Holographic Stray Light Filter for Lidar Signal Integrity
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Solution Overview
Problem
Conventional lidar sensors face interference from stray light, particularly 'ghost images' caused by light outside the field of view reaching the detector, which degrades signal quality and requires frequent recalibration with design changes.
Innovation Solution
An anisotropic holographic stray light filter is developed using volume holograms with multiple layers and holographic functions, allowing specific angles and wavelengths to be blocked or passed through, effectively reducing stray light interference and enhancing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional lens systems are used to collect and image light onto the detector, then the field of view can be covered, but ghost images are generated by stray light reaching the detector through multiple reflections
Solution Approach 1:
A holographic optical element is introduced as an intermediary component between the lens system and the detector. This HOE acts as a mediator that selectively diffracts useful light into the detector while blocking stray light paths, thereby eliminating ghost images without compromising the main signal transmission.
Solution Approach 2:
The holographic optical element is designed with spatially varying diffraction properties. Different regions of the HOE have optimized diffraction efficiencies for specific angular ranges, allowing selective transmission of useful light from the field of view while blocking stray light from outside the field of view at different locations on the element.
2Device complexity
If the receiving optics is stationary, then the system complexity is reduced, but the field of view requirements become more stringent to account for calibration tolerances
Solution Approach 1:
The holographic optical element is designed with specific diffraction angle parameters that compensate for calibration tolerances. By optimizing the grating vector and diffraction geometry, the system maintains accurate field of view coverage without requiring precise mechanical alignment or movement of the receiving optics.
3Measurement precision
If holographic optical elements with volume diffraction are used, then wavelength and angle selectivity are achieved, but the device complexity increases compared to conventional optics
Solution Approach 1:
The holographic optical element combines multiple functions into a single component: it acts as both a beam deflector and a wavelength/angle filter. The volume hologram structure integrates diffraction and filtering functions that would otherwise require separate optical components, reducing the overall system complexity despite the advanced functionality.
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 filter significantly reduces stray light reaching the detector, improving signal-to-noise ratio and enabling higher resolution and range capabilities for lidar sensors, while being cost-effective and adaptable to various optics designs.
Implementation Method 1
the beam deflection is not defined by a refraction but by a diffraction at the volume grating
Implementation Method 2
Because of the volume diffraction, a characteristic wavelength and angle selectivity or also a filter function may additionally be allocated to the holographic optical elements
Implementation Method 3
The filter device blocks optical radiation that impinges upon the filter element from a defined first solid angle
Data Source
AI summary
A filter device for an optical sensor, including a hologram having a defined number of holographic functions, which are developed in such a way that the filter device blocks optical radiation that impinges upon the filter device from a defined first solid angle and optical radiation that impinges upon the filter device from a defined second solid angle is able to pass through the filter device.