A Compact Sensor Integrated in a Single Hollow Core Bragg Fiber for Simultaneous Measurement of Temperature and Strain

A compact sensor integrated in a single hollow core Bragg fiber (HCBF) is proposed and demonstrated for simultaneous measurement of strain and temperature. The sensor is manufactured by splicing a 3-mm-long homemade HCBF sandwiched between two segments of single-mode fibers (SMFs) with a lateral offset at one end. Experimental results demonstrate that both Mach–Zehnder interferometer (MZI) and Bragg resonant mechanism are coexisting in the HCBF-based sensor. Two sensing mechanisms have different strain and temperature sensitivities with good linearity. The axial strain sensitivities of −0.4 and 0.33 pm/
$\mu \varepsilon $
and the temperature sensitivities of 40.8 and 26.5 pm/°C are obtained by monitoring the wavelength shifts with axial strain and temperature in temperature range of 60°–80°. Therefore, simultaneous measurement of temperature and strain can be achieved by using a characteristic matrix approach. Due to the large refractive index (RI) difference between the core and cladding of the Bragg fiber, the length of HCBF for forming mode interference in the sensor could be greatly reduced. This makes the sensor more compact than most previous reports for simultaneous measurement of temperature and strain.