PORTLAND, Ore.ó A new technique harnesses vapor-filled optical waveguides on silicon chips to process data streams encoded on light, allowing optical signals to be slowed down and switched on-chip. This technique sidesteps the current requirement to convert optical signals to electrical signals in applications that detect, buffer, multiplex and store photonic information.
"We can potentially use this to create all-optical switches, single-photon detectors, quantum memory devices, and other exciting possibilities," said Professor Holger Schmidt, an electrical engineer at the University of California at Santa Cruz (UCSC).
In what is claimed to be the world's first demonstration of electromagnetic optical switching on a fully self-contained silicon chip, the technique employs quantum interference effects in an on-chip hollow-core optical waveguide filled with rubidium vapor. A control laser is used to switch the optical signal on and off as well as to slow the data stream's speed by up to 1,200 times.
"By changing the power of a control laser, we can change the speed of lightójust by turning the power control knob," said Schmidt.
The control laser makes the rubidium vapor transparent to the optical signal, thereby switching it on and off, by virtue of putting the rubidium atoms in a coherent superposition of two quantum states. This so-called "electromagnetically induce transparency" allows optical signals to be both switched and slowed by a quantum effect, potentially facilitating the creation of quantum communication networks using silicon photonic chips.
UCSC fabricates arrays of waveguides on a single four inch silicon wafer, here showing 32 atomic spectroscopy chips using them.
The researchers have already successfully used the rubidium filled waveguides to create an atomic spectroscopy device on a single chip, which the group is fabricating 32 at a time on a single silicon wafer.
Researchers at Brigham Young University also contributed to the work, including John Hulbert, Evan Lunt, Katie Hurd, and Aaron Hawkins. Bin Wu, a doctoral candidate at UCSC, performed much of the work. Funding was provided by the Defense Advanced Research Projects Agency and the National Science Foundation.
Intel solves the silicon laser issue by going hybrid--adding InP lasers to its silicon chips. That sounds exotic and expensive, but Intel claims to be perfecting a wafer-scale technology for inexpensively adding InP lasers anywhere you want on a chip:
I agree this is an exiting research. But I also agree with Rich: this is very far from being practical. All these announcements about silicon photonics neglect one fundamental problem: you can't build a laser in silicon. So you can switch, guide, detect, etc. but how are you going to generate the signal??? Anyone? Kris
Silicon photonics is real--in the lab--and will happen eventually, but the III-V semiconductor makers are not going down without a fight. In some ways its a disadvantage to hawk the lower cost of silicon photonics, because the reason designers choose gallium arsenide is often because they are willing to pay for its better performance. These silicon photonics innovations will catch on, but they have to get the performance up before designers will use them.
Whenever I see news about silicon photonics, I get excited because I'm at a CMOS silicon IC design company (Broadcom), and while we have some business having to do with fiber optics, it's on the periphery, to say the least. I'm looking forward to the day when I can put my fiber background together with the electronics. I have to ask whether the rubidium gas is compatible with CMOS processing, though. Man, I can't wait for this stuff to happen for real!
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