Fiber Coupled Acousto-Optic Modulator/Shifter Low Loss

Product Overview

The AOMF Series Fiberoptic Acousto-Optic Modulators from AGILTRON offer high-speed optical intensity modulation and wavelength shifting with superior performance. Based on a proprietary patent-pending design, these modulators feature low insertion loss (~1.2 dB), high extinction ratio (>62 dB), high polarization extinction ratio (>30 dB), low power consumption, and high optical power handling up to 10 W. The AOMF operates by generating an optical grating inside a crystal using a side-mounted piezo actuator driven at its resonance frequency. As light passes through, it is diffracted at the Bragg-aligned exit angle, with the driving electronics modulating the acoustic amplitude to control optical attenuation. Response speed is determined by the resonance frequency, with options at 80 MHz and 200 MHz. The achievable modulation bandwidth is below the resonance frequency. The AOMF supports wavelengths from 350 nm to 2400 nm, is compatible with all fiber types, and is cost-competitive. It operates in a normally opaque state, becoming transparent under Bragg diffraction within a narrow wavelength band. The design inherently produces a positive frequency shift, with negative-shift options available. The device uses fiber optic collimators aligned to an acousto-optic crystal, with no epoxy in the optical path for maximum stability and long-term reliability. The rise and fall times of the acousto-optic modulator are proportional only to the laser beam size.

Features

• Low optical Loss
• High Power
• Low Cost
• Stable
• All Fiber Compatible

Applications

• Fiber Lasers
• Pulse Picker
• Sensor

Specifications

Notes:

• [1]. Without connector. Each connector typically adds 0.2-0.3dB, RL increase by 5dB, and ER reduces by 2dB. 1dB is for 80MHz 80ns rise/fall with special order. PM connector key is aligned to the slow axis as a default. Insertion Loss refers to output - input at ON state. Other wavelength band the loss may be higher.
• [2]. For Single Mode only, multimode reduces depend on mode filled ratio. ER refers to output power ratio between ON/OFF states.
• [3]. (10%-90%). The rise/fall and bandwidth are related to the beam size; small beam has higher insertion loss. In another word, fast response with larger bandwidth will add insertion loss.
• [4]. 50dB is standard for SM, 45dB for 50/125.
• [5]. @1550nm. For shorter wavelength the power handling is reduced due to smaller core size. Higher power version is available by expand the beam inside the fiber tip.

Note: The specifications provided are for general applications with a cost-effective approach. If you need to narrow or expand the tolerance, coverage, limit, or qualifications, please click this link.

Mechanical Dimensions

Diagram showing the Acousto-Optic Modulator (AOM) with fiber input and output ports, a central crystal housing, and overall dimensions. The AOM Driver diagram shows a rectangular unit with ports labeled 'Modulation Input', 'Amplitude', and 'RF Output', along with power and control connections.

Diagram illustrating the RF input connection via an SMA connector.

Ordering Information

The ordering information specifies various parameters to configure the AOMF modulator. Key parameters include:

• Prefix Type: AOMF- (standard), Special = 0
• Wavelength: Options include 1060nm, 1550nm, 1310nm, 980nm, 850nm, 780nm, 630nm, 530nm, 450nm, 2000nm, and Special.
• Insertion Loss: Options for 2.5dB, 1.6dB, 1.5dB.
• Optical Power: Options for 0.5W, 1W, 5W, 10W, and Special.
• Fiber Type: Options include Regular, and specific fiber types listed in the 'Fiber Type Selection Table'.
• Fiber Cover: Options include 'Select fiber below 0.9mm tube', and 'Special'.
• Fiber Length: Options for 0.25m, 0.5m, 1.0m, and Special.
• Connector: Options include FC/PC, FC/APC, SC/PC, SC/APC, ST/PC, LC/PC, 5WFC/PC, 10WFC/PC.
• PER (Polarization Extinction Ratio): Options for Non (1), 18dB (2), 20dB (3), 25dB (4), 29dB (5).
• Wavelength Shift: Options for Non (1), -80MHz (1), +80MHz (2).
• Benchtop: Options for Non (1) and Yes (2).

Fiber Type Selection Table:

• SMF-28 (01), PM1550 (34), MM 50/125μm (71)
• PM1950 (35), MM 62.5μm (72)
• PM1310 (36)
• SM450 (04), PM400 (37)
• SM1950 (05), PM480 (38)
• SM600 (06), PM630 (39)
• 780HP (07), PM850 (40)
• SM800 (08), PM980 (41)
• SM980 (09), PM780 (42)
• Hi1060 (10)
• SM400 (11), PM405 (43)
• PM460 (44)

Benchtop Box Mechanical Dimension: Diagram showing the mechanical dimensions of the optional benchtop unit, which integrates the modulator, driver, and power supply.

