Optimal method of designing triangular-spectrum fiber Bragg gratings with low index modulation and chirp-free structure

Abstract

Combining the traditional nonlinear least squares (NLLS) method with a discrete layer peeling (DLP) algorithm, we propose a new method (for the first time to our knowledge) to synthesize triangular-spectrum fiber Bragg gratings (TS-FBGs) with chirp-free structures. In this method, the DLP algorithm is used to generate an appropriate initial value, and the NLLS method is successfully used to optimize the design parameters from the initial value in the previous step. Numerical results show that our method can design both single- and multiple-channel TS-FBGs with their maximum index modulations being effectively suppressed to a feasible level. These novel TS-FBGs thus designed can act as wavelength readout devices and provide potential applications to wavelength interrogation in optical sensor systems.