Postprocessing of FDTD solutions for precise calculations of eigenfrequencies of photonic periodic structures utilizing the variational expression

This paper presents a method that improves by orders of magnitude the accuracy of the finite-difference time-domain (FDTD)-calculated eigenfrequencies of photonic crystals. The method utilizes a variational expression for the eigenfrequencies of periodic structures. Applications to perfect crystals, waveguides, and resonant cavities are demonstrated. The paper confirms that the method can reduce the computational time by more than 90% while obtaining accuracy in frequency comparable to that obtained solely by the conventional FDTD method.