DGD Measurement in Optical Links via Polarization Scanning
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Solution Overview
Problem
Current methods for measuring differential group delay (DGD) in optical fiber links are unable to provide instantaneous values, are intrusive, and only measure fiber sections, not the entire link, leading to disruptions in traffic and incomplete assessments.
Innovation Solution
A method involving generating a binary optical signal sequence, applying polarization scans at both link inputs and outputs, and introducing a variable additional DGD to achieve equality with the bit rate, allowing for instantaneous DGD measurement without disrupting traffic, using existing WDM link components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If broadband PMD measurement methods are used to estimate DGD, then statistical DGD values can be obtained, but instantaneous DGD values cannot be provided and traffic interruption is required
Solution Approach 1:
The method performs preliminary polarization state scanning at the input end before signal transmission, establishing the relationship between input polarization states and output polarization states. This preliminary action enables subsequent instantaneous DGD measurement without requiring traffic interruption, as the measurement setup is prepared in advance while allowing normal signal transmission during the measurement process.
Solution Approach 2:
The invention introduces polarization controllers at both input and output ends as intermediary devices that manipulate polarization states without disrupting the optical signal transmission. These controllers enable measurement of instantaneous DGD by adjusting polarization states while allowing traffic to continue flowing through the optical link, thus acting as mediators between measurement requirements and traffic continuity.
2Measurement precision
If section-by-section fiber measurement is performed, then DGD of individual sections can be measured, but total link DGD including terminals and OADMs cannot be assessed
Solution Approach 1:
The measurement method is designed to be universal, working for any optical link configuration including fiber sections, terminals, OADMs, and other components. By measuring the total DGD of the entire link from input to output endpoints, the method provides a multi-functional solution that covers all link elements rather than being limited to specific component types or configurations.
Solution Approach 2:
The method segments the measurement approach by independently controlling and scanning polarization states at the input end while independently analyzing output polarization states. This segmentation allows the measurement system to handle complex link configurations with multiple components by treating each section's contribution to total DGD separately while providing the aggregate link performance.
3Measurement precision
If intrusive measurement methods are used, then DGD can be measured, but traffic disruption occurs due to optical line cutting
Solution Approach 1:
The measurement method maintains continuity of useful action by enabling DGD measurement without interrupting the optical signal transmission. The polarization controllers and measurement apparatus are integrated into the link in a non-intrusive manner, allowing both normal traffic flow and measurement operations to occur simultaneously, thus preserving continuous service while providing measurement capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables instantaneous measurement of total DGD across the entire optical fiber link, including terminals and OADMs, without interrupting traffic, by analyzing eye diagrams and histograms to determine the desired DGD values.
Implementation Method 1
the link, including the line fiber and chromatic dispersion compensation fiber sections, the connectors, the multiplexers-demultiplexers, as well as the couplers, filters, isolators, circulators, amplifiers, etc. behaves like a birefringent medium and induces harmful effects for the propagation of the signal which result in particular in a variation of the group time depending on the angle of the polarization of the optical signals transmitted with respect to the fast and slow axes of birefringence local
Data Source
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AI summary
The invention concerns a device for measuring differential group delay T1 in an optical link. In accordance with the invention, the device comprises: in input of said link, a generator (10) for a binary signal sequence at a rate D and a first polarization controller (30) for performing a first scanning of the polarizing states applied to the binary signal of an incoming sequence; in output of said link, a second polarization controller (60) for performing a second scanning of the polarizing states applied to the signal to the signal resulting from the outgoing sequence independently of said first polarizing scanning; an differential group delay emulator (70) for introducing an additional variable differential group delay T2, and an analyzing device (90) for determining the equality between T1 + T2=1/D on the resulting signal sequence. The invention is applicable to fiber-optic metrology.