Abstract: Distributed feedback devices such as distributed feedback lasers are modified by introduction of a central coupling strength discontinuity or other deviation from uniform nature of the distributed perturbations, in order to promote the transmission of oscillation of a single mode in preference over the nearest redundant modes. The class of deviations from uniform coupling strength may be mathematically termed antisymmetric deviations, because they are deviations about the midpoint of the perturbation pattern which result in a distinction of effect of the two halves of the pattern, taking either half as a reference pattern by itself.

Abstract: The stability of passively mode-locked lasers operated to provide short pulses is improved by utilizing saturable absorption which has a composite characteristic consisting of one component of relatively fast recovery time and another of relatively slow recovery time. Very short pulses are achieved with a Rhodamine 6G dye laser in combination with a saturable absorber which utilizes a mixture of DODCI and Malachite Green.