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  • Resultat 1-10 av 82
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  • Adolfsson, Göran, 1981-, et al. (författare)
  • Realization of spectrally engineered semiconductor Fabry-Perot lasers with narrow geometrical tolerances
  • 2011
  • Ingår i: AIP Journal of Applied Physics. - 0021-8979. ; 109:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive index perturbations along the length of the resonator. However, the physical realization of these resonators is a challenge because of very narrow tolerances; in particular the need for precise positioning of the end facets of the resonator in relation to the perturbations, and the excess propagation loss associated with the perturbations, has been a major concern. We report on a method to achieve high-quality end facet mirrors enabling precise positioning relative to the perturbations, the latter which are realized as lateral corrugations of the waveguide. Measurements show that the mirror quality is comparable to that of cleaved mirrors and that the additional loss introduced by the perturbations adds < 10 cm-1 to the overall propagation loss, provided that the perturbations are densely enough spaced along the resonator. This implies that the number of perturbations should be large, which is beneficial for the realization of strongly perturbed resonators enabling the most flexible engineering of the spectral properties of the laser.
  • Baveja, Prashant, 1985-, et al. (författare)
  • Impact of device parameters on thermal performance of high speed oxide confined 850 nm VCSELs
  • 2012
  • Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197. ; 48:1, s. 17-26
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the impact of device parameters, such as inner-aperture diameter and cavity photon lifetime, on thermal rollover mechanisms in 850-nm, oxide-confined, vertical-cavity surface-emitting lasers (VCSELs) designed for high-speed operation. We perform measurements on four different VCSELs of different designs and use our empirical thermal model for calculating the power dissipated with increasing bias currents through various physical processes such as absorption within the cavity, carrier thermalization, carrier leakage, spontaneous carrier recombination, and Joule heating. When reducing the top mirror reflectivity to reduce internal optical absorption loss we find an increase of power dissipation due to carrier leakage. There is therefore a trade-ff between the powers dissipated owing to optical absorption and carrier leakage in the sense that overcompensating for optical absorption enhances carrier leakage (and vice versa). We further find that carrier leakage places the ultimate limit on the thermal performance for this entire class of devices. Our analysis yields useful design optimization strategies for mitigating the impact of carrier leakage and should thereby prove useful for the performance enhancement of 850-nm, highspeed, oxide-confined VCSELs.
  • Baveja, P. P., et al. (författare)
  • Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:16, s. 15490-15505
  • Tidskriftsartikel (refereegranskat)abstract
    • We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 degrees C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-mu m inner-aperture diameter and optimized for highspeed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.
  • Baveja, P. P., et al. (författare)
  • Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
  • 2012
  • Ingår i: Proceedings of SPIE - Conference on Vertical-Cavity Surface-Emitting Lasers XVI (VCSELs) / SPIE Photonics West Symposium, San Fransisco, 25-26 January 2012. - 0277-786X. - 9780819489197 ; 8276
  • Konferensbidrag (refereegranskat)abstract
    • We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them.
  • Davani, H. A., et al. (författare)
  • Polarization investigation of a tunable high-speed short-wavelength bulk-micromachined MEMS-VCSEL
  • 2012
  • Ingår i: Proceedings of SPIE - Conference on Vertical-Cavity Surface-Emitting Lasers XVI (VCSELs) / SPIE Photonics West Symposium, San Fransisco, 25-26 January 2012. - 0277-786X. - 9780819489197 ; 8276
  • Konferensbidrag (refereegranskat)abstract
    • We report the investigation of the state of polarization (SOP) of a tunable vertical-cavity surface-emitting laser (VCSEL) operating near 850 nm with a mode-hop free single-mode tuning range of about 12 nm and an amplitude modulation bandwidth of about 5 GHz. In addition, the effect of a sub-wavelength grating on the device and its influence on the polarization stability and polarization switching has been investigated. The VCSEL with an integrated sub-wavelength grating shows a stable SOP with a polarization mode suppression ratio (PMSR) more than 35 dB during the tuning.
  • Fuchs, Christian, et al. (författare)
  • Spatio-temporal turn-on dynamics of grating relief VCSELs
  • 2007
  • Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197. ; 43:11-12, s. 1227-1234
  • Tidskriftsartikel (refereegranskat)abstract
    • Within a joint collaboration between modeling, technology and experiments, we investigate the polarization-resolved spatial emission and turn-on dynamics of oxide-confined vertical-cavity surface-emitting lasers with an integrated surface-relief grating. By applying a time-resolved imaging technique we demonstrate that the introduced high dichroism also maintains its influence dynamically. This leads to highly polarization-stable spatially fundamental Gaussian mode emission on 100-ps timescale. Finally, the achieved progress, but also the limits of this promising stabilization scheme are discussed.
  • Gierl, C., et al. (författare)
  • Tuneable VCSEL aiming for the application in interconnects and short haul systems
  • 2011
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. Optical Metro Networks and Short-Haul Systems III; San Francisco, CA; 25-27 January 2011. - 0277-786X. - 978-081948496-3 ; 7959
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Widely tunable vertical cavity surface emitting lasers (VCSEL) are of high interest for optical communications, gas spectroscopy and fiber-Bragg-grating measurements. In this paper we present tunable VCSEL operating at wavelength around 850 nm and 1550 nm with tuning ranges up to 20 nm and 76 nm respectively. The first versions of VCSEL operating at 1550 nm with 76 nm tuning range and an output power of 1.3mW were not designed for high speed modulation, but for applications where only stable continious tuning is essential (e.g. gas sensing). The next step was the design of non tunable VCSEL showing high speed modulation frequencies of 10 GHz with side mode supression ratios beyond 50 dB. The latest version of these devices show record output powers of 6.7mW at 20 °C and 3mW at 80 °C. The emphasis of our present and future work lies on the combination of both technologies. The tunable VCSEL operating in the 850 nm-region reaches a modulation bandwidth of 5.5GHz with an output power of 0.8mW.
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