Heterodyne Digital Holography Imaging Without Acousto-Optic Modulators
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Solution Overview
Problem
Heterodyne digital holography image acquisition systems face challenges due to the complexity, cost, and size of acousto-optic modulators, which lead to high light attenuation and require powerful illumination sources, as well as limitations in signal-to-noise ratio and pixel saturation thresholds.
Innovation Solution
The implementation of an oversampling image sensor with a sigma-delta type analog-digital converter, which eliminates the need for multiple acousto-optic modulators and reduces the complexity of the system, allowing for higher light intensities and improved signal-to-noise ratios by oversampling the beat frequency, thereby simplifying and cost-reducing the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If acousto-optic modulators are used to shift beam frequencies, then heterodyne holography can be implemented, but the system complexity, cost, and size increase significantly
Solution Approach 1:
The patent extracts the frequency shifting function from complex acousto-optic modulators and relocates it to the digital domain through oversampling and digital signal processing. The photodiode detects the optical interference pattern, and the oversampled analog-to-digital converter performs the frequency shifting operation digitally, eliminating the need for acousto-optic modulators in the optical path.
Solution Approach 2:
The patent replaces the mechanical/optical frequency shifting mechanism (acousto-optic modulators) with an electrical/digital mechanism (oversampling analog-to-digital converter and digital signal processing). This substitution moves the frequency shifting operation from the optical domain to the digital domain, simplifying the overall system.
2Speed
If multiple acousto-optic modulators are used for frequency shifting, then proper beat frequency can be achieved, but light attenuation increases and powerful illumination sources are required
Solution Approach 1:
The patent extracts the frequency shifting operation from the optical path and performs it digitally. By removing acousto-optic modulators from the optical path, light attenuation is eliminated, and no additional powerful illumination sources are needed to compensate for the lost light intensity.
3Device complexity
If conventional sampling is used at the photodiode output, then the system is simpler, but the signal-to-noise ratio deteriorates and pixel saturation occurs more easily
Solution Approach 1:
The patent applies oversampling, which is excessive sampling beyond the minimum Nyquist rate. By sampling at a rate significantly higher than twice the maximum signal frequency, the system achieves better signal-to-noise ratio through noise averaging and improved digital signal processing capabilities, while the excess samples are processed efficiently through decimation.
4Device complexity
If the system uses standard image sensors, then the design is simpler, but the dynamic range is limited and pixel saturation occurs easily
Solution Approach 1:
The patent uses oversampling to capture more signal information than a single standard pixel measurement would provide. By taking multiple samples per optical cycle and processing them digitally, the system effectively extends the dynamic range beyond what a single standard pixel could measure, preventing saturation while maintaining compatibility with standard image sensor technology.
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 results in a more compact, cost-effective, and efficient image acquisition system with improved signal-to-noise ratios and reduced risk of pixel saturation, enabling higher light intensities and enhanced image acquisition capabilities.
Implementation Method 1
an image sensor having at least one photodiode coupled to an analog-digital converter
Implementation Method 2
The usual holography techniques are based on the use of interference produced by the superposition of two coherent light beams
Implementation Method 3
Heterodyne holography is a holography technique in which the object beam and the reference beam are slightly shifted in frequency
Data Source
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AI summary
The invention relates to a system (400) for acquiring images by means of heterodyne digital holography, comprising an image sensor (409) having at least one photodiode coupled to an oversampling analog-digital converter.