Moving Optical Diffuser Speckle Reduction in Laser Projectors
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Solution Overview
Problem
Laser image projectors face the challenge of speckle reduction, which degrades image sharpness, and existing solutions like time-varying diffusers are too large for small hand-held devices.
Innovation Solution
Incorporating an optical diffuser that introduces angular spread and moves relative to the spatial light modulator, altering the relative optical phases of light rays at each pixel to reduce speckle, with the diffuser's motion frequency exceeding the flicker fusion rate to minimize coherence and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a time-varying diffuser is used to reduce speckle, then image sharpness is improved, but device size increases making it unsuitable for hand-held devices
Solution Approach 1:
The patent employs a moving diffuser that dynamically changes the optical path during operation. The diffuser is positioned to move across the optical path between the laser source and the spatial light modulator, creating time-varying phase modulation that reduces speckle without requiring large device volume.
Solution Approach 2:
The invention introduces motion in a temporal dimension to solve a spatial problem. By making the diffuser move along the optical axis (z-direction) rather than using a large lateral displacement mechanism, the patent achieves speckle reduction while maintaining compact device dimensions suitable for hand-held applications.
2Object-affected harmful factors
If the diffuser moves at high frequency to reduce speckle, then image quality is improved, but device complexity increases
Solution Approach 1:
The patent implements periodic motion of the diffuser at frequencies above the flicker fusion threshold (typically >60 Hz). This periodic movement creates sufficient phase variation to reduce speckle while the human eye perceives a stable image, eliminating the need for complex real-time control systems.
Solution Approach 2:
The system leverages the natural persistence of human vision as a feedback mechanism. By operating the diffuser at frequencies above the flicker fusion rate, the device automatically ensures speckle reduction without requiring additional sensors or complex control algorithms to monitor image quality in real-time.
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
The solution effectively reduces speckle in projected images, enhancing image sharpness and coherence, suitable for compact hand-held devices by leveraging high-frequency motion of the optical diffuser.
Implementation Method 1
an optical diffuser located along an optical path between a laser and the SLM and adapted to transmit light generated by the laser to produce said illumination light beam at the SLM so that, at each pixel of the plurality, the illumination light beam has light rays corresponding to a range of incident angles
Implementation Method 2
The optical device is adapted to move the illumination light beam across the SLM. At each pixel of the plurality, said motion of the illumination light beam changes relative optical phases of the light rays having different incident angles
Implementation Method 3
The optical diffuser is adapted to introduce one angular spread into light transmitted therethrough along a first direction and a different angular spread into said transmitted light along a different second direction
Data Source
AI summary
According to one embodiment, an image projector has a spatial light modulator (SLM) adapted to modulate illumination from a laser with a spatial pattern such that the modulated illumination projects an image on a viewing screen. The image projector further has an optical diffuser located on an optical path between the laser and the SLM. The laser is adapted to illuminate the SLM through the optical diffuser to create an illuminated area at the SLM. The optical diffuser is adapted to introduce an angular spread into the light transmitted therethrough. The image projector is adapted to move the illuminated area with respect to the SLM to mitigate speckle in the projected image.