PMD-compensation techniques

Abstract

PMD has become a serious limitation for the advent of 40G optical transmission systems. Commercial operators still avoid the utilization of optical PMD compensators since crucial questions such as expected performance and reliability are still subject to research and are not yet satisfactory answered for all relevant cases. The common solutions of tackling PMD, e.g., limiting transmission distance or selecting low-PMD fibers, does not necessarily apply for optical OTDM systems with bit rates beyond 160 Gbit/s. This article describes current approaches for PMD compensators with special focus on the requirements of optical OTDM systems.Although Polarization Mode Dispersion (PMD) in optical fibers has been investigated since the late 70s, it became a matter of increasing importance since approximately 1997 due to the commercial advent of 10 Gbit/s optical transmission systems. After having removed limitations caused by chromatic dispersion and non-linear effects in optical WDM systems, the problems caused by PMD still pose an ultimate limit for optical high-speed transmission and have not yet been satisfactory solved.The main reason for the difficulties in compensating PMD-induced distortions probably is that PMD changes statistically with time at different time scales. Therefore, unlike chromatic dispersion, PMD has to be compensated dynamically, e.g., by an active control circuitry. Therefore, the main goal of compensating PMD is not only to find the compensator's optimum settings to combat the PMD-induced distortions but also to keep track of the temporal fluctuations of the transmission link and to maintain the quality of compensation. This gives rise to numerous questions regarding response time, reliability, complexity and cost of such a solution.If the differential group delay (DGD) of a fiber stays well below the duration of a single bit, the PMD-induced impairments can be neglected. However, particularly OTDM systems with bit rates of 160 Gbit/s and bit durations of less than 6.25 ps will be severely disturbed by the DGD levels of common deployed fibers. At these bit rates

Υψίρρυθμα Οπτικά Συστήματα Μετάδοσης Άμεσης Φώρασης Σε Μητροπολιτικά Δίκτυα

“…Έτσι, είναι φανερό πως για συστήματα μετάδοσης με ρυθμούς δεδομένων ≥40 Gb/s η αντιστάθμιση της PMD κρίνεται απαραίτητη. Για το σκοπό αυτό έχουν μελετηθεί και αναπτυχθεί αρκετές τεχνικές, οι οποίες κατά βάσει μπορούν να διαχωριστούν σε δύο κατηγορίες: στις παθητικές (passive) μεθόδους, που ως στόχο έχουν να μετριάσουν την PMD ενός συστήματος, αλλά και στις ενεργητικές (active) που σκοπεύουν απευθείας στην αντιστάθμιση τους [155]. Οι παθητικές μέθοδοι αν και αρκετά απλούστερες στην υλοποίησή τους, δίνουν σχετικά χαμηλή δυνατότητα επέκτασης του ορίου της PMD.…”

Αυτορυθμιζόμενοι Εξισωτές Διασποράς Τρόπων Πόλωσης Για Σύμφωνα Οπτικά Τηλεπικοινωνιακά Συστήματα Υψηλής Φασματικής Απόδοσης

“…The different PMD compensation techniques can be divided into two main categories, depending on whether the compensation is performed electronically [20], [23], [73], [117]- [119], or optically [121]- [136]. In this section of the thesis, we focus on optical PMD compensators (OPMDC), because of their advantage in bit rates > 40 Gb/s, contrary to electrical PMD compensators that limit their performance to 10 Gb/s on IM/DD systems.…”

“…So, first-order PMD compensators are operational in an interval or over a certain bandwidth, based on the above-mentioned functionality. For increasing average DGD, the first-order PMD compensation methods fail due to the existence of higher-order PMD [13], [115], [136]. When the signal spectrum is larger than the operational bandwidth, the compensator is no longer efficient.…”