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suited for long-distance transmission, due to the lower losses. But the opto-electronics didn’t exist for these longer wavelengths. Once the light sources and detectors became available for 1550nm, they discovered that the network they had built didn’t work well with it.’ This, said Daems, was because the
attenuation was significantly higher than expected, because people installed the fibres in the closures often with a bend radius that was too small. ‘Once that happened,’ he continued, ‘we realised that if we design new products, we should look for the complete available bandwidth or range of wavelengths that you can use with optical fibre. It’s the same today and it ranges from 1260nm up to 1625nm. If you build a future-proof network, you must make sure it is qualified for use with 1625nm.’ However, the optical cable standards
had not included that wavelength until recently, but both the ITU-T and International Electrotechnical Commission (IEC) have extended the cable performance requirements to include 1625nm in the last two years. ‘It was not only cable,’ said Daems, ‘but also connectivity components were missing the 1625nm specification, so connectors and splices were all qualified at 1310 and 1550nm, but never for use with 1625nm. You could see surprises in the field where higher losses were seen at that
NG-PON2 spectrum
wavelength. The new edition of IEC 61753-1 general guidance document was published last year in August, and this one states that you have to qualify, also with 1625nm, if you are going to use closures, connectors and passive optical components in your network.’
Next generation This is a positive move, but the next challenge is in convincing end-users to specify this too. ‘The 1625nm really is something that operators have to keep in mind for the next generation of networks,’ said Daems. ‘And, now, of course, 5G will use an enormous amount of channels in fibre, or a lot more fibre. So, they will maximise the use of the existing cables if they can, using wavelength- division multiplexing (WDM) and using all wavelengths from 1260nm up to 1625nm. For the ITU-T, the next generation of transmission equipment is NG-PON and this operates with wavelengths up to 1625nm.’ It is not just the components and
NEW WHITE PAPER: By Daniel Daems Available online now
Increasing data traffic requires full spectral window usage in optical single-mode fiber cables
By Daniel Daems
Increasing data traffic requires full spectral window usage in optical single-mode fiber cables
cables themselves, but also the test and measurement equipment. ‘The recent OTDRs
Increasing data traffic requires full spectral window usage in optical single-mode fiber cables
even operate at 1650nm,’ continued Daems, ‘so it makes them even more sensitive to spot installation mistakes in networks. Again, if you are going to use that wavelength, you need to at least have some pass/fail criteria to decide whether the installed network is good or bad. The message is to use 1625nm for the qualification of cables and components for use in your new generation of networks.’ Another concern is safety, as Daems
explained: ‘The amount of channels or wavelengths you are using today in a fibre is increasing. Each has a certain optical power and if you add it all up, you come to a limit where, if you bend the fibre too sharply, the power of light that escapes from the core is then absorbed by the coating. So much so that the coating starts to heat up and could even burn in severe cases.’ At the longer wavelengths, where the
fibre is the most sensitive for bending, a lot of power could be dissipated in the fibre coating. ‘With that amount of power in some parts of the network,’ said Daems, ‘we are very close to that dangerous limit already, especially if, by accident, you are manipulating a fibre with your fingers that is carrying that much power. Fibres stored with a too-small bend radius will heat up by the optical power that escapes. If you do not use 1625nm for qualifying the product, you will never notice there is a problem until it suddenly happens without any warning.’
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The optical fiber network infrastructures installed today will typically see four generations of transmission systems over the network’s expected lifetime. As recent history has shown, the amount of data traffic these networks will carry will increase dramatically and continuously. In order to cope with this increasing growth and anticipate the networks of tomorrow, a completely open spectral transmission window from 1260nm to 1625nm for data transmission and up to 1650nm for network monitoring is necessary in optical fiber cables.
www.fibre-systems.com/white-paper
www.fibre-systems.com @fibresystemsmag Issue 25 n Autumn 2019 n FiBRE SYSTEMS 27
By Daniel Daems
spectral window usage in o single-mode fiber cables
ITU-T G.982.2 (12/2014)
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