Patent ID: 6868107

Claim:
A method for calculating the beam quality and output wavelength spectrum of a photonic crystal distributed feedback laser having input parameters comprising a) design parameters that include an operating wavelength and a laser waveguide structure, b) additional design parameters that include a length for an active cavity of said laser configuration divided into incremental cavity lengths and a stripe width for a gain stripe of said laser configuration wherein said stripe width is divided into a plurality of incremental stripe widths, and c) a photonic crystal geometry comprising a lattice symmetry, a grating order, a feature having a shape and a size, and a modulation depth of the modal refractive index corresponding to said laser waveguide structure, said method comprising: calculating at least two coupling coefficients and forming a characteristic matrix; repeating the following steps at spaced increments of time until a steady state solution is reached: repeating the following steps for one of said incremental cavity lengths: calculating a gain change and a modal refractive index change for said laser waveguide structure for one incremental stripe width; calculating a spontaneous emission term for said gain change; calculating a gain roll-off term for said gain change; applying said gain change, said modal refractive index change, said spontaneous emission term, and said gain roll-off term to at least two forward-propagating beams and at least two backward-propagating beams for said one incremental stripe width; performing a Fourier transformation with respect to said one incremental stripe width to yield a plurality of diffraction terms; adding said diffraction terms to said characteristic matrix; propagating said at least two forward-propagating beams by said one of said incremental cavity lengths from a first section to a succeeding and adjacent second section with said characteristic matrix; propagating said at least two backward-propagating beams by said one of said incremental cavity lengths from said second section to said first section with said characteristic matrix; performing an inverse Fourier transformation with respect to said stripe width; and applying at least one boundary condition to a facet of said laser configuration for each said time increment; whereby said steady-state solution is used as the basis for evaluating the beam quality and output wavelength spectrum corresponding to said design parameters, said additional design parameters, and said photonic crystal geometry of said laser configuration.