Alternating-Layer Optical Film for Smooth Infrared Transmission
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Solution Overview
Problem
Existing mirror films used in displays do not effectively transmit infrared light, which is necessary for sensors and light sources like fingerprint scanners and IR illumination in automotive displays, due to sharp band edges causing ringing in the transmission spectra and non-monotonic increases in transmittance.
Innovation Solution
The development of an optical film with alternating polymeric layers and a skin layer, where the layers are integrally formed and have specific thicknesses and refractive indices, reducing Fresnel reflections and optimizing the layer thickness profile to achieve a monotonic increase in transmittance from 10% to 70% with a slope greater than 2%/nm, ensuring high reflectance in the visible range and high transmittance in the infrared range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a mirror film is designed with sharp band edges to achieve high reflectance in the visible range, then visible light reflectance is improved, but ringing occurs in the transmission spectra causing non-monotonic transmittance increase and poor infrared transmission
Solution Approach 1:
The patent modifies the thickness parameters of the alternating polymeric layers to create a more gradual band edge transition. By adjusting the layer thicknesses to be less than 250 nm and controlling the number of layers between 50-800, the optical film achieves a monotonic transmittance increase in the infrared range while maintaining high visible reflectance, eliminating the ringing effect caused by overly sharp band edges
Solution Approach 2:
The patent uses composite polymeric materials with different refractive indices arranged in alternating layers. This composite structure allows tuning of the optical properties to achieve both high visible reflectance and smooth infrared transmission, resolving the contradiction between sharp band edge reflectance and transmission quality
2Manufacturing precision
If the optical film uses a large number of alternating layers with small thickness to achieve high visible reflectance, then manufacturing precision is improved, but the complexity of achieving monotonic transmittance increase worsens
Solution Approach 1:
The patent establishes specific parameter ranges for the alternating layers: thickness less than 250 nm and refractive index differences greater than 0.2. These parameter constraints simplify the design space and make it easier to achieve both high manufacturing precision and monotonic transmittance characteristics, reducing the complexity of transmission spectrum control
Solution Approach 2:
The patent applies different refractive index properties to different layers in the alternating structure. By creating local variations in optical properties through the polymeric material selection, the film achieves high visible reflectance while maintaining smooth infrared transmission, managing the complexity through localized property optimization
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 optical film provides enhanced reflectance in the visible range and transmittance in the infrared range, supporting the functionality of sensors and light sources, while minimizing ringing in the transmission spectra.
Implementation Method 1
An optical film including a plurality of alternating polymeric first and second layers disposed on a skin layer... An optical transmittance of the optical film for substantially normally incident light has a band edge separating first and second wavelength ranges
Implementation Method 2
The first and second layers have respective indices of refraction: n1x and n2x along a first polarization state... reducing Fresnel reflections
Data Source
AI summary
An optical film including a plurality of alternating first and second layers disposed on a skin layer is described. The skin layer has an average thickness greater than about 2 microns. A transmittance of the film for substantially normally incident light includes a band edge separating first and second wavelength ranges, where each range is at least 250 nm wide. A reflectance of the film is greater than about 95% for each wavelength in the first wavelength range; an average transmittance of the film is greater than about 80% in the second wavelength range; and a difference between maximum and minimum values of the optical transmittance of the film in the second wavelength range is less than about 30%. The band edge may have a slope that is greater than about 2%/nm. The transmittance may increase monotonically at least from about 10% to about 70% with increasing wavelength.