Sponsoredby:
MODE-GAP
Space division multiplexed systems using few mode fibre – EU project MODE-GAP
(HC-PBGFs) for transmission. The project is also investigating an alternative transmission wavelength window in the 2000nm region offering large bandwidth opportunities. MODE-GAP has achieved record transmission results over solid core at 1550nm and also for PBGF fibre transmission in both the 1550nm and the 2000nm regions. Enhancement of transmission capacity using new fibres requires investigation of a new set of components and sub-systems on which to build. MODE-GAP is investigating solutions from the component level through to system demonstrators. Solid core FMF SDM 1550nm Multimode fibre offers capacity increase in a single fibre format by increasing the number of spatial channels along the fibre. Two-mode group and four-mode group fibres providingsixandtwelvechannelsare being investigated and designed in the project to meet the transmission specifications of the system. Design and refinement of the transmission medium is a fundamental challenge to ensure the optimum information transmission along the fibre, however transmission cannot be considered without the availability of in-line amplifiers or modal multiplexers and demutiplexers. Research in MODE-GAP showed the first usable dual mode group amplifier and has progressed to demonstrate excellent modal gain
flatness and noise performance. Four mode group amplifiers have also been demonstrated, high performance inbothcasesachieved by a novel profiling of the rare earth dopant in the fibre cross-section. Alternative options can be investigated to multiplex and demultiplex the spatial channels, either individual modes can be launched in the fibre or orthogonal mode sets can be selected. DSP methods based on multiple-input multiple output (MIMO) techniques separate the individual channels. The key driver for multiplexing is to demonstrate a low loss, scalable solution and a range of approaches and technology options are being investigated in MODE-GAP. System experiments have been undertaken for 3 distinct spatial modes LP01, LP11a, LP11b each polarization multiplexed to give six channels in total. In-line amplifier and phase plate based mode multiplexer and demutiplexer were utilised. The key result has been 96x3x200Gb/s = 57.6Tb/s net data rate transmission after subtracting the Forward Error Correction overhead representing the highest capacity amplified MDM transmission experiment to date. Hollow core PBGF - 1550nm Hollow core photonic bandgap fibre (HC-PBGF) potentially offers an ultrahigh performance transmission media solution. The air core increases the non-linear threshold thereby increasing the
upper capacity limit however achieving the predicted low loss values represents a huge technical challenge. To this end work in MODE-GAP has focussed on improving the quality of the fibres and driving down the loss. Connecting lengths of PBGF together and to other solid core fibre types presents a potential area for increased losses, and investigations of splicing methods have shown low loss splicing between the fibres. Methods to fabricate production lengths of low- loss PBGF are also being explored within the project. Feasibility of transmission has been demonstrated over 37c HC- PBGF showing 57.6Tb/s WDM- MDM signal transmitted over 310m with full mode demultiplexing. The performance has been further verified for QPSK, 8QAM, 16QAM and 32QAM. Hollow Core PBGF - 2000nm To fully exploit the benefits of PBGF it would be preferable to operate in the lowest loss window around 2000nm. To this end, Thulium doped fibre amplifiers have been investigated showing a gain bandwidth of >250nm, lasers operating from 1820nm to 2050nm and associated fibre components havebeendeveloped for a 2000nm transmission demonstrator. First demonstration of WDM single mode transmission in the 2000nm window along 310m of multimode PBGF has been achieved. To date MODE-GAP has contributed to the global research into potential SDM solutions and shown world first results in transmission and contributing components. In addition to the more conventional approach to MDM-SDM using solid core fibre, MODE-GAP is exploring the potential of alternative fibre and wavelength solutions. More detailed information is available through a series of whitepapers fromwww.modegap.eu Dr Ian Giles, Phoenix Photonics Ltd. is Project manager of the European Union project MODE-GAP
By Dr Ian Giles Y ear on year increase in demand for transmission capacity has stimulated research activity focussed toward investigating next generation solutions to avoid a capacity crunch. Currently deployed single mode fibre networks have a finite capacity limit and cost-effective solutions will need to be found to meet the forecast demand. Space Division Multiplexing (SDM) offers routes to increase capacity with the potential of reduced cost- per-bit. SDM options are; multiple single mode fibres, multi-core fibres or multimode fibres, each exhibiting relative merits. The EU supported project MODE-GAP is exploring SDM over Few Mode Fibre (FMF) using Mode Division Multiplexing (MDM), investigating solid core silica fibres and Hollow Core Photonic Bandgap Fibres
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Figure 1. Mode-division-multiplexed transmission results over 37cell PBGF (1550nm) showing successful transmission over the extended C-Band. Total transmitted datarate 73.7 Tb/s (3 modes x 96 WDM x 256-Gb/s DP-16QAM Frequency [THz]
20 | Optical Connections 2013 | www.opticalconnectionsnews.com |
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