SLM Roof Mirror Layout for Zeroth-Order Diffraction Blocking
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Solution Overview
Problem
Existing methods for blocking zeroth order diffraction in phase-only spatial light modulators either block the central area of the image plane, reducing the field of view, or fail to effectively eliminate the zeroth order diffraction beam, leading to a bright spot at the image center.
Innovation Solution
An opto-mechanical system using a spatial light modulator with a computer-generated hologram and a roof mirror configuration, where mirrors are positioned to reflect laser beam portions in different directions, combined by a tube and objective lens, and pre-compensated with affine transforms to maintain image integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a zeroth order blocker is placed at the center of the focal plane to block the zeroth order diffraction, then the zeroth order diffraction is blocked, but the central area of the image plane becomes non-addressable
Solution Approach 1:
The patent extracts the zeroth order diffraction beam from the optical path by using a beam splitter to separate it from the main beam path. The beam splitter directs the zeroth order beam to a separate path where it can be blocked by a zeroth order blocker without interfering with the image formation in the focal plane, thus removing the harmful effect while preserving the addressable area.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary optical element between the spatial light modulator and the focal plane. This intermediary device separates the zeroth order diffraction beam from the image-forming beams, allowing independent handling of the zeroth order component while maintaining the integrity of the image plane addressable area.
2Object-generated harmful factors
If only half of the field of view of the holographic phase mask is used to avoid center residual zeroth order diffraction, then the zeroth order diffraction is avoided, but half of the field of view of the SLM is lost
Solution Approach 1:
The patent extracts the zeroth order diffraction component from the optical path using a beam splitter, allowing the full field of view to be utilized. By separating the zeroth order beam before it reaches the focal plane, the system can use the complete SLM aperture without needing to discard half of the field of view to avoid the zeroth order artifact.
3Object-generated harmful factors
If spherical phase shift is applied to beamlets in the holographic phase mask to shift the image plane away from the focal plane, then the zeroth order diffraction beam is defocused and appears dimmer, but the image plane is no longer at the focal plane
Solution Approach 1:
The patent extracts the zeroth order diffraction beam from the optical path using a beam splitter positioned at the focal plane. This allows the image plane to remain precisely at the focal plane without requiring spherical phase shifts, thereby maintaining both the suppression of zeroth order diffraction and the precision of image plane positioning.
Solution Approach 2:
The beam splitter acts as an intermediary that separates the zeroth order beam from the image-forming beams at the focal plane. This intermediary approach allows the image plane to remain at the precise focal plane position while still achieving zeroth order diffraction suppression, avoiding the need for spherical phase shifts that would compromise positioning precision.
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
Effectively blocks zeroth order diffraction while maintaining the central area's addressability and utilizing the full field of view, resulting in a zeroth order dot-free image without dark regions.
Implementation Method 1
The wavefront modulation is based on diffraction of light. Since the liquid crystal SLM is pixelated in structure, in addition to the +/- first order diffraction, there is always non-negligible optical power in the residual zeroth order diffraction beam.
Implementation Method 2
a first mirror and a second mirror situated at the focal plane, an edge of the first mirror being adjacent to an edge of the second mirror, the first mirror being configured to reflect a first portion of the modulated laser beam in a first direction, and the second mirror being configured to reflect a second portion of the modulated laser beam in a second direction
Implementation Method 3
a tube lens and an objective lens configured to project the first and second portions into a combined image
Data Source
Figure 1~2
Figure 3(a)~3(d)
Figure 4~5
AI summary
An optical image generation system including: a spatial light modulator (SLM) configured to receive an input collimated laser beam and modulate the wavefront of the laser beam; one or more optical elements configured to project the modulated laser beam onto a focal plane; a first mirror and a second mirror situated at the focal plane, an edge of the first mirror being adjacent to an edge of the second mirror, the first mirror reflects a first portion of the modulated laser beam in a first direction, the second mirror reflects a second portion of the modulated laser beam in a second direction; and an objective lens projects the first and second portions into a combined image; wherein the zeroth order diffraction is block or suppressed at the center of the focal plane.