Waveguide Interferometric Force Sensor Using PRPSR Grating
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Solution Overview
Problem
Existing touch and force detection systems for electronic devices require multiple sensors to detect inputs at multiple locations, which increases complexity and cost, while light-based sensors struggle to efficiently measure distance and displacement across large areas with a single laser source.
Innovation Solution
The use of a deformable input surface with a pressure transfer layer and a partially retroreflective and partially specularly reflective (PRPSR) grating within an optical waveguide, where a single laser light source inserts light that undergoes self-mixing interferometry, allowing detection of force and touch inputs at multiple locations by analyzing changes in the operational parameters of the laser light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple light-based sensor mechanisms are used to detect touch at multiple locations, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Multiple sensing functions are merged into a single optical waveguide system. The waveguide integrates multiple reflection points along its length, allowing one laser source to perform what would traditionally require multiple separate sensors. This combining approach maintains multi-location detection capability while reducing overall system complexity.
Solution Approach 2:
The optical waveguide serves multiple functions simultaneously: it guides laser light, provides multiple reflection points for different locations, and enables touch detection across the entire input surface. This multi-functional design eliminates the need for separate sensor mechanisms at each detection point.
2Device complexity
If a single laser light source is used to detect multiple locations, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The optical waveguide is segmented into multiple functional sections, each with specific reflection characteristics. Different portions of the waveguide correspond to different input surface locations, allowing the single laser source to distinguish between locations based on the specific reflection patterns from each segment.
Solution Approach 2:
Different sections of the optical waveguide are designed with locally optimized properties. The waveguide may have varying refractive indices, reflection coefficients, or geometric characteristics at different positions, enabling each location to be uniquely identified while using the same laser source.
3Ease of manufacture
If traditional capacitance or piezoelectric sensors are used, then ease of manufacture is improved, but measurement precision for light-based detection deteriorates
Solution Approach 1:
The patent replaces traditional mechanical or electrical sensing mechanisms (capacitance or piezoelectric sensors) with an optical-based system. By substituting the mechanical/electrical detection approach with optical interference measurement, the system achieves higher sensitivity while maintaining manufacturability through integration with existing display 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
Enables efficient detection of touch and force inputs across a wide area using a single laser source, reducing the need for multiple sensors and improving the accuracy of location and magnitude determination on electronic device surfaces.
Implementation Method 1
self-mixing interferometry of laser diodes to detect force or touch on input surfaces or displays of electronic devices
Implementation Method 2
optical waveguide to direct the light emitted by the laser diodes
Implementation Method 3
a waveguide to direct the light emitted by the laser diodes
Data Source
AI summary
Disclosed herein are structures, devices, and systems for detecting touch and force inputs at multiple sensing locations on a surface of an electronic device using waveguide-based interferometry. A laser light source, such as a VCSEL, inserts light into a waveguide positioned adjacent to the sensing locations, and an input at a sensing location alters the inserted light in the waveguide allowing for determination of the input's touch or force at the sensing location. Wavelength modulation of the inserted light allows isolation in frequency of the signals from each sensing location. Optical phase locking can be used to lock an absolute distance beat frequency corresponding to a stationary reference point in the waveguide.