MIT Researchers Make Advance Toward Photonic Circuits

MrSeb writes with this excerpt from an article in Extreme Tech: "Light-emitting diodes are a cornerstone of consumer tech. They make thin-and-light TVs and smartphones possible, provide efficient household, handheld, and automobile illumination, and, of course, without LEDs your router would not have blinkenlights. Thanks to some engineers from MIT, though, a new diode looks set to steal the humble LED's thunder. Dubbed a diode for light, and crafted using standard silicon chip fabrication techniques, this is a key discovery that will pave the path to photonic (as opposed to electronic) pathways on computer chips and circuit boards. The diode for light — which is made from a thin layer of garnet — is transparent in one direction, but opaque in the other. Garnet is usually hard to deposit on a silicon wafer, but the MIT researchers found a way to do it."

Comments

What's it got to do with LEDs

[Zouden]

The summary (taken from the first article) implies that these new diodes are going to supersede LEDs, but they have completely different purposes. LEDs make lights, these things don't.

Re:What's it got to do with LEDs

[zlives]

umm they both have light and diodes... so that's 2 out of 3... right

This might actually make it

[bigredradio]

From the article -

The whole system could be made using standard microchip manufacturing machinery, Ross says. “It simplifies making an all-optical chip,” she says. The design of the circuit can be produced “just like an integrated-circuit person can design a whole microprocessor. Now, you can do an integrated optical circuit.” That could make it much easier to commercialize than a system based on different materials, Ross says. “A silicon platform is what you want to use,” she says, because “there’s a huge infrastructure for silicon processing. Everyone knows how to process silicon. That means they can set about developing the chip without having to worry about new fabrication techniques.”

It is good to see someone is coming up with an innovation that can "actually" be introduced. Seems like I read about new innovations every day on slashdot that never get off the ground because completely new manufacturing processes need to be created. Hopefully this will actually make it because it requires fewer changes by manufacturers (which can be significant barriers to innovation).

Re:This might actually make it

[kelemvor4]

manufacturers (which can be significant barriers to innovation).

They certainly can be!

light transistor

[greywire]

Does this mean a light transistor is coming soon?

I am wondering if there is any material that acts as a mirror and can be switched from reflective to transparent electronically? I assume there is not or you wouldn't have devices like MEMS displays. I'm thinking if you had such a material it would be essentially a light transistor.

Re:light transistor

[Anonymous Coward]

Well we currently have devices that can become opaque or transparent depending on signal.

Also, couldn't metamaterials technically be used in this way?
That EM blackhole that was created could be turned in to a one-way channel for light instead of just an infinite spiral to absorption
Reflective could be a mirror that punts it back through another channel that comes out at the same input, shift mirror to allow it through.
Of course, that involves mechanical stuff (even if incredibly tiny), but the use of photonics could possibly decrease the heat and space requirements for boards, so a significantly larger number could probably be used.

Re:light transistor

[Calos]

Light transistors? Not exactly as you describe, that I'm aware... But things that fit a more general description of "light transistor" do exist. They're basically optical ring resonators, but add some standard silicon doping and bias it, you can change the refractive index to stop the resonance. I'm not exactly up on my photonics, but I think in theory you could couple the ring resonator to another pathway which would ultimately go to the display, with the applied voltage controlling whether or not the source signal is coupled through to the display.

Not exactly what you have in mind, probably not efficient or manufacturable.

I have lots of questions

[Hentes]

Could someone with expertise in the topic tell me:

• How does this replace a LED? It's not a light source.
• How does this allow creating optical circuits? You need more than just diodes for a logic gate.
• If I make a sphere out of this, will it act like a black hole?

Re:I have lots of questions

[Wookie Monster]

Making a sphere out of this should be no different than making any type of black colored sphere. The light is converted to heat and the sphere warms up. If the heat is allowed to slowly escape, then equilibrium is reached. Otherwise, the sphere melts and potentially destroys its heat absorbing properties. Or the liquid sphere radiates heat away. In a black hole, heat cannot escape at all.

Re:I have lots of questions

[kelemvor4]

This article is just a rewording of the original article: http://www.mit.edu/newsoffice/2011/optical-computing-diode-1123.html
Fortunately, the kids at ExtremeTech were good enough to at least link the original which isn't nearly as confusing.

Re:I have lots of questions

[Anonymous Coward]

It's not a Light Emitting Diode, it's basically a Light Diode. Light can only pass through in one direction. The way this is normally done is by rotating the polarization of light through two polarizers. Any light of the wrong polarization cannot return back to the light source. This is usually used to protect laser sources and their modulators from return loss reflections in fiber optic systems that make use of polarization maintaining fibers.

Anyway, a 'true' optical transistor can be fashioned out of this if coupled with an optically controlled gain medium. If you have optical transistors, you can create optical NOR or NAND gates, and all basic logic functions can be created solely from these gates.

Just skimming the actual Nature paper itself, it appears they've basically created an optical isolator on a planar optical waveguide circuit.

To answer your last question: no.

You'd be better off with black construction paper for that.

The MIT article is much better...

[divisionbyzero]

It doesn't go off and start talking about LEDs and WDM which just confuses the issue.

http://www.mit.edu/newsoffice/2011/optical-computing-diode-1123.html

Re:Interesting concept

[Semptimilius]

Well, much of the leaking in traditional electronic transistors is due to quantum mechanical effects, which would still apply to photonic devices. (With differences arising from such things as spin.) Some people are using evanescent fields from thin fibre lines to actually couple the signals in the line to other devices.

Switching speed.

[fish_in_the_c]

Just because you can use it to store data doesn't mean it will make a good processor any time soon.
how long does it take to switch states. That's why flash ram is not used in primary memory.

Re:Interesting concept

[marcosdumay]

You surely leak light by the same mechanisms you leak electrons (tunneling), it is just that with light we are used to it, but still don't have a useful workaround. Optical elements also disperse light in a way that is quite similar to a conductor dispersing elecrons, and they also absorb the light (what have no equivalent for electrons).

The biggest advantage of an optical device is that it can act on several signals at once, in a SIMD way.

Re:Hasn't it been supposedly "paved" several times

[timeOday]

Sadly, progress is not made in academia. It's made in the market. Until there is a photonic device on the market they are simply blowing smoke... Wake me up when they have actually got something on the market.

This mentality is a big part of our national decline. Nobody wants to make the investments or do the hard work. They just want to swoop in when the technology is ripe for commercialization and reap all the profit from others' years of investment. Individuals and big companies act this out in different ways, but it boils down to, "just wake me up when I can get it on sale at Walmart."

Great for permanent data storage, I guess...

[CCarrot]

This could be great for long term, non volatile data storage, I suppose, but unless they develop an efficient method of changing the state (i.e., which direction is opaque), I can't see this being much use for processing in general.

On the plus side, maybe we'll finally get to see those data cubes/crystals that popular SF books are always referring to...:-)