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1.	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 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.
2.	Haglund, Erik, 1985, et al. (författare) High-speed lasers for optical interconnects 2012 Ingår i: Swedish Optics and Photonics Days 2012. Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
3.	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/konstnärligt)abstract Longer-reach (>300 m) optical interconnects are needed asdatacenters grow ever larger. Today the reach of 850 nmVCSEL-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.
4.	Kumari, Sulakshna, 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. - : SPIE. - 0277-786X .- 1996-756X. - 9781628414622 ; 9372, s. Art. no. 93720U- 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 (
5.	Larsson, Anders, 1957, et al. (författare) High speed VCSELs for optical interconnects 2012 Ingår i: Conference Proceedings - International Conference on Indium Phosphide and Related Materials. - 1092-8669. - 9781467317252 ; , s. 269-272 Konferensbidrag (refereegranskat)abstract This paper presents an overview of our recent work on high speed, oxide confined, 850 nm vertical cavity surface emitting lasers (VCSELs). With proper active region and cavity designs, and techniques for reducing capacitance and thermal impedance, we have reached a modulation bandwidth of 23 GHz and demonstrated 40 Gbps transmission. Using an integrated mode filter for reducing the spectral width we have extended the reach on multimode fiber at 25 Gbps from 100 to 500 m. Improved link capacity was also demonstrated using a more spectrally efficient multi-level modulation format (4-PAM). Finally, a MEMS-technology for wafer scale integration of tunable high speed VCSELs was developed, enabling a tuning range of 24 nm, a 6 GHz modulation bandwidth, and 5 Gbps transmission.
6.	Larsson, Anders, 1957, et al. (författare) VCSEL design and integration for high-capacity optical interconnects 2017 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510606593 ; 10109, s. 101090M- Konferensbidrag (refereegranskat)abstract Vertical-cavity surface-emitting lasers and multi-mode fibers is the dominating technology for short-reach optical interconnects in datacenters and high performance computing systems at current serial rates of up to 25-28 Gbit/s. This is likely to continue at 50-56 Gbit/s. The technology shows potential for 100 Gbit/s.
7.	Gustavsson, Johan, 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. - 9781479904570 ; , s. OTh4H.4- 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.
8.	Gustavsson, Johan, 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. - 9781467350600 ; , 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.
9.	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. - : Institution of Engineering and Technology (IET). - 1350-911X .- 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.	Haglund, Erik, 1985, et al. (författare) 30 GHz bandwidth 850 nm VCSEL with sub-100 fJ/bit energy dissipation at 25-50 Gbit/s 2015 Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 51:14, s. 1096-1097 Tidskriftsartikel (refereegranskat)abstract A high-speed and energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting laser (VCSEL) for optical interconnects is presented. A record-high modulation bandwidth of 30 GHz is reached for a 3.5 mu m oxide aperture VCSEL, with 25 GHz bandwidth already at a bias current of 1.8 mA. The high bandwidth at low currents enables energy-efficient transmission with a dissipated heat energy in the VCSEL of
11.	Haglund, Erik, 1985, et al. (författare) Demonstration of post-growth wavelength control of VCSELs using high-contrast gratings 2015 Ingår i: HP Laboratories Technical Report. ; 70 Tidskriftsartikel (refereegranskat)abstract We demonstrate post-growth wavelength setting of vertical-cavity surface-emitting lasers (VCSELs) using high-contrast gratings (HCGs). By fabricating HCGs with different duty-cycle and period, the HCG reflection phase can be varied, in effect giving different optical cavity lengths for HCGVCSELs 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 selective removal of an InGaP sacrificial layer. Electrically injected 980-nm HCGVCSELs 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. Device design, fabrication and experimental proof-of-concept are presented.
12.	Haglund, Erik, 1985, et al. (författare) Demonstration of post-growth wavelength setting of VCSELs using high-contrast gratings 2016 Ingår i: Optics Express. - : The Optical Society. - 1094-4087 .- 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.
13.	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. - 0899-9406. - 9784885523069 ; TuD2, s. Article n0 7765746- 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.
