Abstract

A diffraction-coupled array (DCA)^1-3 consists of an array of parallel waveguides which interact through beam diffraction in a common laterally unguided section at one end. If the phase difference between light reflected from the far end of the unguided section and injected back into the waveguide of origin and into its nearest neighbor is 2π, the "in-phase" eigenmode is reinforced, which results in single-lobed far-field patterns. The design criteria are shown in Figure 1. However, the gain profile in the waveguide region of a DCA is spatially distributed such that it favors the "out-of-phase" eigenmode. In order to stabilize the in-phase operation, the adjacent reflections must not only be in-phase, but must also overcome the unfavorable effect of evanescent coupling. We present design criteria and quantity the trade-off between evanescent and diffraction coupling by the modal threshold gain analysis. Experimental observations of far-field patterns for DCAs of DH and LOC lasers are presented and compared with the criteria.

© 1987 Optical Society of America