A Low Bandwidth DFB Laser-Based Interrogator for Terahertz-Range Fiber Bragg Grating Sensors

This letter reports an all-electronic, low bandwidth swept frequency laser used to interrogate terahertz-range fiber Bragg gratings (THz FBGs) for distributed strain sensing applications. A distributed feedback laser with current injection modulation was employed as the swept frequency laser source. Using the resulting narrow bandwidth (~110 GHz) laser frequency sweep, high accuracy distributed strain measurements were achieved. In order to experimentally investigate this concept, a strain test was conducted using the THz FBGs. During the test, the laser sweeping time was limited to less than 2 ms. Highly linear results were found (R
²
= 0.996), with an observed sensitivity of -0.142 GHz/με and the standard deviation of 1.167 με. A multiplexing test was also conducted, and no cross-talk found between sensor elements. These results demonstrate that this interrogation system holds substantial potential as a method of rapid distributed optical fiber frequency-domain sensing.