Spatial filtering of phased array semiconductor lasers using external cavities has attracted considerable attention as a means of producing stable single lobed output beams at high cw power.1,2 We describe the behavior of phased array semiconductor lasers in external cavities with spatial filters. Diffraction-limited single lobed emission from carrier guided semiconductor laser arrays has been experimentally demonstrated in an external cavity consisting of a spherical mirror and a variable slit spatial filter centered on-axis (see Figs. 1 and 2). The effects of such spatially filtering external cavities on index guided arrays have been analyzed using modified coupled-mode theory,3 demonstrating efficient discrimination against high-order supermodes.
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