14.	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/konstnärligt)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
15.	Haglund, Erik, 1985, et al. (författare) High speed 850 nm VCSEL with 30 GHz modulation bandwidth 2015 Ingår i: Proceedings Conference on Lasers and Electro-Optics (CLEO) Europe. - 9781467374750 ; , s. CB-2.4 Konferensbidrag (refereegranskat)
16.	Haglund, Emanuel, 1988, et al. (författare) High-Speed 850-nm VCSELs Operating Error-Free Beyond 50 Gbit/s 2013 Ingår i: Optics and Photonics in Sweden, 22-23 Oct. 2013. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The 850-nm vertical-cavity surface-emitting laser (VCSEL) is a key component in today’s short reach (
17.	Haglund, Erik, 1985, et al. (författare) High-Speed VCSELs with Strong Confinement of Optical Fields and Carriers 2016 Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 34:2, s. 269-277 Tidskriftsartikel (refereegranskat)abstract We present the design, fabrication, and performance of our latest generation high-speed oxide-confined 850-nm verticalcavity surface-emitting lasers. Excellent high-speed properties are obtained by strong confinement of optical fields and carriers. Highspeed modulation is facilitated by using the shortest possible cavity length of one half wavelength and placing oxide apertures close to the active region to efficiently confine charge carriers. The resulting strong current confinement boosts internal quantum efficiency, leading to low threshold currents, high wall-plug efficiency, and state-of-the-art high-speed properties at low bias currents. The temperature dependent static and dynamic performance is analyzed by current-power-voltage and small-signal modulation measurements.
18.	Haglund, Emanuel, 1988, et al. (författare) Hybrid vertical-cavity laser integration on silicon 2017 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510606852 ; 10122, s. 101220H- Konferensbidrag (refereegranskat)abstract The hybrid vertical-cavity laser is a potential low current, high-efficiency, and small footprint light source for silicon photonics integration. As part of the development of such light sources we demonstrate hybrid-cavity VCSELs (HC-VCSELs) on silicon where a GaAs-based half-VCSEL is attached to a dielectric distributed Bragg reflector on silicon by adhesive bonding. HC-VCSELs at 850 nm with sub-mA threshold current, >2 mW output power, and 25 Gbit/s modulation speed are demonstrated. Integration of short-wavelength lasers will enable fully integrated photonic circuits on a silicon-nitride waveguide platform on silicon for applications in life science, bio-photonics, and short-reach optical interconnects.
19.	Haglund, Emanuel, 1988, et al. (författare) Impact of Bonding Interface Thickness on the Performance of Silicon-Integrated Hybrid-Cavity VCSELs 2016 Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. - 9784885523069 ; , s. Article no 7765752- Konferensbidrag (refereegranskat)abstract The dependence of the performance of short-wavelength silicon-integrated hybrid-cavity VCSELs on the thickness of the bonding interface used for the heterogeneous integration has been studied. Performance measures investigated include the emission wavelength, thermal impedance, and variation of threshold current and output power with temperature.
20.	Haglund, Erik, 1985, et al. (författare) Low Spectral Width High-Speed VCSELs 2011 Ingår i: International Nano-Optoelectronic Workshop (iNOW). Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The transmission distance of high-speed multimode 850 nm VCSELs is currently limited by modal dispersion. A design and process to fabricate high-speed VCSELs with a reduced spectral width using a surface relief technique are presented.
21.	Haglund, Erik, 1985, et al. (författare) Mode-filtered semiconductor lasers enable longer-reach optical interconnects 2012 Ingår i: SPIE Newsroom. - : SPIE-Intl Soc Optical Eng. - 1818-2259. Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract An integrated mode filter significantly decreases the spectral width of conventional short-wavelength vertical-cavity surface-emitting lasers, promising longer optical interconnects for future data centers.
22.	Haglund, Erik, 1985, et al. (författare) Multi-wavelength VCSEL arrays using high-contrast gratings 2017 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510606678 ; 10113 Konferensbidrag (refereegranskat)abstract The use of a high-contrast grating (HCG) as the top mirror in a vertical-cavity surface-emitting laser (VCSEL) allows for setting the resonance wavelength by the grating parameters in a post-epitaxial growth fabrication process. Using this technique, we demonstrate electrically driven multi-wavelength VCSEL arrays at ∼980 nm wavelength. The VCSELs are GaAs-based and the suspended GaAs HCGs were fabricated using electron-beam lithography, dry etching and selective removal of an InGaP sacrificial layer. The air-coupled cavity design enabled 4-channel arrays with 5 nm wavelength spacing and sub-mA threshold currents thanks to the high HCG reflectance.
