Platinum diselenide (PtSe ₂ ), a two‐dimensional material, has shown exceptional promise in photodetection applications because of its air stability, high carrier mobility, and layer‐tunable bandgap. However, conventional photoconductive modes face challenges with high dark currents. To address this limitation, all‐optical fiber detection technology with high sensitivity and response, has emerged as a promising approach for developing PtSe ₂ , based devices. In this study, a high‐sensitivity broadband photodetector based on PtSe ₂ with a cascaded Fabry–Pérot interferometer (FPI) is proposed, which utilises the broad spectral absorption property of PtSe ₂ and the interference enhancement mechanism of cascaded F–P cavities to achieve high‐sensitivity broadband photodetection. The experimental results show that the detector has excellent spectral response in the 808–1,550 nm band, with a sensitivity of 3.867 nm/mW at 980 nm and a response time of 37.43 ms/129.17 ms. The sensitivity at 1,550 nm is up to 134.014 nm/mW, with a response time of 75.74 ms/28.66 ms. The double matching of 0.8 eV energy and PtSe ₂ material, which is situated in the range of the material intrinsic absorption peak (1,200–1,600 nm), is responsible for the excellent sensitivity at 1,550 nm. It is also highly matched with the interband jump energy level, which generates more hot carriers per unit optical power and thereby increases the photothermal conversion efficiency. This study provides a new solution for the design of high‐sensitivity, ultra‐wideband optical fiber photodetectors, which has important potential applications in optical communications, environmental monitoring, and sensing.

With the rapid advancement in communication, imaging, and sensing technologies, optimizing the detection bandwidth of photodetectors has become increasingly urgent. In this paper, an ultra-wideband optical fiber photodetector 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-Perot interferometer (FPI). The multiwalled carbon nanotubes (MWCNTs) with photo-thermal 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 designed fiber optic photodetector exhibits excellent sensitivities of 0.181 nm/mW, 0.381 nm/mW, 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 incident 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.