Optical Filter With Complementary Angular Blocking Regions
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Solution Overview
Problem
Optical filters in various applications face challenges in effectively managing light transmission and blocking at different angles, leading to issues like light interference and non-uniform spectral sensitivity, particularly in sensors like pulse oximeters where ambient and internal light sources cause noise.
Innovation Solution
The combination of an interference filter and an angle blocking layer with complementary angular blocking regions, where the interference filter blocks light at one range of incidence angles and the angle blocking layer blocks at another, potentially wavelength-dependent range, to create a thinner system that effectively limits light transmission to a predetermined cone angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single optical filter is used to block light at certain angles, then light blocking is achieved at specific wavelengths, but light leakage occurs at other angles and wavelengths
Solution Approach 1:
The optical filtering function is segmented into two distinct components: an interference filter that blocks light at specific wavelengths and angles, and an angle blocking layer that blocks light at different angular ranges. Each component addresses a specific portion of the angular-wavelength space, and their combination provides comprehensive blocking coverage without the limitations of a single filter.
Solution Approach 2:
The patent combines two different optical filtering mechanisms (interference filter and angle blocking layer) into a composite structure. The interference filter uses wavelength-selective reflection/absorption, while the angle blocking layer uses angular-selective blocking, creating a composite system that leverages the strengths of both approaches to eliminate light leakage.
2Object-affected harmful factors
If optical filters are designed to block a wide angular range, then light interference is reduced, but the transmission zone narrows and light transmission is compromised
Solution Approach 1:
The angular blocking function is segmented between two components: the interference filter handles wavelength-selective blocking at certain angles, while the angle blocking layer handles angular blocking at different ranges. This segmentation allows each component to operate optimally within its designated angular-wavelength domain, maintaining wide angular blocking coverage while preserving the central transmission zone.
3Reliability
If the optical filter system is made thicker to improve blocking performance, then light leakage is reduced, but the device complexity and size increase
Solution Approach 1:
Rather than using a single thick filter attempting to block all angles and wavelengths, the patent employs two thinner filters that each perform partial blocking functions. The interference filter provides wavelength-selective blocking, while the angle blocking layer provides angular-selective blocking, achieving comprehensive coverage with thinner individual components than a single monolithic filter would require.
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 solution achieves sharp transitions from pass to block zones, reduces light leakage, and maintains uniformity across a wide area, even at high angles of incidence, enhancing the performance of optical filters in applications like sensors and display systems by controlling angular intensity distribution and blocking unwanted light sources.
Implementation Method 1
an interference filter having an incidence angle-dependent reflection band
Implementation Method 2
an absorbing layer having an absorption band
Data Source
AI summary
An example optical filter may include an angle blocking layer having a first angular light blocking range θAL relative to a normal axis, and an interference filter adjacent the angle blocking layer having a second angular light blocking range θIF relative to the normal axis. θIF and θAL at least partially overlap. The example optical filter has a predetermined light transmission zone comprising angles from 0° to a maximum light transmission angle θTmax relative to a normal axis of the major surface. The example optical filter has a predetermined angular light blocking zone θB, a union of θIF and θAL. An example optical filter may include an interference filter having an incidence angle-dependent reflection band and an absorbing layer having an absorption band. The incidence angle-dependent reflection band and the absorption band may overlap at at least one wavelength at at least one angle of incidence.