23.	Haglund, Erik, 1985, et al. (författare) Reducing the spectral width of high speed oxide confined VCSELs using an integrated mode filter 2012 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760L- Konferensbidrag (refereegranskat)abstract We have reduced the spectral width of high speed oxide confined 850 nm VCSELs using a shallow surface relief for suppression of higher order transverse modes. The surface relief acts as a mode filter by introducing a spatially varying and therefore mode selective loss. The VCSEL employs multiple oxide layers for reduced capacitance which leads to a strong index guiding and a large spectral width in the absence of a mode filter. With an appropriate choice of surface relief parameters, the RMS spectral width for a 5 jam oxide aperture VCSEL is reduced from 0.6 to 0.3 nm. The small signal modulation bandwidth is 19 GHz. Due to reduced effects of chromatic and modal fiber dispersion, the maximum error-free (bit-error-rate
24.	Haglund, Emanuel, 1988, et al. (författare) Silicon-Integrated Hybrid-Cavity 850-nm VCSELs by Adhesive Bonding: Impact of Bonding Interface Thickness on Laser Performance 2017 Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1558-4542 .- 1077-260X. ; 23:6, s. 1700109- Tidskriftsartikel (refereegranskat)abstract The impact of bonding interface thickness on the performance of 850-nm silicon-integrated hybrid-cavity vertical-cavity surface-emitting lasers (HC-VCSELs) is investigated. The HC-VCSEL is constructed by attaching a III–V “half-VCSEL” to a dielectric distributed Bragg reflector on a Si substrate using ultrathin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding. The thickness of the bonding interface, defined by the DVS-BCB layer together with a thin SiO2 layer on the “half-VCSEL,” can be used to tailor the performance, for e.g., maximum output power or modulation speed at a certain temperature, or temperature-stable performance. Here, we demonstrate an optical output power of 2.3 and 0.9 mW, a modulation bandwidth of 10.0 and 6.4 GHz, and error-free data transmission up to 25 and 10 Gb/s at an ambient temperature of 25 and 85 °C, respectively. The thermal impedance is found to be unaffected by the bonding interface thickness.
25.	Haglund, Emanuel, 1988, et al. (författare) Silicon-integrated short-wavelength VCSELs 2017 Ingår i: Proc. European Semiconductor Laser Workshop. ; , s. C21- Konferensbidrag (refereegranskat)abstract GaAs-based hybrid-cavity VCSELs integrated onto silicon by ultra-thin DVS-BCB adhesive bonding are presented. The hybrid-cavity implies that the optical field extends over both the GaAs- and the Si-based parts, which could allow a fraction of the light in the vertical-cavity to be coupled into an in-plane waveguide. Surface-emitting devices are demonstrated at ~860 nm with up to 2.3 mW optical output power and 12 GHz modulation bandwidth, providing error-free large signal data transmission up to 25 Gb/s.
26.	Haglund, Erik, 1985, et al. (författare) Wavelength Control of VCSELs using High-Contrast Gratings 2017 Ingår i: VII Workshop on Physics and Technology of Semiconductor Lasers. Konferensbidrag (refereegranskat)abstract The vertical-cavity surface-emitting laser (VCSEL) is a well-established light source for sensing and short-reach optical links. The surface emission allows wafer-scale testing enabling low-cost manufacturing, while the VCSELs’ small modal volume leads to low power consumption, high-speed modulation at small currents, and small footprint [1]. Conventional VCSELs consist of an active region sandwiched between two distributed Bragg reflectors (DBRs). Replacing the top DBR with a high-contrast grating reflector offers unique possibilities to engineer and control VCSEL emission wavelength and modal properties [2,3]. A high-contrast grating (HCG) is typically formed by bars of high refractive index suspended in air. HCGs with certain grating parameters (duty cycle, period, and thickness) can function as ultra-thin reflectors with close to 100% reflectivity [4]. Besides the reflectivity, the grating parameters also influence the reflection phase. This enables fabrication of multi-wavelength VCSEL arrays by fabricating HCG-VCSELs with different grating parameters. In order to utilize the extraordinary properties of the HCG, the VCSEL mode must be sensitive to the HCG, which leads to complicated cavity configurations with coupled cavity effects and low optical confinement. This talk will summarize experimental work performed at Chalmers University of Technology in collaboration with Hewlett Packard Enterprise. The design of HCGs and HCG-VCSELs will be presented as well as experimental results from 980 nm HCG-VCSELs and demonstration of post-growth wavelength setting for wavelength-division multiplexing (WDM) VCSEL arrays [5].References[1]Larsson, “Advances in VCSELs for communication and sensing,” IEEE J. Sel. Top. Quantum Electron. 17(6), 1552-1567 (2011).[2]V. Karagodsky, et al., ”Monolithically integrated multi-wavelength VCSEL arrays using high-contrast gratings”, Opt. Express 18(2), 694-699 (2010).[3]S. Inoue, et al., “Highly angular dependent high-contrast grating mirrors and its application for transverse-mode control of VCSELs”, Jpn. J. Appl. Phys. 53, 090306 (2014).[4]C. J. Chang-Hasnain et al., “High-contrast gratings for integrated optoelectronics”, Adv. Opt. Photon. 4, 379-, (2012).[5]E. Haglund, et al., “Demonstration of post-growth wavelength-setting of VCSELs using high-contrast gratings”, Opt, Express 24(3), 1999-2005 (2016).AcknowledgementThis work was been supported by Hewlett Packard Enterprise (HPE), the Swedish Foundation for Strategic Research (SSF) and the Swedish Research Council (VR). The epitaxial material was provided by IQE Europe.
