A double cladding single-mode fiber temperature / humidity sensor based on light intensity modulation is adopted and its structure characteristics and working mechanism are studied. According to optical waveguide theory

mode field distribution and characteristic equation of double cladding fiber are deduced. Corrosion technology of optical fiber

choice of temperature / humidity sensitive material and coating methods are experimentally analyzed. It is found that coating thickness of sensitive materials has great influence on range and linearity of light power output response

so it needs to control thickness of coating layer

in order to achieve ideal modulation depth of light intensity and response linearity.