Monday, February 7, 2011

Photonics: Is Copper Now Best Suited for Jewelry?

By Rafaela Novais

Photonics is a term that is not very common, but is starting to gain space in the news and in our personal world, albeit, behind the scenes. This short article should give you a quick overview of the subject, and not leave you looking like a deer in the headlights whenever the subject comes up. I hope this will familiarize you with the basics of the photonics world and pique your curiosity for more. For the experts, may you be entertained. I have also included several terms in Portuguese which appear in brackets.

According to Merriam-Webster, Photonics is a “branch of physics that deals with the properties and applications of photons, especially, as a medium for transmitting information.” This may include detecting, modulating, transmitting, and receiving light. Most of the photonics applications use light in the visible and near-infrared spectra, with wavelengths ranging from 380nm to 2,500nm.
Most communications applications use wavelengths between 850nm and 1675nm due to the higher stability of the signals in the fiber optic waveguides that are commercially available.Waveguides [guias de ondas]are the media used to transmit waves,such as light. You might also see the term multi-mode waveguide [guia de ondas multímodo].

As early as the 1960, with the inventions of lasers, laser diodes, optical fibers [fibras óticas], and cables, it became clear that the technology could be used, initially, for telecommunications and later, for the broader application of high volume data transfer. At that time, copper was the transmission media of choice.

Today, optical fiber cables make it possible for a signal to travel at very high speeds over long distances with very little signal loss (attenuation), and with virtually no electromagnetic interference. Over long distances, copper cables suffer from attenuation losses which lead to poor signal quality. They also are subject to electromagnetic field coupling effects between the adjacent conductors, known as crosstalk, and their proximity to other sources of electromagnetic noise (such as power sources).

To make a fair comparison between copper and fiber optic cables, I need to introduce you to another basic concept: the way we encode and decode the signals transmitted. On one end of the cable, electronic signals need to be converted to photonic ones to be transmitted and converted back to electronic signals at the other end to be understood by our current electronics. Copper cables transmit signals directly to our electronics. One of the fastest copper cables currently available, the Category 6a 10GBASE-T (10-Gigabit Ethernet) cables, has been developed with increased resistance to crosstalk [diafonia] and performance of up to 500MHz, but its length is limited to 100 meters. This length limit is further reduced in hostile crosstalk or interference environments. On the other hand, a single-mode fiber cable transmitting at an equivalent 10GBASE-ER, including encoding and decoding, would deliver 10GHz over 40 kilometers, without significant attenuation.

Now, one would ask: if fiber cables are so much better, why aren’t they widely available to consumers?

With the high speed, low attenuation, and high bandwidth characteristics, optical fiber cables have become a much more feasible and desirable medium for signal transmission over long distances. For distances shorter than about 100m, copper is still preferred due to its much lower cost. Another issue for fiber is that the infrastructure of most cities does not support fiber cables all the way into homes.

Currently, viable applications of optical cables [cabo de fibra ótica] are high-speed data centers around the world, like facilities that support internet search engines and social networks, financial markets (possibly your bank), and other data centers that need to be highly-available and handle high data traffic. Several companies in the United States, Asia, and Western Europe have recently accelerated work to expand and innovate in this market.

So, don’t go unplugging your old copper cables to use as necklaces just yet. There’s still plenty of use left in them.

Rafaela Novais has worked in the Semiconductor Industry as a memory designer and an automation engineer for more than 12 years. She currently works at Luxtera, the leading CMOS photonics chip provider. Rafaela was born in Brazil and has lived in the United States for over 20 years. She is currently a translation student at New York University, focusing on the English to Brazilian Portuguese Language pair. She’s also a songwriter, poet, loves cooking and dogs.

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