industry lasers
speeds and lower operating currents.
Oclaro has produced a 10 Gbit/s VCSEL chip for use in non- hermetic,high-speed optical interconnects
Selective oxidation is still used in today’s VCSELs, which play a key role in 10 Gbit/s Ethernet and 8/16 Gbit/s Fiber Channel links that transfer data over distances of up to several hundred metres. Only a few fabs worldwide have mastered the production of these devices, which require state-of-the-art processing capabilities. VCSEL fabrication involves a non-lithographic lateral structuring step and the introduction of a highly strained current-blocking layer close to the active region; and implementing these features to yield a reliable product demands careful optimization of the design and manufacturing process.
The rewards of getting this right are strong sales to datacom markets, which order millions of units every year. That’s a significant level of orders for this industry, but it is dwarfed by shipments for consumer applications, which can require 100 million units per year.
An emerging market for VCSELs is
associated with the Light Peak concept. This has evolved into the Thunderbolt interface which can be found on several Apple computers
One consumer market that the GaAs-based VCSEL has already tapped into is the optical mouse sector. Logitech lead the way in 2004, replacing the LED in the navigation engine with a VCSEL. This switch trimmed power consumption; improved tracking, which is a feature valued by gamers; and thanks to a move from a visible to an infrared source, made the mice more compatible with a glass surface. Thanks to all these attractive features, the VCSEL broke into its first high-volume consumer market, wracking up sales of many tens of millions within a few years.
Similar success could also occur in the finger navigation sector. In 2009, smartphone manufacturer Blackberry, which ships about 7 million handsets per quarter, replaced
its mechanical trackball with an optical trackpad. This featured an LED at the time, but again a VCSEL offers several advantages: superior temperature stability; narrower spectral line width; and a symmetrical, more directed beam shape that leads to cheaper collimating optics delivering great performance.
Short, superfast cables
Another growing consumer application are high- speed optical interconnects. Today, USB cables are in our homes, linking external disk drives and headphones to our PCs, while HDMI cables are connecting our DVD and Blu-ray players to high- resolution displays and flat screen TVs.
Although most USB ports are currently based on the USB 2.0 standard, which corresponds to a data rate of 480 Mbit/s, newer standards have a much higher data rate, such as 5 Gbit/s for USB 3.0 and 10.2 Gbit/s for HDMI 1.3. These conventional, electrical higher-speed cables deliver good performance over short reaches, but this quickly deteriorates as links are lengthened beyond 3 metres.
A promising alternative is to move to optical cables. Interest in this technology has mushroomed following Intel’s 2009 announcement of Light Peak, a high-speed optical interconnect for consumer devices using 10 Gbit/s VCSELs. In 2011, the Light Peak concept was implemented in one of the USB ports of Sony’s VAIO Z Laptop series, with a fibre optic cable feeding data to and from the media dock. The release of Sony’s flagship laptop product thus marked the first commercial introduction of high-speed VCSELs in consumer applications.
Since then, the original Light Peak concept has evolved into the Thunderbolt interface, which can be found on several Apple computers and many peripheral devices today. The connection between devices can be electrical for short very distances, or through active optical cables, which boast a data rate of up to 20 Gbit/s for longer distances. What is common to these active optical cables is that VCSELs are at work, hidden away inside the connector, enabling a cable that is thin, flexible, lightweight, and potentially significantly cheaper than its electrical counterpart.
This migration from electrical to fibre-optic
cabling is being enabled not just by high-volume VCSELs, but also new types of fibre 62
www.compoundsemiconductor.net January / February 2013
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