Polarization-Insensitive Resonant Grating Filter Design
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Solution Overview
Problem
Resonant grating optical filters are sensitive to polarization, especially at oblique incidence, making them challenging to tune in wavelength due to their dependence on polarization and requiring complex configurations that are difficult to implement.
Innovation Solution
A polarization-insensitive optical filter design featuring two one-dimensional resonant gratings arranged with a 90-degree angle between their axes, each periodic along different axes, allowing for orthogonal mode excitation and decoupling regardless of polar angle, enabling wavelength tunability by varying the polar angle of incidence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single resonant grating is used to achieve narrow bandwidth filtering, then wavelength selectivity is improved, but polarization sensitivity increases making the filter difficult to tune
Solution Approach 1:
The patent divides the single resonant grating into two separate gratings (first grating and second grating) with different orientations. Each grating couples to different waveguide modes, and by segmenting the function across multiple components, the system achieves polarization independence while maintaining narrow bandwidth filtering capability.
Solution Approach 2:
The patent combines two resonant grating structures working together to achieve a single functional outcome of polarization-independent wavelength filtering. The first grating couples to first waveguide modes while the second grating couples to second waveguide modes, and their combined effect provides both wavelength selectivity and polarization independence.
2Adaptability or versatility
If oblique incidence is used to achieve wavelength tuning, then tunability is improved, but polarization dependence worsens
Solution Approach 1:
The patent introduces asymmetric orientation between the two gratings (first grating and second grating are not aligned) to break the polarization dependence. By arranging the gratings at specific angles relative to each other and to the waveguide modes, the system achieves insensitivity to incident polarization while maintaining angular tunability.
Solution Approach 2:
The patent adds an angular dimension to the grating arrangement by orienting the first grating at an angle θ1 and the second grating at an angle θ2 relative to the waveguide modes. This angular configuration in addition to the wavelength parameter enables simultaneous polarization independence and wavelength tunability.
3Object-affected harmful factors
If complex grating patterns are used to achieve polarization insensitivity, then polarization independence is improved, but device complexity increases
Solution Approach 1:
Instead of using a single complex two-dimensional grating pattern, the patent segments the function into two separate one-dimensional gratings with simpler periodic structures. Each grating has a regular pattern along its respective axis, avoiding the need for complex arbitrary patterns while achieving the same polarization-independent effect.
Solution Approach 2:
Instead of making the grating pattern complex to achieve polarization insensitivity, the patent inverts the approach by using simple periodic gratings and achieving polarization independence through their relative orientation and the resulting mode coupling geometry. The complexity is inverted from the grating pattern itself to the spatial arrangement of multiple simple components.
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 polarization independence and wavelength tunability across a wide range of polar incidence angles, simplifying implementation and maintaining effectiveness over a broad spectral range.
Implementation Method 1
The grating enables coupling, via an evanescent diffraction order, of the energy of an incident beam in free space to an optical mode of the multi-layer structure which acts as a waveguide
Implementation Method 2
Such filters are also known as guided mode resonance filters or Fano resonance filters
Implementation Method 3
Resonant grating optical filters are optical components for filtering in wavelength making it possible to obtain a very narrow bandwidth
Data Source
AI summary
The invention relates to a polarization-insensitive optical filter centered on a wavelength (?0) measured in vacuum, comprising: first and second waveguides (21, 21') each having a propagation mode; a first grating (11) formed in or on the surface of the first waveguide (21), the first grating being periodical at least along a first axis Ox defining a first orthonormal base Oxyz; a second grating (11') formed in or on the surface of the second waveguide (21), the second grating being periodical at least along a second axis Oxy' defining a second orthonormal base Ox'y'z; wherein the first and second gratings are provided above each other and are such that the first axis Ox and the second axis Ox' define an angle ? different from ± p /2 radians so that, when the first grating is illuminated by a light beam, the first and second propagation modes are excited and have orthogonal fields for a predetermined angle of incidence of the light beam.