All-optical modulator plays an important role for various all-optical applications in optical communication. An all-optical modulator was mainly investigated based on few-layer molybdenum disulfide (MoS2)-polyvinyl alcohol (PVA) thin films. In addition, an all-optical modulator based on few-layer tungsten disulfide (WSe2)-polyvinyl alcohol (PVA) thin film was also demonstrated. The modulator was based on polarization interference and the thermo-optic effect of TMDs-PVA thin film. A long-time stable modulated output was obtained. By absorbing the pump at 980 nm, MoS2 or WSe2 generates heat, changes the refractive index of thin film and modifies the polarization of the incident light at 1 550 nm. The obtained thermal all-optical modulator based on MoS2-PVA thin film has a rise time of 526 μs.