Interrogator with Variable Load Light Sources for Optical Fiber Sensing
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Solution Overview
Problem
Distributed optical fiber sensing systems face complications due to the time dynamics of erbium-doped fiber amplifiers causing spikes and ripples in amplified transmitted light, low optical signal-to-noise ratio, and non-linear signal distortions such as self-phase modulation, cross-phase modulation, and four-wave mixing, especially in long optical fiber lines with multiple amplifiers.
Innovation Solution
An apparatus comprising an optical transmitter, an optical receiver, and two load light sources that transmit temporally varying load light to stabilize the gain of rare-earth doped amplifiers, with one load light source operating on an opposite wavelength range to the probe light, reducing distortion and spiking by modulating the load light complementary to the probe light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If multiple erbium-doped fiber amplifiers are used in long optical fiber lines, then the transmission distance and signal strength are improved, but time dynamics of amplifiers cause spikes and ripples in amplified transmitted light
Solution Approach 1:
The patent applies preliminary anti-action by introducing load light that is modulated in anti-phase with the probe light. This pre-compensates for the gain dynamics of erbium-doped amplifiers, counteracting the time-varying gain effects before they can cause spikes and ripples in the transmitted signal. The load light acts as a counterbalancing force that stabilizes the amplifier output.
Solution Approach 2:
The patent utilizes parameter changes by modulating the intensity of load light dynamically. The load light intensity is varied in anti-phase with the probe light intensity, changing the operational parameters of the erbium-doped amplifiers to maintain stable gain despite variations in probe light power. This dynamic parameter adjustment compensates for amplifier time dynamics.
2Length of stationary object
If multiple erbium-doped fiber amplifiers are used to extend transmission distance, then signal coverage is improved, but non-linear signal distortions such as self-phase modulation, cross-phase modulation, and four-wave mixing increase
Solution Approach 1:
The patent applies preliminary anti-action by using load light to pre-compensate for non-linear effects. By modulating load light in anti-phase with probe light, the system counteracts the conditions that lead to self-phase modulation, cross-phase modulation, and four-wave mixing before they can significantly distort the signal.
Solution Approach 2:
The load light acts as an intermediary that mediates the interaction between probe light and erbium-doped amplifiers. It provides a controlled counterbalancing influence that reduces the impact of non-linear optical effects by stabilizing the amplifier gain and reducing intensity fluctuations that drive non-linear distortions.
3Stability of the object's composition
If load light is used to stabilize amplifier gain, then distortion and spiking are reduced, but device complexity increases due to additional load light sources and modulation requirements
Solution Approach 1:
The patent applies merging by combining the probe light and load light into a single optical path and using a shared modulation mechanism. The load light source and its modulator are integrated with the probe light transmission system, allowing both signals to be multiplexed together and reducing the need for separate independent control systems.
Solution Approach 2:
The load light source serves multiple functions: it stabilizes amplifier gain, reduces non-linear distortions, and provides a reference for anti-phase modulation. This multi-functionality reduces the need for additional dedicated components, as the load light mechanism accomplishes multiple stabilization objectives simultaneously.
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
The solution effectively reduces distortion and stabilizes the gain of optical amplifiers, improving the sensitivity of distributed optical fiber sensing systems to environmental disturbances by mitigating the effects of non-linear signal distortions and amplification transients.
Implementation Method 1
Wavelengths of the temporally varying load light are in an amplification range for rare-earth doped amplifiers
Implementation Method 2
an optical interrogating device sends a sequence of suitably prepared optical probe pulses into an optical fiber
Implementation Method 3
The reflectors are typically either approximately randomly formed during fabrication of the optical fiber (e.g. causing Raleigh scattering)
Data Source
Figure 1~2
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Figure 4
AI summary
An apparatus for distributed optical sensing includes an optical transmitter, an optical receiver, and two sources of load light to transmit temporally varying load light. The optical transmitter is connected to transmit probe light to the same optical output as the sources of load light, such that the temporally varying load light from the first load light source occupies a wavelength range on an opposite side of a wavelength range of the optical probe light as the temporally varying load light from the second load light source.