Digital Holography Optical Coherence Tomography Depth Encoding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for 3D imaging of scattering samples using digital holography and optical coherence tomography face challenges in achieving uniformly high three-dimensional resolution over large depth ranges while minimizing sample irradiation and dealing with scattering structures at different depths, which leads to image blurring and reduced transverse resolution.
Innovation Solution
A method combining digital holography with Fourier Domain OCT, where wavelength-dependent holograms are recorded, and the reconstructed wave field is overlaid with a reference light to generate a numerical interferogram, allowing for pixel-by-pixel evaluation and simulation of depth information within the sample, enabling a single measurement to capture the entire sample volume with high resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital holography is used to capture the surface of a sample in multiple focal planes, then the surface imaging capability is improved, but scattering structures at different depths interfere with each other and falsify the image
Solution Approach 1:
The patent extracts depth information from the holographic interference pattern by analyzing the wavelength-dependent phase shifts. By separating the depth encoding function from the transverse imaging function, the method eliminates the interference between scattering structures at different depths while preserving surface imaging capability across multiple focal planes.
Solution Approach 2:
The patent introduces wavelength as an additional dimension for depth encoding. By modulating the reference arm length with a sinusoidal function of wavelength, depth information is encoded in the spectral domain, allowing separation of scattering structures at different depths through Fourier transformation of the wavelength-dependent intensity variations.
2Loss of information
If wavelength scanning digital interference holography is used for tomographic reconstruction, then depth information can be obtained, but the numerical complexity and implementation difficulty increase significantly
Solution Approach 1:
The patent replaces complex numerical tomographic reconstruction algorithms with a simplified phase-modulation approach. Instead of performing full 3D tomographic inversion, the method uses sinusoidal phase modulation in the reference arm to directly encode depth information in the wavelength-dependent intensity pattern, which can be decoded through simple Fourier transformation.
Solution Approach 2:
The patent changes the modulation parameter from spatial domain scanning to wavelength-domain sinusoidal phase modulation. By varying the reference arm length as a sinusoidal function of wavelength rather than performing mechanical scanning, the method achieves depth encoding with significantly reduced numerical complexity and faster acquisition.
3Productivity
If the sample is illuminated over a large area with Fourier domain OCT, then the measurement speed is improved, but the depth of focus and transverse resolution are compromised
Solution Approach 1:
The patent resolves the depth of focus limitation by encoding depth information in the wavelength domain through sinusoidal phase modulation. This allows the system to maintain high transverse resolution across a large illuminated area and extended depth range simultaneously, as the depth discrimination is achieved spectrally rather than through optical focusing.
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 allows for high-resolution 3D imaging of scattering samples over large depth ranges with minimal sample exposure, overcoming the limitations of image blurring and transverse resolution issues by simulating depth information and enabling complete reconstruction of the sample volume without physical superimposition.
Implementation Method 1
The light is split into sample and reference arms by a beam splitter
Implementation Method 2
Light reflected or backscattered by the sample at different distances is directed onto a light-sensitive surface and superimposed there with the reference light. In the image plane, interference creates a spatial distribution of light intensity, the hologram.
Implementation Method 3
In classical holography, the hologram is optically reconstructed by illuminating the developed hologram again with a reference beam. The resulting diffraction wave field has a component that corresponds to the original object wave field.
Implementation Method 4
In digital holography, the light-sensitive surface is formed by an electronic light sensor (e.g. CCD or CMOS camera). A digitally stored hologram can be fed to a processing unit for further evaluation
Implementation Method 5
For example, knowing the light wave field of the reference beam, the light wave field of the light returning from the sample can be calculated in any planes parallel to the camera plane. Knowing the light wave field in the camera plane, it can be propagated numerically, for example by applying the 'Angular Spectrum' method, the Fresnel transform or some other integral transform.
Data Source
Figure 1a~1c
Figure 2a~2b
Figure 3
AI summary
The invention relates to a method for detecting spatially structured sample volumes by means of coherent light and digital holography. The invention also relates to a method for analyzing the depth structure of samples in accordance with optical coherence tomography.