| 1. |
- Sezgin, Ibrahim Can, 1992, et al.
(author)
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A Flexible Multi-Gbps Transmitter Using Ultra-High Speed Sigma- Delta-over- Fiber
- 2018
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In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; 2018-June, s. 1195-1198
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Conference paper (peer-reviewed)abstract
- Sigma-delta-over-fiber (SDoF) using high speed-low cost optical components for datacom enables high speed transmission at X-band. This paper examines the limitations of SDoF in terms of maximum frequencies and highest bit rates. Different modulation formats, symbol rates and carrier frequencies are investigated. A high speed 850 nm vertical-cavity surface-emiting-laser (VCSEL) is used as an optical source to transmit the optical signal over a 50 meter, OM4, multimode fiber (MMF). Error vector magnitude (EVM) less than 6% is achieved at a 12-GHz center frequency for a 8-Gbps QAM256 modulated signal.
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| 2. |
- Bergmann, Michael Alexander, 1989, et al.
(author)
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Towards ultraviolet and blue microcavity lasers
- 2018
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In: Northen Optics and Photonics conference. - 9789163964886 ; 2018
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Conference paper (peer-reviewed)abstract
- The development of III-nitride-based (Al,Ga,In(N)) microcavity lasers is a challenging task. Significant progress in recent years has resulted in realizations of electrically pumped devices with optical output power in the mW-range and with threshold current densities below 20 kA/cm2. However, to become practical, the lifetime and power conversion efficiency of these devices must be improved. Among the challenges are achieving transverse optical mode confinement, highreflectivity mirrors and control over the resonator length. We will highlight our theoretical work on transverse optical mode confinement, emphasising the overwhelming risk of ending up with an optically anti-guided cavity, and its consequences such as very high optical losses that easily could double the threshold gain for lasing. We will show some anti-guided cavities with reasonable threshold gain and built-in modal discrimination. However, all anti-guided cavities are very sensitive to temperature effects and small structural changes in the cavity caused by fabrication imperfections. We have explored electrically conductive distributed Bragg reflectors (DBRs) in both AlN/GaN and ZnO/GaN. The AlN/GaN DBRs were grown with different strain-compensating interlayers, and the DBR without interlayers had the lowest vertical resistivity with a specific series resistance of 0.044 cmfor eight DBRpairs. In the ZnO/GaN DBR, the measured resistance was dominated by lateral and contact contributions, setting a lower measurable limit of ~10 for three DBR-pairs. Numerical simulations show the importance of having in-plane strained layers in the ZnO/GaN DBR, since that leads to cancellation of the spontaneous and piezoelectric polarization. This results in a dramatically reduced vertical resistance, potentially three orders of magnitude lower than what could be measured. cm An alternative to an epitaxially grown DBR is a dielectric DBR, which offers high reflectivity over a broader wavelength range, relaxing the requirements on resonator length control. To deposit a dielectric DBR on the bottom side of the cavity, the sample must first be bonded to a carrier wafer before the substrate can be removed. We used thermocompression gold-gold bonding to successfully bond the laser structure to a Si carrier wafer. The subsequent substrate removal is a challenging process due to the chemical inertness of the III-nitride-based materials. A doping-dependent electrochemical etch technique was used, which allows for the selective removal of a sacrificial (n-doped) layer between the cavity and the substrate. This resulted in nm-precise cavity lift-off with a low root-mean-square surface roughness down to 0.3 nm. Thus, the process is suitable for the fabrication of high-quality optical devices such as microcavity lasers. In addition, the technique offers a new alternative to create III-nitridebased optical resonators, mechanical resonators, thin film LEDs and transistors.
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| 3. |
- Boström, Magnus, 1972-, et al.
(author)
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Conditions for Transformative Learning for Sustainable Development : A Theoretical Review and Approach
- 2018
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In: Sustainability. - : MDPI. - 2071-1050. ; 10:12
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Journal article (peer-reviewed)abstract
- Continued unsustainability and surpassed planetary boundaries require not only scientific and technological advances, but deep and enduring social and cultural changes. The purpose of this article is to contribute a theoretical approach to understand conditions and constraints for societal change towards sustainable development. In order to break with unsustainable norms, habits, practices, and structures, there is a need for learning for transformation, not only adaption. Based on a critical literature review within the field of learning for sustainable development, our approach is a development of the concept of transformative learning, by integrating three additional dimensions—Institutional Structures, Social Practices, and Conflict Perspectives. This approach acknowledges conflicts on macro, meso, and micro levels, as well as structural and cultural constraints. It contends that transformative learning is processual, interactional, long-term, and cumbersome. It takes place within existing institutions and social practices, while also transcending them. The article adopts an interdisciplinary social science perspective that acknowledges the importance of transformative learning in order for communities, organizations, and individuals to be able to deal with global sustainability problems, acknowledging the societal and personal conflicts involved in such transformation.
