Chromatic Dispersion Measurement Using Correlated Pulse Sequences
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Solution Overview
Problem
The OTDR pulse-delay method for measuring chromatic dispersion in optical fiber links faces challenges with dynamic range and acquisition time, particularly in long-haul applications.
Innovation Solution
An improved method using a repeated pulse sequence and correlation detection to enhance the dynamic range and reduce acquisition time, specifically targeting the extraction of a reflective peak at the remote end of the optical fiber link.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the OTDR pulse-delay method is used to measure chromatic dispersion, then the measurement can be performed with low-cost equipment and single-operator simplicity, but the dynamic range is insufficient for long-haul applications over 100 km
Solution Approach 1:
The patent applies periodic action by using a sequence of repeated pulses instead of a single pulse. The pulse sequence includes multiple pulses transmitted at regular intervals, allowing the system to accumulate signal energy over time. This periodic transmission enables improved dynamic range for long-haul measurements while maintaining the simplicity of the OTDR approach.
Solution Approach 2:
The patent implements continuity of useful action through continuous averaging of multiple pulse sequence acquisitions. By repeatedly transmitting pulse sequences and averaging the results, the system continuously accumulates useful signal information while suppressing noise, thereby extending the measurable dynamic range without requiring more complex equipment.
2Measurement precision
If averaging is performed over longer time to improve dynamic range, then the measurement sensitivity increases, but the acquisition time becomes excessive
Solution Approach 1:
The patent resolves this contradiction by using periodic pulse sequences with optimized repetition rates. Instead of continuous single-pulse averaging, the system transmits structured pulse sequences that allow faster convergence of the averaging process, reducing acquisition time while maintaining improved dynamic range.
Solution Approach 2:
The patent applies preliminary action by pre-processing the pulse sequences through correlation detection before final averaging. The correlation operation with a reference pulse shape enhances the signal-to-noise ratio early in the measurement process, allowing the subsequent averaging to converge faster and reduce overall acquisition time.
3Measurement precision
If a single pulse is transmitted at a time, then the measurement process is simple, but the dynamic range is limited and acquisition time increases
Solution Approach 1:
The patent improves measurement efficiency by replacing single-pulse transmission with periodic pulse sequences. Multiple pulses are transmitted in rapid succession within each acquisition, allowing the system to gather more signal information per unit time. This increases productivity while the structured sequence maintains analysis simplicity through correlation-based processing.
Solution Approach 2:
The patent merges multiple pulse measurements into a single correlated detection operation. By combining the information from multiple pulses in the time domain through correlation with a reference sequence, the system achieves improved dynamic range and measurement efficiency simultaneously, rather than requiring separate processing of each pulse.
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
This approach allows for a significant improvement in dynamic range while maintaining or reducing acquisition time, making it more suitable for long-haul applications.
Implementation Method 1
Chromatic dispersion is caused by a physical property of the transmission medium which cause light at different wavelengths to travel at different speeds
Implementation Method 2
analyzes the travel time after a back-reflection from a mirror or non-angled polished (UPC) connector at the other end of the link
Implementation Method 3
A correlation method is then used to detect the sequence of pulses after a back-reflection from a mirror or non-angled polished (UPC) connector at the remote end of the link and extract the position of the reflective peak
Data Source
AI summary
There is provided a chromatic dispersion measurement method and system for characterizing an optical fiber link under test. From a proximal end of the optical fiber link, at least one OTDR acquisition is performed, wherein each OTDR acquisition is performed by propagating in the optical fiber link under test, at least one test signal comprising a plurality of light pulses in accordance with a known sequence of pulses and detecting corresponding return light signal from the optical fiber link so as to obtain a trace representing backscattered and reflected light as a function of distance in the optical fiber link under test, and wherein said test signals have mutually different wavelengths. For each test signal and corresponding wavelength, a position of the reflective peak associated with a remote end of the optical fiber link is extracted from the return light signal by calculating a cross-correlation between the known sequence of pulses and the acquired trace. A value of a chromatic dispersion coefficient associated with said optical fiber link is then calculated from values of the extracted positions and corresponding wavelengths.