Lateral waveguiding in stripe-geometry double-heterostructure lasers below the lasing threshold

Structure in the far-field pattern of current-confined stripe-geometry double-heterostructure lasers in the angle range
\pm 20\deg
is observed at current levels of less than
\frac{1}{4}
of threshold value. The behavior is explained by leaky-mode guiding due to a gain maximum under the stripe and to a negative refractive index step on the order of -0.01.