Laser Speckle Reduction in Wearable Display Apparatus
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Solution Overview
Problem
Wearable display apparatuses, such as head-mounted displays, suffer from image quality deterioration due to speckle noise generated by the exit pupil expander, which scatters light and interferes with the observer's retinal image.
Innovation Solution
Incorporating a high-frequency wave superimposing circuit to reduce coherence in the laser light source, using a multi-mode oscillation state, and employing a temperature adjustment device to shift the oscillation wavelength of laser sources, along with an array of laser light sources emitting different wavelengths, to minimize speckle noise and maintain image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an exit pupil expander is used to expand the luminous flux diameter and expand the range of pupil position for image observation, then the adaptability and ease of operation are improved, but the exit pupil expander becomes a scattering source that generates speckle noise, deteriorating image quality
Solution Approach 1:
The patent changes the wavelength parameter of the laser light by using multiple laser light sources with different wavelengths (e.g., 532nm and 538nm) or by shifting the wavelength through temperature adjustment. This wavelength diversification causes the speckle patterns generated by the exit pupil expander to differ in spatial distribution, and when these patterns are superimposed on the retina, they average out to reduce the overall speckle noise while maintaining the expanded pupil range functionality
2Illumination intensity
If a laser light source is used to generate image light, then the brightness and coherence are improved, but the high coherence causes the exit pupil expander to generate speckle noise
Solution Approach 1:
The patent changes the wavelength parameter by employing multiple laser light sources with different wavelengths or by wavelength-shifting a single laser source through temperature control. This creates multiple sets of speckle patterns with different spatial distributions that, when combined, reduce the visibility of speckle noise while preserving the high brightness characteristic of laser light
Solution Approach 2:
The patent creates a composite light source system that combines multiple laser light sources with different wavelengths. This composite approach maintains the coherence and brightness benefits of individual laser sources while the wavelength diversity causes the speckle patterns to differ, resulting in reduced overall speckle noise when the patterns are superimposed
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 proposed solution effectively reduces speckle noise, enhancing image quality and expanding the exit pupil's size, allowing for a wider range of clear, high-quality image observation without the interference of speckle patterns.
Implementation Method 1
a laser light source unit configured to emit image light composed of laser light
Implementation Method 2
a MEMS mirror configured to reflect laser light emitted from the laser light source unit
Implementation Method 3
in the process where the exit pupil expander expands an angular distribution of the image light, the exit pupil expander as is becomes a scattering source to generate a speckle noise
Implementation Method 4
a first surface relief-type diffraction grating provided at a light incidence portion of the light-guiding plate and on which the image light passing through the exit pupil expander is incident and enters the light-guiding plate, and a second surface relief-type diffraction grating provided at a light emission portion of the light-guiding plate and through which the image light propagating inside the light-guiding plate exits
Data Source
AI summary
A display apparatus includes an image light generating unit that includes a laser light source unit and a MEMS mirror configured to reflect laser light emitted from the laser light source unit, and that is configured to generate image light, an exit pupil expander configured to expand a luminous flux diameter of the image light from the image light generating unit, a light-guiding plate, a first surface relief-type diffraction grating provided at a light incidence portion of the light-guiding plate and on which the image light passing through the exit pupil expander is incident and enters the light-guiding plate, and a second surface relief-type diffraction grating provided at a light emission portion of the light-guiding plate and through which the image light propagating inside the light-guiding plate exits, in which the image light generating unit includes a speckle noise reduction section configured to reduce speckle noise in the image light.