The nanofiber optic evanescent field sensor based on a changed cladding part as a sensor presented numerically. The influences of numerical opening, core radius of the fiber, the wavelength is effected on the light source and the submicron fiber on the sensors are promise to studied in this work. The results pointed out the sensitivity of the sensor increases when the numerical opening of the fiber is increases and the core radius is decreases. The NA of the fiber affects the sensitivity of the sensor. In the uniform core fiber, the increase in the NA increases the sensitivity of the sensor. Therefore, one should choose a fiber with high NA for the design of an evanescent-wave-absorption sensor if the core of the sensing segment uniform in diameter, so that the increase in the penetration depth or number of ray reflections or both, increases the evanescent absorption field and hence the sensitivity of the sensors. Keywords:fiber optic sensor, chemical sensors, biosensors, nanofiber optic.
