Stimulated emission from two-dimensional nested rectangle photonic crystal fibers

In this paper, we use the theory of spontaneous emission of two-level atoms embedded in photonic crystals. The unavoidable existence of a localized field with a defect mode and its basic properties are confirmed, which enables one to study the inherent laws of spontaneous emission from doped media. We combine the theory of spontaneous emission with numerical simulation for studying stimulated emission in a doped localized field and conditions for increasing the emission. The inherent laws for the cases where transmissivity is larger than unity and the negative imaginary part of the complex refractive index in doped compound lattices appears are also studied. The analysis of two-dimensional nested rectangle photonic crystal fibers (PCFs) with and without active impurities was performed using the finite-difference time-domain (FDTD) method. We find that, when active impurities are introduced into photonic crystal fibers, the negative imaginary part of the complex refractive index appears and the doped mode with high quality factor and great mode density occurs in the photonic forbidden band, thus amplifying substantially the stimulated emission.