Robert L. Thornton

Vertical-cavity lasers and their application to laser printing

We present the primary laser printing system performance issues which are the driving forces for multiple beam laser printing. Although edge emitting semiconductor lasers have allowed progress in this area, vertical cavity lasers have substantial advantage in the longer term. We further present needs and issues with VCSEL performance which must be addressed for the application of VCSELs to high performance laser printing. Finally, we explore advanced print architectures which would be enabled by the VCSEL device.

Densely packed surface-emitting laser arrays for printing applications

We report on our efforts to develop a laser printbar consisting of a very dense array of independently addressable laterally-oxidized top-emitting VCSELs. In order to maintain wafer planarity for easy electrical routing, the buried oxidation layer in our structure is accessed through small via holes instead of a more typical mesa etch. Unlike most VCSELs, our devices utilize transparent indium-tin- oxide top contacts that allow for a more compact device design. The 200-element array we fabricated has a linear density of one device every 3 micrometers .

Laterally oxidized vertical-cavity lasers with stable polarization

We disclose a method of eliminating the polarization instability in laterally-oxidized vertical-cavity surface- emitting lasers. By employing an appropriately-shaped device aperture, we are able to make the lasers operate in a single polarization direction through their entire L-I curve.

Measurement of the Q factor of semiconductor laser cavities by Fourier analysis of the emission spectrum

We present a study on a novel method for the determination of the quality factor and the cavity loss in semiconductor lasers. The method we use involves Fourier analysis of the Fabry-Perot mode spectrum when operating the device below lasing threshold. The observation of the decay rate of higher order harmonics in the Fourier analysis of the spectra allows us to determine the amount of cavity propagation loss/gain. As an illustrative example, a Fourier analysis on experimental data for lasers fabricated in the AlGaAs material system will be given. In addition to the measurements on propagation loss/gain, this method allowed also the identification of the density and strength of intra-cavity scattering centers in optically pumped AlGaInN lasers. This is an important capability for the fabrication of blue diode lasers in the gallium-nitride material system.

Dual-wavelength laser by selective intermixing of GaAs/AlGaAs quantum wells

The longer-wavelength quantum well in an AlGaAs/GaAs asymmetric dual quantum well laser structure was selectively removed by localized intermixing. High Si-doping on each side of the longer-wavelength well caused intermixing during an anneal under a SiNx cap, while leaving the other nearby well intact. During an anneal under an exposed GaAs surface layer, both quantum wells remained intact. By patterning the surface with alternating SiNx and exposed GaAs, the longer-wavelength quantum well was selectively intermixed under the SiNx. Integrated broad area lasers were fabricated with threshold current density and external quantum efficiency of 260 A/cm2 and 30%/facet at a wavelength of 751 nm in capped regions and 195 A/cm2, 32%/facet at 824 nm in the uncapped regions. This technique can be used to fabricate close spacing multi-wavelength laser arrays.