A Million Points of Light
Peter Singer, Editor-in-Chief -- Semiconductor International, 6/1/2001
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All that is rapidly changing. Not only are photons being used in inventive new devices — so much so that the old term "optoelectronics" no longer seems adequate — but they may soon be used to communicate signals on the chip itself, through tiny optical waveguides.
Optoelectronics, of course, has been around for decades, consisting primarily of relatively simple III-V-based devices, such as photodetectors and solid-state lasers.
Although some integrated optoelectronic devices have been produced — where digital signal processing and optics coexist on the same chip — these have not been overly successful because it's difficult to marry III-Vs and silicon, and III-V digital processors are comparatively expensive to produce.
What's new are devices that manipulate the photons while they're still in a light format. These include microelectromechanical systems (MEMS) that switch light with mirrors, and planar lightwave circuits that multiplex/demultiplex light signals through optics.
According to market researcher Cahners In-Stat, leading applications for MEMS have traditionally included pressure sensors, accelerometers, inkjet printer nozzles, and read/write heads for hard disk drives. But what's leading the charge now? MEMS-based photonic switching! In 1999, there was no such thing, but by 2004 MEMS switches are expected to become the first MEMS device to surpass the $1B mark.
Presenting even more potential are planar lightwave circuits, which are based on optical waveguides created using manufacturing processes similar to those used to produce semiconductor devices (i.e. fine-line lithography, etching, doping, thin-film deposition, etc.).
The best example of this is DWDM (dense wavelength division multiplexing) devices, but planar technology can also be used to create variable optical attenuators, optical switches, and possibly complete optical add/drop multiplexers — all on one chip. What's especially interesting is that these circuits can be active in the sense that signals can be applied through electrodes to change their optical properties — a far cry from the optoelectronics of yesterday.
Photons are also poised to make their way onto the chip. At first, it's likely that they will be used primarily for clocking on high-speed microprocessors. Here, the light will be generated off the chip and then "piped" on and distributed throughout the chip with optical waveguides made of silicon and silicon dioxide.
Beyond that, it's possible that photons will be used for all on-chip communication — what some in the industry have referred to as "a million points of light." If that sounds implausible, given silicon's historical inability to generate light, consider some new research out of the University of Surrey, in which researchers demonstrated luminescence from silicon at room temperatures with standard manufacturing techniques (see "Dislocation Engineering Enables Light-Emitting Silicon").
Even further down the road, it's possible that optical computing — long touted but as yet unrealized — might well become a reality.
So what does all this mean? For one, you can expect to see more coverage of these kinds of topics within the pages of Semiconductor International. Expect a bunch of new equipment introductions aimed at this new and rapidly growing market. And, most important of all, expect your colleagues to be boning up on optics technology. If you want to join them, keep on reading SI, of course. We've seen the light!
