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Min Hyeong KIM High-Speed Circuits and Systems Laboratory E.E. Engineering at YONSEI UNIVERITY

A hybrid silicon evanescent laser fabricated with a silicon waveguide and Ⅲ-Ⅴ offset quantum wells Hyundai Park, Alexander W. Fang, Satoshi Kodama, and John E. Bowers. Min Hyeong KIM High-Speed Circuits and Systems Laboratory E.E. Engineering at YONSEI UNIVERITY 2011. 4. 13. .

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Min Hyeong KIM High-Speed Circuits and Systems Laboratory E.E. Engineering at YONSEI UNIVERITY

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  1. A hybrid silicon evanescent laser fabricated with a silicon waveguide and Ⅲ-Ⅴ offset quantum wellsHyundai Park, Alexander W. Fang, Satoshi Kodama, and John E. Bowers Min Hyeong KIM High-Speed Circuits and Systems Laboratory E.E. Engineering at YONSEI UNIVERITY 2011. 4. 13.

  2. [ Contents ] • Abstract • Introduction • - Several laser structures • Device structure • Lasing gain material • Waveguides • Bonding technology • Additional layer • Fabrication process • Experimental results • Conclusion & Summary

  3. 1. Abstract • A laser can be utilized on a silicon waveguide bonded to a multiple quantum wells(MQW). • This structure allows the optical waveguide defined by CMOS technology to get an optical gain provided by Ⅲ-Ⅴ materials. • It has a 1538nm laser, pulsed threshold of 30mW, and an output power of 1.4mW. How to implement this structure? How to operate?? Which principles???

  4. 2. Introduction It is challenge to build light-emitting devices on VLSI CMOS technology.Because Si has an indirect bandgap(E_g). How to overcome this challenges? Raman laser Using porous silicon or nanocrystalline-Si SiGe quantum cascade structures Er doped silica Etc…. In this paper, we report the first demonstration of silicon evanescently** coupled laser structure. ** Evanescent wave An evanescent wave is a nearfield standing wave with an intensity that exhibits exponential decay with distance from the boundary at which the wave was formed.

  5. 3. Device structure InP Cladding MQW gain material MQW laser + SL barrier + Bonding technology + SOI waveguide Si Silica Si substrate Light-emitting Process : Current or Laser Pumping >> MQW lasing >> wave evanescent to SOI waveguide >> output guiding

  6. 3. Device structure Ⅰ Ⅱ • Ⅰ. Lasing gain material • – MQW(mutiple quantum wells) • A quantum well laser is a laser diode in which the active region of the device is so narrow that quantum confinement occurs. • The wavelength of the light is determined by the width of the active region. • Much shorter wavelengths can be obtained. • Low threshold current. • The greater efficiency. Ⅱ. Waveguides – SOI structure(last topic)

  7. 3. Device structure • Ⅲ. Bonding technology • – Plasma-Assisted Low Temperature Wafer Bonding Ⅲ • Two samples are bonded together via oxygen plasma assisted wafer bonding • Low temperature annealing(~250℃) preserves the optical gain of MQW. • High temperature annealing makes (1) a surface non-uniformities and (2) gain reduction. Hydrophilic surface bonding : 125℃ Hydrophobic surface bonding : 400℃ Are better choices.

  8. 3. Device structure Ⅳ • Ⅳ. Additional layer • – SL(Superlattice) barrier • Defect-blocking layer : It prevents the deep propagation of defects by fusing process. • Luminescent properties are improved. Non-intentionally doped SL SL interposition Doped SL

  9. 3. Device structure _ detailed design • InP cladding layer • MQW absorber (500nm) • MQW laser structure • MQW absorber (50nm) • InP cladding layer (110nm spacer) • SL barrier (7.5nm) • Si waveguide (W=1.3u, H=0.97u, L=0.78u) • Silica layer (500nm) • Si substrate For operating 1538nm wavelength

  10. 4. Fabrication process Form SiO2 layer on Si substrate _ thermal oxidation for 2 hours at 1050℃ Form Si rib waveguides _ using inductively coupled plasma etching Hetero-bond InP(already completed)/Si _ Plasma-Assisted Low Temperature Wafer Bonding Dice the device for mirroring Polish and HR coat**(High-reflection coatings) for mirroring ** HR coating

  11. 5. Experimental results Laser diode Pumping • [Experimental Conditions] • 980nm laser diode pumping • Through the top InP cladding layer • Recorded on an IR camera through a polarizing beam splitter [Results Pictures] Calculated TE mode profile TE near field image

  12. 5. Experimental results • A laser output almost occurs in the optical mode(Si waveguide) • Slab mode(MQW) do not support lasing output • The pumping threshold increase from 30mW to 50mW between 12℃~20℃. • Quantumefficiency at 12℃ : about 3.2% Cavity length 600um Temperature 12℃ Pump power=1.4* threshold Group index=C/Vg=3.85

  13. 6. Conclusion& Summary • We can make the optically pumped Si evanescent laser consisting of MQW as active region bonded to Si waveguide as a passive device. (conclusion!) • For operating at 1538nm, pump threshold is 30mW and slope efficiency is 3.2%. (conclusion!) • On bonding process, use Plasma-Assisted Low Temperature Wafer Bonding to maintain the optical gain of gain material. • By using SL(Superlattice) barrier, we can block the defects propagation from fusing(bonding) process.

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