Electronic Variable Optical Attenuators, Voltage Controlled & PM Fiber Coupled

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A female BNC connector is located on one end of the barrel, and PM fiber leads with FC/APC connectors are integrated into the opposite end. Each barrel is engraved with the shown information for convenience.

Features

• MEMS-Based Device Provides Attenuation up to >30 dB or >25 dB
• Single Mode PM Operation over Five Wavelength Ranges 
  • 488 to 635 nm
  • 620 to 850 nm
  • 770 to 1100 nm
  • 970 to 1550 nm
  • 1450 to 1610 nm
• Control Optical Power by Applying 0 to 5 V Signal
• Maximum Optical Input Power up to 100 mW, Depending on Model
• Modulation up to 1 kHz
• Input is Protected from Electrostatic Discharge (ESD)

Thorlabs' Fiber-Coupled Electronic Variable Optical Attenuators (VOAs) are microelectromechanical system (MEMS) based devices that provide attenuation up to >30 dB or >25 dB, depending on the model, and a polarization extinction ratio (PER) of >13 dB. They use PANDA polarization-maintaining (PM) fiber with 2.0 mm narrow key FC/APC connectors with the key aligned to the slow axis of the fiber. Driving voltages of 0 to 5 V control optical transmission, which decreases with applied voltage. These high-speed VOAs support modulation up to 1 kHz. Protection diodes integrated into the design limit the input voltage to protect the VOA from ESD, as well as from other over-voltage and under-voltage events.

A plot of the typical relationship between the applied voltage and the optical transmission for each electronic VOA model is included in the Specs tab. Most voltage sources, including power supplies, function generators, and digital-to-analog converters (DACs), can be used to control these electronic VOAs. Use a BNC cable (not included) to connect the electronic VOA to the voltage source. The MEMS VOA is an electrostatic device that inherently requires no current. However, the protection circuitry can draw up to 100 µA for applied voltages of 5 V.

Either of the unit's 0.5 m long fiber leads can be used as the input, as performance is similar in both directions. However, you may find that one of the connectors provides a lower loss connection in your set-up due to the random nature of core alignment. As shown in the image to the right, the barrel of each electronic VOA is etched, for convenience, with information such as the operating wavelength range, maximum optical input power, maximum modulation bandwidth, and driving voltage range. These VOAs are designed for use with polarization-maintaining optical fiber that is single mode within the operating range. Please see the Specs tab for information on the polarization-maintaining fiber integrated into each model.

We also offer non-polarization maintaining single mode fiber versions of these electronic VOAs for system integration with either FC/PC or FC/APC connectors.

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 even more crucial for shorter wavelength VOAs with smaller fiber core diameters. If they are not perfectly aligned, the insertion loss can easily go up many decibels above the specification. Since we cannot control the fibers that are used to connect to these devices, we test the devices for minimum attenuation by using a setup that actively aligns the cores of the fibers and minimizes the connector loss. From this, we obtain the minimum attenuation possible for each device. Unless the user also does the same, or better yet, fusion splices the fibers, they may not achieve the specified minimum attenuation.

Fiber Cleanliness
Fibers with smaller core diameters (<5 μm) must be kept extremely clean because the presence of material at fiber-fiber interfaces, combined with the high optical power density, can lead to significant optical damage. This is especially true at short wavelengths where the photon energy is also high. If care is not taken, the end of the fiber at the FC/PC or FC/APC connector can sustain damage that will reduce the coupling efficiency or possibly even prevent coupling altogether. This type of damage usually requires re-polishing or replacement of the connector. Depending on the specific conditions, this can even happen at average power levels less than 10 mW. Additional caution should be taken with pulsed lasers, since the peak power can be much higher than the average power. Please make sure the fiber ends are kept as clean as possible and cleaned every time a connection is made.

Maximum Optical Input Power
Due to its small fiber core diameter, as well as the high photon energies for light in the 488 nm to 600 nm range, the damage threshold for the V450PA attenuator is lower than for our other models. To avoid damage to the exposed fiber end faces and internal components, the optical input power should never exceed 20 mW, instead of the 100 mW maximum for all other attenuators sold on this page. If you observe decreased transmission or visible damage to the fiber core at the connector faces, re-polishing or replacing the connectors may restore performance if no internal damage has occurred.