Setup Instructions

1. Connect a laser with a wavelength matched to the specified part number to the fiber input.
2. Connect the modulator to the accompanying driver using the provided cable.
3. Connect a DC power supply to the driver (refer to the AOM driver datasheet for detailed specifications).
4. Connect the control signal to the SMA input port.
5. The fiber optical output amplitude and repetition rate will vary according to the electrical control signal.

Application Notes

Fiber Core Alignment

Note that the minimum attenuation for these devices depends on excellent core-to-core alignment when the connectors are mated. This is crucial for shorter wavelengths with smaller fiber core diameters that can increase the loss of many decibels above the specification if they are not perfectly aligned. Different vendors' connectors may not mate well with each other, especially for angled APC.

Fiber Cleanliness

Fibers with smaller core diameters (<5 µm) must be kept extremely clean. Contamination at fiber-fiber interfaces, combined with high optical power density, can lead to significant optical damage. This type of damage usually requires re-polishing or replacement of the connector.

Maximum Optical Input Power

Due to their small fiber core diameters for short wavelength and high photon energies, the damage thresholds for the device are substantially reduced compared to common 1550nm fiber. To avoid damage to the exposed fiber end faces and internal components, the optical input power should never exceed 20 mW for wavelengths shorter than 650nm. AGILTRON produces a special version to increase the power handling by expanding the core side at the fiber ends.

Performance Data

Modulation Response

Graphs displaying Modulation Response (Top Optical/Bottom Electrical) at different frequencies: 1 kHz, 1 MHz, 5 MHz, and 10 MHz. These plots show the average output power (in arbitrary units) as a function of modulation voltage (V), illustrating how attenuation changes with input signal.

Typical Attenuation vs Control Signal for 200MHz AOM

Graph titled 'Typical Attenuation vs Control Signal for 200MHz AOM'. It plots Average Output Power (a.u.) against Modulation (V) for various control signal frequencies (DC, 10Hz, 100Hz, 10kHz, 100kHz, 1MHz). The graph shows that as modulation voltage increases, the output power generally decreases (attenuates), with different curves representing different frequencies.

Typical Stability

Two graphs titled 'Typical Stability (@ -20dBm)'. The top graph shows 'Stability of DC Control' and the bottom graph shows 'Stability of AC Control' (1kHz). Both plots display 'Output (dBm)' versus 'Time (hr)' over a 20-hour period, demonstrating minimal fluctuation (less than 0.1dB) for both DC and AC control methods.

Operational Principles

Acoustic Frequency

The operation of an acousto-optic modulator is based on the Bragg diffraction generated by an acoustic wave (traveling refractive grating) inside a crystal. An RF voltage of the acoustic frequency is applied to the piezoelectric actuator attached to the crystal, generating the acoustic wave. The higher the frequency, the higher the cost to make and higher the power consumption. Diagram illustrating the operation: An incident optical beam enters an acousto-optic crystal. An acoustic wave, generated by a transducer and driven by an RF input, creates a refractive grating within the crystal. This grating diffracts the incident beam into undiffracted and diffracted optical beams, with the diffraction angle determined by the acoustic wave vector.

Modulation Bandwidth

An optical intensity modulator can be achieved by a driving circuit in which the acoustic intensity inside the crystal varies with an input modulation signal. A typical acoustic driver output is shown below: an RF Input electrical signal modulates the intensity profile of the carrier oscillations (acoustic frequency), resulting in a modulated driving signal, which leads to an output optical intensity similar to the RF input. The acoustic frequency intrinsically determines the rise/fall of the optical modulation. The Modulation Bandwidth is proportional to the acoustic frequency. The optical response can be optimized to a certain extent via the driving circuit, such as digital or analog. Diagrams showing signal waveforms over time: RF carrier oscillations, electrical signal, modulated AO drive signal, and the resulting optical signal, illustrating the modulation process.

Optical Wavelength Shift

Due to an energy exchange, all acoustic optical devices apply a frequency shift to the diffracted output beams. These optical wavelength shifts are very small and proportional to the acoustic frequency. Depending on the selected Bragg angle, these devices will either up-shift or down-shift the laser light by the frequency of the applied RF signal.