Information for

For non-scientists this webpage may raise questions concerning the topics of COYOTE. In a try to answer them without scientific and technical terminology, the following sections address the most important questions that may have come to the mind of the interested reader.

Why optical telecommunications?

The Internet spans around the globe for quite some years now. However, exchanging data between continents in virtually no time is by no means straightforward. The link between continents exceeds 10,000 kilometers over which the data signal must not get lost. Transporting data by means of light has proven itself as the most attractive solution to do so: There is just little attenuation within a fiber channel and signals can be periodically amplified and thus re-conditioned.

Optical telecommuncations is, as a matter of fact, not only restricted to trans-continental links. It is omnipresent and addresses medium-and short reach domains such as inter-city metro links or optical access networks that reach till the households. Furthermore, datacenters, which consitute the backbone of the “cloud”, are employing a massive number of optical links in order to interconnect their servers, their circuit boards and even processor cores. Even mobile networks would not function without optical telecommunications: As soon as the radio wave reaches the antenna site, it is digitized and transported over fiber optics to a centralized processing unit that serves the signal reconstruction and reception. As such, more than 90% of the bits that transmitted over ICT networks are passing over optical links to date.

This little clip shows the principal operation of a fiber-optic link for which a water jet composes the fiber channel. Light, in this case with a red wavelength, is guided along the jet as it bends down to the reservoir with a receiving photodiode. In this way classical music can be transmitted over a water jet – as long as my finger doesn’t interrupt the transmission.

Why optics in particular? What are other advantages?

…simply because optics provide a better performance than electronics. An important fact is that the particles of light, the so-called photons, are much more “robust” for communications than their electrical counterparts, the electrons. It is possible to transmit ~10.000-times more data over a single optical fibre compared to an electrical cable. At the moment, it is possible to transmit up to 10 Pb/s over a fibre as thin as a human hair. At the same time, it allows us to operate networks over much longer distances, e.g. more than 10.000 kilometers, and with much higher energy efficiency.

The latter becomes especially important as the energy footprint of ICT becomes larger and larger. Every transmitted bit over metro and core networks generates ~100 bits within the datacenters. Content generation and processing is surging at immense rates, which already exceed these found for transmission capacities. The handling of data streams within the datacenters, which mark the hotspots of out modern ICT infrastructure, is to be best perfomed optically at lowest possible energy consumptions in the order of 5 pJ per transmitted bit. Just to compare with typical performance targets of wireless communications: Assuming that 1 Gb/s is delivered over radio frequencies with an end-to-end power consumption of only 1 Watt, the energy efficiency would already worsen by a factor of 200.

The image besides shows an optical transceiver under the microscope. It accepts local electrical data to transmit it to the outside world via a thin optical fiber. At the same time, it receives photons, in this case at a red wavelength that carries a high-speed data signal.