Polarization Conversion Element for Radial Polarization
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Solution Overview
Problem
Conventional polarization conversion elements, such as those using half wave plates or photonic crystals, are unable to effectively convert linear polarization to radial polarization across a range of wavelengths due to variations in phase difference between ordinary and extraordinary rays, limiting their applicability.
Innovation Solution
A polarization conversion element comprising a phase reversal element and a polarization plane rotation element, where the latter includes a liquid crystal layer with regions of different alignment directions and transparent electrodes to rotate the polarization plane to radial, and a phase reversal element with annular portions to modulate the phase of incident light, allowing conversion of linear to radial polarization across a specified wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional polarization conversion elements (half wave plates or photonic crystals) are used, then linear polarization can be converted to radial polarization at a specific design wavelength, but the conversion fails when the incident light wavelength differs from the design wavelength due to phase difference variations
Solution Approach 1:
The patent employs liquid crystal molecules that can dynamically change their alignment direction in response to applied electric voltage. By controlling the voltage, the alignment directions of liquid crystal molecules in different regions can be adjusted, enabling the polarization conversion element to adapt to different wavelengths of incident light and maintain effective radial polarization conversion across a broad wavelength range
Solution Approach 2:
The patent changes the physical state and orientation parameters of liquid crystal molecules through electric field control. By adjusting the alignment directions of liquid crystal molecules in different regions via applied voltage, the optical path difference between ordinary and extraordinary rays is modified, allowing the element to compensate for wavelength variations and maintain polarization conversion accuracy
2Length of moving object
If short wavelength light sources (violet or ultra violet) are used to achieve smaller beam spots, then the beam spot diameter decreases, but the cost increases and light transmittance of optical materials decreases
Solution Approach 1:
The patent changes the polarization state parameter of the light beam from linear to radial polarization. This parameter change enables the use of longer wavelength light sources while still achieving small beam spot diameters through the unique focusing properties of radially polarized light, thereby avoiding the cost and material transmittance issues associated with short wavelength sources
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
Enables the conversion of linear polarization to radial polarization at arbitrary wavelengths, allowing for adjustable polarization states and improved focusing capabilities, such as smaller beam spots and increased depth of focus, without the need for expensive short-wavelength light sources.
Implementation Method 1
The liquid crystal layer has a plurality of regions disposed along circumferential direction with a first intersection point of the polarization plane rotation element and the optical axis as the center, and an alignment direction of the liquid crystal molecules included in each of the plurality of regions is different from each other
Implementation Method 2
Each of the plurality of regions of the liquid crystal layer rotates, when an electric voltage in accordance with prescribed wavelength is applied between the two first transparent electrodes, the polarization plane of the component of the linear polarization transmitting the region so as to become parallel to the radial direction
Implementation Method 3
The phase reversal element includes first annular portions and second annular portions alternately disposed along radial direction with the second intersection point of the phase reversal element and the optical axis as a center, the phase of the linear polarization or radial polarization incident on the first annular portion being reversed relative to the phase of the linear polarization or radial polarization incident on the second annular portion
Implementation Method 4
two first transparent electrodes disposed in opposition to each other so as to sandwich the liquid crystal layer between... when an electric voltage in accordance with prescribed wavelength is applied between the two first transparent electrodes
Data Source
AI summary
A polarization conversion element includes a phase reversal element and a polarization plane rotation element including a liquid crystal layer. The liquid crystal layer has a plurality of regions disposed along circumferential direction with the intersection point of the polarization plane rotation element and the optical axis as the center with alignment directions different from each other. When electric voltage in accordance with the wavelength of linear polarization incident on the polarization plane rotation element is applied, each region rotates the polarization plane of the polarization component transmitted by each region, and thereby converts linear polarization to radial polarization. The phase reversal element reverses, among the first and the second annular portions alternately disposed along the radial direction with the optical axis as the center, the phase of light incident on the first annular portion relative to the phase of light incident on the second annular portion.