Optical Pulse Reflectometer LP11 Mode Sensitivity
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Solution Overview
Problem
In optical fiber networks, modal crosstalk between LP01 and LP11 modes leads to degraded detection sensitivity for bends and lateral pressures due to mixing of loss information from both modes.
Innovation Solution
An optical pulse test apparatus that amplifies backscattered light in the LP11 mode and attenuates backscattered light in the LP01 mode using stimulated Brillouin scattering, allowing for separation and detection of LP11 mode loss information, comprising a light generation unit, mode demultiplexing unit, local oscillation light generation unit, light reception unit, and arithmetic processing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If modal crosstalk between LP01 and LP11 modes is present in optical fiber networks, then both modes are detected, but detection sensitivity for bends and lateral pressures is degraded due to mixing of loss information
Solution Approach 1:
The patent segments the mixed mode signals by separating LP01 and LP11 mode components through mode demultiplexing. The optical pulse test apparatus divides the composite backscattered light into distinct mode components, allowing independent analysis of each mode's loss characteristics without contamination from the other mode.
Solution Approach 2:
The patent extracts the LP11 mode signal from the mixed mode crosstalk by using mode demultiplexing techniques. The apparatus selectively extracts the higher-order mode component that is sensitive to bends and lateral pressures, isolating it from the dominant LP01 mode to enable precise measurement of mechanical characteristics.
2Measurement precision
If only fundamental mode (LP01) backscattered light is detected, then the system is simple, but detection sensitivity for bends and lateral pressures is insufficient
Solution Approach 1:
The patent introduces dynamic mode control by selectively adjusting the detection sensitivity for different modes. The apparatus can dynamically switch between detecting only LP01 mode for simple loss measurement or enabling LP11 mode detection for high-sensitivity mechanical characteristic measurement, adapting the system complexity to the measurement requirements.
Solution Approach 2:
The patent introduces a mode demultiplexing unit as an intermediary component that enables selective detection of different modes. This intermediary device allows the system to access LP11 mode information when needed without permanently complicating the basic OTDR architecture, providing a modular approach to enhanced measurement capability.
3Measurement precision
If LP11 mode backscattered light is detected directly without amplification, then the system is simple, but the weak signal cannot be distinguished from noise
Solution Approach 1:
The patent changes the signal parameter by applying selective amplification to the LP11 mode backscattered light. The optical pulse test apparatus uses mode-selective amplification to enhance the weak LP11 mode signal while leaving the LP01 mode signal unchanged, creating a differentiated signal level that enables noise-free detection of the higher-order mode.
Solution Approach 2:
The patent applies partial amplification only to the LP11 mode component rather than amplifying all backscattered light uniformly. This selective amplification approach provides just enough gain to the weak LP11 signal for noise-free detection without excessively amplifying the already-strong LP01 signal, which would not provide additional useful information.
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 high-sensitivity detection of bends and lateral pressures in optical fiber networks with modal crosstalk by isolating and amplifying LP11 mode loss information, improving detection sensitivity.
Implementation Method 1
generate first light having an optical frequency for amplifying backscattered light in an LP11 mode out of the backscattered light beams in two LP modes through stimulated Brillouin scattering, and second light having an optical frequency for attenuating backscattered light in an LP01 mode out of the backscattered light beams in the two LP modes through stimulated Brillouin scattering
Implementation Method 2
generate local oscillation light by which the backscattered light separated by the mode demultiplexing unit is heterodyne-detected
Data Source
AI summary
An optical pulse test apparatus according to the present disclosure includes a light generation unit configured to generate an optical pulse for generating backscattered light beams in an optical fiber under test and generate first light having an optical frequency for amplifying backscattered light in an LP11 mode out of the backscattered light beams in two LP modes through stimulated Brillouin scattering, and second light having an optical frequency for attenuating backscattered light in an LP01 mode out of the backscattered light beams in the two LP modes through stimulated Brillouin scattering, a mode demultiplexing unit configured to input the optical pulse, the first light, and the second light generated by the light generation unit into the optical fiber under test in the LP01 mode and separate, out of the backscattered light beams generated by the optical pulse, the backscattered light in the LP11 mode, a local oscillation light generation unit configured to generate local oscillation light by which the backscattered light separated by the mode demultiplexing unit is heterodyne-detected, a light reception unit configured to multiplex the backscattered light in the LP11 mode separated by the mode demultiplexing unit and the local oscillation light generated by the local oscillation light generation unit and photoelectrically convert the multiplexed light into an electrical signal, and an arithmetic processing unit configured to calculate a time-intensity distribution of the electrical signal obtained by the light reception unit photoelectrically converting the backscattered light in the LP11 mode.