Under-Display Optical Proximity Sensing Without OLED Bright Spots
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Solution Overview
Problem
The integration of optical proximity sensors behind OLED displays in smartphones can cause screen distortion due to infra-red or near infra-red light energy passing through, leading to visible bright spots on black screens.
Innovation Solution
Incorporating a microlens or microlens array and/or optical diffuser between the light emitter and the OLED screen to reduce the maximum energy density of the light beam, and using multiple light emitters to spread out optical energy, ensuring sufficient energy for proximity sensing while minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the proximity sensor is moved behind the OLED display to maximize screen area, then the screen area is increased and the sensor can be integrated without bezel apertures, but the IR or NIR light from the sensor causes screen distortion and visible bright spots on the OLED
Solution Approach 1:
An optical diffuser or microlens array is introduced as an intermediary component between the light emitter and the OLED display. This intermediary scatters or redistributes the IR/NIR light beam, reducing the peak energy density that reaches the OLED while maintaining sufficient total energy for proximity sensing. The diffuser acts as a mediator that decouples the harmful concentrated energy from the useful sensing function.
Solution Approach 2:
The patent changes the spatial distribution parameter of the light energy by using optical elements that transform the concentrated beam into a scattered pattern. This parameter change from concentrated to distributed energy reduces the peak intensity (energy density) incident on the OLED screen, thereby eliminating the bright spot distortion while preserving the overall light energy needed for accurate proximity detection.
2Object-affected harmful factors
If multiple light emitters are used to spread out optical energy and reduce maximum energy density, then screen distortion is reduced, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent segments the single light emitter into multiple VCSELs (vertical-cavity surface-emitting lasers) arranged in an array. Each VCSEL emits a lower energy beam, and collectively they provide the necessary total energy for proximity sensing. This segmentation distributes the optical energy across multiple sources, reducing the maximum energy density incident on the OLED screen while maintaining sufficient sensing capability.
Solution Approach 2:
Instead of using a single emitter, the patent transitions to a two-dimensional array of multiple emitters. This dimensional change allows the energy to be spread out spatially across the array, reducing peak energy density in any single location on the display while maintaining adequate total energy flux for proximity detection.
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 effectively reduces or eliminates screen distortion by distributing the light energy more uniformly, maintaining performance for proximity sensing without causing visible spots on the OLED screen.
Implementation Method 1
The means for reducing the maximum energy density of the light beam can include, for example, a microlens, a microlens array
Implementation Method 2
The means for reducing the maximum energy density of the light beam can include, for example, a microlens, a microlens array, and/or an optical diffuser
Implementation Method 3
a light emitter operable to produce light having a wavelength for transmission through the display screen toward a target object
Implementation Method 4
a light sensor operable to sense light reflected by the target object and having the wavelength
Data Source
AI summary
An apparatus includes a display screen, and an optical proximity sensor module disposed behind the display screen. The optical proximity sensor module includes a light emitter operable to produce light having a wavelength for transmission through the display screen toward a target object, and a light sensor operable to sense light reflected by the target object and having the wavelength. The optical proximity sensor module can includes means for reducing a maximum energy density of a light beam produced by the light emitter. The means for reducing the maximum energy density of the light beam is disposed between the light emitter and the display screen so as to intersect the light beam produced by the light emitter. In some cases, there are multiple light emitters collectively operable to provide sufficient optical energy for proximity sensing without producing a visible spot on the display screen. These and other techniques can help reduce or eliminate display screen distortion caused by energy from the light emitters.