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Acousto-Optic Modulator

Acousto-Optic Modulators

Acousto-optic modulators (AOM) allow the intensity of light to be controlled and modulated at rates that far exceed mechanical shutters, even up to 70 MHz. Our modulators are optimized for low scatter and high laser damage threshold. Rise time, modulation rate, beam diameter, and power handling needs of the application need to be understood in order to identify the best acousto-optic modulator and RF driver solution.

An acousto-optic modulator (AOM) uses sound waves within a crystal to create a diffraction grating. As the power of the applied RF signal is varied, the amount of diffracted light varies proportionally. Modulators can be used like a shutter (cycling light on and off at a set frequency), or as a variable attenuator (controlling the intensity of transmitted light dynamically).

The most important factor in selecting a modulator is the required speed. This influences the choice of material, modulator design, and RF driver to be used. The speed of a modulator is described by the rise time, which determines how quickly the modulator can respond to the applied RF driver, and limits the modulation rate. Rise time is proportional to the time required for the acoustic wave to traverse the optical beam and for this reason is influenced by the beam diameter within the modulator.

Modulators fall into two general categories as regards speed. Very fast modulators can provide modulation frequencies up to ~70 MHz and can have a rise time as low as 4 ns. The input beam must be focused very tightly focused into the modulator to achieve this speed. Lower frequency modulators do not have this constraint, however, and can accept larger input beams. Their rise time is usually specified relative to the input beam diameter, in ns/mm.

In addition to speed, we also consider other selection criteria when identifying the right modulator and RF driver:

  • Wavelength of operation
  • Optical power
  • Type of modulation needed (analog or digital)
  • Beam diameter
  • Desired contrast ratio
  • Light polarization

大多数应用需要在调制器的“ON”和“OFF”状态之间具有高对比度,从而利用第一阶衍射光束。这导致消光比为40 dB和更高,但导致偏转光束的较低吞吐量(通常为85-90%)。在诸如强度调平的一些应用中,变速器更重要,并且对比度为约10dB是可接受的。这允许使用未限制的0级光束,通常导致> 99%的光吞吐量。

Applications of Modulators

Heterodyne interferometry, intensity levelling, intensity modulation, laser cooling, laser Doppler velocimetry, laser Doppler vibrometry (LDV), laser linewidth measurements, LIDAR, marking, material processing, micromachining, printing, via drilling

Product Wavelength Rise / Fall Time Active Aperture Operating Frequency Optical Material Type