"Non-reciprocal light propagation in a silicon photonic circuit,"

[HysteryDiagnosis]

http://www.sciencedaily.com/releases/2011/08/110804141714.htm


ScienceDaily (Aug. 5, 2011) — Stretching for thousands of miles beneath oceans, optical fibers now connect every continent except for Antarctica. With less data loss and higher bandwidth, optical-fiber technology allows information to zip around the world, bringing pictures, video, and other data from every corner of the globe to your computer in a split second. But although optical fibers are increasingly replacing copper wires, carrying information via photons instead of electrons, today's computer technology still relies on electronic chips.

Snip:

>>In that paper, the researchers describe a new technique to isolate light signals on a silicon chip, solving a longstanding problem in engineering photonic chips.

An isolated light signal can only travel in one direction. If light weren't isolated, signals sent and received between different components on a photonic circuit could interfere with one another, causing the chip to become unstable. In an electrical circuit, a device called a diode isolates electrical signals by allowing current to travel in one direction but not the other. The goal, then, is to create the photonic analog of a diode, a device called an optical isolator. "This is something scientists have been pursuing for 20 years," Feng says.<<

[Hissyspit]

1. More details:

An isolated light signal can only travel in one direction. If light weren't isolated, signals sent and received between different components on a photonic circuit could interfere with one another, causing the chip to become unstable. In an electrical circuit, a device called a diode isolates electrical signals by allowing current to travel in one direction but not the other. The goal, then, is to create the photonic analog of a diode, a device called an optical isolator. "This is something scientists have been pursuing for 20 years," Feng says.

Normally, a light beam has exactly the same properties when it moves forward as when it's reflected backward. "If you can see me, then I can see you," he says. In order to isolate light, its properties need to somehow change when going in the opposite direction. An optical isolator can then block light that has these changed properties, which allows light signals to travel only in one direction between devices on a chip.

"We want to build something where you can see me, but I can't see you," Feng explains. "That means there's no signal from your side to me. The device on my side is isolated; it won't be affected by my surroundings, so the functionality of my device will be stable."

- snip -

Although this work is just a proof-of-principle experiment, the researchers are already building an optical isolator that can be integrated onto a silicon chip. An optical isolator is essential for building the integrated, nanoscale photonic devices and components that will enable future integrated information systems on a chip. Current, state-of-the-art photonic chips operate at 10 gigabits per second (Gbps) -- hundreds of times the data-transfer rates of today's personal computers -- with the next generation expected to soon hit 40 Gbps. But without built-in optical isolators, those chips are much simpler than their electronic counterparts and are not yet ready for the market. Optical isolators like those based on the researchers' designs will therefore be crucial for commercially viable photonic chips.

[ElboRuum]

2. My God... It's full of stars!...

Link is highly awesome. FSM be praised.

[caraher]

3. I wonder how this scales up

I use optical isolators (the conventional Faraday-effect type) and they're a pain and a bit pricey to boot. I work in a different realm - substantially higher power levels - but it might be worth accepting the coupling losses if they can make a fiber that's reasonably cheap.

[HysteryDiagnosis]

4. How many times will a laser bounce between to perfectly reflective surfaces without

a loss in either intensity or speed? I have a curious bent about that sort of thing.

[Fumesucker]

5. It depends how far apart the mirrors are...

And what is in between..

[HysteryDiagnosis]

6. How many years would it take for the laser to lose some of its momentum? n/t

[caraher]

7. It also depends on mirror size

Fumesucker's basically right if the mirrors are infinitely large (though in that case, it doesn't matter how far apart the mirrors are). But if you were to set up two "perfect" mirrors of finite size some distance apart in a "perfect" vacuum, light's wave aspect results in losses to diffraction (photons are not simply little "marbles" of light traveling straight-line paths between the mirrors). Calculating such losses is part of, for instance, laser design.

There's a parameter in optics known as the "finesse" of this kind of optical system (two mirrors facing one another are called a "cavity"). You can think of the finesse as the number of round-trips a photon would be expected to make before being lost, and it's usually dominated by the reflectivity of the mirrors being less than 100%. For the best cavities that number is about a million. If you want to translate that into a time, if the mirrors were separated by about 6 inches (15 cm) one round trip would take about a nanosecond. Thus a million round trips would take a millisecond. Even with the best mirrors you can't hold onto a photon very long!

[HysteryDiagnosis]

8. The double slit experiment chaps my butt, I really don't understand how QED does

the stuff it does, but there it is.