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| 3. |
- Sezgin, Ibrahim Can, 1992, et al.
(författare)
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A Flexible Multi-Gbps Transmitter Using Ultra-High Speed Sigma- Delta-over- Fiber
- 2018
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; 2018-June, s. 1195-1198
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Konferensbidrag (refereegranskat)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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| 4. |
- Sezgin, Ibrahim Can, 1992, et al.
(författare)
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A Low-Complexity Distributed-MIMO Testbed Based on High-Speed Sigma-Delta-Over-Fiber
- 2019
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 67:7, s. 2861-2872
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Tidskriftsartikel (refereegranskat)abstract
- Distributed multiple-input-multiple-output (D-MIMO) is a very promising technique to improve capacity and quality of service for emerging 5G systems. In this paper, we propose a flexible and low-cost testbed for D-MIMO systems, where a sigma-delta over fiber (SDoF) solution is proposed to address the fundamental challenge of phase-coherent transmission between multiple distributed access points (APs) from a central unit (CU). Employing low-cost standardized optical data interconnects, SDoF, brings a very flexible and software controlled transmission of RF signals over optical fiber. An SDoF-based D-MIMO testbed with a CU feeding 12 distributed APs has been realized and experimentally evaluated. Initial experiments of D-MIMO and conventional colocated MIMO systems at 2.365 GHz have been performed to demonstrate the flexibility and potential of the proposed testbed as a new powerful tool in the design and analysis of emerging communication system concepts.
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| 5. |
- Sezgin, Ibrahim Can, 1992, et al.
(författare)
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Effect of VCSEL Characteristics on Ultra-High Speed Sigma-Delta-Over-Fiber Communication Links
- 2019
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 37:9, s. 2109-2119
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Tidskriftsartikel (refereegranskat)abstract
- State-of-the-art high-speed multi-mode vertical-cavity surface-emitting-lasers (VCSELs) have a 3-dB analog bandwidth of ∼25 GHz and can operate up to 55 Gbps error-free, without need of equalization electronics. This makes them strong candidates as optical sources for ultra-high speed sigma-delta-over-fiber (SDoF) communication links. This paper examines the effects of VCSEL characteristics on a 32-Gbps SDoF communication link with a 50 m, OM4, multimode optical fiber. Three high-speed, 850-nm-wavelength VCSELs with oxide aperture sizes of 8.3, 6.6, and 4.6 μm were tested. The effects of different modulation voltage amplitudes and bias currents were also investigated. The link performance and VCSEL power consumption were used as figures-of-merits. By avoiding sub-laser threshold modulation for the VCSEL, each of three VCSELs could provide similar link performance. We show that, compared to conventional datacom links, eased bit-error-rate requirements enabled by bi-level nature of sigma-delta modulation makes it possible to use significantly lower VCSEL bias currents. This in turn enables a reduced VCSEL power consumption (50% lower heat-to-bit ratio) and a potential longer VCSEL lifespan. For a SDoF modulated, 160-Mbaud, QAM64 signal centered at 12 GHz an error vector magnitude of -28 dB was achieved with the VCSEL having oxide aperture size of 4.6 μm operating at only 2 mA bias current and 0.25 V modulation amplitude. This results in a heat-to-bit ratio of only 0.1 mW/Gb/s (or equivalently 0.1 pJ/b), and a current density in the VCSEL that is less than 10 kA/cm2.
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| 6. |
- Sezgin, Ibrahim Can, 1992, et al.
(författare)
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Evaluation of Distributed MIMO Communication Using a Low-Complexity Sigma-Delta-over-Fiber Testbed
- 2019
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; 2019-June, s. 754-757
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Konferensbidrag (refereegranskat)abstract
- Distributing the antennas of a base station is a method to increase the coverage and the capacity of a conventional, co-located MIMO communication system. However, physically separated antennas/access points (AP) creates a fundamental challenge of RF phase synchronization required for joint/coordinated transmission in distributed MIMO (D-MIMO) systems. In this paper we compare co-located-and distributed-MIMO wireless communication thru various measurements using a fully synchronized, low-complexity, twelve-channel testbed based on sigma-delta-over-fiber (SDoF). Single and multi-user measurements are performed in a laboratory environment and the error-vector-magnitude (EVM), the received power and signal-to-interference ratio (SIR) is calculated. We show that distributing the access points improves the received symbol EVM up to 1.6-dB and increases the coverage of the service area by delivering more uniform received power levels.
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| 7. |
- Bamiedakis, N., et al.
(författare)
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40 Gb/s Data Transmission Over a 1-m-Long Multimode Polymer Spiral Waveguide for Board-Level Optical Interconnects
- 2015
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 33:4, s. 882-888
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Tidskriftsartikel (refereegranskat)abstract
- Optical interconnects have attracted considerable attention for use in short-reach communication links within high-performance electronic systems, such as data centers, supercomputers, and data storage systems. Multimode polymer waveguides, in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER
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| 8. |
- Bergmann, Michael Alexander, 1989, et al.
(författare)
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Towards ultraviolet and blue microcavity lasers
- 2018
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Ingår i: Northen Optics and Photonics conference. - 9789163964886 ; 2018
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Konferensbidrag (refereegranskat)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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| 9. |
- Boström, Magnus, 1972-, et al.
(författare)
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Conditions for Transformative Learning for Sustainable Development : A Theoretical Review and Approach
- 2018
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Ingår i: Sustainability. - : MDPI. - 2071-1050. ; 10:12
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Castro, Jose Manuel, et al.
(författare)
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48.7 Gb/s 4-PAM Transmission over 200 m of High Bandwidth MMF using an 850 nm VCSEL
- 2015
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 27:17, s. 1799-1801
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate 4-PAM 48.67 Gb/s transmission, using a directly modulated VCSEL, over 50, 100 and 200 m of multimode fiber with partial dispersion compensation properties. The results of our experiments indicate that 200 m reach is achievable with forward error correcting codes with small overhead.
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