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.

High-speed and high-resolution interrogation of FBG sensors using wavelength-to-time mapping and Gaussian filters

“…Power arising from the FBG residual sidelobes are the main factor limiting the linear operational range in the conventional measurement method, which involves the differential detection of the overall received power Pi, i.e. the integral of the product R(λ)Fi(λ) [18,19]. Nevertheless, in the proposed method, the grating sidelobes are temporally separated from the main lobe in the detected signal due to the wavelength-to-time mapping, and thus, they do not contribute to the amplitude measurement.…”

“…This scheme has been proven to provide ultra-high sensitivity, and it is a promising solution for interrogation of FBGs with a wide spectrum [18]. However, the wavelength range in which the system shows a linear dependence is limited as power reflected from the grating sidelobes become non-negligible [18][19]. In fact, this shortcoming is common to every filtering-based techniques.…”

“…Consequently, measurement distortions arising from residual power due to the FBG side lobes are avoided, and the linear operational range is considerably extended. Moreover, in contrast to previous works in which the FBG spectral width must be either much narrower [17] or equal [18] to that of the Gaussian filters, we generalize the method for FBG sensors having an arbitrary spectral bandwidth, so the proposed system is further improved in terms of flexibility. Theoretical analysis and experimental results are presented and discussed.…”

Overlap-Proof Fiber Bragg Grating Sensing System Using Spectral Encoding

“…The product between two different codewords (or even between shifted versions of the same codeword) is constrained to a lower value, which is the cross-correlation product (XC) [7]. From this concept, we can identify the central position of the encoded sensors by evaluating the auto-correlation product between each codeword and the total measured reflection spectrum (similar to the approaches presented in [9], [10]). Fig.…”

Fast and reliable interrogation of USFBG sensors based on MG-Y laser discrete wavelength channels

“…However, due to their inherent broad spectra which are unfavorable for many spectral interrogation techniques, such USFBGs have rarely been used as sensors. Even so, several important advantages can be envisaged if USFBGs can be used as grating sensors, especially for distributed measurements [5]. Recently, we have introduced USFBGs potentials as weak sensing units and have demonstrated an identical USFBG based distributed microwave-photonic sensing system [6].…”