MWCNTs /PDMS mixed polymer-modified optical microfiber coupler to tune the dispersion turning point for enhancing high sensitivity visible light detection

Visible light detection plays a significant role in communication, Remote Sensing, phototherapy, photodiagnosis, and security Fields. In this work, a novel visible light detector is proposed based on multi-walled carbon nanotubes and polydimethylsiloxane (MWCNTs/PDMS) mixed polymer modified optical microfiber coupler (OMC) working at the dispersion turning point (DTP). The position of the DTP can be controllably adjusted by optimizing the concentration of the mixed polymer and the waist diameter of OMC. The theoretical and experimental results show that the DTP was around 1500 nm when the concentration of MWCNTs/PDMS hybrid polymers was 1 mg/mL and the waist diameter of the OMC was 6.2 μm, which is much larger than those in the prior methods to tune DTP and boost the device's toughness. Benefiting from the photothermal effect of MWCNTs, the high thermo-optic coefficient of PDMS and the high refractive index sensitivity near the DTP, the proposed sensor achieves a high sensitivity of -0.322 nm/mW (22.80 nm/(W·cm-2)) under 405 nm light illuminate, with response times of 0.57 s (rise time) and 0.4 s (fall time), respectively. The proposed device demonstrates exceptional photodetection sensitivity, remarkable stability, and potential application in the fields of vehicle communication and healthcare.