Acousto-optic tunable filters
- Technology
- Acousto-optics
- Partner
- Isomet
Isomet’s electronically controlled acousto-optic filters (AOTF) are specially designed for use with broadband light sources and are often used with non-coherent and divergent light.
Tunable AOTFs make use of the inherent dependence of wavelength sensitivity in relation to so-called Bragg diffraction and thus enable specific wavelengths of broadband light sources to be filtered out by applying different radio frequencies (RF). Corresponding RF drivers are also available.
Range features
A high level overview of what this range offers
- Wavelength range: VIS, NIR, and mid-IR
- Tunable filters and line filters
- Fast switching times and fine spectral bandwidths for the selection of discrete laser wavelengths from multi-line laser sources
- Active apertures from 2.5×2.5mm² up to 10x10mm²
- Acceptance angle of 2.5° up to 6°
- Low input angular sensitivity
- High wavelength selectivity
- Intensity modulation through the level of HF power
- Suitable synthesisers also with an integrated amplifier
Downloads
for Acousto-optic tunable filters
What’s in this range?
All the variants in the range and a comparison of what they offer
| Model | Spectral range [nm] | Active aperture [mm²] | Acceptance angle [Deg.] | Optical bandwidth [nm] | Drive frequency [MHz] |
|---|---|---|---|---|---|
AOLF615-1046 | VIS | 2.5 x 2.5 | 3.5 – 4.5 | 1.0 – 6.0 | 109 – 65 |
AOLF615-1082 | VIS | 2.5 x 2.5 | 3.5 – 4.5 | 1.0 – 6.0 | 109 – 65 |
AOTF614-08 | VIS, NIR | 5 x 5 | 3.5 – 6.0 | 1.0 – 22.0 | 140 – 35 |
AOTF614-16 | VIS, NIR | 5 x 5 | 2.5 – 4.2 | 0.6 – 11.0 | 140 – 35 |
AOTF614-24 | VIS, NIR | 5 x 5 | 3.5 – 6.0 | 0.4 – 7.0 | 140 – 35 |
AOTF1110-VB | VIS, NIR | 10 x 10 | 5.7 (nominal) | Variable | 80 – 50 |
AOTF920-14 | NIR | 5 x 5 | 3.4 – 6.1 | 2.0 – 27.0 | 95 – 26 |
AOTF920-20 | NIR | 5 x 5 | 2.6 – 4.9 | 1.5 – 18.5 | 95 – 26 |
AOTF920-24 | NIR | 5 x 5 | 2.8 – 5.0 | 1.0 – 15.5 | 95 – 26 |
AOTF-1550-SLS | 1550 | 3 x 3 | – | 2.0 | 81 – 84 |
AOTF-1331 | 2500 – 4000 | 7 x 7 | 5 | 30 – 50 | 24 – 39 |
FAQs
for Acousto-optic tunable filters
An AOTF is an electronically tunable optical filter that selectively transmits or deflects light of specific wavelengths using the acousto-optic effect. A high-frequency acoustic wave is generated inside a crystal and periodically modulates its refractive index. This periodic modulation acts like a diffraction grating that efficiently diffracts only light of a certain wavelength. Changing the RF frequency allows the desired wavelength to be selected—without mechanical movement.
The AOTF is based on the acousto-optic effect, specifically the diffraction of light by an acoustic wave in a transparent medium. The acoustic wave creates a spatially periodic change in the refractive index, forming a moving diffraction grating. This is a form of Brillouin scattering, where light is diffracted by the acoustic grating.
Only light of a specific wavelength satisfies the Bragg condition and is efficiently diffracted at a defined angle. Other wavelengths are barely diffracted. This results in a bandpass-like spectral filtering:
- Only light of the “matching” wavelength (depending on RF frequency) is transmitted or extracted
- The filter wavelength is precisely controlled via the RF frequency
The spectral resolution Δλ describes the ability to distinguish between two closely spaced wavelengths. It depends on:
- Crystal length (longer = higher resolution)
- Aperture size (larger = better selection)
- Sound velocity in the medium
- Diffraction geometry (collinear vs. non-collinear) Typically, Δλ ranges from 1–10 nm, depending on design.
The bandwidth describes the range of wavelengths that are diffracted simultaneously with significant efficiency (FWHM). Typically 0.1–5 nm in the visible range, depending on the crystal parameters, light source, and RF power. A smaller bandwidth corresponds to higher spectral selectivity but often comes with lower diffraction efficiency.
Very fast—typically in the range of 10 µs to <1 µs, depending on the design and crystal. The limitation is due to the transit time of the acoustic wave across the beam diameter. Therefore, AOTFs are ideal for fast spectral imaging (hyperspectral cameras) or real-time spectroscopy.
The tuning range is the spectral range over which the filter can be electronically adjusted. It depends on:
- RF frequency range of the driver (e.g., 30–120 MHz)
- Material dispersion (e.g., in TeO₂)
Typical tuning ranges:
- VIS: 400–700 nm
- NIR: 900–1700 nm
- SWIR: up to 2500 nm
