Sometimes it is necessary to attenuate the light signal or to filter its spectrum within a fiber-optic link. A simple Connectorized U-bracket allows setting the desired intensity attenuation or spectral filtering by inserting the appropriate filter insert. To state the obvious, it is necessary that NAs and diameters of input and output fibers are of the same or similar type unless some loss is tolerated.

The inserts are available with attenuating filter to reduce a laser power, or with spectral filters to filter excitation or emission spectrum in fluorescence measurement.  A descriptive code is engraved on the insert.