Third-order nonlinearities in organic semiconducting polymers via spatial self-phase modulation

Abstract

The nonlinear refraction in two organic semiconducting polymers, namely MEH-PPV and PBDB-T, has been studied via spatial self-phase modulation (SSPM) using a 532 nm CW laser excitation. The results indicate that SSPM arises from both the optical Kerr and thermo-optical effects, which contribute significantly to the refractive index modulation of the polymer solution dispersions. The intensity-dependent evolution of the SSPM patterns, particularly the increase in the number of concentric diffraction rings, was analyzed to determine the nonlinear refraction (NLR) coefficients of MEH-PPV and PBDB-T, yielding values of ~ 9.707 × 10^− 11 m²/W and ~ 1.281 × 10^− 10 m²/W, respectively. This implies that the strong third-order nonlinear optical response of these polymers makes them suitable for all-optical switching, optical modulation, and photonic devices. The time evolution of SSPM patterns was investigated in both polymers, revealing modulation of NLR coefficients, primarily due to thermally induced convection and fluid motion. It offers novel platforms for thermal metrology based on optical nonlinearity and temperature-sensitive all-optical switching. Furthermore, this study provides valuable insight into the SSPM mechanism in organic semiconducting polymer systems, paving the way for future studies and establishing a foundation for continued exploration of nonlinear optical phenomena.