News Article
980nm VCSELs Exhibit High Performance at Elevated Temperatures
German researchers have demonstrated that the lasers, produced by IQE, are capable of operating at 25Gbit/s at elevated temperatures. This makes them ideal for very short optical links within high-performance computers.
A team of researchers from the Technical University of Berlin has published work in Applied Physics Journal demonstrating record data transmission rates from an oxide confined 980nm Vertical Cavity Surface Emitting Laser (VCSEL) operating at 85°C.
The VCSEL devices fabricated on wafers produced using Metal Organic Chemical Vapour Deposition (MOCVD), are capable of operating at 25Gbit/s at elevated temperatures, making them ideal for very short optical links within high-performance computers.
“Since temperatures inside computers are as high as 85 °C, or even higher, good temperature stability is indispensable for robust, inexpensive optical links,” says Dieter Bimberg, head of the research team in 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 980 nm sources in all these applications.
“980 nm has the crucial advantage of transparency of the GaAs substrate, so one can easily realise bottom-emitting devices, increasing and simplifying packaging density. This is very important, for example, in the case of a large number of VCSELs for parallel optical links.”
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 GaAs0.88P 0.12tensile strained barriers.
Output from a 10 micron diameter oxide aperture VCSEL is 4.3mW at 20 °C and 2.6 mW at 85°C. This relatively small reduction in power stems from an intentional red-shift detuning of 15 nm between the quantum well gain peak and the cavity resonance. The devices have bit error rates at 25 Gbit/s of less than 10-12.
Future targets for the team are to speed the 980 nm VCSELs to 40Gbit/s and maintain this rate at 100°C.
