In this paper, we propose a low cost cascaded ultranarrow-band fiber Bragg gratings based light source which could adopt wavelength modulation spectroscopy technique to precisely sense the CO and CO2 gas generated in the industrial process of iron and steel smelting. By using the T-Matrix method, we calculate and propose an improved grating structure to decrease the size of this light source. By theoretical calculation, when we repeatedly pull and release the single mode optical fiber containing FBG1 and FBG2 with the maximum axial strain of 300 µɛ, we could utilize the light source to successfully and simultaneously scan the typical near infrared absorption spectral band of CO and CO2 gas, so as to sense them with wavelength modulation spectroscopy technique.