27.	Kögel, Benjamin, 1979, et al. (författare) Integrated MEMS-tunable VCSELs for reconfigurable optical interconnects 2012 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760Q- Konferensbidrag (refereegranskat)abstract A simple and low-cost technology for tunable vertical-cavity surface-emitting lasers (VCSELs) with curved movable micromirror is presented. The micro-electro-mechanical system (MEMS) is integrated with the active optical component (so-called half-VCSEL) by means of surface-micromachining, using a reflown photoresist droplet as sacrificial layer. The technology is demonstrated for electrically pumped, short-wavelength (850nm) tunable VCSEts. Fabricated devices with 10 mu m oxide aperture are singlemode with sidemode suppression >35 dB, tunable over 24 mit with output power up to 0.5 mW, and have a beam divergence angle
28.	Kögel, Benjamin, 1979, et al. (författare) Integrated MEMS-Tunable VCSELs Using a Self-Aligned Reflow Process 2012 Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:2, s. 144-152 Tidskriftsartikel (refereegranskat)abstract A simple microelectromechanical systems technology for wafer-scale integration of tunable vertical-cavity surface-emitting lasers (VCSELs) is presented. The key element is a self-aligned reflow process to form photoresist droplets, which serve as sacrificial layer and preform for a curved micromirror. Using a 3-D electromagnetic model, the half-symmetric cavity is optimized for singlemode emission. The technology is demonstrated for electrically pumped, short-wavelength (850 nm) tunable VCSELs, but is transferable to other wavelengths and material systems. Fabricated devices with 10 mu m large current aperture are singlemode and tunable over 24 nm. An improved high-speed design with reduced parasitic capacitance enables direct modulation with 3dB-bandwidths up to 6 GHz and data transmission at 5Gbit/s. Small signal analysis shows that the intrinsic parameters (resonance frequency and damping) are wavelength dependent through the differential gain.
29.	Kögel, Benjamin, 1979, et al. (författare) Integrated Tunable VCSELs With Simple MEMS Technology 2010 Ingår i: Semiconductor Laser Conference (ISLC), 2010 22nd IEEE International. - 0899-9406. - 9781424456833 Konferensbidrag (refereegranskat)abstract A simple MEMS technology for wafer-scale fabrication of tunable VCSELs is presented. Reflown photo-resist droplets serve as preform for making curved movable micro-mirrors. First devices show a tuning range of 15 nm with mW-output power.
30.	Kögel, Benjamin, 1979, et al. (författare) Singlemode tunable VCSELs with integrated MEMS technology 2011 Ingår i: European Conference on Laser and Electro-Optics (CLEO/Europe). Konferensbidrag (refereegranskat)abstract A simple MEMS technology for wafer-scale integration of short-wavelength tunable VCSELs is presented. Using a 3D model the half-symmetric cavity is optimized for singlemode emission from 10 μm large apertures over 12 nm tuning range.
31.	Larsson, Anders, 1957, et al. (författare) 1060 nm VCSELs for long-reach optical interconnects 2018 Ingår i: Optical Fiber Technology. - : Elsevier BV. - 1095-9912 .- 1068-5200. ; 44, s. 36-42 Tidskriftsartikel (refereegranskat)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.
