Pancharatnam Phase Beam Steering with Vertical LC Alignment
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Solution Overview
Problem
Existing tunable beam steering devices face challenges with slow switching times and low efficiency, particularly at large steering angles, due to mechanical or in-plane electric field approaches.
Innovation Solution
A Pancharatnam phase device with vertical alignment of liquid crystal directors and a novel two-step voltage scheme that combines localized in-plane electric fields and diagonal bulk fields to create a linear spiral director configuration, enhancing steering efficiency and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If in-plane electric field approach is used to achieve fast switching speed, then switching speed is improved, but efficiency is degraded at large steering angles due to trapped pi wall defects
Solution Approach 1:
The patent inverts the conventional approach by using vertical surface alignment instead of planar alignment, and applying out-of-plane electric fields instead of in-plane fields. This inversion eliminates the topological defects (trapped pi walls) that cause efficiency loss while maintaining fast switching speeds through the high restoring force of the vertical alignment configuration.
Solution Approach 2:
The patent changes the alignment parameter from planar to vertical, and modifies the electric field direction from in-plane to out-of-plane. This parameter change fundamentally alters the director configuration, enabling the formation of spiral patterns without topological defects and achieving both fast switching and high efficiency at large steering angles.
2Shape
If vertical alignment with strong in-plane fields is used to pin directors, then large steering angles are achieved, but switching speed becomes slow and efficiency degrades for large spiral pitches
Solution Approach 1:
The patent inverts the field configuration by using out-of-plane electric fields instead of strong in-plane fields. This inversion maintains the ability to achieve large steering angles through vertical alignment while eliminating the slow switching and efficiency degradation associated with pinned director configurations.
3Speed
If planar alignment with in-plane electric fields is used, then fast relaxation times are achieved, but trapped pi wall defects cause significant efficiency loss at large steering angles
Solution Approach 1:
The patent inverts the alignment and field configuration from planar/in-plane to vertical/out-of-plane. This inversion eliminates the topological defects (trapped pi walls) that cause efficiency loss while preserving the fast relaxation times through the high restoring force provided by the vertical alignment and out-of-plane electric fields.
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 device achieves high steering angles up to ±15° with efficiencies over 90%, significantly outperforming previous devices in terms of speed and efficiency, particularly for wide apertures.
Implementation Method 1
A Pancharatnam phase device (PPD) for beam steering has the structure shown in FIG. 1. It includes a thin film of birefringent material, where the phase retardation of the material is 1⁄2 wave
Implementation Method 2
the phase difference between light exiting from two points in the aperture is related to their difference in the value of β with the relation: Γ=2*β
Implementation Method 3
a first means for providing surface localized in-plane electric fields on a first substrate and on a second substrate... a second means for providing electric fields between the two substrates that can be at an angle to the surface normal, or along the surface normal
Data Source
AI summary
A tunable optical beam steering device includes: a first means for providing surface localized in-plane electric fields on a first substrate and also on a second substrate that together define a sandwich structure containing a liquid crystal material; a second means for providing electric fields between the two substrates that can be at an angle to the surface normal, or along the surface normal; and an alignment layer on a surface of each substrate that causes the liquid crystal director to align with a small angle relative to the surface normal and whose projection onto the plane of the substrates is different on the two substrates.