Decai Sun

Low-threshold laterally oxidized GaInP-AlGaInP quantum-well laser diodes

Low-threshold, high-efficiency edge-emitting visible AIGaInP-GaInP laser diodes using a buried AlAs native oxides for carrier and optical confinement are described. The lasers incorporate a thin AlAs layer in the upper cladding region, which when laterally wet oxidized, forms a narrow aperture. The lasers operate with room temperature, continuous-wave (CW) threshold currents of 11 mA with external differential quantum efficiency of 34% per facet for an uncoated 300-/spl mu/m-long 3.5-/spl mu/m-wide device. As-fabricated lasers exhibited modest performance under CW operation. Post-fabrication annealing was shown to dramatically improve the device characteristics.

Hybrid integration of light-emitters and detectors with SOI-based micro-opto-electro-mechanical systems (MOEMS)

A multidisciplinary team of end users and suppliers has collaborated to develop a novel yet broadly enabling process for the design, fabrication and assembly of Micro-Opto- Electro-Mechanical Systems (MOEMS). A key goal is to overcome the shortcomings of the polysilicon layer used for fabricating optical components in a conventional surface micromachining process. These shortcomings include the controllability and uniformity of material stress that is a major cause of curvature and deformation in released microstructures. The approach taken by the consortium to overcome this issue is to use the single-crystal-silicon (SCS) device layer of a silicon-on-insulator (SOI) wafer for the primary structural layer. Since optical flatness and mechanical reliability are of utmost importance in the realization of such devices, the use of the silicon device layer is seen as an excellent choice for devices which rely on the optical integrity of the materials used in their construction. A three-layer polysilicon process consisting of two structural layers is integrated on top of the silicon device layer. This add-on process allows for the formation of sliders, hinges, torsional springs, comb drives and other actuating mechanisms for positioning and movement of the optical components. Flip-chip bonding techniques are also being developed for the hybrid integration of edge and surface emitting lasers on the front and back surfaces of the silicon wafer, adding to the functionality and broadly enabling nature of this process. In addition to process development, the MOEMS manufacturing Consortium is extending Micro-Electro-Mechanical Systems (MEMS) modeling and simulation design tools into the optical domain, and using the newly developed infrastructure for fabrication of prototype micro-optical systems in the areas of industrial automation, optical switching for telecommunications and laser printing.

Multiwavelength light emitters for scanning applications fabricated by flipchip bonding

We present a multiwavelength light source which was fabricated using a self-aligned flipchip bonding technique. The device consists of an InGaN-GaN light-emitting diode emitting light at around 420 nm, on top of which we flipchip-bonded a monolithically integrated red/infrared dual-beam laser. The upper two lasers were built by selective removal of the red laser, and subsequent regrowth of an infrared laser structure. Since all processes, including the deposition of the PbSn solder bumps for bonding, were based on photolithographic precision, tight alignment tolerances of /spl plusmn//spl mu/m in the lateral direction could be fulfilled between the ridge waveguides of the three light emitters. For a high-speed color scanning system, this is an important design criterion because it will allow the use of a single scanning optics for the three laser beams.

TE/TM cross-polarization laser diodes using tensile-strained quantum wells

Polarization characteristics of TE/TM cross-polarization semiconductor laser diodes are discussed in this paper. Broad area lasers fabricated from tensile strained In0.5+(delta )Ga0.5-(delta )P/(AlGa)0.5In0.5P quantum well laser structures oscillate in TE/TM dual polarizations. Polarization dominance changes from TE to TM as the cavity length of the laser is increased from 250 micrometers to 650 micrometers. The polarization-dependent gain property of a tensile-strained quantum well laser is analyzed from a simple theoretical model. In a slightly tensile strain quantum well, where light-hole and heavy-hole ground states are nearly degenerate in the valence band due to the strain and quantization effect, gain is provided for TM and TE modes simultaneously, and the two mode gain curves cross at certain injection level. Polarization switching is made possible by changing the threshold gain of the laser. The threshold gain dependent polarization switching is utilized to fabricate closely spaced independently-addressable dual beam cross polarization lasers. Results on 650 nm broad area dual beam cross polarization laser are presented. For dual polarization infrared lasers, a dual quantum well structure in which gains for TE and TM modes are provided by lattice-matched and tensile-strained quantum wells separately is designed. Eight-hundred-thirty-five nm broad area laser fabricated from a GaAs and GaAs0.95P0.05 dual quantum well structure oscillating in TE/TM dual polarizations is demonstrated.

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.