Spectral characteristics and space division multiplexing scheme of long period fiber grating pair

Abstract Due to the transmission mode and multiple loss peak of a long period fiber grating pair (LPGP), there are some difficulties in multiplexing and demodulating it. To realize the multi-point detection of LPGP, a new distributed demodulation system based on space division multiplexing is proposed. The relationship between the spectra of the LPGP and the grating parameters (grating length, grating period, separation of the long period fiber grating) were investigated, and a series of rules for optimizing the spectrum characteristics of the LPGP were obtained. By using optical switches, the traditional spectrometer demodulation is combined with computer technology to design a multiplex demodulation system of distributed LPGPs. Spectrum reduction, resonant wavelength, and temperature demodulation of the LPGP were realized. The experimental results show that the demodulation speed of the system is 1.1 seconds and the wavelength accuracy is 0.01 nm. The designed system has the advantages of high precision, strong compatibility and friendly operation interface. This multiplexing method is appealing to construct distributed LPGP sensors since it is easy to extend multiplexing channels.