**Types of Optical Gas Sensors**


#### *Optical Gas Sensors DOI: http://dx.doi.org/10.5772/intechopen.108971*

A waveguide with a fiber core and surrounding cladding makes up its primary part. The core allows a small amount of light to transmit in form of evanescent waves perpendicular to the axis of fiber with exponentially diminished intensity in the cladding. On the other hand, majority of the light travels along with the fiber core via total internal reflection because core has a greater refractive index than the cladding. The alteration in the refractive index of the cladding is caused by the adsorption of the molecules of gas on its surface, which in turn affects the wavelength and intensity of the output light signals. Due to the limited selectivity of the gas adsorptioninduced variation in the overall refractive index of the material, the cladding is typically modified with molecules or nano-materials that have a particular affinity for the target gas.
