Azimuthal mode discrimination in radially chirpedconcentric-circle-grating distributed feedback lasers

摘要

We report a theoretical investigation analyzing the thresholdnmodes of a concentric-circle-grating (CCG) distributed feedback lasernwith a radially chirped first-order Bragg grating. A numericalncoupled-mode analysis of a chirped CCG laser shows improved azimuthalnmode discrimination for chirped gratings with linear, quadratic, andnsquare-root radial dependence. Negatively chirped gratings, in which thengrating period decreases with radius, result in improved thresholdndiscrimination between the circularly symmetric fundamental mode andnhigher order modes; positively chirped gratings, in which the gratingnperiod increases with radius, result in decreased threshold for highernorder modes in general. Also, the intensity for the fundamental mode atnthe grating center can be reduced by an order of magnitude usingnlinearly chirped gratings