Interference Filter Layer Stack for Stable LiDAR Photon Rejection

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Solution Overview

Problem

Existing interference filters in Lidar systems allow too many solar photons to pass through, leading to a low signal-to-noise ratio due to mixing with laser photons, and have significant angular and thermal dependencies, which affect their performance in applications like self-driving cars, remote sensing, and drone surveillance.

Innovation Solution

The interference filter is designed with alternating high and low index layers, including amorphous silicon, amorphous germanium, and oxide layers, to minimize angular and thermal dependencies, using materials like hydrogenated amorphous silicon and germanium alloys to ensure high transmission of laser photons while rejecting ambient photons, and employing substrates with higher CTE to stabilize the filter against thermal changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional interference filters are used, then solar photons are transmitted through the filter, but the signal-to-noise ratio becomes unacceptable due to mixing with laser photons

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidtransmission of solar photons

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the optical parameters of the filter by using alternating high and low index layers with optimized thicknesses. This creates a narrow passband that selectively transmits laser wavelengths while blocking solar photons, thereby improving signal-to-noise ratio without sacrificing necessary photon transmission

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite layer structures combining materials with different refractive indices (high index and low index layers). This composite approach enables precise control over the transmission spectrum, allowing the filter to distinguish between laser photons and solar photons based on wavelength

Inventive Principle:

Principle #40Composite materials

2Ease of operation

If standard interference filters are used, then photon transmission is achieved, but angular dependence significantly affects filter performance

Engineering Contradiction:

Improvephoton transmissionVSAvoidangular dependence

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The patent modifies the structural parameters of the interference filter, specifically the thickness and refractive index of alternating layers. This configuration creates a flanger response curve that maintains consistent transmission characteristics across varying angles of incidence, reducing angular dependence while preserving photon transmission capability

Inventive Principle:

Principle #35Parameter changes

3Reliability

If conventional filter designs are used, then initial transmission performance is achieved, but thermal dependence causes performance degradation over temperature ranges

Engineering Contradiction:

Improvetransmission performanceVSAvoidthermal dependence

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent optimizes the physical and optical parameters of the filter layers to compensate for thermal effects. By carefully selecting layer thicknesses and refractive indices, the filter maintains stable transmission characteristics across temperature variations, reducing thermal dependence while preserving transmission performance

Inventive Principle:

Principle #35Parameter changes

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 achieves a high transmission of laser photons and minimizes ambient photon transmission, significantly improving the signal-to-noise ratio and maintaining performance across various angles and temperatures.

Implementation Method 1

The present disclosure generally relates to an interference filter with minimal angular and thermal dependence

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 2

Amorphous germanium or amorphous silicon are provided as layers within the filter to enable the filter to have a reduced dependence on the AOI

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

The method also includes increasing optical thickness in the filter with reduced temperature and decreasing the optical thickness in the filter with increased temperature to provide the reduced thermal dependence

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS12571978B2Interference filter with minimal angular and thermal dependence

Publication Date: 2026.03.10 OMEGA OPTICAL LLC

AI summary

A method includes positioning a substrate at an initial position. The method also includes placing a filter onto the substrate. The filter is configured with a first set of layers with a maximized index and a second set of layers with a maximized index. The index for the first set of layers is greater than the index for the second set of layers. The filter has a reduced/minimal dependence on an angle of incidence (AOI) and reduced/minimal thermal dependence. The filter transmits signal photons onto a photon detector, rejects ambient photons, and increases signal-to-noise ratio of the photon detector.