32.	Larsson, Anders, 1957, et al. (författare) High-speed tunable and fixed-wavelength VCSELs for short-reach optical links and interconnects 2012 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276, s. Article Number: 82760H- Konferensbidrag (refereegranskat)abstract This paper presents a review of recent work on high speed tunable and fixed wavelength vertical cavity surface emitting lasers (VCSELs) at Chalmers University of Technology. All VCSELs are GaAs-based, employ an oxide aperture for current and/or optical confinement, and emit around 850 nm. With proper active region and cavity designs, and techniques for reducing capacitance and thermal impedance, our fixed wavelength VCSELs have reached a modulation bandwidth of 23 GHz, which has enabled error-free 40 Gbps back-to-back transmission and 35 Gbps transmission over 100 m of multimode fiber. A MEMS-technology for wafer scale integration of tunable high speed VCSELs has also been developed. A tuning range of 24 nm and a modulation bandwidth of 6 GHz have been achieved, enabling error-free back-to-back transmission at 5 Gbps.
33.	Larsson, Anders, 1957, et al. (författare) High Speed VCSELs and VCSEL Arrays for Single and Multicore Fiber Interconnects 2015 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628414714 ; 9381, s. Art. no. 93810D- Konferensbidrag (refereegranskat)abstract Our recent work on high speed 850 nm VCSELs and VCSEL arrays is reviewed. With a modulation bandwidth approaching 30 GHz, our VCSELs have enabled transmitters and links operating at data rates in excess of 70 Gbps (at IBM) and transmission over onboard polymer waveguides at 40 Gbps ( at University of Cambridge). VCSELs with an integrated mode filter for single mode emission have enabled transmission at 25 Gbps over > 1 km of multimode fiber and a speed-distance product of 40 Gbps . km. Dense VCSEL arrays for multicore fiber interconnects have demonstrated 240 Gbps aggregate capacity with excellent uniformity and low crosstalk between the 40 Gbps channels.
34.	Larsson, Anders, 1957, et al. (författare) High-Speed VCSELs for Datacom 2016 Ingår i: Proceedings European Conference on Optical Communication. - 9783800742745 ; , s. 977-979 Konferensbidrag (refereegranskat)
35.	Larsson, Anders, 1957, et al. (författare) High-Speed VCSELs for OOK and Multilevel PAM Modulation 2017 Ingår i: 30TH ANNUAL CONFERENCE OF THE IEEE PHOTONICS SOCIETY (IPC). - 2374-0140. - 9781509065783 ; 2017-January, s. 355-356 Konferensbidrag (refereegranskat)abstract The short-reach optical interconnects used in datacenters and high-performance computing systems are dominated by vertical-cavity surface-emitting laser (VCSEL) and multimode fiber (MMF) links1. The VCSEL-MMF technology is the most cost and power efficient and offers the smallest footprint. VCSELs for 25-28 Gbit/s OOK lanes are in production2 while 25-28 Gbaud PAM-4 with forward-error-correction (FEC) is considered for next generation 50-56 Gbit/s lanes3. For this transition, as well as future developments towards even higher speed, the VCSEL dynamics and high-speed properties are of utmost importance. Improved dynamics may enable 50-56 Gbit/s PAM-4 without FEC and even 50-56 Gbit/s OOK, which would reduce complexity, power consumption, and latency.
36.	Larsson, Anders, 1957, et al. (författare) VCSEL modulation capacity: Continued improvements or physical limits? 2017 Ingår i: 6th IEEE Photonics Society Optical Interconnects Conference, OI 2017. - 9781509050154 ; , s. 53-54 Konferensbidrag (refereegranskat)abstract The short-reach optical interconnects used in datacenters and high-performance computing systems are dominated by VCSEL and multimode fiber (MMF) links 1 . The VCSEL-MMF technology is the most cost and power efficient and offers the smallest footprint. VCSELs operating at 25-28 Gbit/s are in production 2 while research has extended the VCSEL modulation bandwidth to 30 GHz 3 (Fig.1) and enabled OOK-NRZ data transmission up to 57 Gbit/s at 25°C 4 and 50 Gbit/s at 85°C 5 , without equalization or forward-error-correction (FEC). A VCSEL energy dissipation below 100 fJ/bit has been demonstrated at 25-50 Gbit/s 3 (Fig.1). The need for higher interconnect capacity raises the question whether the speed and dynamics of VCSELs can be further improved or whether physical limits preventing this have been reached. Higher speed VCSELs would enable higher lane rates and therefore reduced number of lanes and increased bandwidth density for a given aggregate interconnect capacity.
