Correlation OTDR Without Terminal Reflector
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Solution Overview
Problem
Existing correlation OTDR techniques require a terminal reflector for demarcation, complicating system installation, deployment, and maintenance, and do not provide OTDR fibre characterization or allow implementation in transceivers used for data traffic.
Innovation Solution
A method and apparatus for performing OTDR on an optical fibre using a correlation OTDR technique without an ADC, which sets a decision threshold for a photodetector, transmits coded optical radiation pulses, detects backscattered and reflected signals, and combines correlation signals to generate an OTDR trace.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a terminal reflector is used for demarcation in correlation OTDR, then the reflection signal can be detected, but system installation, deployment and maintenance become complicated
Solution Approach 1:
The patent removes the terminal reflector from the system by using the natural reflection from the fibre end itself. The correlation processing technique enables detection of this weak reflection without requiring an additional reflector component, thereby simplifying installation and maintenance while maintaining reflection detection capability.
Solution Approach 2:
The fibre end itself serves as the reflection source rather than requiring an external terminal reflector. The system uses the fibre's own properties to generate the necessary reflection signal, eliminating the need for separate demarcation components and reducing system complexity.
2Measurement precision
If conventional correlation OTDR technique is used without ADC, then sub-ns resolution is achieved, but OTDR fibre characterization and reflection site detection are not provided
Solution Approach 1:
The patent performs preliminary correlation processing on the detected signals to enhance the reflection and backscatter profiles. By applying correlation techniques with coded sequences before final analysis, the system maintains sub-ns resolution while recovering fibre characterization information that would otherwise be lost in noise.
Solution Approach 2:
The system uses feedback from the correlation processing results to adjust detection parameters and enhance signal recovery. The correlation output provides feedback information about fibre characteristics that is used to improve subsequent measurements and enable comprehensive fibre characterization.
3Reliability
If circulator is used in correlation OTDR setup, then OTDR measurement is enabled, but normal transceiver operation for data traffic is hindered
Solution Approach 1:
The patent designs the transceiver to perform both data transmission and OTDR measurement functions using the same optical path without requiring a circulator. The system can switch between normal data traffic mode and OTDR measurement mode, making the transceiver universal and eliminating the need for separate measurement hardware that would hinder data operation.
Solution Approach 2:
The patent merges the OTDR measurement functionality with the existing transceiver data transmission path. By combining both functions into a single integrated system without additional circulator components, the transceiver can operate flexibly for both data traffic and fibre characterization without operational hindrance.
4Ease of manufacture
If standard SFP transceivers are used for OTDR, then integration is simplified, but squelching mode is entered when no input is present
Solution Approach 1:
The patent uses periodic transmission of coded optical sequences into the fibre during OTDR mode. This periodic action ensures the transceiver receives continuous input signals and remains active, preventing entry into squelching mode while maintaining compatibility with standard SFP transceiver designs.
Solution Approach 2:
The system changes operational parameters by transmitting specific coded sequences at controlled intervals during OTDR measurements. This parameter adjustment keeps the transceiver in an active state rather than entering squelching mode, ensuring reliable operation while maintaining ease of integration with standard SFP transceivers.
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
Achieves sub-ns resolution and characterizes optical fibres by identifying scattering and reflection sites without a terminal reflector, allowing remote operation and integration with transceivers used for data transmission.
Implementation Method 1
detecting optical radiation backscattered and/or reflected from the optical fibre using the photodetector
Implementation Method 2
transmitting a first signal into an optical fibre, wherein the first signal comprises a sequence of optical radiation pulses
Implementation Method 3
The optical pulse may be backscattered from scattering sites which result due to imperfections in the optical fibre
Data Source
AI summary
The present application relates to a method for performing optical time domain reflectometry (OTDR) on an optical fibre. The method comprises: a) setting (1010) a decision threshold of a photodetector; b) transmitting (1020) a first signal into an optical fibre, wherein the first signal comprises a sequence of optical radiation pulses based on a coded sequence; c) detecting (1030) optical radiation backscattered and/or reflected from the optical fibre using the photodetector; d) obtaining (1040) a measurement signal comprising bit sequences based on the detected optical radiation and the decision threshold of the photodetector; e) comparing (1050) the measurement signal with the first signal to obtain a correlation signal; f) adjusting (1060) the decision threshold of the photodetector; g) repeating (1070) steps (b)-(f) to obtain a plurality of correlation signals; and e) combining (1080) the plurality of correlation signals to obtain an OTDR trace of the optical fibre. The present application also relates to a computer program product, an apparatus for performing OTDR, an optical plug and a fibre optic system.