MODAL DISCRIMINATION IN LEAKY-MODE (ANTIGUIDED) ARRAYS

We report the fabrication of a ten-element anti-guided (leaky-mode) array that operates in an in-phase mode with a diffraction-limited far-field pattern at drive currents up to 8.7 times the threshold current (pulsed) and an output power of 400 mW (both facets). This device evidences good discrimination against the out-of-phase leaky mode without the benefit of a "Talbot" spatial filter, relying instead on mode-sensitive interelement losses in an overlying GaAs layer. We have studied this device using two numerical models that allow, for the first time, predictions of mode discrimination near threshold including full two-dimensional waveguiding and all three of the major mode discrimination mechanisms. Results from the more realistic of the two models predict in-phase-mode operation for certain restricted ranges of waveguide dielectric constant in agreement with experiment. This behavior is shown to result from resonances between the waveguide modes and the modes of the active region. Our model therefore successfully explains the narrow range of waveguide dielectric constants observed for devices operating in the in-phase mode. These results suggest that improved yields would result from a different type of leaky-mode array employing smaller, rectangularly shaped waveguides.