The heteroepitaxial ridge-overgrown distributed feedback laser

A new distributed feedback laser, the heteroepitaxial ridge-overgrown distributed feedback (HRO-DFB) laser, is proposed and demonstrated. The growth steps permit post-active-layer growth determination of the grating period, and the fabrication of this laser is simple with an automatic alignment of the current confinement to the ridge-overgrowths, which form the strip-loaded waveguide of the laser. The lateral overgrowth extending over the oxide films on both sides of the window stripe enhances the effect of grating feedback. Both LPE and MO-CVD have been employed successfully for the ridge overgrowth. The HRO-DFB laser was shown to operate in stable single-longitudinal mode with no observable mode partition events under 2 Gbit/s pseudorandom pulse modulation. The dynamic spectral width under 2 Gbit/s modulation was typically 0.5-2 Å. Other characteristics of these 1.5 μm HRO-DFB lasers include ∼8 mW/facet of single-longitudinal mode output power, and narrow beam divergence of 10° operating in the fundamental transverse mode in the junction plane. The CW thresholds were usually 50-100 mA. Transmission experiments with dispersive fibers (17 ps/km-nm) at~1.55 at 2 Gbits/s over 82 km and at 420 Mbits/s over 203 km confirmed that the HRO-DFB laser is an excellent a single-frequency optical source for use in optical communication applications.