Holographic Grating Recording via Scanning Beam Interference
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Solution Overview
Problem
Existing methods for recording large-sized, highly homogeneous holographic diffraction gratings face challenges such as the need for large and expensive optics, non-uniform exposure dosage, parasitic diffraction patterns, and difficulties in beam expansion without truncation, which result in reduced performance and usability.
Innovation Solution
A method involving two-dimensional scanning of an input beam into two output beams that interfere on a recording medium, allowing for smaller beam sizes and mitigating distortions and inhomogeneities, with beam power modulation for controlled diffraction efficiency profiling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If large-sized beams are used for recording large holograms, then the coverage area is improved, but the exposure dosage uniformity deteriorates
Solution Approach 1:
The patent segments the large hologram recording area into multiple smaller sub-areas, each illuminated by a well-collimated beam. The beam is scanned across different positions to cover the entire large area, ensuring uniform exposure dosage in each sub-area while maintaining overall large-area coverage.
2Area of stationary object
If beam expansion is increased to improve coverage, then the recording area is improved, but parasitic diffraction patterns increase
Solution Approach 1:
The patent employs dynamic beam scanning instead of static large-beam illumination. The beam position is continuously varied across the recording medium, which prevents the formation of stable parasitic diffraction patterns while still achieving large-area coverage through the scanning motion.
3Area of stationary object
If beam expansion is applied to increase coverage, then the recording area is improved, but beam truncation increases
Solution Approach 1:
The patent segments the large recording area into multiple smaller regions that are sequentially illuminated by a compact beam during scanning. This avoids the need for large beam expansion that would cause truncation at apertures, while still achieving comprehensive coverage of the entire large area through the scanning process.
4Manufacturing precision
If spatial filtering is applied to reduce distortions, then beam quality is improved, but loss of usable power increases
Solution Approach 1:
The patent applies spatial filtering only partially - using simple aperture stops rather than complex spatial filter systems. This provides sufficient beam quality improvement for the application while minimizing power loss, balancing the trade-off between wavefront quality and usable power.
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 enables the recording of large-sized, high-homogeneous gratings with improved uniformity and reduced parasitic patterns, maintaining high diffraction efficiency and grating quality even with non-planar or distorted beam wavefronts.
Implementation Method 1
produce a diffraction grating in the recording medium by interference between the two output beams of light
Implementation Method 2
splitting the scanned input beam of light into two output beams of light, each one of the two output beams of light passing along a different path
Data Source
AI summary
A method and apparatus for scanning an input beam of light in a two dimensional pattern; splitting the scanned input beam of light into two output beams of light, each one of the two output beams of light passing along a different path to a common region in a recording medium, such region scanning the recording medium during the scanning of the input beam of light to produce a diffraction grating in the recording medium by interference between the two output beams of light.