**5. Conclusions**

In this Chapter, a complete design cycle of phased array lasers based on photonic crystals processed in dielectric membranes has been given. First, full-wave electromagnetic computations with the FDTD method allow us to determine a photonic bandgap of the selected passive photonic crystal lattices processed in a dielectric membrane. Second, a single- either multi-channel waveguide array is introduced into the lattice and dispersive properties of the modes within the corresponding photonic bandgap are computed. The goal is to evaluate the spectrum, where a single-mode propagation of the supermodes is possible along the channels. Third, for given geometry settings and the mode's wavelength spectrum, the above-threshold laser small-signal gain characteristic is computed with the non-orthogonal coupled mode theory. Gain computations are two-fold. In the first approach, numerical computations of an electric field envelope within a passive structure are executed with the aid of the FDTD method, while the second method is based on an equivalent effective waveguide structure. Both methods provide similar values of the optimum reflection coefficient of the output mirror.
