Optical Trigger Multiplication for OFDR Sampling
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Solution Overview
Problem
Conventional optical frequency domain reflectometry (OFDR) systems are limited by the frequency of the sampling signal, which restricts the length of the device under test due to the Nyquist criteria, making it impractical to increase sampling frequency without extending the reference interferometer path length.
Innovation Solution
The system generates multiple triggers per period of a varying reference signal, using a 4×4 optical coupler to split the signal into 90-degree out-of-phase components, allowing optical detectors to produce electrical signals that trigger at zero-crossings and equal magnitudes, resulting in evenly spaced triggers across the signal period, even with non-linear frequency sweeping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the path length difference of the reference interferometer is increased to increase the sampling frequency, then the sampling frequency increases, but the device complexity and practical difficulty increase
Solution Approach 1:
The patent segments the single sampling trigger per period into multiple triggers per period by utilizing quadrature detection. The reference interferometer output is split into two signals 90 degrees out of phase, and zero-crossings are detected in both signals, generating multiple sampling triggers within each period of the reference signal, thereby achieving higher effective sampling frequency without increasing the interferometer path length.
Solution Approach 2:
The patent introduces an intermediary processing stage between the reference interferometer and the sampling trigger generation. By using quadrature detection and signal processing to generate multiple triggers per period from the interferometer output, it mediates between the fixed interferometer path length and the desired higher sampling frequency, resolving the contradiction without physical modification of the interferometer.
2Measurement precision
If the sampling frequency is increased to resolve higher frequency signals from the device under test, then the measurable length of the device increases, but the reference interferometer path length must be increased which presents practical difficulties
Solution Approach 1:
The patent applies segmentation by dividing each period of the reference signal into multiple sampling opportunities. Instead of a single trigger per period, the quadrature detection method identifies zero-crossings in both in-phase and quadrature signals, creating multiple triggers per period. This segments the sampling process temporally, enabling higher effective sampling frequency and thus extended measurement range without increasing the physical interferometer length.
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 enhances sampling frequency without increasing the reference interferometer length, enabling longer device testing while maintaining uniform wavenumber sampling and high-resolution discrete Fourier analysis.
Implementation Method 1
passed through a 4×4 optical coupler which splits the signal and provides output signals that include a first signal and a second signal that is 90 degrees out of phase with the first signal
Implementation Method 2
Optical detectors are used to convert these optical signals to electrical signals
Implementation Method 3
A trigger unit then detects points at which the two electrical signals have zero-crossings, and at which the magnitudes of the signals are equal
Implementation Method 4
The reference interferometer produces a reference signal
Data Source
AI summary
Systems and methods for providing trigger signals in an optical interrogator, wherein multiple triggers are generated within each period of a varying reference signal, and wherein the triggers are evenly spaced according to the wavenumber of the reference signal. In one embodiment, an optical frequency domain reflectometry system provides a laser beam to a reference interferometer to produce a reference signal. This signal is passed through a 4×4 optical coupler which splits the signal into a first signal and a second signal that is 90 degrees out of phase with the first signal. These signals are converted to electrical signals, and a trigger unit generates triggers at points at which the two electrical signals have zero-crossings, and at which the magnitudes of the signals are equal. The resulting triggers remain evenly spaced within the period of the reference signals, even when the period is changed.