Optical Frequency Filter With Refractive Index Inclusions
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Solution Overview
Problem
Existing optical filters face challenges in achieving good rejection over a wide spectral range, limited transmission in a narrow spectral range, and angular insensitivity, while being compact and of simplified manufacture.
Innovation Solution
An optical frequency filter with a support layer of high refractive index and inclusions of lower refractive index, where the height and width of the inclusions are optimized to form a wavelength-selective structure, enhancing rejection and transmission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reflective elements are suspended directly above air to minimize refractive index difference, then transmission resonance is improved, but manufacturing difficulty increases significantly
Solution Approach 1:
The patent introduces a support layer with intermediate refractive index between air and the high-index dielectric material. This intermediary layer enables practical manufacturing by providing mechanical support while maintaining optimal optical performance through controlled refractive index matching, eliminating the need for difficult suspended structures.
2Ease of manufacture
If conventional slit grating with half-wave plate is used to simplify manufacture, then manufacturing is easier, but spectral rejection range is limited and poor
Solution Approach 1:
The patent employs a composite structure combining metal reflective elements with high-index dielectric material in a periodic grating configuration. This composite approach achieves both manufacturing feasibility and superior spectral rejection by leveraging the complementary properties of different materials - the metal provides reflectivity while the dielectric enables resonant enhancement.
Solution Approach 2:
The patent optimizes multiple parameters including slot width (w < P/3), slot height (h between P/2 and P), and periodicity (P) to achieve wavelength-selective transmission. By carefully controlling these geometric parameters, the filter achieves broad spectral rejection while maintaining narrow transmission windows, overcoming the limitations of conventional designs.
3Reliability
If filter dimensions are optimized for a given wavelength, then transmission at that wavelength is maximized, but transmission peaks appear outside the desired wavelength range
Solution Approach 1:
The patent employs multiple parameter optimizations including slot width (w < P/3), slot height (h between P/2 and P), and periodicity (P) to achieve wavelength-selective transmission. By carefully controlling these geometric parameters, the filter achieves broad spectral rejection while maintaining narrow transmission windows, overcoming the limitations of conventional designs.
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 very good rejection over a wide spectral range, good transmission in a narrow range, and is angularly insensitive, while being compact and cost-effective to produce.
Implementation Method 1
the period P, the height and the width of the slots being chosen so as to optimize transmission so that the reflective elements form a wavelength-selective structure
Implementation Method 2
the support layer is formed of a material of refractive index nh and comprises inclusions in a material of refractive index nb, nb being strictly less than nh
Data Source
Figure 1~2f
Figure 3~4
Figure 5~6
AI summary
The filter (1) has a support layer (11) on which a set of reflecting elements (10) i.e. rectangular paving stones, defining a periodic network having parallel slots is formed. The support layer is made of a material having a refraction index, and includes inclusions (111) formed in a material having another refractive index lower than the former index. The inclusions level on a surface (112) of the support layer opposed to the reflecting elements. The inclusions are provided with specific height and width, and each inclusion is located partly between two reflecting elements. An independent claim is also included for a detector.