Simultaneous measurement of temperature and external refractive index by use of a hybrid grating in D fibre with enhanced sensitivity by HF etching

We propose a dual-parameter optical sensor device achieved by UV inscription of a hybrid long-period grating–fiber Bragg grating structure in D fiber. The hybrid configuration permits the detection of the temperature from the latter’s response and measurement of the external refractive index from the former’s response. In addition, the host D fiber permits effective modification of the device’s sensitivity by cladding etching. The grating sensor has been used to measure the concentrations of aqueous sugar solutions, demonstrating its potential capability to detect concentration changes as small as 0.01%.