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Acousto-Optic Modulators for Fiber Optics

Acousto-optic modulators (AOMs) enable you to rapidly switch on or off laser beams or modulate their intensity by means of light interaction with acoustic waves in an optically polished piece of crystal or glass.

An electric signal is used to vibrate a transducer attached to an acousto-optic crystal or glass, creating soundwaves that scatter light beams in either isotropic or anisotropic ways.

Bragg Cells

An acousto-optic modulator typically employs a phased array of interdigital transducers in an interdigital layout. Each individual transducer element is driven by RF signals with specified amplitude and phase; their power then generates phase shift that forms an ordered phase grating with desired phase response characteristics; in general, their diffraction efficiency increases with increased drive power up until saturation occurs at higher powers.

Acousto-optic (AO) modulators typically employ phased array acoustic transducers for interaction with guided wave AO mode, preferably using birefringent crystals such as LiNbO3, Hg2 Cl2, or Hg2 Br2. The interaction medium should ideally consist of these birefringent materials for maximum effect.

Acoustic Bragg Diffraction allows laser beams incident on crystals to have their optical intensity altered by changes in index of refraction in the volume containing their grating (see Figure 1). These changes result from periodic expansion and compression of an acoustic wave, creating regions of high and low density inside Bragg cells and changing phase diffraction patterns accordingly, thus changing which way optical beams reflect off their surfaces.

Once controlled properly, acoustic phase shifting produces an acousto-optic modulator with fast repetition rate and large optical aperture. Furthermore, its unique polarization-independent operation makes this device suitable for devices using longitudinal or shear acoustic waves in conjunction with an isotropic interaction medium.

Contrary to mechanical choppers, acousto-optical modulators are highly stable devices which can operate at high speeds without risking signal integrity loss. With these advantages in mind, optical switches are ideal for use as an acousto-optical chopper in lock-in detection systems or an optical gate for fiber optic communications. Acousto-optical modulators offer an eco-friendly alternative to electric chokes that rely on electronic switches with moving parts prone to vibration, wear, and damage. Furthermore, these modulators are less costly than equivalent laser systems; thus making the acousto-optical commutator an attractive option for high speed applications as well as larger systems sizes.


Transducers are devices designed to convert input energy into proportional output energy, or vice versa. There are two main categories of transducers based on how they convert it; active transducers require external power source in order to function; passive ones do not. Active transducers are commonly known as power transducers while their counterparts don’t.

Acousto-Optic Modulators (AOM) are widely utilized across a range of fields such as fiber optic lasers for Q-switching, signal modulation in telecom networks and frequency control in spectroscopy. AOM operate using the photoelastic effect – interactions between light and acoustic waves within a crystal that results in periodic fluctuations of its refractive index resulting in light diffracting into distinct frequencies in an organized fashion.

An AOM is comprised of a piezoelectric transducer that generates sound waves in the crystal material, and a mirror which directs light beams at specified angles. When vibrated by an RF drive signal, its vibration causes acoustic waves that cause changes in refractive index, thus producing an Acousto-Optic Bragg cell that diffracts incoming laser beam into different orders; tuning this cell further can maximize first order diffraction through changing orientation of its acoustic waves within its crystal structure.

Acoustic waves produced in an AOM can also be used to control the intensity of its diffraction pattern. By altering its intensity, first order diffraction order intensity can also be altered allowing users to produce various pulse shapes using AOMs.

AOMs come with different combinations of insertion loss, extinction ratio and rise time options to suit various applications. Their high acousto-optic efficiency and low noise/power consumption makes them suitable for switching, pulse picking, fast attenuators or attenuators among many others.


Crystals are solid materials composed of atoms or molecules organized in an ordered, repeating pattern spanning across all three spatial dimensions. Their scientific study is known as crystallography; typical forms include ionic, metallic, covalent network or molecular crystals that may either insulating, semi-conducting or conducting depending on which types of atoms or molecules compose their make up as well as bonding relationships among them.

A crystal’s “grain” or order can be best described by its periodic arrangement; its lattice structure being held together by single and multiple covalent bonds between its atoms, giving rise to periodic arrangements within it and giving a crystal its characteristic “grain”.

Utilizing a piezoelectric transducer, an RF drive signal is applied to an acousto-optic modulator crystal that generates acoustic waves within it, which then cause periodic changes in refractive index that diffract light – creating a frequency shift which modulates laser intensity.

Acousto-optic devices can also be used for phase modulation of laser beams. When aligned correctly to a Bragg cell, phase modulation occurs with each frequency shift in acoustic waves emitted by crystal. This can help create complex pulse shapes.

AeroDIODE now offers fiber coupled acousto-optic modulators online and with fast delivery, for convenient amplitude modulation of laser light through singlemode fibers. These modules provide an easy solution for controlling timing, intensity and temporal shape of laser output as precisely as a few nanoseconds. A selection of RF drivers compatible with either analog or digital input trigger signals are also available to trigger the modulators; additionally a TOMBAK pulse picker synchronization board can support advanced mode locked laser applications.


Acousto-optic modulators can be utilized in numerous applications for high-speed amplitude or frequency control of laser light, using radiofrequency sound waves to utilize their acousto-optic effect and shift light frequencies accordingly. They are most frequently seen used in laser Q-switching applications or signal modulation applications in telecom. Furthermore, these modulators have also found use within spectroscopy for frequency regulation purposes.

An acousto-optic modulator typically comprises of a crystal or piece of glass that is transparent for visible and near-infrared wavelengths of light, such as visible or near-infrared radiation. An electric signal applied to its transducer produces vibrations and sound waves within it that alter its density, eventually changing the refractive index over time and producing an output beam with altered frequency characteristics.

An acousto-optic modulator’s operation depends on factors like its size, material composition and design; typical materials for such modulators include tellurium dioxide, crystalline quartz and fused silica; chalcogenide glasses like Flint Glass; lithium niobate and gallium phosphide for infrared applications. Selection depends upon various criteria including diffraction efficiency, optical damage threshold threshold and mode area requirements.

An acousto-optic modulator’s grating is typically optimized to maximize low scatter and high laser damage threshold, providing an effective diffraction grating for laser beams. Diffraction angle is limited to first order to reduce stray light while increasing wave frequency (RF driving signal) increases efficiency; however this decreases optical damage threshold.

Acoustic-optic modulators are often designed with both high extinction ratio and low insertion loss in mind, along with stable polarization for optimal performance. Telecommunications companies frequently rely on these devices for fast amplitude modulation of laser light in single-mode fiber. They’re also popularly employed for applications like optical signal processing and narrow line width laser measurement.

G&H’s Fiber-Q Acoustic Optic Modulator is an economical and compact hermetic solution designed for direct integration into fiber-optic systems. When combined with an RF driver, this device can perform fast amplitude modulation and high frequency shifting within visible and near infrared wavelength ranges. Insertion loss, extinction ratio and modulation rate depend on which specific RF driving conditions are selected – G&H’s team can assist in finding an RF driver suitable for your application.
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