Index-guided Lateral Modes Observed From Gain-guided Twin-stripe Laser Diode Arrays

Gain-guided twin-stripe lasers have been observed to lase in index-guided modes. This index-guide is created by a dip in the carrier concentration between the stripes. The first lasing mode of a twin-stripe array, having 4-μm wide stripes with a 8-μm center-to-center spacing, is the zeroth-order index-guided mode. This mode has been identified by a single-lobed far field and a near-field profile tightly confined between the stripes. At higher currents, a double-lobed near-field intensity profile is observed to lase simultaneously at a 10-20-Å wavelength shorter than the wavelength of the fundamental. Although the far field is double-lobed, suggestive of an out-of-phase gain-guided array mode, careful measurements of the near field indicate that this double-lobed mode is the first-order index-guided lateral mode. The small lateral extent beyond the stripes in the near field and the lack of interference fringes between the stripes is inconsistent with a gain-guided super-mode.