Further fibre capacity increase for accommodation of new services

Bandwidth of optical fibre was considered immense, almost non exhaustible, despite the fact that for long haul transmission was dedicated only small part of optical spectrum determined by simplest available optical amplifiers. Improvement of transmission systems capacity was achieved via simple increase of serial rate of lambdas in past. But during development of systems from 10 Gbps to 40 Gbps, it was clearly showed that further increase in serial speed of systems is not possible. It brought necessity of high speed electronics (40GHz), limited reach and very strict design rules in terms of CD or PMD. The improvement was reached by employing complex modulation format as DP-QPSK, such lambda, while carrying 100Gbps, has symbol rate (serial rate) only 25 GBaud. The lambda occupies 50GHz part of transmission spectrum; it corresponds to about 0.4nm and traditional transmission system operating in C band can transport 80 or 88 of these lambdas. When considering upgrade to 400 Gbs or 1Tbps rates it is possible to further increase modulation format complexity to keep symbol rate low. Unfortunately more complex modulation formats require higher OSNR at detection and this fact significantly limits the optical reach of system. Research teams around the globe work hard on 400 Gbps/1Tbps transmission and their results shows that it will not be possible fit these channel in 50GHz. This also means that it won’t be possible to accommodate 80 channels in traditional C band where EDFAs achieves highest efficiency. Especially in order to necessary further increase of transmission capacity, the search for available spectrum for new services (including non-data) offer utilization of other transmission bands than C band. Amplification based on well proven EDFA technology is also available for L band with some known issues. S band can be utilized on new “low water peak” fibres, but amplifiers for whole S band are still immature and based on fluoride glass. It is worth of noting that EDFAs could cover upper part of S band bringing further 50nm of transmission spectrum. Raman technology can cover all C, L or S bands, but require of high power levels is therefore omitted. In proposed text we will present experiences and results from design and operation of simultaneous transmission systems over optical fibre line. The utilization of both communication C and L bands over real fibre line will be shown. Other possible designs will be discussed together with feasibility of multivendor approach in optical network.



  • Josef Vojtěch
  • Miloslav Hůla
  • Jan Radil
  • Vladimír Smotlacha
  • Pavel Škoda
  • Stanislav Šíma

Part of session

The optical last mile

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