Parameter optimisation of pi-shifted distributed feedback fiber Bragg grating Raman lasers

π-shifted distributed feedback (DFB) fiber Bragg grating (FBG) Raman lasers have been demonstrated in the last few years [1, 2] and many attempts at optimisation have been made using theoretical calculations [3]. However, due to the limitations of resolution of the coupled-mode equations, theoretical optimisation has been limited to a few case studies. By using a simple approximation, we demonstrate here in a detailed study, all possible cases for Raman generation in DFB lasers. DFB emission is approximated as single-frequency and solved in the Fourier Domain. The pump depletion equation is solved separately with an initial approximation of the fields which is then adjusted iteratively to fit the calculated fields until a solution is found. The control parameters during fabrication are the FBG coupling strength (ł
_ac
), its length and the value and position of the phase shift. Other parameters more difficult to control also include losses and non-linear coefficient. All these parameters have been varied to determine the threshold and slope efficiency of DFB lasers in typical high NA silica fiber. These calculations have been corroborated with complete resolution of the coupled-mode equations as previously reported in the literature.