Liquid Crystal Pre-Tilt Angle Control for Equal Diffraction Efficiency
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Solution Overview
Problem
Controllable diffraction devices for light modulators face challenges in achieving equal diffraction efficiency in opposite spatial directions due to domain formation and smoothing effects, which reduce the optical performance and angular deflection range.
Innovation Solution
The solution involves pre-orienting liquid crystals near the alignment layer with a controlled pre-tilt angle to ensure equal saw-tooth refractive index distributions in opposite directions, using a combination of polar and azimuthal pre-tilt angles to minimize smoothing effects and enhance diffraction efficiency, and employing a method to switch azimuthal pre-tilt angles for variable diffraction efficiency adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If liquid crystals are oriented by surface alignment dominated by interactions between the alignment layer and the liquid crystals, then the LC molecules are oriented at a specific angle to the substrates, but domain formation occurs leading to disclinations that negatively influence optical performance
Solution Approach 1:
The patent introduces different pre-tilt angles in different regions of the liquid crystal layer. Specifically, LC molecules close to the alignment layer are pre-oriented by a first pre-tilt angle, while LC molecules in the bulk are oriented by a second pre-tilt angle. This local differentiation prevents domain formation and disclinations while maintaining precise orientation control, thereby resolving the contradiction between manufacturing precision and optical performance reliability.
2Reliability
If LC molecules are pre-oriented by a pre-tilt angle to prevent domain formation, then optical performance is improved, but diffraction efficiency in opposite spatial directions becomes unequal
Solution Approach 1:
The patent deliberately introduces asymmetry through different pre-tilt angles for different LC molecule regions, then compensates for it by applying specific voltage patterns to the electrodes. The first and second pre-tilt angles are designed to create asymmetric orientation that, when combined with the electric field distribution, produces symmetric diffraction efficiency in opposite directions. This resolves the contradiction by using controlled asymmetry as a means to achieve the desired symmetry in optical output.
3Productivity
If a saw-tooth shaped refractive index distribution is realized by applying different electric voltages to neighbouring electrodes, then light diffraction is achieved, but smoothing effects reduce the sharpness and diffraction efficiency
Solution Approach 1:
The patent changes the parameter of pre-tilt angle for liquid crystal molecules at different positions within the liquid crystal layer. By setting LC molecules close to the alignment layer with a first pre-tilt angle and bulk LC molecules with a second pre-tilt angle, the patent modifies the physical state parameters of the LC material to reduce smoothing effects. This enhances the sharpness of the saw-tooth refractive index distribution while maintaining the light diffraction capability, resolving the contradiction between productivity and manufacturing precision.
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 approach results in improved diffraction efficiency and sharpness for both left/right and up/down directions, enabling effective holographic displays with symmetrical tracking capabilities and enhanced optical performance.
Implementation Method 1
surface alignment dominated by interactions between the alignment layer and the liquid crystals
Implementation Method 2
the LC molecules in a LC device are oriented in the absence of an electrical field by an angle, which is typically in the range of 3° to 8°, to the substrates and to the electrodes on these substrates due to surface alignment
Implementation Method 3
LC molecules with a positive dielectric anisotropy are used for this mode. If the field is switched on, a force acts on the LC molecules to orient them parallel to the field
Implementation Method 4
an electric field is generated between two substrates of the diffraction device, which influences the orientation of liquid crystals arranged between the substrates
Implementation Method 5
The phase and/or the amplitude of a light wave field, which is substantially collimated, can be varied by means of the light modulator
Implementation Method 6
the light wave field varied by the (spatial) light modulator can be diffracted in a variable and predetermined manner by the diffraction device having the variable diffracting structure
Implementation Method 7
an electric field is generated between two substrates of the diffraction device, which influences the orientation of liquid crystals arranged between the substrates such that a saw-tooth shaped phase profile is obtained providing a saw-tooth shaped refractive index distribution
Data Source
AI summary
The present invention relates to a controllable diffraction device for a light modulator device. The controllable diffraction device comprises at least two substrates, at least one electrode on each of said substrates facing each other, and liquid crystals forming at least one liquid crystal layer arranged between said electrodes on said substrates. The orientation of the liquid crystals is controllable by a voltage supplied to the electrodes. The liquid crystal layer is provided on at least one alignment layer arranged on at least one electrode on said substrates. The liquid crystals close to the alignment layer are pre-oriented by at least one pre-tilt angle relative to the alignment layer such that the resulting light diffraction in opposite spatial directions is approximately equal.