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| 2. |
- Gustavsson, Johan, 1974, et al.
(författare)
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High-speed, high-temperature VCSELs for optical interconnects
- 2013
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Ingår i: 2013 IEEE Photonics Society Summer Topical Meeting Series, PSSTMS 2013. - 9781467350600 ; , s. 7-8
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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.
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| 3. |
- Haglund, Erik, 1985, et al.
(författare)
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850 nm datacom VCSELs for higher-speed and longer-reach transmission
- 2013
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Ingår i: European VCSEL Day 2013.
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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.
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| 4. |
- Haglund, Erik, 1985, et al.
(författare)
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GaAs High-Contrast Gratings with InGaP Sacrificial Layer for Multi-Wavelength VCSEL Arrays
- 2016
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Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. - 9784885523069 ; TuD2, s. Article n0 7765746-
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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.
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| 5. |
- Haglund, Erik, 1985, et al.
(författare)
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High-contrast gratings for WDM VCSEL arrays
- 2014
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Ingår i: Optics & Photonics in Sweden, 11-12 Nov. 2014, Göteborg.
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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
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| 6. |
- Haglund, Erik, 1985, et al.
(författare)
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Mode-filtered semiconductor lasers enable longer-reach optical interconnects
- 2012
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Ingår i: SPIE Newsroom. - : SPIE-Intl Soc Optical Eng. - 1818-2259.
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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.
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| 7. |
- Haglund, Erik, 1985, et al.
(författare)
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Quasi-single mode VCSELs for longer-reach multimode fiber optical interconnects
- 2014
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Ingår i: Summers School on Optical Interconnects, 3-6 June 2014, Thessaloniki.
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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.
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| 8. |
- Haglund, Erik, 1985, et al.
(författare)
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Wavelength Control of VCSELs using High-Contrast Gratings
- 2017
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Ingår i: VII Workshop on Physics and Technology of Semiconductor Lasers.
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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.
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| 9. |
- Hashemi, Seyed Ehsan, 1986, et al.
(författare)
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Engineering the transverse optical guiding in GaN-based VCSELs to avoid detrimental optical loss
- 2012
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Ingår i: International Workshop on Nitride Semiconductors 2012, October 14-19, 2012, Sapporo, Japan, p. ThP-OD-33.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In order to improve the current injection in GaN-based blue vertical cavity surface emitting lasers (VCSELs) a dielectric aperture is generally used in combination with an indium-tin-oxide (ITO) layer on the top intracavity p-contact layer. The most straightforward way to realize this introduces a depression of the structure near the optical axis and we show, by using a 2D effective index method and a 3D coupled-cavity beam propagation method, that this typically results in optically anti-guided structures with associated high optical losses and thus very high threshold gains. Remarkably, the threshold gain reduces with increased negative guiding, which is due to improved lateral confinement and reduction of lateral leakage. Still, moderately positively guided designs should be preferred to avoid the detrimental effect of lateral leakage and high diffraction loss. To ensure positive index guiding, we propose to planarize the structure or introduce an elevation near the optical axis by additional processing, with an associated reduction in threshold material gain from 6000 cm-1 to 2000 cm-1 for the studied structures.
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