Off-axis interferometer with diffraction grating for low-noise holography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Prior art interferometers require highly coherent light sources, which lead to coherent noise and high costs, and are limited by the need for sequential image recording in on-line configurations, while off-axis configurations with partially coherent light sources face challenges in maintaining interference and recording full complex amplitude information.
Innovation Solution
An off-axis digital holographic microscope using a diffraction grating to split incident light into diffracted and non-diffracted beams, allowing interference fringes to be recorded with partially coherent light sources, such as LEDs, without disrupting temporal coherence, enabling fast and low-noise color digital holographic recording.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly coherent light sources (lasers) are used in interferometers, then interference fringes can be observed, but coherent noise (speckle field) appears and costs increase
Solution Approach 1:
The patent changes the coherence parameter of the light source from highly coherent (laser) to partially coherent (LED), thereby eliminating coherent noise while maintaining the ability to observe interference fringes through the specific optical path configuration
2Measurement precision
If on-line configuration is used with small angle between beams, then sequential recording is required, but acquisition speed is limited by camera frame rate
Solution Approach 1:
The patent introduces an angular dimension (off-axis configuration) between the reference and object beams, which allows the complex amplitude to be encoded in the spatial frequency domain, enabling single-shot acquisition instead of sequential recording
3Loss of information
If off-axis configuration is used with partially coherent light, then full complex amplitude information can be recorded, but path length differences disrupt temporal coherence
Solution Approach 1:
The patent optimizes the angular separation parameter between beams and controls the optical path difference to remain within the coherence length of partially coherent light, enabling full complex amplitude recording without losing temporal coherence
Solution Approach 2:
The patent replaces the need for mechanical phase shifting (as in on-line configurations) with an optical path configuration that encodes phase information spatially, allowing single-shot acquisition with partially coherent light
4Productivity
If off-axis configuration is used, then single-shot recording is enabled, but highly coherent light is compulsory to maintain interference
Solution Approach 1:
The patent simultaneously optimizes multiple parameters: angular separation between beams, optical path difference, and spatial filtering, to enable off-axis configuration with partially coherent light sources, achieving both fast single-shot acquisition and elimination of coherent noise
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 the use of low-cost, partially coherent light sources for off-axis digital holographic microscopy, allowing simultaneous recording of full-color holograms without coherent noise and facilitating fast acquisition of dynamic events.
Implementation Method 1
splits an incident light beam into a non-diffracted light beam and a diffracted light beam
Implementation Method 2
the diffracted and the non-diffracted light beams interfere with each other, forming an interference pattern
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention is related to an off-axis interferometer able to work with partially coherent light sources. This results in the capability to implement fast colour digital holographic recording at a very low noise levels. The interferometer comprises a grating (G) optically conjugated with the recording plane (CCD) for producing diffracted light beams, and an optical stop (8) for stopping excess diffracted light beams.