Polarization-Independent Multifocal System Using Geometric Phase Lenses
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Solution Overview
Problem
Existing focusing systems for augmented reality (AR) applications face challenges in providing multifocal focusing with fast switching, scalability, polarization-independent operation, compact size, and low power consumption, as they often rely on mechanical components or polarization-dependent methods that are not scalable or efficient.
Innovation Solution
A multifocal system utilizing a polarization beam splitter (PBS), variable-focusing modules with geometric phase lenses (GPLs), and an electronic controller to split and recombine light beams orthogonally, enabling variable and selectable optical powers while maintaining polarization independence and high power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mechanical components are used for focusing adjustment, then focusing capability is achieved, but switching speed is slow and device size is large
Solution Approach 1:
The patent replaces mechanical focusing components with a geometric phase lens (GPL) based optical system. The GPL uses the geometric phase effect to achieve focusing without mechanical movement, enabling fast switching between different focal lengths by simply changing the input light's polarization state or spatial profile, thereby eliminating slow mechanical adjustment mechanisms.
Solution Approach 2:
The patent changes the parameter of input light (spatial profile or polarization state) to control the focal length of the GPL. By modulating the input light's parameters rather than moving mechanical components, the system achieves fast switching between multiple focal lengths, directly improving switching speed while reducing mechanical complexity.
2Loss of energy
If polarization-dependent focusing is used, then focusing capability is achieved, but light power is lost due to filtering
Solution Approach 1:
The patent uses a spatial light modulator (SLM) to shape only the necessary portion of the input light beam's spatial profile, rather than filtering out entire polarization components. This partial action approach maintains most of the input light power while achieving the desired polarization-independent focusing, thereby reducing energy loss.
Solution Approach 2:
The patent introduces a spatial light modulator (SLM) as an intermediary between the unpolarized light source and the GPL. The SLM converts the unpolarized light into a structured beam profile that the GPL can focus, acting as a mediator that enables polarization-independent operation without requiring polarization filtering, thus preserving light power.
3Adaptability or versatility
If multiple focal lengths are provided, then multifocal capability is achieved, but device complexity increases
Solution Approach 1:
The patent makes the single GPL perform multiple focusing functions by varying the input light parameters. The same GPL can focus light at different focal lengths depending on the input beam's spatial profile or polarization state, eliminating the need for multiple physical lenses or complex switching mechanisms, thereby achieving multifocal capability with simple system architecture.
Solution Approach 2:
The patent introduces dynamic control of the input light parameters (via SLM or polarization modulation) to enable the GPL to switch between different focal lengths on demand. This dynamic parameter control allows a single static GPL to provide multiple focal lengths, achieving adaptability without increasing hardware complexity.
4Volume of moving object
If compact size is achieved, then portability is improved, but optical path length is limited
Solution Approach 1:
The patent uses the geometric phase effect in the GPL, which operates in the transverse spatial dimension rather than requiring long propagation distances. This allows the optical system to achieve significant focusing power in a compact transverse footprint, enabling short optical path lengths while maintaining compact device size suitable for portable applications.
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 system achieves efficient multifocal focusing with fast switching and scalability, supporting polarization-independent operation, reducing hardware requirements and power consumption, and enabling the use in compact AR displays.
Implementation Method 1
a first optical assembly (200) configured to provide an optical power for focusing the incident circularly polarized light beam to form an exit circularly polarized light beam. The optical assembly (200) comprises a stack of optical elements including at least one geometric phase lens (GPL). The optical power provided by the GPL depends on the handedness of a circularly polarized (CP) light beam processed by the GPL.
Implementation Method 2
a front-end quarter-wave plate (QWP) for converting the input linearly polarized light beam into an incident circularly polarized light beam. The rear-end QWP is used for converting the exit CP light beam to a first intermediate linearly polarized (LP) light beam.
Implementation Method 3
The rear-end LC HWP is located at the second end for transforming the first intermediate LP light beam into the output LP light beam leaving from the second end. The rear-end LC HWP is electrically reconfigurable to either maintain or 90°-rotate a polarization orientation of the first intermediate LP light beam.
Data Source
AI summary
Polarization-independent focusing is advantageously achieved by a multifocal system having a polarization beam splitter (PBS) to split an unpolarized light beam into two orthogonally linearly-polarized (LP) light beams. The two LP light beams are reflected by mirrors to travel in opposite directions and enter into a variable-focusing module at two ends thereof, respectively. The module includes waveplates to convert the LP light beams into two circularly-polarized (CP) light beams at both ends of an optical assembly. The optical assembly is formed with a stack of birefringent optical elements including at least one geometric phase lens and one polarization selector that may be electrically modulated to select the optical power in focusing the two CP light beams. Followed by the waveplates converting two focused CP light beams to two focused LP light beams and upon mirror reflection, the beams are finally recombined by the PBS to form one focused light beam.