Optical Accelerometer Using VCSEL Polarization for Bias Stability

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Solution Overview

Problem

Existing optical accelerometer systems face issues with bias uncertainty, instability, and damage from excessive accelerations, leading to calibration challenges and noise in inertial measurement and navigation systems.

Innovation Solution

An optical accelerometer system utilizing a VCSEL laser that generates an optical beam with alternating linear polarizations, reflected by a spring-mounted mirror, and detected by photodetectors to generate an acceleration signal based on frequency changes, which is processed to calculate external acceleration, providing robustness and immunity to excessive accelerations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If electrostatic force-balanced accelerometer is used, then acceleration measurement capability is provided, but bias uncertainty and instability occur leading to measurement errors

Engineering Contradiction:

Improveacceleration measurement accuracyVSAvoidbias stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces the electrostatic force-balancing mechanism with an optical detection system. A proof mass is suspended by springs and detected optically using a laser beam and photodetector, eliminating the need for electrostatic forcing electrodes and complex feedback control while maintaining measurement capability and improving bias stability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an optical intermediary system (laser beam and photodetector) to detect the position of the proof mass. This optical mediator allows non-contact measurement of displacement, avoiding the harmful effects of electrostatic forces while providing precise acceleration measurement

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If pendulous electrostatic force-balanced accelerometer is used, then acceleration sensing is achieved, but damage from excessive input accelerations occurs requiring recalibration

Engineering Contradiction:

Improveaccelerometer functionalityVSAvoiddamage from excessive acceleration

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent employs soft suspension springs that can accommodate large displacements without damage. These springs act as mechanical cushions that protect the proof mass and suspension system from damage during excessive acceleration events, allowing the accelerometer to survive and continue operation without recalibration

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Ease of manufacture

If electrostatic forcing system is used, then position control of proof mass is achieved, but transient behavior and non-modelability cause bias uncertainty

Engineering Contradiction:

Improveposition control capabilityVSAvoidbias uncertainty

Core Design Contradiction:

Ease of manufactureVSLoss of information

Solution Approach 1:

The patent eliminates the electrostatic forcing system entirely and uses passive spring suspension with optical detection. This removes the complex electrostatic control electronics and eliminates transient behavior and non-modelability issues associated with electrostatic forcing, providing more predictable and modelable system behavior

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system achieves precise acceleration measurement with reduced noise and stability, minimizing the need for frequent calibration and improving accuracy in navigation and guidance systems.

Implementation Method 1

at least one photodetector configured to receive at least a portion of at least one of the optical beam and the reflected optical beam and to generate an acceleration signal

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

a mirror that is coupled to an accelerometer housing via a spring and is configured to reflect the optical beam

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

a mirror that is coupled to an accelerometer housing via a spring

Methodology Applied

Scientific EffectHooke's Law: Hooke's Law

Implementation Method 4

a laser configured to emit an optical beam at a linear polarization that periodically transitions between a first linear polarization and a second linear polarization in response to a reflected portion of the optical beam

Methodology Applied

Scientific EffectPolarization: Polarisation

Data Source

PatentEP2859302B1Optical accelerometer system

Publication Date: 2020.07.01 NORTHROP GRUMMAN SYSTEMS CORP

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AI summary

One embodiment includes an accelerometer system. The system includes a laser configured to emit an optical beam at a linear polarization. The system also includes an optical cavity system. The optical cavity system includes a mirror that is coupled to an accelerometer housing via a spring and is configured to reflect the optical beam. The optical cavity system also includes at least one photodetector configured to receive at least a portion of at least one of the optical beam and the reflected optical beam and to generate an acceleration signal that is indicative of motion of the mirror resulting from an external acceleration acting upon the accelerometer housing. The system further includes an acceleration processor configured to calculate a magnitude of the external acceleration based on the acceleration signal.