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Sökning: WFRF:(Haglund Åsa 1976 )

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  • Haglund, Erik, 1985-, et al. (författare)
  • 850 nm datacom VCSELs for higher-speed and longer-reach transmission
  • 2013
  • Ingår i: European VCSEL Day 2013.
  • Konferensbidrag (refereegranskat)abstract
    • The 850 nm GaAs-based VCSEL is already the dominating technology for transmitters in optical interconnects up to 100 m in datacenters, thanks to low-cost fabrication, excellent high-speed properties at low currents and the existence of high-speed OM4 multimode fiber optimized for this particular wavelength. Future datacenters will require faster and more energy-efficient VCSELs to increase the overall bandwidth and reduce the power consumption of the datacenter network. In addition, longer-reach interconnects exceeding 1 km will also be required as datacenters grow into large multi-building complexes. By optimizing the doping profiles of the DBRs to reduce resistance, using a short (½-λ) cavity to improve longitudinal optical confinement and optimizing the photon lifetime for optimal damping, we obtained a record-high small-signal modulation bandwidth of 28 GHz for a ~4 µm oxide aperture VCSEL. A 7 µm oxide aperture VCSEL (~27 GHz bandwidth) enabled error-free transmission (bit-error-rate < 10-12) at 47 Gbit/s back-to-back (BTB) and 44 Gbit/s over 50 m of OM4 fiber, using a VI-systems R40-850 photoreceiver (30 GHz) with an integrated limiting transimpedance amplifier. The high bandwidth also allows for error-free transmission at 40 Gbit/s BTB at 85°C. By instead using a New Focus 1484-A-50 photoreceiver (22 GHz) with a linear amplifier, 50 Gbit/s error-free transmission was achieved BTB at room temperature. At longer transmission distances (> 300 m), the large spectral width of VCSELs leads to severe signal degradation by fiber dispersion. We have investigated two methods of fabricating low-spectral width quasi-single mode VCSELs to mitigate this problem. By using a small oxide aperture of ~3 µm, error-free transmission was achieved at 22 Gbit/s over 1.1 km of OM4 fiber. An alternative approach is to use an integrated mode filter in the form of a shallow surface relief to reduce the spectral width of the VCSEL. The mode filter allows for the use of a larger oxide aperture and thereby enables a lower resistance and operation at a lower current density. A 5 µm oxide aperture VCSEL with a mode filter enabled error-free transmission at 25 Gbit/s over 500 m of OM4 fiber.
  • Haglund, Erik, 1985-, et al. (författare)
  • Quasi-single mode VCSELs for longer-reach multimode fiber optical interconnects
  • 2014
  • Ingår i: Summers School on Optical Interconnects, 3-6 June 2014, Thessaloniki.
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Longer-reach (>300 m) optical interconnects are needed as datacenters grow ever larger. Today the reach of 850 nm VCSEL-based optical interconnects is mainly limited by fiber dispersion. By reducing the spectral width of the VCSEL, the effects of fiber dispersion may be reduced, effectively increasing the error-free transmission distance.
  • Kumari, S., et al. (författare)
  • Integration of GaAs-based VCSEL array on SiN platform with HCG reflectors for WDM applications
  • 2015
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X. - 978-1-62841-462-2 ; 9372
  • Konferensbidrag (refereegranskat)abstract
    • We present a GaAs-based VCSEL structure, BCB bonded to a Si3N4 waveguide circuit, where one DBR is substituted by a free-standing Si3N4 high-contrast-grating (HCG) reflector realized in the Si3N4 waveguide layer. This design enables solutions for on-chip spectroscopic sensing, and the dense integration of 850-nm WDM data communication transmitters where individual channel wavelengths are set by varying the HCG parameters. RCWA shows that a 300nm-thick Si3N4 HCG with 800nm period and 40% duty cycle reflects strongly (<99%) over a 75nm wavelength range around 850nm. A design with a standing-optical-field minimum at the III-V/airgap interface maximizes the HCG's influence on the VCSEL wavelength, allowing for a 15-nm-wide wavelength setting range with low threshold gain (<1000 cm-1).
  • Gustavsson, Johan S., 1974-, et al. (författare)
  • High speed 850nm VCSELs for >40Gb/s transmission
  • 2013
  • Ingår i: 2013 Optical Fiber Communication Conference and Exposition and the National Fiber Optic Engineers Conference, OFC/NFOEC 2013. - 978-147990457-0
  • Konferensbidrag (refereegranskat)abstract
    • VCSELs capable of direct modulation exceeding 40Gb/s are needed in next generation optical interconnect standards. Using a refined high-speed design we demonstrate GaAs-based VCSELs having record-high 28GHz modulation bandwidth, and that operate error-free at 47Gb/s.
  • Gustavsson, Johan S., 1974-, et al. (författare)
  • High-speed, high-temperature VCSELs for optical interconnects
  • 2013
  • Ingår i: 2013 IEEE Photonics Society Summer Topical Meeting Series, PSSTMS 2013. ; s. 7-8
  • Konferensbidrag (refereegranskat)abstract
    • Directly modulated VCSELs operating at 40Gb/s are required for next generation optical interconnect standards. Using a refined high-speed design we demonstrate GaAs-based VCSELs that operate error-free at 47Gb/s at 25°C, and 40Gb/s at 85°C.
