Acousto-optic modulator Core working principle

What is acousto-optic modulator

An acousto-optic modulator (AOM modulator) is a precision optical device based on the acousto-optic effect, which dynamically controls the amplitude (intensity), frequency, phase, or spatial direction of a laser beam through the interaction of ultrasound and light waves.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    1. Acousto-optic modulator Core working principle

Ultrasonic field generation: Radio frequency (RF) electrical signals drive piezoelectric transducers to generate high-frequency ultrasonic waves in acousto-optic media such as tellurium dioxide, lithium niobate, quartz, etc.

Refractive index modulation: When ultrasound propagates in a medium, it causes periodic changes in the density of the medium (photoelastic effect), forming an equivalent “moving phase grating”.

Light sound interaction: When a laser beam passes through the grating at a specific angle (Bragg angle), Bragg diffraction occurs, producing 0th order (undeflected) and 1st order (deflected) diffracted light. By controlling the frequency and power of ultrasound, the intensity, frequency, and direction of diffracted light can be precisely controlled.

2. Acousto-optic modulator Core functions and working modes

Intensity modulation (switching and amplitude modulation): By controlling the on/off or power level of the ultrasonic field, nanosecond level high-speed switching (digital modulation) or continuous adjustment of the intensity of the laser beam (analog modulation) can be achieved. It is commonly used for laser pulse selection and optical switching.

Frequency shift: The diffracted light frequency undergoes a slight frequency shift (Δ f=ultrasonic frequency) due to the movement of the ultrasonic field, which can be used for laser Doppler velocimetry, heterodyne interference detection, etc.

Beam deflection (scanning): By changing the ultrasonic frequency to alter the diffraction angle, fast and inertial scanning of the beam is achieved, commonly used in laser imaging and micro/nano processing.

3. Acousto-optic modulator Core structure

Acousto optic medium: a transparent crystal or glass in which light and sound interact, determining the diffraction efficiency and bandwidth of the device.

Piezoelectric transducer: converts radio frequency electrical signals into ultrasonic waves and couples them into an acousto-optic medium.

Drive circuit: Provides high-frequency RF signals and achieves the superposition of modulated signals.

Sound absorption/reflection device: used to absorb or reflect ultrasonic waves to form traveling waves or standing waves, avoiding interference of reflected waves on the optical path.

4. AOM modulator Technical advantages and application scenarios

Advantages: No mechanical moving parts, extremely fast response speed (nanosecond level), high modulation bandwidth, high power tolerance (kilowatt level), and wide wavelength compatibility range (ultraviolet to infrared).

Application: Widely used in ultrafast laser system (such as Q-switching, mode locking, pulse selection), laser processing (micro nano processing, laser annealing), laser radar, fiber optic communication, spectral analysis, and laser medical fields.