Liquid Crystal Shutter for Laser Projector Calibration
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Solution Overview
Problem
Laser light sources in projectors face challenges in accurately producing desired optical power levels due to variations over time and temperature, leading to potential image artifacts from calibration pulses escaping into the user's field of view.
Innovation Solution
A calibration mechanism is implemented using a shutter mechanism to prevent light from reaching the image plane during calibration, allowing for higher power calibration pulses and longer calibration periods without distorting the projected image, utilizing photodetectors to measure optical power and adjust drive current values accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration pulses are used to measure laser light source output, then measurement precision is improved, but image artifacts occur when light escapes into the user's field of view
Solution Approach 1:
The patent divides the optical path into two separate paths: a calibration path for measurement and a projection path for image display. The beam splitter separates calibration light from projection light, allowing calibration pulses to be measured without contaminating the user's field of view with artifact-causing light
Solution Approach 2:
The beam splitter acts as an intermediary element that redirects calibration light to a photodetector while allowing projection light to pass through to the image plane. This mediator enables simultaneous calibration measurement and artifact-free image projection
2Measurement precision
If higher power calibration pulses are used, then measurement precision is improved, but image distortion occurs when light reaches the image plane
Solution Approach 1:
The optical system is segmented into separate calibration and projection channels. High-power calibration pulses can be sent through the calibration path to the photodetector without affecting the projection path, enabling accurate measurement without image distortion
Solution Approach 2:
The beam splitter and shutter work together as intermediaries to isolate high-power calibration pulses from the image plane. The shutter blocks calibration light during projection, while the beam splitter directs it to the photodetector, allowing high-power calibration without compromising image quality
3Productivity
If calibration is performed during normal operation, then productivity is improved, but light from calibration pulses may escape into the user's field of view
Solution Approach 1:
The shutter operates periodically to block calibration light during projection intervals while allowing calibration pulses during designated time windows. This periodic action enables continuous calibration during normal operation without causing artifacts when the shutter is closed
Solution Approach 2:
The time domain is segmented into calibration intervals and projection intervals. During calibration intervals, the shutter blocks the projection path while allowing calibration pulses; during projection intervals, the shutter opens to allow image display. This temporal segmentation enables continuous operation without artifacts
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 solution ensures accurate optical power control, minimizing image artifacts and maintaining image quality by compensating for variations in laser light source characteristics in real-time, even during normal operation.
Implementation Method 1
In one embodiment, the shutter mechanism includes a liquid crystal shutter that is transmissive when no voltage is applied and reflective when a voltage is applied
Implementation Method 2
A photodetector measures the optical power produced in response to the calibration pulse
Data Source
AI summary
A projection apparatus includes a shutter mechanism to prevent light from reaching an image plane during calibration of light sources. The shutter mechanism may include liquid crystal material that exhibits an effective index of refraction that varies with applied voltage. During calibration, a light beam is shuttered, light sources are driven by calibration data, and optical power is measured.