  • Haglund, Erik, 1985-, et al. (författare)
  • 25 Gbit/s transmission over 500 m multimode fibre using 850 nm VCSEL with integrated mode filter
  • 2012
  • Ingår i: Electronics Letters. - 0013-5194. ; 48:9, s. 517-518
  • Tidskriftsartikel (refereegranskat)abstract
    • An integrated mode filter in the form of a shallow surface relief was used to reduce the spectral width of a high-speed 850 nm vertical-cavity surface-emitting laser (VCSEL). The mode filter reduced the RMS spectral width from 0.9 to 0.3 nm for a VCSEL with an oxide aperture as large as 5 mu m. Because of reduced effects of chromatic and modal fibre dispersion, the mode filter significantly increases the maximum error-free (bit error rate < 10(-12)) transmission distance, enabling transmission at 25 Gbit/s over 500 m of multimode OM3+ fibre.
  • Haglund, Erik, 1985-, et al. (författare)
  • Demonstration of post-growth wavelength setting of VCSELs using high-contrast gratings
  • 2016
  • Ingår i: Optics Express. - 1094-4087. ; 24:3, s. 1999-2005
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate, for the first time, post-growth wavelength setting of electrically-injected vertical-cavity surface-emitting lasers (VCSELs) by using high-contrast gratings (HCGs) with different grating parameters. By fabricating HCGs with different duty cycle and period, the HCG reflection phase can be varied, in effect giving different optical cavity lengths for HCG-VCSELs with different grating parameters. This enables fabrication of monolithic multi-wavelength HCG-VCSEL arrays for wavelength-division multiplexing (WDM). The GaAs HCG is suspended in air by removing a sacrificial layer of InGaP. Electrically-injected 980-nm HCG-VCSELs with sub-mA threshold currents indicate high reflectivity from the GaAs HCGs. Lasing over a wavelength span of 15 nm was achieved, enabling a 4-channel WDM array with 5 nm channel spacing. A large wavelength setting span was enabled by an air-coupled cavity design and the use of only the HCG as top mirror.
  • Haglund, Erik, 1985-, et al. (författare)
  • GaAs High-Contrast Gratings with InGaP Sacrificial Layer for Multi-Wavelength VCSEL Arrays
  • 2016
  • Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference (ISLC 2016). - 1947-6981. - 978-4-8855-2306-9 ; TuD2
  • Konferensbidrag (refereegranskat)abstract
    • We report on highly reflective suspended GaAs high-contrast gratings (HCGs) using an InGaP sacrificial layer. A high reflectivity approaching 100% was observed both in direct reflectivity measurement and by low threshold currents in fabricated multi-wavelength HCG-VCSEL arrays.
  • Haglund, Erik, 1985-, et al. (författare)
  • High-contrast gratings for WDM VCSEL arrays
  • 2014
  • Ingår i: Optics & Photonics in Sweden, 11-12 Nov. 2014, Göteborg.
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • Vertical-cavity surface-emitting lasers (VCSELs) have become the workhorse of short-reach optical interconnects in datacenters and supercomputers. The last few years have seen an impressive increase in VCSEL modulation bandwidth, enabling record-high single-channel data rates exceeding 60 Gbit/s [1]. In addition to higher single-channel rates, interconnect capacity may be enhanced by employing multiplexing techniques such coarse wavelength division multiplexing (WDM). WDM VCSEL arrays can be designed using a high-contrast grating (HCG) as top mirror instead of a distributed Bragg reflector (DBR) [2]. The HCG consists of a subwavelength grating of high refractive index material (GaAs) surrounded by low refractive index material (air), see figure 1. The result is a thin, broad-band and highly reflective mirror. The reflection from the HCG has a varying phase depending on grating geometry. This can be used to set the HCG-VCSEL wavelength in a post-growth process by fabricating gratings with different period and duty-cycle. A first proof of concept has been realized and HCG-VCSELs showing resonances covering a span exceeding 20 nm have been demonstrated. Figure 1: Top: schematic figure of HCG-VCSEL array. Left: Top and cross-sectional SEM image of HCG. Right: Simulated and experimental HCG-VCSEL resonance wavelength for different duty cycles and periods (p) measured by electroluminescence. References [1] D. Kuchta et al., “64Gb/s Transmission over 57m MMF using an NRZ Modulated 850nm VCSEL,” OFC 2014 [2] V. Karagodsky et al., “Monolithically integrated multi-wavelength VCSEL arrays using high-contrast gratings,” Opt. Express, 18(2), 2010
  • Haglund, Erik, 1985-, et al. (författare)
  • High-speed lasers for optical interconnects
  • 2012
  • Ingår i: Swedish Optics and Photonics Days 2012.
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • In the era of cloud computing, with services such as video streaming, social networking, and online storage and file sharing, the demand for online data processing and storage capacity is growing rapidly. These services are hosted in huge data centers that need not only fast servers but also fast communication between servers. Because copper cables have high attenuation at high frequencies, the most promising solution is to use fiber optical links (called optical interconnects) to connect different parts of the data center. Today, gallium arsenide-based vertical-cavity surface-emitting lasers (VCSELs) emitting at 850 nm are the standard light source in transmitters used in commercially available optical interconnects, operating at up to 14 Gbit/s with a link length of up to 300 m. These lasers have the advantages of low power consumption, fast direct modulation at low currents, and low-cost manufacturing. To keep up with the demand of increasing optical interconnect capacity, the Photonics Laboratory at Chalmers university of Technology is conducting research into improving the speed, reach and capacity of VCSELs for optical interconnects.
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