Sub-wavelength Grating Phase Control via Local Quality
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Solution Overview
Problem
Current sub-wavelength grating technologies lack the ability to efficiently control phase front changes in reflected light while maintaining high reflectivity, limiting their application in optical devices such as mirrors with specific optical properties.
Innovation Solution
Planar sub-wavelength dielectric gratings with a grating layer composed of a higher refractive index material than the substrate, configured with specific grating patterns to control phase changes in reflected light, allowing operation as cylindrical or spherical mirrors, and fabricated using conventional lithography and etching techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If sub-wavelength grating mirrors are used to replace top dielectric stacks, then the device becomes more compact and cheaper to fabricate with polarization control, but the ability to control phase front changes in reflected light is limited
Solution Approach 1:
The patent applies local quality by varying the grating period and duty cycle across different regions of the grating layer to create spatially dependent phase shifts. This allows the same grating structure to simultaneously provide high reflectivity and controlled phase front modifications, enabling functionality such as focusing or diverging reflected light while maintaining manufacturing simplicity
Solution Approach 2:
The patent utilizes parameter changes by modulating the grating period and duty cycle as key variables to control the phase response of reflected light. By adjusting these geometric parameters across the grating structure, the system achieves versatile optical functions including phase front shaping and beam steering, all while using conventional fabrication techniques
2Reliability
If high-index-contrast gratings are used, then resonant effects are enhanced with broadband reflection and high angular tolerance, but the guided waves are rapidly scattered and do not propagate very far laterally
Solution Approach 1:
The patent applies local quality by creating spatially varying grating periods and duty cycles that locally control the phase response. This allows different regions of the grating to serve different functions: some regions provide strong resonant reflection while others control the phase front of reflected light, achieving both high reliability and controlled propagation characteristics
Solution Approach 2:
The patent introduces dynamics by making the grating structure adaptable through varying geometric parameters. The grating can be designed with specific period and duty cycle profiles that dynamically control the scattering behavior of guided waves, allowing optimization of both reflection strength and lateral propagation characteristics for different 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
Enables the creation of optical devices with controlled phase front changes and high reflectivity, enabling operation as focusing or diverging mirrors with arbitrary reflecting surfaces, expanding the range of grating applications.
Implementation Method 1
Resonant effects in dielectric gratings were identified in the early 1990's as having promising applications to free-space optical filtering and sensing. Resonant effects typically occur in sub-wavelength gratings, where the first-order diffracted mode corresponds not to freely propagating light but to a guided wave trapped in some dielectric layer.
Implementation Method 2
The trapped wave is re-scattered in the 0th diffracted order and interfaces with the incident light to create a pronounced modulation of transmission and reflection.
Implementation Method 3
sub-wavelength grating mirrors have been used to replace the top dielectric stacks in vertical-cavity surface-emitting lasers, and in novel micro-electromechanical devices
Data Source
AI summary
Examples include a method for fabricating a grating mirror using a computing device that comprises calculating a target phase change across the grating mirror. The target phase change may correspond to a target wavefront shape in a beam of light reflected from a grating patter. The method may also comprise generating the grating pattern comprising a plurality of lines with line widths, line period spacings, and line thicknesses corresponding to the target phase change across the grating mirror using the computing device. In such examples, a set of coordinates may be generated using the computing device with each coordinate identifying a location of a line of the plurality of lines, a line width of the line, a line period spacing of the line, and a line thickness of the line.