Straight and Segmented Structure Evanescent Wave Sensor With Different Sensing Region Length

A comparative study of optical fiber evanescent wave sensors based on straight and segmented structure (SS) has been carried out. The waveguide modes of the straight and the SS are simulated and analyzed using beam propagation method, which shows the high-order modes are excited repeatedly at the first transition of the each segmented region. The sensors are made using the chemical corrosion method. The sensitivity of the sensors is tested using the different concentration methylene blue solution. With the fixed core diameters, the sensitivity of the SS sensor is higher than that of the conventional single straight sensor, while the sensing region length of the former (1 and 1 cm) is shorter than that of the latter (3 cm). The experimental results are consistent with theoretical models and simulation analysis. The SS can effectively improve the sensitivity of the sensor, and has sufficient robust, which is suitable for materials spectrum measurements.