This invention relates to a new optical geometry for using a linear variable
filter as an optical spectral filter. An elliptical beam geometry with the minor
beam axis oriented along the linearly varying axis of the filter is used. The beam
is incident at a slight angle relative to the long axis of the beam. Ultimately
this geometry produces a filter which has minimum spectral broadening from both
angular and beam extent effects. Furthermore, this geometry results in low back
reflectance and higher input beam power damage thresholds. The optical filter includes
means for tuning a wavelength response of the filter. Further, the optical filter
can afford Add/Drop functionality by providing optical circulators at the input
and output ports.
