Roughened Acoustic Absorber Surface for AO Devices
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Solution Overview
Problem
Acoustic absorbers in acousto-optic devices face issues with unwanted backward acoustic reflections and heating due to conventional smooth surfaces, leading to frequency shifts and mechanical stress, which can cause malfunctions and damage.
Innovation Solution
Implementing a roughened surface with a root mean square (rms) surface roughness of at least 1 μm and feature periodicities matching the bulk acoustic wave wavelength on the second face of the AO crystal, converting acoustic waves to surface-localized waves for efficient dumping and reducing reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a smooth surface is used for acoustic beam dumping, then the acoustic absorber can be simple in structure, but backward acoustic reflections occur causing frequency shifts and harmonics
Solution Approach 1:
The patent applies local quality by creating a roughened surface with specific micro-scale features (rms roughness of 0.1-10 μm) only on the acoustic beam dumping surface, while other surfaces remain smooth. This localized surface modification targets the specific problem of backward reflections without complicating the entire device structure.
Solution Approach 2:
The patent changes the surface roughness parameter from optically smooth to a controlled roughness range (0.1-10 μm rms) with specific feature periodicities (0.1-10 times the acoustic wavelength). This parameter change transforms the surface properties to convert backward-traveling acoustic waves into surface-localized waves, suppressing reflections while maintaining structural simplicity.
2Reliability
If a roughened surface is implemented to suppress backward reflections, then acoustic wave dumping efficiency improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a broad but controlled range for surface roughness (0.1-10 μm rms) and feature periodicity (0.1-10 times acoustic wavelength), allowing manufacturing flexibility while achieving the desired acoustic wave conversion. This parameter range provides sufficient tolerance for manufacturing variations.
Solution Approach 2:
The patent applies partial action by requiring the roughened surface only over a portion of the acoustic beam dumping surface (at least 50% of the transducer face area), rather than the entire surface. This reduces the total manufacturing precision burden while still achieving effective suppression of backward reflections.
3Temperature
If conventional smooth surfaces are used, then manufacturing is easier, but heating of the acoustic absorber and AO crystal increases
Solution Approach 1:
The roughened surface is applied locally to the acoustic beam dumping surface where acoustic waves are absorbed, specifically targeting the region that generates heat. This localized treatment reduces heating at the critical location without requiring complex processing of the entire device.
Solution Approach 2:
By changing the surface roughness parameter to 0.1-10 μm rms with appropriate feature periodicities, the patent enhances acoustic wave conversion to surface-localized waves, which are then absorbed more efficiently. This reduces the acoustic energy that would otherwise be converted to heat in the bulk material, lowering temperatures while using standard surface processing techniques.
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 effectively suppresses backward acoustic reflections and reduces heating, enhancing the efficiency and reliability of AO devices by spreading acoustic energy laterally, thus preventing malfunctions and damage.
Implementation Method 1
a roughened surface with surface features on at least the face of the AO device receiving the acoustic wave after interacting with the optical beam
Implementation Method 2
converting acoustic waves to surface-localized waves for efficient dumping and reducing reflections
Data Source
AI summary
An acousto-optic (AO) device includes an AO crystal having a plurality of faces including a first face and a second face. An input transducer bonded to the first face (top electrode) for receiving a radio frequency (RF) signal and launching bulk acoustic waves (BAWs) configured to interact with an optical beam propagating in the AO crystal, wherein the BAWs are received at least in part by the second face after interacting with the optical beam. The second face has a roughened surface portion over an area of at least (≧) 50% of an area of the top electrode, and a root mean square (rms) surface roughness≧1 μm and a surface profile derivable from a Fourier transform which provides at least one a first spatial frequency peak from 1 cycle/mm to 300 cycles/mm or at least one band of spatial frequency peaks from 1 cycle/mm to 300 cycles/mm.