Projection Device Speckle Reduction via Scanning Diffuser
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Solution Overview
Problem
Existing projection devices using coherent light sources face issues with speckle occurrence, which are not effectively suppressed by current techniques, leading to visible brightness irregularities and increased mechanical complexity and power consumption.
Innovation Solution
A projection device design incorporating a light diffusion element, such as a hologram recording medium, and a scan device that changes the propagation direction of coherent light beams to overlap and diffuse light uniformly on spatial light modulators, reducing speckle visibility and miniaturizing the optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a scattering plate is rotated to reduce speckles, then speckle visibility is reduced, but device complexity and power consumption increase
Solution Approach 1:
The patent replaces the mechanical rotation system with an optical solution using a diffuser plate positioned at the focal point of the projection optical system. The diffuser plate randomly scatters light without requiring mechanical movement, thereby eliminating motors, control systems, and mechanical complexity while maintaining speckle reduction effectiveness.
Solution Approach 2:
The diffuser plate acts as an intermediary element between the light source and the spatial light modulator. It introduces random phase variations to the coherent light beam, transforming the speckle pattern without requiring mechanical motion. This intermediary component achieves speckle reduction through passive optical scattering rather than active mechanical rotation.
2Illumination intensity
If high pressure mercury lamp is used as light source, then illumination is achieved, but lifecycle is short and replacement frequency increases
Solution Approach 1:
The patent changes the fundamental parameter of the light source from incoherent broadband emission (mercury lamp) to coherent narrowband emission (laser). This parameter change enables the use of a semiconductor laser with significantly longer operational lifetime while maintaining sufficient illumination intensity for projection display applications.
Solution Approach 2:
The patent replaces the expensive, short-lived high pressure mercury lamp with a cheaper, long-lived semiconductor laser diode. The laser diode's solid-state construction and lower operating temperatures enable extended operational life without requiring frequent replacements, reducing maintenance costs and system downtime.
3Adaptability or versatility
If dichiroic mirror is used to extract primary color components, then light beam separation is achieved, but apparatus size increases
Solution Approach 1:
The patent extracts and removes the bulky dichroic mirror component from the optical system. Instead of using dichroic mirrors to separate primary color components, the system uses a single laser source with wavelength-specific spatial light modulators, eliminating the need for complex beam separation optics and reducing overall apparatus volume.
Solution Approach 2:
The patent implements a universal approach where a single laser source serves multiple functions by sequentially illuminating different wavelength-specific spatial light modulators. This multi-functional approach eliminates the need for separate light paths and color separation optics, compacting the optical system while maintaining full-color display capability.
4Area of stationary object
If light beam is spread in illumination device, then illumination area is increased, but light intensity loss increases
Solution Approach 1:
The patent employs time-sequential illumination where the single laser beam periodically illuminates different spatial light modulators in succession. This periodic action allows the narrow laser beam to cover multiple display areas over time without requiring spatial spreading, thereby maintaining high light intensity while achieving comprehensive illumination coverage.
Solution Approach 2:
The patent introduces dynamic temporal multiplexing where the illumination beam is rapidly switched between different spatial light modulators. This dynamic approach creates the perception of simultaneous illumination across multiple areas while actually using a focused, high-intensity beam that moves through time, avoiding the energy losses associated with static beam spreading.
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 minimizes speckle visibility, maintains high light use efficiency, and simplifies the optical system, allowing for seamless multi-screen video display with reduced optical system size and power consumption.
Implementation Method 1
a light diffusion element, such as a hologram recording medium, and a scan device that changes the propagation direction of coherent light beams to overlap and diffuse light uniformly on spatial light modulators
Implementation Method 2
a scan device configured to change a propagation direction of the coherent light beam and allow the coherent light beam to scan the light diffusion element
Data Source
AI summary
Provided are a projection device and a projection-type video display device capable of displaying a plurality of videos, allowing speckles to be inconspicuous, and miniaturizing an optical system. A projection device includes an optical element including light diffusion elements capable of diffusing light, an irradiation device configured to irradiate the optical element with illumination light beams, each illumination light beam scanning the corresponding light diffusion element, spatial light modulators, each spatial light modulator being illuminated with illumination light beam which is incident from the irradiation device to each light diffusion element to be diffused, and projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen. The illumination light beam, which is incident to each position of each light diffusion element to be diffused, overlappedly illuminates on corresponding spatial light modulator.