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Distributed aggregation of spectrally efficient single- and dual-polarization super-channels by optical frequency conversion in fiber

: Elschner, R.; Richter, T.; Schmidt-Langhorst, C.; Kato, T.; Tanimura, T.; Watanabe, S.; Schubert, C.


Journal of Lightwave Technology 34 (2016), No.2, pp.618-625
ISSN: 0733-8724
Journal Article
Fraunhofer HHI ()

Recently developed upgrade options for distributed ultra-dense frequency-division multiplexing toward large aggregation capacity are discussed. The concept, originally demonstrated for distributed coherent optical orthogonal frequency-division multiplexing, is based on optical frequency conversion in fiber. It enables precise frequency allocation of the successively multiplexed subcarriers within the super-channel without the need of absolute optical frequency control, i.e., allowing for use of free-running lasers at the individual multiplexing nodes. Follow-up experiments proved the applicability of this concept also to Nyquist wavelength-division multiplexing (WDM) with extremely small guard bands by successfully demonstrating the distributed aggregation of a spectrally efficient 400-Gb/s single-polarization zero-guard-band Nyquist-WDM super-channel using 4× 28-GBd 16-ary quadrature-amplitude modulation (16QAM) subcarriers. Recently, we further extended the concept to distributed generation of dual-polarization super-channels. This extension allowed for the distributed aggregation of a 400-Gb/s Nyquist-WDM super-channel using 4× 28-GBd polarization-division multiplexed quaternary phase-shift keying (PDM-QPSK) subcarriers. In this invited contribution, we review and compare in detail both experiments enabling 400-Gb/s aggregation capacity. Additionally, we discuss a viable option for operation under random fiber birefringence regardless of the polarization-dependent nature of the underlying optical frequency conversion process.