All-optical Photodetector Based On Photothermal Effect Of MXene Nb₂CTx

Photodetector plays an increasingly important role in aerospace,military and civil fields,and is a key component of electronic products,military products,medical equipment and other devices.Current photodetectors are mainly made of crystalline silicon,which have the disadvantages of high cost,complicated operation,and difficulty in integration.The emergence of photodetectors based on two-dimensional materials not only makes up for the shortage of current silicon-based photodetectors,but also has the advantages of good flexibility and easy processing.As a new twodimensional transition metal carbon/nitrogen（MXene）,Niobium carbide（Nb₂CT_x）has strong light absorption characteristics,excellent photothermal conversion efficiency and high thermal conductivity from visible to near-infrared wavelengths,which has great potential in improving the performance of photodetectors.With the development of optical fiber technology,the all-optical photodetectors in composite fiber structure eliminate photoelectric conversion,and have the advantages of simple structure,low power consumption,and compatible with optical fiber communication systems.In this paper,the excellent photothermal effect of MXene Nb₂CT_x nanosheets are combined with the optical fiber for all-optical detection in the wavelength range of 405 nm-1550 nm,which has broad application prospects in the field of all-optical network research.The main research contents of the paper are as follows:1.The fabrication method and principle of photothermal photodetector are introduced.First,the basic steps of manufacturing the microfiber（MF,microfiber）are introduced,and the mode transmission characteristics of MF are analyzed.When the diameter of the fiber decreases,the constrained ability of MF to the transmitted light in the fiber core weakens,and the evanescent field increases.Secondly,the photothermal spectroscopy method is introduced,and the process of photothermal signal generation of materials is described in detail.Finally,the principle of the photodetector based on photothermal effect of MXene Nb₂CT_x is expounded.MXene Nb₂CT_x can effectively convert the absorbed light energy into heat,changing the temperature and the refractive index of MXene Nb₂CT_x,thereby realizing all-optical detection.2.Combining the photothermal effect of MXene Nb₂CT_x with the strong evanescent field characteristics of microfiber（MF）,it realizes broadband all-optical detection with high sensitivity and fast response,the light transmission characteristics and time response of the all-optical photodetector are analyzed theoretically and experimentally.The photothermal effect of MXene Nb₂CT_x significantly changes the light transmission conditions of the MF.The results show that the sensitivities of 82.24 nm/W·cm2,38.85 nm/W·cm2 and 24.56 nm/W·cm2 are achieved at the detection wavelengths of 405 nm,980 nm and 1550 nm,respectively,and the minimum detection limit is 2 mW/cm2.The rise and fall response times are 0.1 and 0.07 ms,respectively.3.An all-optical photodetector of Sagnac loop based on photothermal effect of MXene Nb₂CT_x is designed.The spectral transmission characteristics of 405 nm,980 nm and 1550 nm laser irradiation at different light powers are studied.The results show that,in the range of 0-20 mW light power,the sensitivities of the device based on photothermal effect of MXene Nb₂CT_x are 3.216 nm/W·cm2,1.699 nm/W·cm2 and 1.055 nm/W·cm2,respectively,and the minimum detection limit is 62 mW/cm2.The rise and fall response time are 0.37 ms and 0.32 ms,respectively.4.Based on photothermal effect of MXene Nb₂CT_x,an all-optical broadband photodetector based on composite long-period fiber grating is designed.The spectral transmission characteristics of laser irradiation under different light powers and response time characteristics are studied.The results show that the sensitivity of the device is 1.645 nm/W·cm2,the detection limit is 122 mW/cm2,and the rise and fall response times are 0.67 ms and 0.63 ms,respectively.The proposed all-optical photodetector scheme provides a new pathway to further study the high-performance all-optical photodetectors based on photothermal effect of MXene Nb₂CT_x.