The Structure and Preparation Method of Spectrally Shifted Double-Comb Tilted Fiber Bragg Gratings

Tilted fiber Bragg gratings (TFBGs) have peaks in the transmission spectrum associated with cladding modes. The spectral distances between these peaks depend on the geometry of the optical fiber including the cladding, tilt angle and structure period. In this letter we propose to increase the number of peaks in the spectrum without changing the geometry of the optical fiber. Such effect can be achieved by producing two structures on the same section of optical fiber, one of which has shifted spectral peaks relative to the other. The spectral shift occurs as a result of a change in the period of the structure obtained by stretching the optical fiber during its writing. We show here the properties of such a method for increasing the number of modes by analysing both simulated and experimental spectra.