Fiber Coupled Acousto-Optic Modulators (FAOM)

Acousto-optic modulators (AOM) are generally used outside the laser cavity to change the intensity of the incoming laser (amplitude-modulated AM). This can be simple ON/OFF modulation for quick switching or variable level modulation to achieve intensity modulation. The modulation mode is determined by the type of RF driver and can be digital (ON/OFF) or analog (sinusoidal, square wave, linear, random…). 

Generally, the RF driver of AOM adopts fixed frequency, the key parameter of the AOM is the rise/fall time, which defines the achievable “speed” or amplitude modulation bandwidth of the modulation. The rise/fall time is proportional to the beam diameter inside the modulator. Therefore, the diameter of the incident laser beam must be controlled in order to obtain a fast rise time. The AOM can be used as a shutter (cyclic switch at a set frequency) or as a variable attenuator (dynamically controlling the intensity of the transmitted light). Laser modulation is achieved by controlling the sound wave in the acousto-optic crystal caused by radio frequency.

SIMTRUM offers a series of free-space (up to 24 channels in a single channel) and fiber-coupled (bias-preserving and non-bias-preserving) AOM with a frequency range of up to 300 MHz and a rise as low as 6 ns. We provide AOM-matched series of RF drivers you can choose the corresponding RF driver according to the product specification.

AO Fiber-Coupled ModulatorsA

Product Brochure Link:  

Related ltems： Free-Space Modulators

Applications of AOM

• Laser light and Intensity modulation
• Laser radar or laser scanning
• Laser switch
• Laser Chopper

Main Product package list

• Fiber Coupled AOM
• RF Driver (Optional)

Advantages of AOM

• High-Speed Modulation: AOM can achieve extremely high modulation speeds, typically reaching tens of megahertz (MHz) to several gigahertz (GHz).
• High Stability and Precision: By precisely controlling the frequency and intensity of sound waves, AOM can achieve highly stable and precise beam modulation.
• Wide Wavelength Range: AOM is suitable for lasers of various wavelengths, from ultraviolet to infrared.
• No Mechanical Movement: AOM modulates the beam through sound waves, eliminating the need for mechanical components, reducing wear and maintenance requirements.

Fiber Coupled AOM Dimension

(Note: this is general reference size, for specific AOM please refer to product brochures)

RF Driver can generate RF signals and control the switch, frequency, power, etc. of the RF signal through external modulation signals. By modulating the RF signal, modulation of the laser ON/OFF, laser power, beam deflection, and other modulation can be achieved. There are various options for RF driver, such as fixed frequency or tunable bandwidth, with RF frequency mainly ranging from 20MHz to 250MHz.

RF power ranging from 1W to 150W, trigger frequency ranging from 1Hz to 1MHz, load of 50ohm, available for digital and analog modulation, 24VDC power supply.

SIMTRUM has a professional R & D and production team, the whole process of product independent production, can be customized according to customer needs.

Our driver support both Digital and Analog single, We are able to provide a range of RF driver based on Frequency, Output power and DC input. below are our driver general specification Range, the cost of RF drive was mainly determined by output power.

< 20W : Estimate cost ~1100USD
>20-100W : Estimate cost ~1600USD
>100W : Estimate cost ~2000USD

Water Cooled RF driver

Conduction cooled RF driver

Fin Cooled RF driver

RF Driver Control logic

Working Principle of Fiber Coupled AOM (Acousto-Optic Modulator)

The working principle of an Acousto-Optic Modulator (AOM) is based on the acousto-optic effect, which utilizes changes in the refractive index caused by the propagation of sound waves in an optical medium to modulate a light beam.

Specifically, the AOM modulates the light beam through sound waves (ultrasound) propagating in a material, usually a transparent crystal or glass.

1.Generation of Sound Waves:A radio frequency (RF) signal is applied to a piezoelectric crystal (transducer). Due to the piezoelectric effect, the piezoelectric crystal generates ultrasound. The ultrasound propagates through the acousto-optic medium, forming a series of density variations known as acoustic waves (acoustic grating).

2.Refractive Index Change:As the ultrasound propagates through the acousto-optic medium, it causes periodic changes in the medium's refractive index, forming a dynamic grating. This dynamic grating diffracts the passing light beam. 

3.Light Beam Modulation:

• Frequency Modulation: Due to the high frequency of the sound waves (usually in the range of tens to hundreds of megahertz), the frequency of the incident light beam is modulated by the sound wave frequency, causing a shift in the incident light beam's frequency by one sound wave frequency.
• Intensity Modulation: By adjusting the power of the RF signal, the intensity of the ultrasound can be changed, thus altering the diffraction efficiency of the dynamic grating to achieve modulation of the light beam's intensity.
• Direction Modulation: The angle of the diffracted beam depends on the frequency of the sound waves and the incident angle of the light beam. The direction of the diffracted beam can be adjusted by changing the frequency of the RF signal.

4.Diffracted Beam:When the incident light beam passes through the acousto-optic medium, it is diffracted into multiple orders of beams by the dynamic grating. Typically, the +1 order or -1 order diffracted beam is used, while the intensity of other orders is relatively low and can be neglected.

Commonly Used Formulas for AOM ( Acousto-Optic Modulator )

• Diffraction Efficiency Calculation Formula: Where I_0th is the output intensity of the 0th order light when the RF is off, and I_1st is the output intensity of the 1st order light when the RF is on.

• Insert Loss Calculation Formula:
• Saturation Power Calculation Formula: Where L is the electrode length, λ is the wavelength, H is the electrode width, M² is the acousto-optic figure of merit, and K is the conversion loss factor, typically 1.12.

• Rise Time Calculation Formula:

Where T is the optical rise time,D is the distance, and V is the velocity. This formula defines the transmission time of the acoustic wave across the waist of the AO crystal and is used to approximate the optical rise time for a Gaussian beam.

 𝜃_{𝐵𝑟𝑎𝑔𝑔}=𝜆𝑓/2𝑣    𝜃_𝑆𝑒𝑝=𝜆𝑓/𝑣    𝜃_𝑆𝑒𝑝=2𝜃_{𝐵𝑟𝑎𝑔𝑔}

 𝜆=Wavelength,  𝑓=Frequence， V=Sound speed in Material

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