Ocean Optics - Inventor of the World's First Miniature Spectrometer
Ocean Optics - Inventor of the World's First Miniature Spectrometer

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Ocean Optics - Inventor of the World's First Miniature Spectrometer


Fiber Optic Variable Attenuator

Fiber Optic Variable Attenuator

The FVA-UV Fiber Optic Variable Attenuator is an opto-mechanical device that helps control the amount of light (signal) transmitted between two fibers. The FVA-UV couples the fibers via SMA 905 connectors, attenuating light uniformly at all wavelengths from the UV-VIS through Shortwave NIR.

Also available are adapters (FVA-ADP-UV and -VIS) for connecting the attenuator directly to any light source having a collimating lens at its aperture.

  • Attenuates light uniformly across UV-VIS-NIR
  • Works with any diameter optical fiber
  • Allows manual adjustment from 0-100%
  • Connects attenuator directly to light source via optional adapter

The FVA-UV is an anodized aluminum block with 3/8-24 threaded ports to accommodate a 74-UV Collimating Lens. A mechanical adjustment wheel is used to control the amount of illumination reaching the "read" side of the setup. The adjustment wheel is cut to 0.15" diameter in the open position, decreasing to 0.060" diameter at 90 rotation and from 0.060" to 0.006" for rotation between 91-180. A 6-32 Nylon thumbscrew locks the adjustment wheel in place.


Attenuation wavelengths: ~200-2000 nm
Dimensions: 1.5" x 1.5" x 1.0"
Assembly ports: 3/8-24 threads for collimating lenses
Adjustment wheel:
  • Diameter = 3/32"
  • Material = black anodized aluminum with knurled edge
Adjustment wheel lock: 6-32 Nylon thumb screw
  • FVA-UV to connect attenuator directly to UV light source with a collimating lens at its aperture
  • FVA-VIS to connect attenuator directly to VIS light source with a collimating lens at its aperture
Connector: SMA 905

Why the need for signal attenuation?

For high-intensity light level applications such as laser characterization, more light will reach the spectrometer than likely can be read successfully by the spectrometer's high-sensitivity detector. Also, some absorbance experiments may require signal attenuation; too much light can saturate the reference measurement.

Detector saturation can be avoided by using different gratings, changing the optical bench entrance aperture (by installing slits or using small-diameter optical fibers) or adding neutral-density filters to the optical path. Another option is to adjust the spectrometer integration time to limit the interval during which the detector collects light -- akin to changing the shutter speed on a camera to a fast exposure time. The FVA-UV fits in where these signal-reduction techniques are either unworkable or undesirable.



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