Liquid Crystal Polarization Gratings for Broadband Scene Projection
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Solution Overview
Problem
Existing infrared scene generation technologies, such as resistor arrays, IR LEDs, and LCoS devices, are limited by high cost, slow operation frequency, and narrow spectral bandwidth, making them unsuitable for high-resolution, broadband applications.
Innovation Solution
A spatial light modulator using arrays of cycloidal diffractive waveplates (CDWs) or liquid crystal polarization gratings (LCPGs) for broadband achromatic operation, capable of high-speed and fine-resolution scene projection, with improved heat dissipation and reduced fabrication costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If resistor arrays are used for infrared scene generation, then the device can produce infrared imagery, but the operation frequency is slow due to heating and cooling limitations
Solution Approach 1:
The patent replaces the thermal-mechanical resistor array system with an electro-optic liquid crystal system. Instead of heating and cooling resistors to generate infrared radiation, the invention uses liquid crystal molecules that can be electrically controlled to modulate infrared light transmission, enabling much faster response times without thermal inertia constraints
Solution Approach 2:
The patent changes the operating parameter from thermal control (resistor temperature) to electrical control (liquid crystal molecular orientation). By applying different voltages to the liquid crystal pixels, the infrared transmission can be rapidly switched between states, achieving high-speed operation limited only by the liquid crystal response time rather than thermal time constants
2Adaptability or versatility
If LCoS devices are used for infrared scene generation, then the device can provide viable spatial light modulation, but the spectral bandwidth is narrow and operation is limited to specific wavelengths
Solution Approach 1:
The patent designs the liquid crystal polarization grating system to be universally applicable across multiple spectral ranges. The liquid crystal molecules and alignment layers are configured to operate effectively from ultraviolet through visible to infrared wavelengths, allowing a single device structure to provide spatial light modulation across the entire electromagnetic spectrum rather than being limited to narrow infrared bands
Solution Approach 2:
The patent uses composite material structures including liquid crystal layers combined with specific alignment layers and substrate materials that are optimized for broadband performance. This composite approach enables the device to maintain liquid crystal ordering and optical anisotropy across a wide spectral range, achieving reliable operation from UV to infrared wavelengths simultaneously
3Ease of manufacture
If IR LEDs are used for infrared scene generation, then the device can provide infrared light emission, but the fabrication cost is high
Solution Approach 1:
The patent replaces expensive IR LED components with relatively inexpensive liquid crystal display technologies that can be manufactured using standard LCD fabrication processes. The liquid crystal pixels can be produced at lower cost through established liquid crystal on glass (LCOS) or transmissive LCD manufacturing techniques, making infrared scene generation more cost-effective
Solution Approach 2:
The patent uses liquid crystal pixels to create optical copies or modulations of infrared light patterns rather than generating light directly through expensive IR LED emission. The liquid crystal layer acts as a spatial light modulator that can replicate and control infrared scenes at lower cost by modulating transmitted infrared radiation rather than requiring direct infrared light emission from each pixel
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 CDW-based spatial light modulator achieves high-speed, broadband infrared scene generation with superior resolution and cost-effectiveness compared to existing technologies, applicable across various spectral ranges including ultraviolet, visible, near-infrared, and infrared.
Implementation Method 1
each of the plurality of pixels includes a liquid crystal layer disposed between two substrates
Implementation Method 2
one or more of the two substrates is coated with a photo-alignment layer adjacent to the liquid crystal layer
Implementation Method 3
a grating period of the pixel selected such that, when the voltage is applied to the pixel and light is passed therethrough, optical energy from the light in plus and minus first orders is deflected toward sides of the pixel
Implementation Method 4
coated with transparent electrodes. At least a pixel in the plurality of pixels may be switchable by applying a voltage thereto
Data Source
AI summary
A projector includes a beam homogenizer receiving light from a light source and creating a predetermined illumination, and a spatial light modulator including grating stages to receive the predetermined illumination. Each grating stage may include a plurality of pixels where corresponding pixels in the grating stages are aligned with one another. Each of the pixels may include a liquid crystal layer disposed between two substrates, where a pixel is switchable by applying a voltage thereto, with a grating period of the pixel selected such that, when the voltage is applied to the pixel and light is passed therethrough, optical energy from the light in plus and minus first orders is deflected toward sides of the pixel and optical energy from a zero order of the light is allowed to pass through the pixel, with a polarization state of the light maintained through the pixel.