QUASI-PERIODIC COMPLEX-COUPLED DISTRIBUTED-FEEDBACK STRUCTURES WITH AN EXPONENTIAL-LIKE GRADIENT OF COUPLING

We investigate theoretically the linear properties of quasi-periodic c omplex-coupled distributed-feedback (DFB) structures in which the coup ling constants experience a longitudinal variation along the propagati on axis according to an exponential-like relationship (esp, sh, ch,... ). The results of the simulations are in good accordance with what cou ld be expected at first sight from the particular form taken in this c ase by the coupled-wave equations, In particular, the gradient of coup ling can provide a shift, either of the apparent average absorption (r espectively, gain) or of the detuning from Bragg resonance, depending upon its exact form, Moreover, we show that this shift is asymmetric w ith respect to the direction of propagation, leading to a nonreciproca l behavior in reflection. We extend our analysis up to the laser modes at threshold.