Handbook of Biomedical Optics

136 Handbook of Biomedical Optics

is typically 1%–1.5% of the peak wavelength. Circular variable l-

ters (CVF) comprise an alternative option having transmission

that varies along the rotation angle of the lter. Typically, tunable

light sources based on either gratings, or LVFs, CVFs employ rect-

angular-to-circular ber optic bundles, with the rectangular end

being attached to the source’s exit slit. e circular end is attached

to other optical instruments or illuminates directly the target. It

should be noted that by decreasing the slit’s width, the FWHM

can decrease down to the lter’s specication, but at the same

time, light throughput ...