A study of lateral modes in wide double-heterostructure GaAs-GaAlAs laser diodes

Higher-order lateral modes produced in wide GaAs-GaAlAs DH lasers were spectrally analyzed and photographed by the use of spatially resolved spectroscopy. These modes behave differently in mesa- and stripe-geometry lasers. They were studied in detail as a function of pumping current for the mesa structure. The spacing between lateral modes could be approximated by a simple model based on a sandwich-type symmetrical dielectric waveguide. Stripe-geometry lasers follow Hermitian-Gaussian mode patterns which are produced by parabolic refractive-index profiles. An anomalous development of mode intensities near threshold was observed in the mesa diode. Immediately above threshold, higher orders dominated the near-field patterns. Explanation for this could be found in the lateral optical gain profile produced by the interaction of the nonlinear characteristics of the p-n junction and the geometrical series spreading resistance of the substrate.