Temperature Compensated Strain Sensor Based on Long-Period Gratings and Microspheres

In this letter, we present a new structure composed by a long-period grating (LPG) and a microsphere in series, which works as a modal interferometer besides allowing the mode coupled to the cladding to be coupled back to the core. The LPG was written by the electric arc technique and the microsphere was fabricated using a splicing machine. It is possible to use this new structure for simultaneous measurement of strain and temperature. It also allows one to obtain a temperature compensated strain sensor by using a proper data processing algorithm, which utilizes two distinct wavelengths for strain and temperature. Then, a strain sensitivity of 0.86 pm/με and a reduced temperature sensitivity of 0.7 pm/°C were achieved.