Abstract
We describe a cost effective scheme to automatically separate two polarization channels in a polarization division multiplexing (PDM) system, without having to modify the existing transmitter or receiver electronics or software. We experimentally validate the concept by achieving an extinction ratio of more than 28-dB between two demultiplexed channels. Finally, we successfully demonstrate the PDM scheme in a 1.12-Tb/s (14x2x40-Gb/s) system over 62-km of transmission fiber.
Highlights
Increasing the transmission capacity or spectral efficiency of an existing fiber system without having to change any part of transmission hardware or software is an attractive proposition for carriers or system operators, because it can significantly reduce the system “down” time and minimize the equipment and installation cost for system upgrade
The conceptual diagram of the automated detection scheme for a PDM system is shown in Fig. 2 [13]: Optical data streams with orthogonal states of polarization (SOP) (TX1 and TX2) are generated from the same or different light sources at the same wavelength, and are multiplexed through a polarization beam combiner (PBC)
As long as there is a power difference between the two channels ( P1 − P2 ≠ 0 ), the voltage difference between the two power monitors depends on the orientation angle θ and ellipticity angle ε, which can be changed by the dynamic polarization controller
Summary
Increasing the transmission capacity or spectral efficiency of an existing fiber system without having to change any part of transmission hardware or software is an attractive proposition for carriers or system operators, because it can significantly reduce the system “down” time and minimize the equipment and installation cost for system upgrade. Proposed schemes include (i) monitoring of clock tone or pilot tones [5,6,7,8] (ii) multi-level electronic detection [9,10], and (iii) cross-correlation detection of the two demultiplexed channels [11] Each of these schemes has one or more of the following drawbacks: (i) it requires high-speed electronics, thereby making it bit-rate dependent; and more importantly (ii) it requires modification or even significant re-design of existing transceivers, making it more difficult to upgrade existing systems. Using the detected power difference between the two channels as the feedback signal to control the dynamic polarization controller, the two polarization channels at the same wavelength can be readily separated and detected by two identical receivers This scheme requires no modification of the existing transmitter, receiver, or transmission link. We show the results of a successful system demonstration of the scheme by doubling the transmission capacity of a DWDM system containing 14 WDM channels at 40-Gb/s per channel over 62-km LS (LEAF-Submarine by Corning Inc.) fiber transmission
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