Single-Ended PMD Measurement Using Periodic Light Pulses
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Solution Overview
Problem
Existing single-ended PMD measurement methods require long acquisition times due to the need for averaging many OTDR acquisitions, which increases operational costs and measurement time compared to two-ended solutions.
Innovation Solution
The method involves using a polarization-sensitive Optical Time Domain Reflectometer (POTDR) to inject repeated light pulses into the optical fiber from a proximal end and detecting the polarization-analyzed return light signal. This process includes performing multiple acquisitions at closely-spaced wavelengths and averaging the amplitudes of the reflected light pulses to calculate the PMD, reducing acquisition time while maintaining dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If repeated polarization-sensitive OTDR acquisitions are performed with waiting time for round-trip of light pulse, then measurement precision is improved, but measurement time increases significantly
Solution Approach 1:
The patent applies periodic action by using pulsed light instead of continuous light, where light pulses are sent through the fiber at regular intervals. This allows the system to measure backscattered light from multiple pulses within a compressed time frame, reducing the total acquisition time while maintaining the precision benefits of multiple measurements.
Solution Approach 2:
The patent implements continuity of useful action by performing multiple OTDR acquisitions in rapid succession without waiting for complete round-trip time between each acquisition. The system continuously accumulates backscattered light data from multiple pulses, eliminating the idle waiting time while maintaining measurement precision through signal averaging.
2Measurement precision
If multiple OTDR acquisitions are averaged to reduce noise, then measurement precision is improved, but device complexity and operational costs increase
Solution Approach 1:
The patent applies self-service by using the fiber's own backscattered light as the measurement signal. The system sends light pulses through the fiber and measures the naturally occurring backscattered light, eliminating the need for external reflectors or complex measurement equipment at the far end. This simplifies the overall system while enabling precise PMD measurements through multiple acquisitions.
3Ease of operation
If single-ended measurement approach is used, then ease of operation is improved, but measurement time increases compared to two-ended solutions
Solution Approach 1:
The patent uses periodic pulsed light to enable single-ended PMD measurement without requiring coordination with distant equipment. By sending multiple pulses and measuring backscattered light from each pulse in rapid succession, the system achieves both operational simplicity (single-ended access) and improved measurement speed compared to traditional single-ended methods.
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 significantly reduces the acquisition time for PMD measurement while improving the dynamic range, making it more efficient and cost-effective compared to traditional methods.
Implementation Method 1
an optical fiber under test in which a test signal comprising repeated light pulses is propagated
Implementation Method 2
detecting a corresponding polarization-analyzed return light signal coming back from the optical fiber
Data Source
AI summary
There is provided a method of measuring the PMD of an optical fiber under test (FUT). A polarization-sensitive optical time domain reflectometer (POTDR) is used to inject into the FUT and from a proximal end thereof, a test signal comprising a series of repeated light pulses and detecting a corresponding polarization-analyzed return light signal coming back from the optical fiber and representing back-reflected light from a light reflector connected to a distal end of the FUT, said return light signal comprising repeated reflected light pulses. The plurality of polarization-sensitive acquisitions defines at least one pair of acquisitions performed with mutually different but closely-spaced wavelengths and substantially the same state of polarization (SOP), a center of said wavelengths defining a center wavelength for said at least one pair. The process may be repeated for a plurality of pairs of acquisitions performed with at least one of a plurality of mutually-different center wavelengths and a plurality of mutually-different states of polarization (SOP). For each said acquisitions, respective amplitudes of at least part of the repeated reflected light pulses are averaged so as to obtain an averaged reflected power. The PMD is obtained by, for each said pairs of said acquisitions, computing a value of a difference between the two averaged reflected powers corresponding to said pair, followed by the mean-square value of computed values of difference over said at least one of a plurality of mutually-different center wavelengths and a plurality of mutually-different states of polarizations (SOPs) and, from said mean-square value, calculating a value of the PMD for the optical fiber under test.