Through-Display Interferometric Proximity Sensing With Waveguide Coupling
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Solution Overview
Problem
Conventional through-display proximity sensors suffer from poor accuracy and precision due to self-reflection and scattering of emitted light, leading to undesirable device behaviors such as unexpected touch screen enabling/disabling, display brightness changes, and speaker volume adjustments.
Innovation Solution
An optical sensing system with a light emitter and photosensitive element, optically coupled via a waveguide, operates as a heterodyne interferometer to determine object proximity and velocity by analyzing light reflections through the display, leveraging field strength fading rather than intensity-based methods, which reduces noise and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional reflective infrared sensors are used to detect proximity through the display, then the sensor can detect objects nearby, but self-reflection and scattering of emitted light by the display reduces signal to noise ratio and measurement precision
Solution Approach 1:
The patent replaces conventional intensity-based detection with interferometric detection using a heterodyne interferometer. This substitutes the measurement mechanism from simple light intensity monitoring to coherent light field interference analysis, enabling discrimination between object-reflected light and display-self-reflected light based on their different optical path characteristics
Solution Approach 2:
The patent introduces an optical waveguide as an intermediary component that couples the light emitter and photosensitive element while establishing a reference optical path. The waveguide enables the interferometric measurement by providing a stable reference beam that interferes with the object-reflected light, allowing precise extraction of proximity information despite the presence of display self-reflection noise
2Reliability
If conventional intensity-based proximity sensing is used, then the system can operate through the display, but accuracy and precision are poor leading to unexpected device behaviors
Solution Approach 1:
The patent replaces intensity-based sensing with interferometric sensing using a heterodyne interferometer. This substitution transforms the measurement principle from monitoring overall light intensity to analyzing the interference pattern between reference and object-reflected light beams, enabling reliable proximity detection even in the presence of display self-reflection and scattering
Solution Approach 2:
The patent changes the detection parameter from light intensity magnitude to light field phase and frequency characteristics. By using heterodyne interferometry, the system detects proximity through changes in the interference pattern's frequency and phase, which are not affected by the absolute intensity variations caused by display self-reflection, thereby improving reliability
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 approach significantly improves signal-to-noise ratio, enabling more accurate and efficient proximity and velocity sensing with reduced power usage, allowing for precise control of device functions like enabling/disabling touch screens and adjusting display brightness.
Implementation Method 1
the light emitter is configured to emit light, and to illuminate the object, through the display
Implementation Method 2
The photodiode can be configured to receive light reflecting from the object, which may in many constructions also pass through the display
Implementation Method 3
The optical sensing system further includes an optical waveguide coupling the light emitter and the photosensitive element
Implementation Method 4
the optical sensing system can be operated as an interferometric optical sensor or, more specifically, as a heterodyne interferometer
Implementation Method 5
Output from the optical sensing system can be analyzed in frequency and/or time domain to determine a velocity of the object relative to the electronic device
Data Source
AI summary
An optical sensing system includes a transmitter side and a receiver side, and is configured to be positioned below a display of an electronic device. The transmitter side includes a light emitter. The receiver side includes an array of photodiodes. The light emitter of the transmitter side and the array of photodiodes of the receiver side are optically coupled via a waveguide. As a result of this construction, the optical sensing system can be operated as an interferometric optical sensor.