The cw electro-optical properties of (Al,Ga)As modified-strip buried-heterostructure lasers

Abstract

This paper presents a detailed study of the cw propeties of a modified-strip buried-heterostructure (MSBH) laser. Included are studies of the electrical, electro-optical, and optical beam properties, together with spectral characteristics, and temperature dependence of thresholds. A variation of this type of laser, a passive-mirror modified-strip buried heterostructure is also described. The MSBH laser possesses many desirable properties including excellent linearity of the lasing emission consistent with a second-harmonic content more than 40 dB below the fundamental, constant proportionality between the light emitted from the two mirror facets, ’’kink-free’’ emission to the maximum cw power levels measured (35 mW/mirror facet), nearly round near-field intensity distribution with an ellipicity of 1.3 : 1, lasing emission in the lowest-order transverse mode, full angle half-power perpendicular to the junction plane of 27.3° (significantly smaller than any other practical cw DH laser structure), and narrow cw spectra (emission is typically in only a few longitudinal modes). MSBH lasers are nonastigmatic signal sources so that diffraction-limited spherical optics can be used. Pulsations are not observed if the active stripe is free of absorbing defects. cw operation of 10 mW/mirror facet was obtained at ambient temperatures to 90 °C with a T0 of 126 °K. For 380-μm-long lasers pulsed threshold currents of 78 mA dc, slope efficiencies of 63%, forward resistances of 2 Ω, and zero-biased capacitances of 15 pF have been measured. At the operating power of 3 mW/mirror facet, the optical power density at the mirror facet is low (?104 W/cm2) which may have positive reliability implications. The passive-mirror form of the MSBH laser (PM-MSBH laser), with the potential for avoiding surface effects which have been implicated as a cause of pulsations and laser degradation, have been measured with thresholds of 104 mA dc and slope efficiencies of 31%.