Numerical Calculation For The Transmission Spectrum Of Novel LPFG And Its Application

From the basic theories of optical fiber and solving the eigen-equation of core model and the dispersion equation of cladding model, the two important parameters, i.e. the effective refractive index of core model and cladding models, of the optical fiber grating are obtained. The transmitted spectrum of long period fiber grating is investigated using the coupled-mode theory.The transmitted spectrum of a novel long period fiber grating written with the high frequency CO₂ laser pulses is theoretically analyzed. The refractive index modulation of this novel long period fiber grating is approximated as triangular wave. Based on the coupled-mode theory and the three-layered model, the coupling coefficient and the coupled-mode equation are derived. The numerical calculation is carried out in detail. The calculation results agreed with the experimental results. The theoretical model raised in this paper is verified.The temperature, surrounding refractive index and strain characteristics of a long period fiber grating are analyzed. A method for simultaneous measuring the temperature and refractive index is proposed. The operational principle is derived; an experiment is conducted; the theoretical results are compared with the standard ones, showing that the two results are in accordance with each other.