Correlation OTDR Embeds Pseudo Noise Signal in Data Stream
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Solution Overview
Problem
Existing optical time domain reflectometers (OTDRs) for detecting anomalies in optical fibers are intrusive, as they do not allow data transmission during testing, and face a trade-off between resolution and range, limiting their ability to accurately detect anomalies over long distances without disrupting communication.
Innovation Solution
A correlation OTDR system embeds an OTDR signal within a digital data signal transmitted across the optical fiber, using amplitude modulation with a pseudo noise sequence, allowing for unobtrusive anomaly detection while payload data is communicated, by correlating reflected sequences with delayed versions to identify anomaly locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow pulse is used in OTDR testing, then resolution is improved, but the range is limited due to signal attenuation
Solution Approach 1:
The patent uses periodic pulsing of the laser source synchronized with the data signal transmission. By sending OTDR test pulses periodically along with the data signal in a time-division multiplexed manner, the system achieves both high resolution (through narrow periodic pulses) and extended range (through accumulated signal energy over multiple periods), resolving the traditional trade-off between resolution and range
Solution Approach 2:
The patent merges the OTDR testing function with the data communication function by combining test pulses and data signals into a single optical channel. This integration allows the system to simultaneously perform high-resolution anomaly detection and maintain long-range communication capability without requiring separate dedicated testing infrastructure
2Measurement precision
If OTDR testing is performed on an optical fiber, then anomaly detection is enabled, but data transmission is interrupted
Solution Approach 1:
The system implements periodic insertion of OTDR test pulses within the data signal stream at controlled intervals. This periodic testing approach allows anomaly detection to occur continuously over time without requiring complete interruption of data transmission, maintaining both monitoring capability and communication productivity
Solution Approach 2:
The patent applies partial action by inserting test pulses at low amplitude relative to the data signal, and at low duty cycle within the data stream. This partial integration allows the OTDR testing function to operate without fully disrupting the data transmission, enabling simultaneous operation of both functions with minimal interference
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 continuous, accurate detection of anomalies along optical fibers with high resolution and long range without interfering with data communication, allowing for quick alarm responses to changes in fiber characteristics.
Implementation Method 1
an optical transmitter that is configured to transmit, across the optical fiber, an optical data signal that is amplitude modulated with a pseudo noise sequence
Implementation Method 2
such returns are produced by scattering of the light (Rayleigh backscatter) all along length of the fiber
Implementation Method 3
in some cases by localized reflections (Fresnel reflections) at particular points along the fiber
Implementation Method 4
The reflected PN sequence and delayed PN sequence are input into a bank of correlators for which each correlator corresponds to a discrete delay and, hence, location on the fiber
Data Source
AI summary
A correlation optical time domain reflectometer (OTDR) system embeds an OTDR signal in a digital data signal that is to be converted into an optical signal and transmitted across an optical fiber to a remote receiver. In particular, the digital data signal is amplitude modulated with the OTDR signal, which is based on a pseudo noise (PN) sequence, such as an M-sequence. The amplitude modulation is relatively small, for example, less than about 10% of the digital data signal's peak amplitude in an effort to limit the OTDR signal's effect on communication performance. A sequence recovery element receives reflections from the optical fiber and converts the reflections to digital samples. Each digital sample from the sequence recovery element is correlated by correlators that respectively correspond to delays and, hence, locations along the optical fiber, and accumulators accumulate the correlation values from the correlators. Based on the accumulated values, the correlation OTDR system unobtrusively identifies anomaly locations along the optical fiber while payload data is being communicated across the fiber.