Fig. 1. Schematic of the device. (a) Schematic of tapered nanofiber; (b) schematic of experimental device of nanofiber methane sensor

Fig. 2. Directly absorption signal. (a) Methane absorption spectrum obtained using a nanofiber with a diameter of 500 nm; (b) absorption signal after subtracting the background light intensity

Fig. 3. The second harmonic signals. (a) Second harmonic signal under different incident optical power when using 500-nm diameter fiber; (b) relationship between incident optical power and second harmonic signal amplitude

Fig. 4. The second harmonic signals. (a) Second harmonic signals under different pressures when using 500-nm diameter fiber; (b) relationship between pressure and second harmonic signal's amplitude

Fig. 5. Influence of pressure on the second harmonic signal. (a) Pressure broadening of methane and its linear fitting; (b) pressure frequency shifting of methane and its linear fitting