Multi-Color Off-Axis Digital Holography for 3D Surface Profiling
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Solution Overview
Problem
Conventional multi-color digital holographic systems face challenges with phase wrapping and measurement speed due to the use of monochromatic light sources and CCDs, which restrict the height of samples and require multiple shots for different wavelengths, making the process complex and time-consuming.
Innovation Solution
A multi-color off-axis digital holographic system utilizing a light emitting diode (LED) capable of emitting red, green, and blue beams, combined with an interference object lens module and a color imaging device, performs zero-filling and reconstruction operations to obtain phase information, allowing for one-shot measurement of three-dimensional surface profiles without phase wrapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a monochromatic light source is used for illumination, then the system structure is simple, but the measurement range is restricted by phase wrapping when sample height exceeds half the wavelength
Solution Approach 1:
The patent changes the wavelength parameter by using a multi-color LED light source that emits multiple wavelengths (red, green, blue) simultaneously. This allows the system to overcome phase wrapping limitations by having multiple holograms at different wavelengths, enabling measurement of samples with heights exceeding half the wavelength of any single color while maintaining relatively simple system structure.
2Device complexity
If a monochromatic CCD is used to capture holograms, then the imaging process is simple, but three separate shots are required to obtain holograms at different wavelengths, making the process time-consuming
Solution Approach 1:
The patent merges multiple wavelength hologram capture into a single shot by using a multi-color LED that emits multiple wavelengths simultaneously and a color CCD that can capture all wavelengths in one exposure. This eliminates the need for three separate shots required when using a monochromatic CCD, significantly improving measurement speed while maintaining imaging simplicity.
Solution Approach 2:
The color CCD is designed to serve multiple functions by capturing holograms at different wavelengths (red, green, blue) simultaneously in a single shot. This multi-functional capability allows the system to obtain multiple holograms needed for eliminating phase wrapping effects without requiring multiple separate imaging processes, thus improving productivity.
3Measurement precision
If the angle between reference beam and object beam is increased to separate virtual image and DC term, then reconstruction accuracy improves, but the included angle is limited by the pixel size of the CCD camera
Solution Approach 1:
The patent changes the wavelength parameter to resolve the angle limitation issue. By using multiple wavelengths from the multi-color LED, the system can achieve better separation of virtual image and DC term through wavelength-dependent phase variations, effectively overcoming the pixel size limitation that would otherwise constrain the usable angle between beams.
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
Enables quick and efficient capture of holograms with multiple wavelengths, preventing phase wrapping and improving measurement speed, while generating accurate three-dimensional surface profiles with synthetic wavelengths, thus overcoming height limitations and reconstruction errors.
Implementation Method 1
a light emitting diode capable of emitting a red, a green and a blue beams as its light source
Implementation Method 2
forming a hologram on a surface of the color imaging device by holographic interference
Implementation Method 3
digital processing of the photoelectric signals from a CCD (Charge Coupled Device) array
Implementation Method 4
the reconstructed three dimensional holographic image is composed of a real image, a virtual image and a so-called DC term
Data Source
AI summary
A multi-color off-axis digital holographic system and the imaging method thereof are disclosed. The multi-color off-axis digital holographic system comprises: a plurality of light emitting diodes, for provide a red (R) beam, a green (G) beam and a blue (B) beam; an interference object lens module, for receiving the R, G, and B beams to generate a beam containing an interference signal; a color imaging device, for receiving the beam containing the interference signal and thus forming a hologram on a surface of the color imaging device by holographic interference while registering the hologram; and a processing device, for receiving the registered hologram form the color imaging device; wherein the processing device perform a zero-filling and reconstructing operations upon the received hologram to obtain phase information of the R, G and B beams. With the aforesaid system, a three-dimensional surface profile with respect to a RG synthetic wavelength is obtained according to a calculation using the phase information of the R and G beams as well as the wavelengths thereof, and similarly, a three-dimensional surface profile with respect to a GB synthetic wavelength is obtained according to a calculation using the phase information of the G and B beams as well as the wavelengths thereof. Thereafter, by performing a calculation using the RG synthetic wavelength and its phase as well as the GB synthetic wavelength and its phase, an overall three-dimensional surface profile with respect to a complete synthetic wavelength is obtained.