Spatial Light Modulator Layout for Fast Phase-Only Holography
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Solution Overview
Problem
Existing spatial light modulators face challenges in achieving high switching speed and resolution due to the limitations of liquid crystal thickness and birefringence, leading to distorted phase modulation and pixel crosstalk.
Innovation Solution
A projector design utilizing a spatial light modulator with liquid crystals rotatable between two directions, allowing for oblique incidence and structured illumination, which minimizes liquid crystal thickness and enables full birefringence access, thereby enhancing switching speed and reducing pixel crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the liquid crystal layer is increased to provide full 2π phase retardation, then the phase modulation range is improved, but the switching speed decreases
Solution Approach 1:
The patent changes the optical parameters by using oblique incidence geometry and optimizing the relationship between liquid crystal thickness, birefringence, and incidence angle. This allows achieving full 2π phase modulation with thinner liquid crystal layers, thereby improving switching speed while maintaining phase modulation range.
Solution Approach 2:
The patent employs dynamic control of liquid crystal orientation through electric fields, allowing the liquid crystal molecules to rotate between different orientations. This dynamic response enables fast switching between different phase states without requiring thick liquid crystal layers.
2Measurement precision
If the linear dimension of each pixel is reduced to increase resolution, then the resolution is improved, but fringing electric fields at the edges distort the phase modulation
Solution Approach 1:
The patent applies different characteristics to different regions by optimizing the liquid crystal layer thickness and electrode design specifically for small pixel dimensions. The local optimization of electrical field distribution and liquid crystal alignment compensates for fringing effects at pixel edges, maintaining uniform phase modulation even in sub-10-micron pixels.
3Speed
If higher birefringence liquid crystals are used to increase switching speed, then the switching speed is improved, but the access to full birefringence is limited by conventional normal incidence illumination
Solution Approach 1:
The patent transitions from conventional normal incidence (one-dimensional illumination) to oblique incidence geometry, adding angular dimensionality to the light interaction with liquid crystals. This dimensional change enables accessing the full birefringence range of the liquid crystal material, allowing accurate 2π phase modulation while using thin layers for fast switching.
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 achieves phase-only modulation with increased switching speed and reduced pixel crosstalk, enabling high-quality holographic projections.
Implementation Method 1
Liquid crystal on silicon, 'LCoS', spatial light modulators exploit the birefringence of liquid crystals to provide controllable phase modulation
Implementation Method 2
The light source is arranged to illuminate the array of pixels with polarised light such that the light is spatially-modulated in accordance with the phase pattern
Implementation Method 3
Document WO 2019/048867 A1 describes a holographic projector using a reflective liquid crystal spatial modulator
Data Source
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AI summary
There is disclosed a projector arranged to project a light pattern. The projector comprises a spatial light modulator and a light source. The spatial light modulator has an array of pixels arranged to display a phase pattern. The array of pixels may be a substantially planar array of pixels. Each pixel comprises liquid crystals having a director rotatable in a plane of rotation between a first direction and a second direction. The light source is arranged to illuminate the array of pixels with polarised light such that the light is spatially-modulated in accordance with the phase pattern to form the light pattern. It may be said that the light pattern corresponds to the phase pattern. The angle of incidence of the light on the array of pixels is greater than zero and the light is s-polarised. The first direction is parallel to the polarisation direction of the light. The second direction is in the plane of incidence.