Swept Source OCT Apparatus with Polarization Feedback Control
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Solution Overview
Problem
Spectral OCT is limited by spectrometer losses and polarization effects, which reduce resolution, and swept source scanning is difficult to stabilize for B-scans due to the need for a high sweep rate, making it challenging to perform sectional imaging beyond single-axis scans.
Innovation Solution
A frequency modulated laser is used for high-speed scanning in the X-Y plane with a slow wavelength modulation, allowing for Fourier transformation to produce B-scan images, utilizing a narrowband source and a galvo-scanner for rapid scanning and stable frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a broadband source is used with a spectrometer for spectral OCT, then depth resolution is improved, but signal loss and polarization effects reduce the achievable resolution
Solution Approach 1:
The patent extracts the spectral analysis function from the spectrometer and relocates it to the light source itself. By using a swept-source laser that sequentially emits different wavelengths, the system eliminates the need for a spectrometer, thereby removing the associated signal losses and polarization effects while maintaining depth resolution capability through Fourier transformation of the temporal signal.
Solution Approach 2:
The patent replaces the mechanical spectrometer system with an electronically controlled swept-source laser. Instead of using a dispersive optical element and detector array, the system uses a tunable laser source whose wavelength is programmatically swept, substituting a complex optical-mechanical system with a more compact and efficient electronic control approach.
2Device complexity
If a narrowband swept-source laser is used for OCT imaging, then the need for a spectrometer is eliminated, but achieving high sweep rates for B-scan imaging becomes difficult to stabilize
Solution Approach 1:
The patent implements feedback control through a polarization controller that monitors and adjusts the laser's polarization state in real-time. This feedback mechanism compensates for polarization-mode dispersion and frequency modulation instability, enabling reliable high-speed B-scan imaging. The system continuously monitors the polarization state and adjusts it to maintain optimal performance throughout the wavelength sweep.
Solution Approach 2:
The patent employs dynamic adjustment of the polarization controller during the wavelength sweep to compensate for time-varying polarization effects. By making the system adaptive and responsive to changing conditions, the patent achieves stable frequency modulation performance even at high sweep rates required for B-scan imaging.
3Productivity
If a high sweep rate is used for B-scan imaging, then imaging speed is improved, but frequency modulation stability becomes difficult to maintain
Solution Approach 1:
The patent uses a polarization controller with feedback control to monitor and correct polarization state changes that occur during high-speed wavelength sweeping. This real-time adjustment compensates for the destabilizing effects of rapid frequency modulation, enabling the system to maintain imaging speed while preserving frequency modulation stability.
Solution Approach 2:
The patent dynamically adjusts polarization parameters during the wavelength sweep to compensate for high-speed operation effects. By changing the polarization state as a function of time and wavelength, the system maintains stable frequency modulation characteristics even at the high sweep rates required for productive B-scan imaging.
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 enables faster cross-sectional imaging and improved signal-to-noise ratio by allowing B-scan imaging without the need for a spectrometer, while maintaining stability and reducing scanning time, thus overcoming the limitations of prior art.
Implementation Method 1
OCT is a technique wherein imaging information can be obtained in the depth or z-direction of a sample... the depth position of object locations is determined from the wavelength spectrum of light scattered from the sample
Implementation Method 2
a frequency modulated laser wherein the image is scanned repeatedly at high speed along a scanning line in the x-y plane while the wavelength of the laser is modulated at a relatively low rate
Implementation Method 3
the spectrum of the light scattered by the object is obtained by a diode array in the object plane. In this case the optical A scan is obtained from a Fourier transform of the spectral intensity distribution of the light reflected by the object
Data Source
AI summary
A method of performing spectral OCT imaging on a target involves repeatedly scanning said target along a transverse scanning line with an object beam derived from an OCT interferometer having a narrowband source. The wavelength of the narrowband source is modulated over a range of wavelengths at a rate that is slow relative to the rate of scanning the target. The object beam returned from the target is detected to produce a set of data obtained from multiple scans along said scanning line over the entire range of wavelengths. The data is then processed to extract an OCT image (typically a B-scan) of the target containing depth information.