37.	Larsson, Anders, 1957, et al. (författare) VCSEL modulation speed: Status and prospects 2019 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 10938 Konferensbidrag (refereegranskat)
38.	Roelkens, Gunther, et al. (författare) 850 nm hybrid vertical cavity laser integration for on-chip silicon photonics light sources 2017 Ingår i: Optical Fiber Communication Conference (OFC), 19-23 March 2017. - 9781943580231 ; , s. W3E.6- Konferensbidrag (refereegranskat)abstract The realization of 850 nm hybrid III-V/dielectric VCSELs is reported in order to realize low power consumption integrated light sources for SiN waveguide circuits, which find applications both in short-reach optical communication and optical sensors.
39.	Safaisini, Rashid, 1981, et al. (författare) 20 Gbit/s error-free operation of 850 nm oxide-confined VCSELs beyond 1 km of multimode fibre 2012 Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 48:19, s. 1225-U81 Tidskriftsartikel (refereegranskat)abstract Error-free transmission over 1.1 km of OM4 multimode fibre is demonstrated at 20 Gbit/s bit rate using a narrow spectral width, high-speed 850 nm vertical-cavity surface-emitting laser.
40.	Safaisini, Rashid, 1981, et al. (författare) 22 Gb/s error-free data transmission beyond 1 km of multi-mode fiber using 850 nm VCSELs 2013 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819494085 ; 8639 Konferensbidrag (refereegranskat)abstract The first error-free data transmission beyond 1 km of multi-mode fiber at bit-rates exceeding 20 Gb/s is demonstrated using a high modulation bandwidth, quasi-single mode (SMSR similar to 20 dB) 850 nm VCSEL. A VCSEL with small similar to 3 mu m aperture shows quasi-single mode operation with a narrow spectral width. The top mirror reflectivity of the VCSEL is optimized for high speed and high output power by shallow etching. A combination of narrow spectral width and high optical power reduces the effects of fiber dispersion and fiber and connector losses and enables such a long transmission distance at high bit-rates.
41.	Safaisini, Rashid, 1981, et al. (författare) High-Speed 850 nm Quasi-Single Mode VCSELs for Extended Reach Optical Interconnects 2013 Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 5:7, s. 686-695 Tidskriftsartikel (refereegranskat)abstract This paper presents recent results on high-speed, quasi-single-mode, 850 nm vertical-cavity surface-emitting lasers (VCSELs) with a narrow spectral width for extended-reach optical interconnects. The top mirror reflectivity is adjusted for high output power, slope efficiency, and small signal modulation bandwidth. An oxide confined VCSEL with an ∼3 μm aperture diameter delivers 2 mW of output power and reaches a resonance frequency as high as 25 GHz and a modulation bandwidth exceeding 20 GHz. A small K-factor of 0.17 ns and a large D-factor of 17.3 GHz/mA1/2, extracted from the VCSEL modulation response, along with the improved DC and modal properties enable energy-efficient data transmission at high bit rates over long-distance multimode fiber. Error-free transmission at bit rates exceeding 20 Gbits/s over 1.1 km of OM4 fiber is demonstrated and shown to be limited mainly by the photoreceiver bandwidth. A theoretical investigation of the dependence of link performance on photoreceiver bandwidth is also presented.
42.	Simpanen, Ewa, 1987, et al. (författare) 1060 nm single and multimode VCSELs for up to 50 Gb/s modulation 2017 Ingår i: Proceedings of IEEE Photonics Conference 2017. - : IEEE. - 9781509065776 ; 2017-January, s. 65-66 Konferensbidrag (refereegranskat)abstract We present the design and performance of 1060 nm VCSELs with up to 50 Gb/s intrinsic speed and demonstrate 25 Gb/s transmission over 1000 m of 1060 nm optimized MMF using a single-mode VCSEL and mode-selective launch.
