Interferometric System Spatial Carrier Frequency Polychromatic Imaging
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Solution Overview
Problem
Current interferometric systems face limitations in using broadband waves due to coherence noise and limited field of view, especially when observing samples immersed in scattering media, and require multiple images with different phase shifts for complete information, which increases noise and restricts observation of rapidly varying phenomena.
Innovation Solution
An interferometric system with a spatial carrier frequency using an extended, temporally and spatially incoherent source, where waves are split into two branches with identical imaging setups and a diffraction grating to ensure achromatic interference, allowing holographic imaging with low-coherence waves like white light, enabling real-time imaging and reconstruction from a single hologram.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Mach-Zehnder or Michelson interferometers are used with zero angle interference, then coherence noise is eliminated and depth discrimination is improved, but complete object wave information requires capturing at least 3 images with different phase shifts which increases noise and prevents observation of rapidly varying phenomena
Solution Approach 1:
The interference pattern is segmented into multiple spatial frequencies through the use of a diffraction grating, allowing simultaneous encoding of multiple phase information in a single captured image. This enables complete object wave reconstruction from one interferogram rather than requiring multiple sequential images.
Solution Approach 2:
The patent transitions from temporal multiplexing (capturing multiple images at different times with different phase shifts) to spatial multiplexing (encoding multiple phase information simultaneously in space through carrier frequency fringes). This dimensional change allows real-time observation of dynamic phenomena.
2Productivity
If holographic systems use non-zero angle interference to reconstruct object wave from a single interferogram, then imaging speed is improved, but broadband waves cannot be used because waves with different wavelengths have different spatial frequencies causing loss of interference structure in large portions of the field of view
Solution Approach 1:
The patent changes the spatial frequency parameter of the interference pattern by introducing a carrier frequency through the diffraction grating. This modification makes the spatial frequency of fringes independent of the wavelength of incident light, allowing broadband sources to be used without losing interference structure across the field of view.
3Loss of information
If holographic systems use coherent or partially spatially incoherent waves to achieve interference in the whole field of view, then single interferogram reconstruction is enabled, but coherence noise is introduced and capability to observe samples in scattering media is limited
Solution Approach 1:
The diffraction grating acts as an intermediary element that creates a spatial carrier frequency in the reference beam. This intermediary structure enables the use of completely incoherent broadband light sources while still achieving interference in the whole field of view, eliminating coherence noise while preserving complete object wave information.
4Area of stationary object
If the field of view is increased to observe more of the sample, then more complete information is obtained, but the holographic condition limits the field of view to two times smaller compared to systems in the first group
Solution Approach 1:
The patent applies local quality modification by introducing a spatial carrier frequency specifically in the reference beam path using a diffraction grating. This local modification enables the reference beam to interfere with the object beam across the entire field of view, providing complete object wave information throughout the expanded field of view without the limitations of traditional holographic conditions.
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 solution enables holographic imaging of objects immersed in scattering media with reduced noise and increased field of view, allowing for accurate depth measurement and phase analysis with high spatial frequency fringes, and can be used for both reflected and transmitted-light microscopy.
Implementation Method 1
The +1st order diffracted beam from a diffraction grating, here in the form of a transmission or reflection grating, inserted into the reference branch
Implementation Method 2
after which a wave splitter is inserted and used to split the incoming waves into two separate branches of the interferometer
Implementation Method 3
On the axis of the first branch, there is an arbitrarily designed first imaging setup located and on the axis of the second branch the second imaging setup is located
Implementation Method 4
the first imaging setup may image in transmitted-waves and the second one in reflected-waves
Implementation Method 5
the created interference structure has for each wavelength equal and sufficiently high spatial frequency (density of fringes)
Data Source
Figure 1~2
Figure 3
AI summary
In the interferometric system, the image plane 3.3 of an imaging setup 3.1 of an object branch is imaged by means of an output imaging setup 4 via a transmission system 6.1 of reflectors to the output plane 7 and simultaneously in the image plane 3.4 of an imaging setup 3.2 of a reference branch is a reflection type diffraction grating 5 located, which is imaged by the output imaging setup 4 via a transmission system 6.2 of reflectors also to the output plane 7 of the interferometer where an achromatic off-axis hologram is formed by the interference of waves coming from both the object branch and the reference branch and where a detector is located. The transmission systems of reflectors 6.1 and 6.2 are adjusted in such a way that axes of both branches coincide at an entrance to the output plane 7 and they are parallel with a normal line of the output plane 7, and an axial beam, diffracted by the reflection type diffraction grating 5 at an angle α, enters into the output plane 7 at an angle β, and the relation between angle β and α is sin(β) = sin(α)/m, where m is a magnification of the output imaging setup 4. The system enables the achievement of a holographic imaging of an object by means of low-coherence waves, e.g. white light from an extended light source. Incoherent waves allow the imaging of objects immersed in scattering media. The imaging is carried out in real time. It is possible to use a single digitally recorded hologram of a part of the observed object and numerically reconstruct the object wave, it means its intensity and phase. Intensity imaging is depth discriminated; therefore it represents a cross-section through the observed sample. The cross-section thickness depends on a degree of coherence of the used waves and, if light microscopy is considered, it can be narrower than an optical cross-section obtained by a confocal microscope. The phase image corresponds to the difference of times of propagation through the object and the reference branches caused by the observed sample, it is quantitative and may be used for measuring a depth of reflective samples with accuracy in orders of thousandths of a wavelength, or, for example, in case of transmitted-light microscopic imaging, it can be used to weigh cells or to analyze an intracellular mass movement.