Simultaneous measurement of refractive index and temperature by using dual long-period gratings with an etching process

A new structure of long-period grating (LPG) sensor is introduced for simultaneous measurement of the refractive index (RI) and temperature. This type of grating device consists of two LPG sections, one of which is post etched by hydrofluoric acid (HF) solution and, therefore, has an improved RI sensitivity (the demonstrated improvement of sensitivity is 3.6 times). The experimental results show that this LPG sensor has a good performance in terms of linearity and sensitivity.