43.	Simpanen, Ewa, 1987, et al. (författare) 1060 nm single-mode vertical-cavity surface-emitting laser operating at 50 Gbit/s data rate 2017 Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 53:13, s. 869-870 Tidskriftsartikel (refereegranskat)abstract An energy efficient 1060 nm GaAs-based oxide-confined vertical-cavity surface-emitting laser designed for high-speed modulation and singlemode emission has been developed. A record data rate of 50 Gbit/ s at an energy dissipation of 100 fJ/ bit is demonstrated for a device with > 50 dB side-mode-suppression and 0.2 mA threshold current, making this laser a promising light source for long-reach optical interconnects.
44.	Simpanen, Ewa, 1987, et al. (författare) 1060 nm VCSEL for up to 40 Gbit/s Data Transmission 2016 Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. - 9784885523069 ; , s. Article no 7765757- Konferensbidrag (refereegranskat)abstract A GaAs-based 1060 nm VCSEL with strained InGaAs/GaAsP QWs, doped DBRs, a short optical cavity, and multiple oxide apertures is presented. Modulation up to 40 Gbit/s at 25°C and 30 Gbit/s at 85°C is demonstrated.
45.	Szczerba, Krzysztof, 1985, et al. (författare) 30 Gbps 4-PAM transmission over 200m of MMF using an 850 nm VCSEL 2011 Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:26, s. B203-B208 Tidskriftsartikel (refereegranskat)abstract We present high speed real time, error free 4-PAMtransmissionfor short range optical links based on a VCSEL operating at 850 nm, a multimode fibre and a simple intensity detector. Transmission speeds of 25 Gbps and 30 Gbps are demonstrated, and the maximum fibre reaches were 300 m and 200 m, respectively. The 4-PAM is also compared with OOK transmission at 25 Gbps, and we find that at this bit rate 4-PAM increases the error free transmission distance in the multimode fibre by 100 m, compared to OOK.
46.	Szczerba, Krzysztof, 1985, et al. (författare) 30 Gbps 4-PAM transmission over 200m of MMF using an 850 nm VCSEL 2011 Ingår i: European Conference and Exposition on Optical Communications, ECOC. - 2162-2701. - 9781557529312 ; , s. 1-3 Konferensbidrag (refereegranskat)abstract Real time, error free 4-PAM transmission at 25 Gbps and 30 Gbps over 300 m and200m of multimode fiber, respectively, using a VCSEL operating at the wavelength of 850 nm.
47.	Szczerba, Krzysztof, 1985, et al. (författare) 4-PAM for high-speed short-range optical communications 2012 Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 4:11, s. 885-894 Tidskriftsartikel (refereegranskat)abstract In this work, we compare 4-pulse amplitudemodulation and on–off keying modulation formats at highspeed for short-range optical communication systems. Thetransmission system comprised a directly modulated verticalcavitysurface-emitting laser operating at a wavelength of850 nm, an OM3Å multimode fiber link, and a photodetectordetecting the intensity at the receiver end. The modulationformats were compared both at the same bit-rate and at thesame symbol rate. The maximum bit-rate used was 25 Gbps.Propagation distances up to 600 m were investigated at12.5 Gbps. All measurements were done in real time andwithout any equalization.
48.	Westbergh, Petter, 1981, et al. (författare) High-speed 850 nm VCSELs operating error free up to 57 Gbit/s 2013 Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 49:16, s. 1021-1023 Tidskriftsartikel (refereegranskat)abstract Error-free transmission is demonstrated at bit rates up to 57 Gbit/s back-to-back, up to 55 Gbit/s over 50 m fibre and up to 43 Gbit/s over 100 m fibre using an oxide-confined 850 nm high-speed vertical cavity surface-emitting laser with a photon lifetime optimised for high-speed data transmission.
49.	Westbergh, Petter, 1981, et al. (författare) High speed VCSELs for short reach communication 2011 Ingår i: European Semiconductor Laser Worshop 2011. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
50.	Gebski, M., et al. (författare) Ultra-thin VCSELs based on monolithic subwavelength high-index contrast surface gratings 2017 Ingår i: 2016 IEEE Photonics Conference, IPC 2016. ; , s. 653-654 Konferensbidrag (refereegranskat)abstract We present for the first time the measured power reflectance of GaAs monolithic high index contrast surface gratings (MHCGs) and computer simulations of various reduced-vertical-dimension VCSEL designs that employ these MHCG structures. We demonstrate the first optically-pumped MHCG DBR VCSELs with emission near 980 nm.

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