Abstract
We demonstrate experimentally a novel type of coherent low cost Gigabit-to-the-User Ultra-Dense-Wavelength Division Multiplexing (UD-WDM) PON, featuring 6.25 GHz channel spacing and long reach. Polarization-independent coherent detection is achieved by exploiting a novel scheme which requires only a 3 × 3 coupler, three photodiodes, basic analogue processing and a common DFB as local oscillator (LO). This avoids the conventional polarization diversity approach. The DFB LO is free running, i.e. not locked in frequency, and is tuned to detect any of the eight channels by simply changing its temperature in a range of 2° C. We achieve 70 km long-reach transmission plus 30 dB attenuation, for a total of > 45 dB optical distribution network loss. This indicates that this solution could be effectively exploited to overlay existing PON infrastructures by UD-WDM.
Highlights
Optical coherent transmission systems are expected to be soon introduced in access networks, namely wavelength division multiplexing passive optical networks (WDM-PON) [1,2,3,4]
We tackle this key issue and we focus on UDWDM-PON by means of coherent detection, realized by avoiding expensive narrow line-width lasers and digital signal processing [6]
We previously demonstrated that a 3 × 3 phase diversity receiver [7], realized with common DFBs and simple analog electrical processing, works effectively with Gigabit class intensity modulated signals in UDWDM-PON [8]
Summary
Optical coherent transmission systems are expected to be soon introduced in access networks, namely wavelength division multiplexing passive optical networks (WDM-PON) [1,2,3,4]. A scheme for extending effectively this approach to a polarization-independent (PI) configuration was presented theoretically [9]: considering the previous phase-diversity receiver, with a symmetric 3 × 3 coupler, polarization-independent (PI) operation can be obtained if the incoming signal is split and injected into two arms of the coupler, , provided that the frequency detuning between the LO and the signal carrier is high enough (around 70% of the bitrate [10]) We preliminary assessed this receiver experimentally in single-channel operation [10], confirming that the PI implementation adds a negligible power penalty. We note that this scheme allows co-existence with legacy networks (e.g. the G-PON) operating on different wavelength bands, without dedicated colored optical filters in the Optical Distribution Network (ODN) which is today composed only of power splitters
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