Mono- or Multifrequency Optical Filter with Half-Wave Plate Support
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Solution Overview
Problem
Current micro- or nano-structured frequency-selective optical filters have limited adjustability, poor rejection rates outside the transmission band, and are unable to efficiently transmit both polarizations, making them unsuitable for applications requiring wide spectral rejection and compactness.
Innovation Solution
A mono-frequency optical filter with elements of negative electric permittivity, featuring a periodic network of slots on a half-wave plate support layer with high refractive index contrast, allowing for adjustable transmission peaks and enhanced rejection rates, and the ability to transmit multiple polarizations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a metal network of slits is used with thickness at least equal to half the wavelength, then the transmission amplitude can be adjusted, but the rejection rate outside the bandwidth remains less than 90% and typically less than 80%
Solution Approach 1:
The patent combines metal slits with a dielectric layer having high refractive index to form a composite structure. This composite material approach enables both precise transmission amplitude control through slit dimensions and high rejection rate (>90%) through the dielectric layer's optical properties, resolving the contradiction between manufacturability and reliability.
Solution Approach 2:
The patent introduces a dielectric layer parameter (refractive index) that fundamentally changes the optical response of the filter. By selecting dielectric materials with high refractive indices, the system achieves enhanced rejection rates while maintaining transmission control, representing a parameter change from pure metal structures to metal-dielectric composites.
2Adaptability or versatility
If the refractive index of the support is chosen as low as possible (air), then the transmission of the network is disturbed as much as possible, but the structure becomes tricky to achieve technologically
Solution Approach 1:
The patent replaces the complex suspended structure in air with a practical dielectric layer that can be easily deposited using standard thin-film techniques. This substitution maintains the optical performance benefits while dramatically improving ease of manufacture, effectively replacing a fragile, difficult-to-implement structure with a robust, manufacturable alternative.
3Measurement precision
If a periodic network of thin bands is embedded in a dielectric layer waveguide, then the transmission peak width can be reduced to 1% of the wavelength, but the spectral range over which good rejection is ensured is very limited
Solution Approach 1:
The patent segments the optical filtering function into two distinct components: the metal slit network provides narrow transmission peak selection, while the separate dielectric layer provides broad spectral rejection. This segmentation allows each component to optimize its specific function without compromising the other, achieving both narrow peak width and wide rejection range simultaneously.
4Adaptability or versatility
If two arrays of bands of different orientation are juxtaposed to transmit two different polarizations, then both polarizations can be transmitted, but the compactness of the filter is greatly impaired
Solution Approach 1:
The patent makes the single dielectric layer universal by enabling it to work with metal slit networks oriented in different directions. The same dielectric layer provides high rejection for both x-polarized and y-polarized light, regardless of the metal slit orientation. This multi-functionality allows polarization diversity without requiring separate dielectric layers, maintaining compactness.
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 filter achieves a selective transmission peak with a rejection rate greater than 90% over a wide spectral range, from 250 nanometers to a hundred micrometers, and can transmit one or more polarizations, simplifying design and manufacturing while maintaining compactness.
Implementation Method 1
a periodic network of through slots parallel, the periodicity, the height, and the width of the slots being chosen so that said array of slots forms a wavelength-selective structure
Implementation Method 2
The amplitude and the rate of rejection of this type of filter are suffered and typically very unsatisfactory. In particular, the rejection rate is less than 90%
Implementation Method 3
the refractive index of the support is systematically chosen as low as possible in order to disturb the transmission of the network of slots as much as possible
Implementation Method 4
which has a selective transmission passband, namely a width at mid-height of the transmission peak less than 10% of the wavelength for which the peak is maximum, while remaining usable in practice with good rejection over a spectral range around the transmission peak
Data Source
Figure 1~2
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Figure 6~7
AI summary
The invention relates to a monofrequency optical filter (10), including reflective elements (12) which are formed on one surface of a dielectric support layer (16) and which define at least one periodic array (14) of parallel grooves passing across same. The periodicity, height, and width of said periodic groove array are selected so as to form a structure, the wavelength of which can be selected from within a predetermined range of wavelengths. According to the invention, the thickness and refractive index of the support layer (16) are selected so that said layer (16) forms a half-wave plate for a wavelength of the predetermined wavelength range. The filter, when in contact with the surface of the support layer (16) that is opposite the surface on which the groove array (14) is formed, includes a medium (18), the refractive index of which is less than that of the support layer (16) so as to obtain a guided mode that resonates in the support layer (16). The period of the or each periodic groove array (14) is between approximately Formula (I) and approximately Formula (II), where λ is a wavelength of the predetermined wavelength range and n1 is the refractive index of the support layer. Moreover, the refractive indices of the support layer (16) and the medium (18) fulfill the Formula (III) relationship, where n1 is the support layer index and n2 is the index for the medium (18).