Monolithic Photonic Crystal Mirror for Broad Hemispheric Reflectance
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Solution Overview
Problem
Existing mirrors and photovoltaic systems face limitations in achieving high reflectance across a broad range of wavelengths, including from the visible to mid-infrared, and in omnidirectional and polarized light conditions, which is necessary for applications beyond solar energy, such as energy storage in molten metals.
Innovation Solution
A mirror design comprising a plurality of one-dimensional photonic crystals, where each crystal consists of alternating layers of high and low refractive index materials, strategically arranged to create a broad hemispheric total reflection band by calculating and optimizing the thicknesses of these layers to achieve reflectance close to unity across a wide spectral range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single one-dimensional photonic crystal is used, then the mirror structure is simple, but the reflectance bandwidth is narrow and cannot cover from visible to mid-infrared
Solution Approach 1:
The mirror is divided into multiple one-dimensional photonic crystals, each designed to reflect a specific wavelength band. By segmenting the overall reflection task across multiple crystals with different layer thicknesses and material compositions, the system achieves broadspectral coverage from visible to mid-infrared while maintaining a relatively simple one-dimensional layered structure for each crystal.
Solution Approach 2:
Each photonic crystal uses composite dielectric materials with different refractive indices arranged in alternating layers. This composite structure creates photonic bandgaps that enable high reflectance. By varying the materials and thicknesses across multiple crystals, the system compositestheir individual reflection bands to achieve a broad overall reflectance bandwidth.
2Manufacturing precision
If the photonic crystal layers are optimized for normal incidence, then the reflectance at normal incidence is high, but the reflectance decreases for oblique incidence and different polarizations
Solution Approach 1:
Different photonic crystals in the stack are designed with different local optimizations. Some crystals are optimized for normal incidence, while others are designed to handle oblique incidence and different polarizations. This local differentiation across the stack ensures that collectively, the mirror maintains high reflectance across all angles and polarizations.
Solution Approach 2:
The mirror system is designed to perform multiple functions simultaneously: reflecting normal incidence light, oblique incidence light, TE-polarized light, and TM-polarized light across a broad spectral range. By making the system universal in its functionality through the combination of multiple photonic crystals, it achieves omnidirectional and polarization-independent high reflectance.
3Adaptability or versatility
If three-dimensional photonic crystals are used to achieve angle-independent bandgaps, then the angular independence is improved, but the manufacturing complexity and cost increase significantly
Solution Approach 1:
Instead of using complex three-dimensional photonic crystal structures, the invention transitions to a one-dimensional layered structure approach. By stacking multiple one-dimensional photonic crystals with different layer configurations, the system achieves angle-independent reflectance without the manufacturing complexity of 3D structures. This dimensional simplification maintains the essential photonic bandgap functionality while greatly easing fabrication.
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 enables a mirror with virtually unity reflectance in a broad range of wavelengths from the visible to mid-infrared, effective for both hemispherical incidence and various polarizations, significantly enhancing applications like thermal insulation and energy storage.
Implementation Method 1
A photon having an energy within said bandgap, incident on the photonic crystal, cannot enter the photonic crystal and therefore is totally reflected, that is, the reflectance of the photonic crystal at said energy is equal to one
Implementation Method 2
Photonic crystals are structures where a unit cell formed by one or several materials of variable index of refraction is repeated periodically and indefinitely in space
Data Source
AI summary
The present invention refers to a mirror comprising a plurality of one-dimensional photonic crystals, the mirror having very high reflectance in a very broad range of wavelengths, a broad range of directions, even hemispheric, and all the polarizations of the incident photons. The invention also refers to a method for designing said mirror and a photovoltaic cell comprising such a mirror.