Optical Displacement Sensor Diffractive Elements Dynamic Range
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Solution Overview
Problem
Existing displacement sensors, such as microphones, face limitations in sensitivity, dynamic range, and cost due to reliance on capacitor structures and complex optics, with dynamic range typically limited to λ/8 and susceptible to illumination intensity variations.
Innovation Solution
The use of multiple diffractive elements with controlled height offsets and phase differences to generate signals with phase offsets, allowing for multiple phase readout, differential, or quadratic readout, which increases dynamic range and cancels illumination fluctuations, enabling accurate displacement measurement independent of light source intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single diffractive element is used for displacement sensing, then the device structure is simple, but the dynamic range is limited to approximately λ/8
Solution Approach 1:
The patent divides the sensing system into multiple independent diffractive elements (at least two), each contributing to the overall measurement. By segmenting the sensing function across multiple elements with different heights or positions, the system achieves extended dynamic range while maintaining manageable device complexity through modular design.
Solution Approach 2:
The patent extends the sensing capability from a single measurement dimension to multiple dimensions by introducing diffractive elements at different heights or positions. This dimensional extension allows the system to resolve displacements beyond the λ/8 limit of a single element, effectively trading controlled structural complexity for significantly enhanced measurement capability.
2Measurement precision
If multiple diffractive elements with different heights are used to extend dynamic range, then the measurement precision is improved, but the device complexity increases
Solution Approach 1:
The patent divides the sensing system into multiple independent diffractive elements (at least two), each contributing to the overall measurement. By segmenting the sensing function across multiple elements with different heights or positions, the system achieves extended dynamic range while maintaining manageable device complexity through modular design.
Solution Approach 2:
The patent combines the output signals from multiple diffractive elements through signal processing to achieve extended dynamic range. By merging the phase information from elements at different heights, the system reconstructs displacement measurements that exceed the λ/8 limit of any single element, effectively combining multiple limited-range measurements into a wide-range measurement capability.
3Device complexity
If conventional capacitor structures are used for displacement sensing, then the device structure is simple, but the sensitivity and measurement precision are insufficient
Solution Approach 1:
The patent replaces conventional capacitor-based mechanical sensing with an optical diffraction-based system. By substituting the mechanical/electrical measurement principle with optical diffraction and phase measurement, the system achieves significantly enhanced sensitivity and measurement precision while maintaining a relatively simple device structure through the use of diffractive optical elements.
4Illumination intensity
If a totally reflecting membrane is used in Fabry-Perot devices, then the reflected light intensity is high, but there is no modulation of reflected light with cavity length change
Solution Approach 1:
The patent replaces the Fabry-Perot cavity reflection principle with a diffraction-based measurement principle. Instead of relying on cavity resonance and reflected light intensity modulation, the system uses diffractive elements to create phase-modulated signals that are insensitive to membrane reflectivity, thereby maintaining signal modulation capability even with highly reflective surfaces.
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 enhances sensitivity, linearity, and dynamic range, allowing displacement measurement over several wavelengths without requiring precise alignment or accurate idle position, and reduces the impact of light source variations, making the sensor more cost-effective and robust.
Implementation Method 1
The diffractive patterns direct light into their different diffraction orders (including the 0th diffraction order, i.e. reflection), and the intensity in some of the diffraction orders can be measured in order to generate different signals.
Implementation Method 2
at least one light source transmitting light in at least one chosen wavelength range into said cavities
Implementation Method 3
at least one light detector receiving light from the cavities, wherein each pair is adapted to provide a maximum diffractive efficiency at chosen wavelengths within said range
Data Source
AI summary
The present invention relates to an optical displacement sensor comprising a first at least partially reflective surface and a second surface having a diffractive pattern, the surfaces being provided on elements having a variable distance between them, each surface pair defining a cavity between them. The sensor also comprising at least one light source transmitting light at least one a chosen wavelength range into said cavities and at least one light detector receiving light from the cavities, wherein said diffractive patterns are adapted to direct light toward at least one detector provided in a known position relative to said diffractive surfaces.