Interrogation of Ultrashort Bragg Grating Sensors Using Shifted Optical Gaussian Filters

Abstract

Ultrashort fiber Bragg gratings (FBGs) possess significant potential as weak sensing units for distributed measurements, the exploitation of which, however, have been usually limited by their inherent wide spectra which is undesirable for most traditional wavelength measurements. In this letter, we propose to use shifted optical Gaussian filters to interrogate such wide spectrum gratings. However, instead of acting like Gaussian edge filters as previously done, to take advantage of spectral feature of ultrashort gratings, here they have a role which is more like shifted matched filters. The measurement inherits the important features of a common shifted Gaussian filter interrogation technique, namely its high flexibility, natural insensitivity to intensity variations, promising future for multichannel interrogation, and a potentially wider measuring range relative to common intensity-based approaches. We believe that this simple concept for ultrashort Bragg gratings should offer the strong foundation for their future applications in distributed measurements. Interrogation of a strain-tuned ultrashort grating was accomplished, with a wide sensitivity tuning range from 2.8 to 10.4 dB/nm achieved.