role for all optical functional properties. The change of refractive index due to optical intensity is important for making photo-devices such as optical switching, optical memory, and logic circuits. In the present work, we have investigated the polythiophene family derivatives i.e. poly(3-octylthiophene) (P3OT) and polymethylmethacrylate (PMMA) composites materials. The poly(3-octylthiophene)/polymethylmethacrylate (P3OT/PMMA) composite thin films were prepared by spin coating as composing a prism-coupling waveguide. The UV-visible absorption spectrum of the composite film was recorded in the range 300-900 nm using UV-visible spectrophotometer. The thickness of the composite films was measured as 3 μm using a surface profile measuring system. The optical bistability of P3OT/PMMA waveguide was measured using an Nd:YAG laser with a wavelength of 1064 nm, pulse width of 5 ns and a repetition frequency of 10 Hz. The optical bistable characteristics of P3OT/PMMA composite films were measured with different input laser power intensities (0.16, 0.20, 0.24 and 0.26 GW/m 2 ) and the measured optical bistability shows good stability and hysteresis characteristics.However, in terms of the input laser power dependence of optical bistability, the switching on-off position shifts with the increase in the input laser power intensity was observed. In the input laser power dependence of optical bistability, the switching on-off position shifted with the increase of input laser power intensity. The optical bistable behaviors are very stable for P3OT/PMMA composite thin film after exposed to organic gas. It suggests that the composite film exposed to organic gas has larger grain size, better molecular orientation, homogeneous bulk and smooth surface than before organic gas treatment. The effect of organic gas treatment and PMMA molecular weight on the optical bistable behavior of P3OT/PMMA composite waveguide was investigated. The shift of on-off position of the optical bistability is decreased with the composite films treated with organic gas due to the smooth surface, better molecular orientation than before organic gas treatment.