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 (similar to 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/mu epsilon and the standard deviation of 1.167 mu epsilon. 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.