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| 2. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Realization of spectrally engineered semiconductor Fabry-Perot lasers with narrow geometrical tolerances
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:9, s. 093112-
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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 majorconcern. 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 mirrorsand that the additional loss introduced by the perturbations adds
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| 3. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Spectral engineering of semiconductor Fabry–Perot laser cavities in the weakly and strongly perturbed regimes
- 2010
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Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 27:1, s. 118-127
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Tidskriftsartikel (refereegranskat)abstract
- By inserting index perturbations at certain positions along a semiconductor Fabry–Perot laser cavity thethreshold gain for one or several of the longitudinal cavity modes can be selectively lowered to facilitate, e.g.,single-mode or two-color operation. Previous design methods were limited to a fairly small number of perturbations,leading to only weakly perturbed cavities and thus a limited freedom in tailoring the spectral propertiesof the laser. In our approach we fully account for all multiple-reflection events and use a search spacethat permits any distribution of the locations and lengths of the perturbations. We are therefore able to designcavities with almost arbitrary spectral properties with very low threshold gain values for, e.g., the lasingmodes of a two-color cavity. Constraining the design by reducing the geometrical freedom, which can be used toincrease the smallest feature size to simplify fabrication, we seamlessly approach the weakly perturbed regimewhile maintaining much of the freedom for spectral engineering.
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| 4. |
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| 5. |
- Arafin, S., et al.
(författare)
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Comprehensive analysis of electrically-pumped GaSb-based VCSELs
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:18, s. 17267-17282
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 mu m based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.
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| 6. |
- Arafin, S., et al.
(författare)
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Large-Area Single-Mode GaSb-based VCSELs using an Inverted Surface Relief
- 2010
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Ingår i: 23rd Annual Meeting of the IEEE Photonics Society, PHOTINICS 2010. - 9781424453689 ; , s. 61-62
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Konferensbidrag (refereegranskat)abstract
- Large-area GaSb-based BTJ VCSELs at ∼2.35 μm were fabricated using an inverted surface relief technique to support the single transverse mode operation. The devices operate in continuous-wave and are (electro-)thermally tunable over 6 nm.
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| 7. |
- Baveja, Prashant, 1985, et al.
(författare)
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Impact of device parameters on thermal performance of high speed oxide confined 850 nm VCSELs
- 2012
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:1, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- We study the impact of device parameters, such asinner-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 topmirror 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 ofdevices. 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.
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| 8. |
- Baveja, P. P., et al.
(författare)
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Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:16, s. 15490-15505
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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.
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| 9. |
- Baveja, P. P., et al.
(författare)
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Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276
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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.
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| 10. |
- Berland, Kristian, 1983, et al.
(författare)
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Temperature stability of intersubband transitions in AlN/GaN quantum wells
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:4, s. 043507-
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Tidskriftsartikel (refereegranskat)abstract
- Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400 degrees C. The self-consistent Schroumldinger-Poisson modeling includes temperature effects of the band gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by similar to 6 meV at 400 degrees C relative to its room temperature value.
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