Optical Module Encapsulant Refractive Index Matching
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Solution Overview
Problem
Conventional photoplethysmography (PPG) sensors face issues due to refractive index mismatch between the emitter and the cover, leading to decreased external quantum efficiency (EQE) and water ingress, which affects reliability.
Innovation Solution
The optical module design includes a carrier with an optical device and a conductive element, where encapsulants are used to reduce refractive index mismatch and provide a water-resistant structure, enhancing sensitivity and usability with integrated ECG functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a cover or housing is used to accommodate the emitter and receiver, then the structural integrity and protection are improved, but the refractive index mismatch between the emitter and cover decreases the external quantum efficiency
Solution Approach 1:
The patent introduces an encapsulant as an intermediary material between the optical components (emitter and receiver) and the cover. This encapsulant has a refractive index that is optimized to reduce the refractive index mismatch at the interface, thereby improving external quantum efficiency while still providing structural protection through the cover housing.
Solution Approach 2:
The patent changes the refractive index parameter of the material surrounding the optical components by using a specific encapsulant material. This parameter change reduces the refractive index difference between the semiconductor material and the cover, thereby improving light extraction efficiency and external quantum efficiency.
2Ease of manufacture
If a gap exists between the emitter and the cover, then assembly tolerance is improved, but water ingress occurs leading to reliability issues
Solution Approach 1:
The encapsulant serves as a mediator that fills the gap between the optical components and the cover. It provides both mechanical compliance to accommodate assembly tolerances and water-blocking functionality to prevent water ingress, thereby simultaneously addressing manufacturing ease and reliability concerns.
Solution Approach 2:
The encapsulant acts as a flexible sealing layer that can deform to accommodate assembly variations while maintaining a hermetic seal. This flexible film structure allows for easier assembly with tolerance compensation while preventing water penetration that would compromise reliability.
3Adaptability or versatility
If the sensing surface has separate conductive and non-conductive regions, then ECG functionality is enabled, but the device complexity increases
Solution Approach 1:
The sensing surface is designed with regions that serve multiple functions: the conductive regions serve both as electrical contacts for ECG measurement and as part of the optical sensing interface. This multi-functionality enables ECG capability without requiring entirely separate structures, thereby limiting the increase in device complexity.
Solution Approach 2:
The sensing surface has spatially varying properties with conductive regions positioned specifically for ECG electrode functionality and non-conductive regions for optical sensing. This local differentiation allows each region to be optimized for its specific function while maintaining overall device integration.
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 increases the external quantum efficiency, reduces the size of the optical module, and addresses water ingress issues while providing a 2-lead or 3-lead ECG function for improved usability.
Implementation Method 1
encapsulants are used to reduce refractive index mismatch
Data Source
AI summary
An optical module is disclosed. The optical module includes a carrier, an optical device disposed over the carrier, and a sensing surface facing away from the carrier. The sensing surface includes a transmissive region and a non-transmissive region adjacent to the transmissive region.