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- Gustavsson, Johan, 1974, et al.
(författare)
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High-speed 850-nm VCSELs for 40 Gb/s transmission
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We have explored the possibility to extend the data transmission rate for standard 850-nm GaAs-based VCSELs beyond the 10 Gbit/s limit of today's commercially available directly-modulated devices. By sophisticated tailoring of the design for high-speed performance we demonstrate that 10 Gb/s is far from the upper limit. For example, the thermal conductivity of the bottom mirror is improved by the use of binary compounds, and the electrical parasitics are kept at a minimum by incorporating a large diameter double layered oxide aperture in the design. We also show that the intrinsic high speed performance is significantly improved by replacing the traditional GaAs QWs with strained InGaAs QWs in the active region. The best overall performance is achieved for a device with a 9 μm diameter oxide aperture, having in a threshold current of 0.6 mA, a maximum output power of 9 mW, a thermal resistance of 1.9 °C/mW, and a differential resistance of 80 Ω. The measured 3dB bandwidth exceeds 20 GHz, and we experimentally demonstrate that the device is capable of error-free transmission (BER
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| 2. |
- Gustavsson, Johan, 1974, et al.
(författare)
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Optimized active region design for high speed 850 nm VCSELs
- 2009
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Ingår i: CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference; Munich; Germany; 14 June 2009 through 19 June 2009. - 9781424440801 ; , s. Art. no. 5192928-
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Konferensbidrag (refereegranskat)abstract
- Short wavelength (850 nm) VCSELs operating at speeds of 25 Gb/s and above are needed for future highcapacity, short reach data communication links. The modulation bandwidth is intrinsically limited by thedifferential gain of the QWs used in the active region of the VCSEL. In this work we explore the use of strainedInGaAs/AlGaAs QWs and benchmark the performance against conventional GaAs/AlGaAs QWs.An 8-band k⋅p model [1] was used to calculate the energy band dispersions, using band offsets from modelsolid theory [2]. In all cases, the QW and barrier compositions and QW thickness were chosen for a gain peak at845 nm, enabling emission at 850 nm with a small detuning between the gain peak and the cavity resonance.With increasing In-concentration the QW thickness is reduced and the Al-concentration in the barrier isincreased to maintain the gain peak at 845 nm and the number of QWs is increased to maintain opticalconfinement and enable operation at a low carrier density for high differential gain. It was found that theincorporation of up to 10% In leads to a significant reduction in threshold carrier density and increase indifferential gain. This is due to an increased separation and reduced mixing between the highest heavy-hole andlight-hole valence bands (Fig.1). A further increase of In concentration leads to a less marked improvement.With an optimum active region design (5 x 4 nm In0.10Ga0.90As/Al0.37Ga0.63As QWs) a differential gain twice ashigh as that of a conventional design with 3 x 8 nm GaAs/Al0.30Ga0.70As QWs was predicted (Table 1).The improvement of differential gain was experimentally confirmed by extracting the resonance frequencyand its dependence on current from the modulation response of VCSELs with optimized InGaAs/AlGaAs QWand conventional GaAs/AlGaAs QW active regions. The differential gain was calculated from the correspondingD-factors (Fig.2) [3]. Excellent agreement was obtained between theory and experiments (Table 1).VCSELs with an optimized InGaAs/AlGaAs QW active region have a modulation bandwidth of 20 GHz at25° and 15 GHz at 85°C [4] and have enabled error-free transmission over 50 (100) m multimode fiber up to 32(25) Gb/s at a bias current density as low as 11 kA/cm2 under direct current modulation.
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| 3. |
- 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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