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| 4. |
- Grabowski, Alexander, 1993, et al.
(author)
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Large-Signal Circuit Model for Datacom VCSELs
- 2018
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In: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. ; 2018-September, s. 193-194
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Conference paper (peer-reviewed)abstract
- We present a physics-based equivalent-circuit model for datacom VCSELs, with ambient temperature and self-heating effects accounted for. This circuit model is unique in accounting for carrier capture dynamics between active region continuum and quantum well bound states. OOK/PAM4 simulations are demonstrated at 25°C and 85°C.
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| 5. |
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| 6. |
- Haglund, Erik, 1985, et al.
(author)
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Vertical-Cavity Silicon-Integrated Lasers by Bonding and Transfer Printing
- 2018
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In: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. ; 2018-September, s. 241-242
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Conference paper (peer-reviewed)abstract
- We present the design and performance of the first current-driven hybrid-vertical-cavity silicon-integrated laser with in-plane waveguide emission. We also show results from preliminary work on transfer printing for large-scale integration of such light sources on silicon photonic integrated circuits.
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| 7. |
- Kumari, Sulakshna, et al.
(author)
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Vertical-Cavity Silicon-Integrated Laser with In-Plane Waveguide Emission at 850 nm
- 2018
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In: Laser and Photonics Reviews. - : Wiley. - 1863-8899 .- 1863-8880. ; 12:2, s. 1700206-
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Journal article (peer-reviewed)abstract
- A continuous-wave electrically-pumped short-wavelength hybrid vertical-cavity silicon-integrated laser (VCSIL) with in-plane emission into a silicon nitride (SiN) waveguide is experimentally demonstrated. The coupling from the vertical cavity into the in-plane SiN waveguide is achieved by a weak grating on the SiN waveguide placed inside the cavity. The grating provides coupling, sets the polarization of the lasing output, and provides transverse mode control. A 5 mu m oxide-aperture diameter device with a threshold current of 1.1 mA produces 73 mu W single-sided waveguide-coupled optical output power at 2.6 mA bias current at a wavelength of 856 nm and a side-mode suppression ratio (SMSR) of 29 dB.
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| 8. |
- Larsson, Anders, 1957, et al.
(author)
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1060 nm VCSELs for long-reach optical interconnects
- 2018
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In: Optical Fiber Technology. - : Elsevier BV. - 1095-9912 .- 1068-5200. ; 44, s. 36-42
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Journal article (peer-reviewed)abstract
- Reach extension of high capacity optical interconnects based on vertical-cavity surface-emitting lasers (VCSELs) and multimode fibers (MMFs), as needed for large-scale data centers, would benefit from high-speed GaAs-based VCSELs at 1060 nm. At this wavelength, the chromatic dispersion and attenuation of the optical fiber are much reduced in comparison with 850 nm. We present single and multimode 1060 nm VCSELs based on designs derived partly from our high-speed 850 nm VCSEL designs. The single-mode VCSEL, with a modulation bandwidth exceeding 22 GHz, supports back-to-back data rates up to 50 Gbps at 25 °C and 40 Gbps at 85 °C under binary NRZ (OOK) modulation. Using mode-selective launch, we demonstrate error-free 25 Gbps transmission over 1000 m of 1060 nm optimized MMF. Higher data rates and/or longer distances will be possible with equalization, forward-error-correction, and/or multilevel modulation.
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| 9. |
- Lavrencik, Justin, et al.
(author)
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Optimum VCSEL Apertures for High-Speed Multimode Fiber Links
- 2018
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In: 2018 Optical Fiber Communications Conference and Exposition, OFC 2018 - Proceedings. - 9781943580385
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Conference paper (peer-reviewed)abstract
- Cross-correlations of VCSEL transverse mode groups with different apertures are used to predict dispersion dependent RIN. Experiments with wideband multimode fiber confirm the noise enhancement dependence on aperture, which increases with fewer mode VCSELs.
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| 10. |
- Lavrencik, Justin, et al.
(author)
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Power Efficient Modulation Formats for Error-Free VeSEL MMF Links
- 2018
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In: European Conference on Optical Communication, ECOC. ; 2018-September
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Conference paper (peer-reviewed)abstract
- We determine the most efficient modulation format for deployable 25Gbps, 50Gbps, and 100Gbps links. Error-free performance was tested and compared for PAM-2, PAM-4, and duobinary until maximum data rates were achieved. The link includes unpackaged 850nm VCSELs and transmitter equalization.
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