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37. |
- Hashemi, Seyed Ehsan, 1986, et al.
(författare)
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Engineering the transverse optical guiding in GaN-based VCSELs to avoid detrimental optical loss
- 2012
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Ingår i: International Workshop on Nitride Semiconductors 2012, October 14-19, 2012, Sapporo, Japan, p. ThP-OD-33.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In order to improve the current injection in GaN-based blue vertical cavity surface emitting lasers (VCSELs) a dielectric aperture is generally used in combination with an indium-tin-oxide (ITO) layer on the top intracavity p-contact layer. The most straightforward way to realize this introduces a depression of the structure near the optical axis and we show, by using a 2D effective index method and a 3D coupled-cavity beam propagation method, that this typically results in optically anti-guided structures with associated high optical losses and thus very high threshold gains. Remarkably, the threshold gain reduces with increased negative guiding, which is due to improved lateral confinement and reduction of lateral leakage. Still, moderately positively guided designs should be preferred to avoid the detrimental effect of lateral leakage and high diffraction loss. To ensure positive index guiding, we propose to planarize the structure or introduce an elevation near the optical axis by additional processing, with an associated reduction in threshold material gain from 6000 cm-1 to 2000 cm-1 for the studied structures.
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38. |
- Healy, S. B., et al.
(författare)
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Active Region Design for High-Speed 850-nm VCSELs
- 2010
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 46:4, s. 506-512
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Tidskriftsartikel (refereegranskat)abstract
- Higher speed short-wavelength (850 nm) VCSELs are required for future high-capacity, short-reach data communication links. The modulation bandwidth of such devices is intrinsically limited by the differential gain of the quantum wells (QWs) used in the active region. We present gain calculations using an 8-band k.p Hamiltonian which show that the incorporation of 10% In in an InGaAs/AlGaAs QW structure can approximately double the differential gain compared to a GaAs/AlGaAs QW structure, with little additional improvement achieved by further increasing the In composition in the QW. This improvement is confirmed by extracting the differential gain value from measurements of the modulation response of VCSELs with optimized InGaAs/AlGaAs QW and conventional GaAs/AlGaAs QW active regions. Excellent agreement is obtained between the theoretically and experimentally determined values of the differential gain, confirming the benefits of strained InGaAs QW structures for high-speed 850-nm VCSEL applications.
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39. |
- Ingham, J.D., et al.
(författare)
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32 Gb/s multilevel modulation of an 850 nm VCSEL for next-generation datacommunication standards
- 2011
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Ingår i: 2011 Conference on Lasers and Electro-Optics, CLEO 2011; Baltimore, MD; 1 May 2011 through 6 May 2011. - Washington, D.C. : OSA. - 2162-2701. - 9781557529107
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Konferensbidrag (refereegranskat)abstract
- An 850 nm vertical-cavity surface-emitting laser is modulated at 32 Gb/s using pulseamplitude modulation with four levels. Transmitter predistortion generates an optimized modulation waveform, which requires a receiver bandwidth of only 15 GHz.
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