Study on Uneven Characteristics of comb reflection spectra of fiber Bragg grating Fabry-Perot cavity

Uneven Characteristics of the reflection peaks´ interval of fiber Bragg grating Fabry-Perot (F-P) cavity is studied by using the general Fabry-Perot interference condition and the phase characteristic of the fiber Bragg grating reflection. The span inhomogeneity of the comb spectrum is studied. The relationship between the numbers, interval of the reflection peaks and the fiber Bragg grating Fabry-Perit cavity structure is derived. The effect of the time delay of the fiber Bragg grating on comb spectrum of Bragg grating F-P cavity is analyzed. Theoretical result is given through the transfer matrix. Analyses shows that the number of the reflection peak in central profile is directly proportional to the length of the single fiber Bragg grating and inversely proportional to the space of the fiber Bragg gratings. The interval of the reflection peaks are not equal because of the difference of the time delay of the weakly coupled fiber Bragg gratins. The span of the peaks near the central wavelength are larger and others smaller.