Acousto-Optic Filter Design for Reduced Wavelength Angular Spread
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Solution Overview
Problem
Conventional acousto-optic tunable filters exhibit significant wavelength-dependent angular spread of output light, which is detrimental to high-resolution imaging applications like confocal microscopy and limits simultaneous illumination of a sample with multiple wavelengths.
Innovation Solution
A novel filter design deviating from the parallel-tangent condition, limiting angular acceptance range to collinear light entry, reduces wavelength-dependent angular spread by adjusting filter parameters such as entrance and emission surface orientations and transducer angles, enabling simultaneous illumination of a sample with multiple wavelengths at the same exit angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional acousto-optic tunable filter designs are used, then diffraction efficiency is improved, but wavelength-dependent angular spread of output light increases
Solution Approach 1:
The patent modifies the angular characteristic of the AOTF by changing design parameters such as the orientation of the filter crystal with respect to the incident light direction and the length of the transducer. These parameter changes create an angular characteristic with an extremum that provides collinear output for multiple wavelengths, resolving the contradiction between maintaining diffraction efficiency and controlling angular spread.
2Power
If conventional filter designs are used, then diffraction efficiency is improved, but simultaneous illumination with multiple wavelengths at the same location is prevented
Solution Approach 1:
By modifying the angular characteristic through parameter changes in the filter design, the system enables multiple wavelengths to exit at the same angle, allowing simultaneous illumination of the same sample location with multiple wavelengths while maintaining diffraction efficiency.
Solution Approach 2:
The modified AOTF design provides multi-functionality by enabling both high diffraction efficiency and simultaneous multi-wavelength illumination capability, making the device adaptable for applications like Raman spectroscopy that require both features.
3Ease of operation
If conventional filter designs are used, then angular spread is tolerated in some applications, but high resolution imaging applications require collinear light output which is not achieved
Solution Approach 1:
The patent applies parameter changes to the filter design to create an angular characteristic with an extremum, which provides collinear output for multiple wavelengths. This resolves the contradiction by achieving the collinear output required for high-resolution imaging while maintaining ease of operation.
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 new filter design significantly reduces angular spread, allowing for efficient, collinear illumination of a sample with multiple wavelengths, enhancing image quality in applications like confocal microscopy and enabling simultaneous multi-wavelength illumination.
Implementation Method 1
applying a specific radio frequency signal to a piezoelectric transducer which generates an acoustic wave in the filter crystal
Implementation Method 2
The acoustic wave causes refractive index fluctuations in the filter material, these fluctuations acting as a diffraction grating
Implementation Method 3
the light propagating through the filter material is diffracted in case that the light wavelength matches the diffraction grating
Data Source
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AI summary
An optical filter device (102) for illuminating a sample (104) comprises a light supply unit (108) configured to generate input light (110) of a predetermined spectral bandwidth in a collinear manner, an acousto-optic tunable filter (112) configured to receive the input light (110) and to emit diffracted output light (126) including multiple wavelengths from the spectral bandwidth at exit angles towards the sample (104), said exit angles defining an angular spread (C) among the multiple wavelengths of the output light (126). The angular spread (C) among the multiple wavelengths of the output light (126) is determined by an angular characteristic (W2-W5) varying from a minimum wavelength to a maximum wavelength. The angular characteristic (W2-W5) has an extremum at an intermediate wavelength between the minimum wavelength and the maximum wavelength to provide at least one group (P1-P3, T1-T3) of different wavelengths having the same exit angle.