Ocean Optics - 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.

The FVA-ADP-UV and FVA-ADP-VIS, which are adapters for connecting the attenuator directly to any light source having a collimating lens at its aperture, are available for $115 each.

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 digitized successfully by the spectrometer's high-sensitivity linear CCD-array detector. Also, some absorbance experiments may require signal attenuation; too much light can saturate the reference measurement.

In some instances, 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 (through software) 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.

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.

With the proper FVA-UV attenuator adapter, users can connect the attenuator directly to any light source that has a collimating lens at its aperture.

Sample Transmission Spectra

These sample transmission spectra show the FVA-UV adjustment wheel at various positions.

Specifications

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
Adapters:	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

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