In this paper, we will present the recent progress of electrically-pumped directly-modulated tunable 1550 nm VCSEL development at Bandwidth9. The device is fabricated from an all epitaxial VCSEL structure grown on an InP substrate, with a monolithically integrated tuning arm for continuous wavelength tuning. We have demonstrated over 1 mW CW output power and over 20 nm tuning range in C-band and error free transmission performance at 2.5 Gbps over 100 km SMF-28 fiber. The reliability test data of the tunable VCSELs shows a projected failure rate of less than 400 FITS.
Joel Kubby, Jim Calamita, Jen-Tsorng Chang, Jingkuang Chen, Peter Gulvin, C.-C. Lin, Robert Lofthus, Bill Nowak, Yi Su, Alex Tran, David Burns, Janusz Bryzek, John Gilbert, Charles Hsu, Tom Korsmeyer, Arthur Morris, Thomas Plowman, Vladimir Rabinovich, Troy Daiber, Bruce Scharf, Andrew Zosel, Li Fan, Jim Hartman, Anis Husain, Nena Golubovic-Laikopoulos, Raji Mali, Tom Pumo, Steve Delvecchio, Shifang Zhou, Michel Rosa, Decai Sun
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.
This paper presents and discusses experimental results which successfully demonstrate using flip-chip techniques, the bonding and operation of a GaAs edge emitting laser on a silicon substrate having recessed bonding pads. The flip chip alignment and bonding technique is discussed first, focusing on experimental results for both flux and flux-less forms of solder bump processing, the developed flux-less technique is shown to provide comparable solder bump integrity and yield. Subsequent to the newly developed solder bump fabrication methodology shown, a recessed bonding pad design is introduced and demonstrated experimentally to aid in the final coarse alignment and assembly of the GaAs laser device onto a silicon substrate. Together both the flux-less solder bump and bonding pad recess design and fabrication processes provide increased reliability for integration with MEMS and MOEMS based devices and systems over traditional methods for hybrid device attachment.
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.
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.
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