Photonic Crystal Microcavity Amplifier

Amplification in rare-earth doped solid state planar optical structures has attracted a lot of interest in recent years due to the fact that the rare earth ions show sharp absorption and emission bands and relatively long luminescence lifetimes. In particular the erbium (Er) ion is very attractive because of its intra 4f-transition from the first excited state to the ground state around 1.53 mum (4I13/2-4I15/2). The main problem of the erbium doped waveguide amplifiers (EDWAs) is that high values of the Er3+ concentration are required to reach high gain figures in a compact length, but in this way the concentration quenching effects become very considerable and detrimental to the optical gain, since they reduce the population in the first excited state. A good solution to overcome this dramatic drawback is to consider erbium doped photonic crystal amplifier (EDPCA). In fact the small group velocity of electromagnetic eigenmodes brings about the enhancement of stimulated emission if the photonic crystals are doped by active media as the rare earth ions E3+r or Yt3+. This phenomenon originates from the long interaction time between radiation field and the matter caused by the small group velocity near the edge of the photonic band gap. The efficient confinement of light is achievable not only by tuning the input signal at the band edge of the gap of the photonic crystal but it is also obtainable by introducing local defects inside photonic crystals. The density of electromagnetic states inside a cavity is significantly modified and the spontaneous emission of atoms in a cavity can be either enhanced or inhibited. Erbium doped silica-titania one-dimensional photonic crystal microcavities have been analyzed by solving the erbium rate equations and the Maxwell equations by means of an auxiliary differential equation finite difference time domain technique. Since the performance of optical amplifiers depends on the populations of the energy levels participating in radiative transitions, determined principally by the distribution and concentration of the rare-earth ions and by the pumping conditions, the relations between these parameters and the transmittance of the EDPCMA have been studied