Determination of refractive index of liquids and solvents at various temperatures is of paramount importance in several chemical, pharmaceutical, bio-chemical, food processing, etc., industries. In the measurement of a parameter, the degree of accuracy plays a crucial role in deciding the application of the substance to a specific purpose. In the present paper a spectroscopic signal enabled refractive index sensor operating at the temperature range of 10oC to 60oC using a source of 660nm wavelength, which offers sensitivity of the order of fifth decimal place has been described. The present experimental setup consists of a borosilicate uniform U-shaped glass rod connected between a source of 660nm and a benchmark power detector. The working principle of the sensor involves the interaction between the evanescent wave of U-shaped glass rod and external medium consisting of mixture of Toluene and 1-Butanol at different temperatures ranging from 10oC to 60oC. The absorption of evanescent wave by the chemical solution used to attenuate and modulate the intensity of the light in the U-shaped glass of the fiber. The relationship between absorbing property of the external medium and the intensity of the light reaching the detector at various temperatures can provide the calibration of the sensor, which in turn used to measure the refractive index of liquids either dark or transparent in the temperature range of 10oC to 60oC.