Light propagation characteristics in photonic crystal fibers with [alpha]-power profiles of air hole diameter distributions and their application to fiber collimator

Light propagation characteristics in photonic crystal fibers (PCFs) with [alpha]-power profiles of air hole diameter distributions were theoretically investigated. It was clarified that the intensity peak of the beam propagating in the PCF with Gaussian beam excitation varied periodically with little power attenuation. It was found that the envelope of the periodic intensity variation depended on [alpha]. We theoretically demonstrated that the PCF with the [alpha]-power profile of the air hole diameter distribution could be applied to a collimator for a conventional PCF with uniform air holes in Gaussian beam excitation to reduce coupling loss, where a PCF of appropriate length with the [alpha]-power air hole diameter distribution was spliced to a conventional PCF. It was also found that the coupling efficiency was higher for a larger [alpha].