Ultrawideband Optic Fiber Photodetector Based on Carbon Nanotube Photothermal Effect

With the rapid advancement in communication, imaging, and sensing technologies, optimizing the detection bandwidth of photodetectors (PDs) has become increasingly urgent. In this article, an ultrawideband optical fiber PD based on the photothermal effect of carbon nanotubes is proposed. The device consists of a multimode fiber (MMF) and polydimethylsiloxane (PDMS) filled between two MMF segments to form a fiber-optic Fabry-P & eacute;rot interferometer (FPI). The multiwalled carbon nanotubes (MWCNTs) with photothermal effect mixed with PDMS are coated on the outer side of the FPI to form a double-layer structure with the inner layer of PDMS and the outer layer of MWCNTs mixed with PDMS. This structure can enhance photothermal absorption without reducing intracavity loss. When illuminated, the photothermal effect of MWCNTs induces thermal expansion of PDMS, tuning the FPI's refractive index and causing a blue shift in the transmission spectrum. The results show that the desig ned fiber optic PD exhibits excellent sensitivities of 0.181, 0.381, and 0.494 nm/mW across the near-infrared (NIR), visible, and ultraviolet (UV) wavelength bands, respectively. Moreover, the detector is capable of accurately capturing the signal variations at very low in cident optical power, which can be detected to milliwatts of the optical power of the weak optical signals. It is shown that the detector exhibits the potential for high responsivity over the full spectral range.