Diffractive Optical Element Antireflection Layer 0th-Order Light
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Solution Overview
Problem
Existing diffractive optical elements face challenges in achieving wide-range light irradiation while minimizing the generation of undesired 0th-order light, which can lead to reduced light utilization efficiency and accuracy issues in projection and measurement devices.
Innovation Solution
A diffractive optical element with a substrate, protrusion and recess structure, and an antireflection layer that provides an effective refractive index difference of 0.70 or more between the protrusions and recesses, allowing for an exit angle range of 60° or more and a diffraction efficiency of 65% or more, reducing 0th-order light generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the pitch of the protrusion and recess portion is made small or the height is increased to achieve wide exit angle range, then the aspect ratio is increased, but the ratio of side surface area to total surface area increases causing increased reflection and generation of undesired 0th-order light
Solution Approach 1:
An antireflection layer is introduced as an intermediary component between the protrusion and recess portion and the incident light source. This layer has a refractive index specifically designed to be between that of air and the protrusion material, creating a gradient that reduces reflection at the interface. The antireflection layer acts as a mediator that allows light to transition smoothly from air into the high-aspect-ratio structures without generating harmful reflections or 0th-order light.
2Adaptability or versatility
If the aspect ratio of protrusions is increased to achieve wide angular range of light application, then the exit angle range is improved, but the influence of reflection at side surfaces increases reducing light utilization efficiency
Solution Approach 1:
The antireflection layer serves as an intermediary that reduces energy loss through reflection. By positioning this layer with an intermediate refractive index between air and the protrusion material, it creates a gradual optical transition that minimizes reflective losses at the interface, thereby improving light utilization efficiency while maintaining the high aspect ratio structures needed for wide angular coverage.
3Adaptability or versatility
If strong 0th-order light is generated due to increased aspect ratio, then wide angle of view is achieved, but eye safety is compromised
Solution Approach 1:
The antireflection layer acts as a protective intermediary that prevents the generation of strong 0th-order light. By reducing reflection at the interface through its intermediate refractive index, it eliminates the harmful effect of 0th-order light generation while preserving the wide angle of view functionality provided by the high aspect ratio protrusion structures.
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 solution enhances light utilization efficiency and reduces 0th-order light, enabling effective wide-range light irradiation in projection and measurement devices, improving accuracy and performance.
Implementation Method 1
Diffractive optical elements having such a protrusion and recess structure diffract light by giving it a desired difference of optical path length utilizing a diffractive index difference between a material (e.g. air having a refractive index of 1) that fills up the recesses and a material of the protrusions
Implementation Method 2
utilizing a diffractive index difference between a material (e.g. air having a refractive index of 1) that fills up the recesses and a material of the protrusions
Implementation Method 3
the ratio of the area of the side surfaces (of the protrusions) of the protrusion and recess portion capable of serving as interfaces for light traveling through the protrusion and recess portion to the area of all surfaces is increased, which may increase the influence of reflection at the side surfaces of protrusions
Data Source
AI summary
A diffractive optical element includes: a substrate; a protrusion and recess portion that is formed on one surface of the substrate and imposes predetermined diffraction on incident light; and an antireflection layer provided between the substrate and the protrusion and recess portion. An effective refractive index difference Δn in a wavelength range of the incident light between a first medium constituting a protrusion of the protrusion and recess portion and a second medium constituting a recess of the protrusion and recess portion is 0.70 or more. An exit angle range θout of diffraction light exiting from the protrusion and recess portion when the incident light enters the substrate from a normal direction of the substrate is 60° or more. Total efficiency of diffraction light exiting from the protrusion and recess portion in the exit angle range is 65% or more.