- News
27 January 2011
TU Berlin demos 980nm VCSELs on IQE material capable of high performance at elevated temperatures
A team of researchers led by Dieter Bimberg at the Technical University of Berlin in Germany has published work in Applied Physics Letters demonstrating record data transmission rates from an oxide-confined 980nm vertical-cavity surface-emitting laser (VCSEL) operating at 85ºC.
The VCSEL devices fabricated on wafers produced by IQE’s optoelectronic facility in Cardiff, UK are capable of operating at 25Gb/s at elevated temperatures, suiting very-short-reach optical links within high-performance computers.
“Since temperatures inside computers are as high as 85ºC, or even higher, good temperature stability is indispensable for robust, inexpensive optical links,” says Dieter Bimberg, head of the research team at the TU Berlin.
Most short-reach optical links and local and storage-area networks currently operate at a wavelength of 850nm, but Bimberg believes there is a strong case for 980nm sources in all these applications. “980 nm has the crucial advantage of transparency of the GaAs substrate, so one can easily realize bottom-emitting devices, increasing and simplifying packaging density,” he says. “This is very important, for example, in the case of a large number of VCSELs for parallel optical links.”
The VCSEL wafers are produced by IQE’s metal-organic chemical vapor deposition (MOCVD) reactors at its facility in Cardiff, UK. The epitaxial structure contained 24 pairs of Al0.12Ga0.88As and Al0.90Ga0.10As layers for the bottom mirror, and a further 37 pairs for the top mirror. Sandwiched between these mirrors is an active region with five compressively strained 4.2nm-thick In0.21Ga0.79As quantum wells interlaced with 6nm-thick GaAs0.88P0.12 tensile-strained barriers.
Output from a 10μm-diameter oxide aperture VCSEL is 4.3mW at 20ºC and 2.6mW at 85ºC. This relatively small reduction in power stems from an intentional red-shift detuning of 15nm between the quantum well gain peak and the cavity resonance. The devices have bit error rates (BER) at 25Gb/s of less than 10–12.
Future targets for the team are to speed the 980nm VCSELs to 40Gb/s and maintain this rate at 100ºC.
IQE demos 40GB/s VCSEL technology for next-gen optical communications
IQE VCSELs GaAs substrate AlGaAs
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