Tunable Light Source Spectral Shaping for OCT Signal Processing
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Solution Overview
Problem
In optical coherence tomography with swept sources, the window function currently results in a significant loss of signal parts, limiting the usable spectral range and signal intensity, necessitating a method to minimize this loss.
Innovation Solution
The method involves determining the sweep velocity curve using a Mach-Zehnder interferometer with fiber Bragg gratings and a tunable light source with a Gaussian light intensity distribution in k-space, allowing for adaptation of the modulation frequency to match the window function, thereby optimizing signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a window function is applied to process the signal, then side wall suppression is improved, but a significant portion of the signal is lost (windowed out)
Solution Approach 1:
The patent changes the spectral shape parameter of the light source to match the window function shape. By adjusting the laser current to generate a Gaussian spectral profile that corresponds to the window function, the signal passes through the windowing process with minimal attenuation, thereby reducing signal loss while maintaining side wall suppression capability.
Solution Approach 2:
The patent applies preliminary shaping to the light source spectrum before the signal processing stage. By pre-configuring the light source to have a Gaussian spectral profile that matches the window function, the system prepares the signal in advance to minimize subsequent losses during windowing operations.
2Quantity of substance
If the spectral shape of the light source is changed to match the window function, then the usable spectral range and signal intensity are increased, but the complexity of controlling and measuring the spectral shape is increased
Solution Approach 1:
The patent implements a feedback mechanism where the actual spectral shape of the light source is measured and compared to the desired Gaussian profile. The system then adjusts the laser current accordingly to minimize deviations, automatically maintaining the optimal spectral shape without requiring complex manual control.
Solution Approach 2:
The patent replaces complex mechanical or optical spectral shaping elements with electronic control of the laser current. By using electrical parameters to control the spectral shape rather than mechanical adjustments, the system reduces complexity while achieving the desired Gaussian profile.
3Illumination intensity
If the sweep velocity profile is adjusted to optimize the spectral shape, then signal intensity is improved, but the measurement time and sweep duration are affected
Solution Approach 1:
The patent employs non-uniform sweep velocity with periodic acceleration and deceleration patterns. The sweep slows down at regions where the spectral density is lower and speeds up where it is higher, optimizing the sampling of the spectrum while maintaining the overall sweep duration and achieving improved signal intensity through better spectral matching.
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 the usable spectral range and signal intensity by aligning the light source's spectral shape with the window function, improving sidewall suppression and measurement sensitivity.
Implementation Method 1
determining the sweep velocity profile using a Mach-Zehnder interferometer (MZI)
Implementation Method 2
arranging two Fiber Bragg gratings of known and different reflection wavelengths in the beam propagation path
Implementation Method 3
the current of a semiconductor laser amplifier (SOA) of the light source can be modulated
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for signal processing in optical coherence tomography by means of a tunable light source (swept source), comprising the following steps: tuning the light source and sensing a signal intensity of the light source in linear dependence on the respective wave number (k) of the tunable light source and producing a signal intensity distribution in dependence on k; applying a window function to the sensed signal intensity distribution and producing a weighted signal intensity distribution; and applying a fast Fourier transform (FFT) to the weighted signal intensity distribution; and characterized in that, in the tuning of the light source, the tuned frequency spectrum is limited to a passband of the window function.