Angle Diversity Speckle Reduction in Laser Spot Displays
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Solution Overview
Problem
Rastered or flying spot displays suffer from speckle noise due to the coherence of laser light, which degrades image quality, and existing methods to reduce speckle noise either compromise display resolution or are not applicable due to the short duration of light exposure on the screen.
Innovation Solution
The implementation of angle diversity by dividing a central light beam into sub-beams with decaying intensity and focusing them to converge at different angles on the display screen, using a double-sided mirror with a partially reflective front surface and a near-perfectly reflective parabolic rear surface, increases angular diversity and decorrelates speckle patterns without degrading resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If time averaging of multiple speckle patterns is used to reduce speckle noise, then speckle noise is decreased, but this method cannot be applied in rastered or flying spot displays because the light beam is only present at any given spot on the screen for a very short period of time
Solution Approach 1:
The patent divides the single laser beam into multiple spatially separated sub-beams using a diffractive optical element. This segmentation creates multiple independent speckle patterns simultaneously, allowing the system to achieve speckle reduction without time averaging by having multiple patterns present at once rather than sequentially over time.
Solution Approach 2:
The patent transitions from temporal averaging (averaging over time) to spatial averaging (averaging across multiple simultaneous speckle patterns in space). By using a diffractive optical element to create multiple sub-beams at different positions, the system achieves speckle reduction through spatial diversity rather than temporal accumulation, making it applicable to fast scanning displays.
2Object-affected harmful factors
If the mode of the lasers is altered to reduce speckle noise, then speckle noise is decreased, but altering the single-mode nature of the laser would generally result in an unacceptable loss of display resolution
Solution Approach 1:
Instead of altering the laser mode, the patent segments the single-mode laser beam into multiple sub-beams using a diffractive optical element. This allows the system to maintain the high coherence and resolution benefits of single-mode lasers while creating multiple independent speckle patterns through spatial segmentation, thereby reducing speckle noise without sacrificing resolution.
Solution Approach 2:
The patent introduces a diffractive optical element as an intermediary component between the laser source and the display screen. This intermediary divides the laser beam into multiple sub-beams, creating spatial diversity and uncorrelated speckle patterns without requiring changes to the laser itself or compromising the beam quality and resolution.
3Object-affected harmful factors
If angle diversity is used to reduce speckle noise by dividing a central light beam into sub-beams, then speckle noise is reduced and image quality is improved, but the depth of field and image focus may be reduced
Solution Approach 1:
The patent uses a diffractive optical element with specific geometric parameters (groove spacing, depth, and orientation) to control the angular separation of sub-beams. By optimizing these parameters, the system achieves sufficient angle diversity for speckle reduction while maintaining the focus quality and depth of field required for clear image display.
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 effectively reduces speckle noise by increasing the number of uncorrelated speckle patterns, leading to improved image quality without compromising resolution, although it may reduce the depth of field and image focus.
Implementation Method 1
a double-sided mirror configured to divide and separate the rasterized light beam into a plurality of beamlets
Implementation Method 2
The double-sided mirror also focuses the beamlets to converge with the first sub-beam on the display screen at different angles to the display screen
Implementation Method 3
light waves scattered by nearby points on the screen often interfere at the observer location (such as a human eye or camera). This interference generally introduces an amplitude or brightness noise in the perceived light, commonly described as 'speckle'
Data Source
AI summary
Improvement of speckling noise is discussed in which a central light beam received at a double-sided mirror is divided into a plurality of sub-beams. An intensity of these sub-beams decays from a second sub-beam to a last sub-beam of the plurality. Each sub-beam is also separated at the double-sided mirror by at least a first length, such as the coherence length or intrinsic divergence, and reflected toward a display screen. The configuration of the double-sided mirror focuses the sub-beams to converge with a first sub-beam on the display screen at different angles. The decreasing intensity and different angles of impact with the screen decreases the spatial coherence of the display light. The angle diversity and combination of multiple sub-beams having different intensities offers a non-time-averaging means to decrease speckle noise without downgrading the beam quality or display resolution.