850 nm datacom VCSELs for higher-speed and longer-reach transmission
Paper in proceeding, 2013

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.


vertical-cavity surface-emitting laser

quasi-single mode




Erik Haglund

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Petter Westbergh

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Emanuel Haglund

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Rashid Safaisini

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Johan Gustavsson

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Krzysztof Szczerba

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Åsa Haglund

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

Anders Larsson

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

European VCSEL Day 2013

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Information and Communication Technology

Nanoscience and Nanotechnology

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Nano Technology

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