3719 Warren Avenue Bellwood,
Illinois 60104 USA






How Can Acousto-Optic Devices Be Used in Optical Communication?

Acousto-optic effect refers to the interaction of high frequency sound waves with certain crystals that causes periodic fluctuations in their refractive index, creating the “acousto-optic effect.”

This change can be used to amplitude modulate, deflect or shift the optical frequency of laser light and has been implemented into devices such as Q-switches, mode-lockers and beam deflectors.

What is an acousto-optic device?

An acousto-optic device is a type of optical modulator that utilizes sound waves to modulate the amplitude, frequency and phase of light passing through an acousto-optic material. They can be found in applications such as Q-switches, ion traps and optical tweezers.

Acoustic interaction within crystals may either be isotropic (longitudinal) or anisotropic (shear). An isotropic interaction allows incident and diffracted beams to see equal refractive index values, providing minimal energy loss during travel of an acoustic wave – making this ideal for high performance devices.

An anisotropic interaction occurs when an acoustic wave travels with significant energy loss, and both incident and diffracted beams experience different refractive index values, leading to reduced velocity or, even further, the dispersal of laser light beams into several orders.

These diffractions occur at any angle of incidence and are typically observed in materials with relatively low acoustic frequencies, small acousto-optic interaction lengths and large polarization dispersion – fused silica being one such material.

Acousto-optic tunable filters are an optical component which utilize sound waves to modify the wavelength of light. Commonly referred to as Bragg cells or acousto-optic deflectors, this device can be found in Q-switches, telecom systems and spectroscopy applications.

An acousto-optic tunable filter is created by attaching an acoustic transducer to a photoelastic medium like glass or quartz and matching its impedance with that of its bonding layers, to achieve time-dependent strain and frequency-dependent efficiency in its performance.

There are various acousto-optic materials, with fused silica, lithium niobate and tellurium dioxide being the most commonly used ones. All three exhibit the acousto-optic effect and make up most devices using this effect.

How does an acousto-optic device work?

An acousto-optic device operates by applying an RF drive signal to a piezoelectric transducer, which then generates an intense sound wave. This causes changes to occur within transparent crystal or glass material and generates periodic diffraction patterns which then serve as the optical output for an acousto-optic modulator.

An acousto-optic device produces a diffraction pattern known as a Bragg cell that can be designed to maximize laser beam diffraction into one first order position due to photoelastic effect produced when an acoustic wave interacts with light.

Most acousto-optic devices operate in the Bragg regime, whereby the number of diffraction orders (known as bessel functions) produced by an acoustic wave is determined by its Q factor – an index determined by both frequency and amplitude – while wavelength has some influence as well.

An acousto-optic cell can achieve high diffraction efficiencies with shorter wavelength acoustic waves; however, longer waves produce lower efficiencies primarily because their frequencies vary slightly relative to that of radio frequency signals, causing the direction of diffracted beams to change subtly and cause them to shift further away from each other.

To maximize diffraction efficiencies, it is necessary to optimize the rise time and modulation rate of an acousto-optic modulator. These parameters measure how long it takes an acoustic wave from a driver to travel from it into a cell; their timing depends on both diameter of laser beam entering it as well as speed of sound wave entering cell; typically for one millimeter laser beams this period takes around 150 nanoseconds (typical rise time for 1-millimeter laser beam is 100 nanoseconds).

An acoustic wave that enters a cell is diverted toward an absorber on the other side of the crystal and directed there for processing, so any remaining reflections do not cause secondary diffraction. When shorter wavelengths are utilized, this task may be achieved by applying soundwaves directly onto surfaces composed of piezoelectric materials like zinc oxide, gallium arsenide, aluminum nitride or lithium niobate thin-film piezoelectric materials (such as zinc oxide, gallium arsenide), aluminum nitride or lithium niobate thin-film piezoelectric materials such as zinc oxide, gallium arsenide and aluminum nitride or lithium niobate ( respectively).

Can an acousto-optic device be used in optical communication?

Acousto-optic devices can be used in optical communication to modulate and shape the light that is transmitted, by injecting acoustic waves into it and diffracting them. Acoustic waves may be produced either using piezoelectric materials or devices designed to generate soundwaves.

Tuning the frequency of an acoustic wave allows us to manipulate its resonance frequency, which makes acousto-optic tunable filters so useful; light is sent over fibre optic cable directly into the filter where it can then be altered by our tuning parameters.

Building AOMs and AODs using thin crystals cut to an appropriate angle to optimize resonance can be accomplished using an RF driver whose impedance matches up perfectly with each crystal’s impedance characteristics.

AOMs and AODs have numerous applications, from Q-switch lasers and ion traps to optical tweezers and optical spectrometers.

However, AOMs and AODs require input light that is polarized. This is because acoustic waves may either be longitudinal or shear in nature which affects how they interact with input light.

Acoustic waves can also be generated with interdigital transducers placed directly onto a thin-film piezoelectric material surface, and have proven themselves highly effective for frequency shifting and optical modulation applications.

This technique is attractive due to the high acoustic power that can be achieved and low insertion loss of surface acoustic waves. To minimize standing-wave effects, however, the acoustic waves must be contained within an approximate thickness of few millimetres in order to be within safe limits of thickness.

An advanced new acousto-optic device has been invented that can shape and steer beams of light at speeds never seen before. Researchers created an array of 64 piezoelectric elements acting as loudspeakers whose complex sound fields produce deflected and sculpted any light passing through them, thus creating beams of light which move at rapid rates in real time – an impressive advancement for holography and optical tweezers alike.

What are the limitations of an acousto-optic device?

Acousto-optic devices may be used for optical communication; however, there are a few restrictions. Chief among them is an inability to produce uniform spectral passband across a range of wavelengths; sidelobes also degrade performance significantly.

Acousto-optic tunable filters (AOTFs) can be tuned to an expansive wavelength range, but their bandwidth is constrained by two factors: (1) electroacoustic bandwidth of piezoelectric transducer; and (2) acoustic attenuation across optical aperture. For crystalline materials, attenuation increases proportionally to frequency squared; therefore limiting linear aperture size within visible and near infrared light ranges.

To achieve a wide bandwidth, an AOTF designer often employs an array of transducers bonded together on one crystal; these transducers operate at different acoustic frequencies for greater effectiveness and spatial resolution – however this approach requires additional drive power.

However, most AOTFs are unaffected by this restriction as their performance relies on the quality and physical properties of both transducers and crystals used. One way of evaluating an acousto-optic material’s figure of merit is through measuring various parameters including index of refraction, density, wave velocity and wavelength resolving power.

Fused quartz, tellurium dioxide and lithium niobate are among the most popularly used acousto-optic materials, while gallium phosphide and boron nitride are being developed further as potential materials for these applications.

The acousto-optic figure of merit (AOFM) is an important element in designing acousto-optical deflectors, modulators and tunable filters. For each device type it reflects the relationship between various variables relevant to device function (such as deflection efficiency or wavelength resolving power) and overall figure of merit of crystal or piezoelectric material used for manufacturing it.

As well as considering acoustic figure of merit, device designers must also factor in other crucial performance parameters, including drive power and solid angular aperture. These can be optimized by changing material density or wave amplitude accordingly to achieve the desired properties.
Scroll to Top