Demo Site

Thursday, April 23, 2009

Moving data using silicon chips


Using photons rather than electrons to move data in chips

Today the world is hungry for bandwidth and speed. But this is limited by the way we use to connect various points. If you think am speaking about two buildings or even two countries, you are wrong. Am speaking about interconnections in a single chip. At present the interconnects in an IC is made with copper. But what is happening is at luxurious speeds as 10 billion B/s (bits per seconds) these interconnects prove to be less efficient.

Continuous experiments have given many alternatives but at the cost of high price. The best one from the array is by using optical fibers and thus replacing photons instead of electrons. The advantage of this method is that the overall cost is less compared to other methods and the data rate you can achieve is far more than that achievable through copper connects.

What’s the big deal with these interconnects anyway huh? Imagine you can download movies with just a click rather than waiting for hours, simultaneous streaming of audio, video, teleconferencing, and you name it. Sounds cool, isn’t it? This is what is possible if we have optical fiber interconnects in the chip level.

clip_image001clip_image002clip_image003The superiority of optical connection is best explained by the following example. Optical data can travel for long distances (say 10 km) without any attenuation. The data rate can be increased by a technique called WDM-wavelength division multiplexing.

Myself is a communication engineer, so I will elaborate on this. Distortion, interference these occurs when the wavelength/frequency of two signals in a single medium becomes equal or very close. So if you can transmit several distinct frequencies at the same time, then you can use the single medium to transmit all these at the same time. In short you are multiplying the capability of the medium’s data carrying capacity. Currently using WDM you can transmit over 40 different data signals into a thin hair strand size optical fiber, all running at the data rate of 10 GBps. wonderful isn’t it, copper connects can’t even dream about it.

So why isn’t this new technology not in your chips yet ? It isn’t simple as it sounds. Optical devices are made with materials such as lithium niobate, indium phosphide etc which are very exotic compared to silicon. So its very costly and expensive to fabricate these into a normal chips.

A normal optical fiber communication link requires the following parts. Modulator-to convert electrical data into light Transmitter-to transmit this light into the fiber Optical fiber-the medium Receiver-to receive the optical data Demodulator-to convert optical data back to electrical data

What we need to do is to manufacture all these devices onto a single chip. This is the ultimate goal. What this step exactly means is you make the modulator, source, medium, detector, demodulator etc on the same silicon substrate. Researches have now enabled silicon to have optical properties. An optical channel can be made in silicon by literally etching a channel in the substrate. For source, silicon laser has been developed by Intel’s state-of-the art facilities. As for all the other parts, researches are going on.

Although they encountered many problems, they are troubleshooting them one by one. In short, the time for a single chip that is half the size of a postage stamp which is able to handle all the operations of whole building won’t be too long in the future.

By Amit Samantaray


Post a Comment