A new method for fiber Bragg grating wavelength demodulation with calibration

Abstract

A wavelength calibration method is proposed to improve Fiber Bragg Grating (FBG) Wavelength detection precision. The reflected spectra of two reference FBG elements and a sensing FBG element are scanned by narrow band light from a fiber F-P tunable filter (FFP-TF) driven by triangular waveform voltage. Sequence numbers of FBG and peak position of spectra are identified with full spectrum analysis. Two reference FBG elements with fixed wavelength are used to monitor the transmission wavelength of filter and to construct the relationship between wavelength and the driving voltage, the driving voltage of the sensing FBG spectrum peak is scaled as the Bragg wavelength with the linear interpolation method. In the temperature experiment, three peak-seek methods such as centroid method, differential method and Gaussian-fit method are introduced and the temperature measurement precisions of ±1C^o,±0.5C^o and ±0.3C^o are achieved respectively, corresponding to the wavelength error of ±10pm, ±5pm and ±3pm. Finally, multipoint FBG sensing system is accomplished with calibration and wavelength measurement precisions of ±10pm is obtained. The experimental results shows that the new method can reduce the wavelength measurement error caused by nonlinearity in piezoelectric transducer (PZT) response and wavelength drift due to PZT hysteresis.