Asymmetric L-Shaped Diffractive Grating Modulator
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Solution Overview
Problem
Existing micro-electromechanical systems (MEMS) based deformable mirror light valves face challenges in achieving high optical efficiency, contrast ratio, and fast response time due to limitations in diffractive grating modulators, particularly with symmetrical and asymmetrical designs that suffer from low diffraction efficiency and fabrication complexities.
Innovation Solution
The development of asymmetric deformable diffractive grating modulators with L-shaped cross sections, featuring a split pedestal and a flexible reflective member that can flex independently about an axis parallel to its long dimension, allowing for varying curvature and improved light modulation, is achieved through specific MEMS fabrication steps involving dielectric layers, electrodes, and sacrificial layers to create a structure that minimizes constraints and enhances optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a symmetrical T-shaped diffractive element design is used, then the structure is simple to fabricate, but the diffraction efficiency is very low with a typical contrast of about 5%
Solution Approach 1:
The patent applies asymmetry by transitioning from a symmetrical T-shaped diffractive element to an asymmetrical L-shaped design. The L-shaped configuration with a reflective ribbon having a supported portion mounted on a pedestal and an unsupported elongated portion laterally extending along the pedestal creates asymmetric light diffraction patterns that significantly improve diffraction efficiency and contrast ratio while maintaining fabricability through standard MEMS processes
2Loss of energy
If an asymmetrical L-shaped diffractive element is used, then the diffraction efficiency improves, but fabrication challenges and compromises arise to fulfill electrical, mechanical and optical performance requirements
Solution Approach 1:
The patent applies segmentation by dividing the reflective ribbon into distinct functional zones: a supported portion mounted on a pedestal and an unsupported elongated portion laterally extending along the pedestal. This segmentation allows independent optimization of mechanical support and optical performance, enabling the structure to achieve high diffraction efficiency while remaining compatible with standard MEMS fabrication processes
Solution Approach 2:
The patent applies local quality by providing different structural characteristics at different locations of the reflective ribbon. The supported portion at the pedestal provides mechanical stability and electrical connection, while the unsupported elongated portion provides the necessary flexibility for large-amplitude deflection and optimal optical diffraction, allowing each region to be optimized for its specific function
3Device complexity
If cantilever mirror type light valves are used, then the structure is simple, but the response time is slow of about 10 microseconds due to low natural frequency and large deflection required
Solution Approach 1:
The patent applies dynamics by designing the reflective ribbon as a flexible, dynamically responsive element rather than a rigid mirror. The ribbon's flexibility allows for rapid deflection with small actuation voltages, achieving response times of about 100 nanoseconds. The dynamic design enables the ribbon to respond quickly to electrostatic forces from the underlying electrode while maintaining structural integrity through its anchored configuration
4Speed
If membrane light valves are used, then the response time is relatively higher, but they are difficult to fabricate
Solution Approach 1:
The patent applies copying by using a planar reflective ribbon structure that replicates the functional benefits of complex curved membrane surfaces without requiring difficult three-dimensional fabrication. The flat ribbon with asymmetric L-shaped configuration can be fabricated using standard planar MEMS processes, avoiding the complex curvature formation required for membrane light valves while achieving similar optical performance
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
This design enhances optical efficiency, contrast ratio, and response time by decoupling the requirements for bending and restoring force, eliminating undesirable reflections, and reducing optical distortions, thereby improving the overall performance of light modulation in spatial light modulators.
Implementation Method 1
upon application of an electrostatic force, the diffractive element flexes independently about an axis parallel to the long dimension of each reflective member to vary the curvature of the reflective member
Implementation Method 2
the diffractive element acts to reflect a beam of light as a planar mirror
Data Source
AI summary
A micro-electromechanical structure for modulating light beams includes multiple asymmetric deformable diffractive elements, each having an L-shaped cross section, split pedestal and flexible reflective member. The reflective member has an elongated shape, and a supported part and unsupported part. The split pedestal extends along the long dimension of the supported part of the reflective member and is anchored to a substrate which supports one or more electrodes or serves as an electrode. The diffractive element is movable between a non-energized position wherein the diffractive element acts to reflect a beam of light as a planar mirror, to an energized position wherein upon application of an electrostatic force, the diffractive element flexes independently about an axis parallel to the long dimension of each reflective member to vary a curvature of the reflective member to form a blazed grating.