Acousto-Optic Deflector Bandwidth Extension via Beam Blanking
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Solution Overview
Problem
Acousto-optic deflectors are limited to a bandwidth of less than one octave due to design rules that prevent higher diffraction orders, leading to inefficiencies in scanning and potential ghost images.
Innovation Solution
An extended frequency chirp of at least 6.1 MHz/μs is used to drive the acousto-optic deflector, combined with aperture framing and blanking intervals, allowing operation beyond one octave while minimizing ghost images through careful placement of field and aperture stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the AOD operates over a bandwidth of less than one octave, then higher diffraction orders are avoided, but the scanning speed and throughput are limited
Solution Approach 1:
The patent extracts and removes higher diffraction orders using a spatial filter (aperture stop) positioned at the focal plane of a lens. This allows the AOD to operate over more than one octave bandwidth while preventing harmful higher diffraction orders from reaching the workpiece, thus resolving the contradiction between expanded bandwidth and avoidance of diffraction artifacts
Solution Approach 2:
The patent applies preliminary blanking of the beam before it enters the AOD during frequency transitions. This preliminary action prevents higher diffraction orders from being generated in the first place during octave transitions, allowing faster scanning without the harmful effects that would normally limit the bandwidth
2Speed
If the frequency chirp sweep time is reduced to increase scanning speed, then the proportion of time consumed by beam blanking increases, but faster scanning is needed
Solution Approach 1:
The patent changes the operating parameters by allowing the AOD to operate over more than one octave bandwidth. This parameter change reduces the total frequency sweep range required, thereby reducing the absolute blanking time needed while maintaining or increasing scanning speed across the same angular range
3Productivity
If the AOD bandwidth is extended beyond one octave, then scanning speed and throughput improve, but higher diffraction orders create ghost images
Solution Approach 1:
The patent uses a spatial filter (aperture stop) to extract and remove higher diffraction orders that cause ghost images. This allows the system to operate over more than one octave bandwidth, improving throughput while eliminating the harmful ghost image artifacts through physical filtering of the diffracted light paths
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 increases the effective bandwidth and scanning speed of acousto-optic deflectors by 10-30% beyond traditional limits, enhancing throughput and reducing the proportion of the chirp signal consumed by blanking, thus improving the efficiency and performance of patterning and inspection systems.
Implementation Method 1
An ultrasonic wave generated at the surface or within the confines of the light control element sets up conditions in the element which produce a change in the optical parameters (e.g., refractive index) directly controlling the light
Implementation Method 2
The diffraction of light that passes through the AOD is a function of time as the deflection-causing signal varies
Data Source
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Figure 3~5
AI summary
The technology described applies an extended frequency range of over one octave to drive an acousto-optic deflector, thereby defying a design rule of thumb that limited bandwidth to just under one octave. A combination of extended frequency range and well-timed beam blanking reduces the proportion of a so-called chirp signal that is consumed by beam blanking. This increases the working, effective portion of the sweep signal.