An optic-fiber evanescent wave sensor based on new type D-shaped fiber is designed. By letting the energy of the evanescent wave field and the analyte interact with each other directly and increasing the effective area of the sensing fiber

the sensitivity of the sensor is improved greatly. Compared with the sensors fabricated by B.Culshaw and G.Stewart

the new sensor is found to be three orders of magnitude more sensitive. Per equal length

the sensor’s sensitivity is about 1.2 times of the open-path cell sensing. Also we propose a new

low-cost and efficient method fabricating D-shaped fiber based on machine grinding.