Three port optical filter

摘要

A three port filter device is formed from a thin film filter element and a pair of lensing devices. A focusing lensing device is used, with a dual-fiber termination disposed at the object plane of the focusing lensing device. A collimating lensing device is disposed between the focusing lens image plane and the thin film filter element. The third optical port is coupled to the collimated signal passing through the filter element. The focusing lens may be moved along the optical axis to modify the spacing of the dual-fiber termination image appearing at the image plane. The change in spacing results in changing the angle of incidence of the optical signal propagating toward the thin film optical element. Since the pass wavelength of the thin film element is a function of the angle of incidence, the movement of the focusing lens may be used to "tune" the pass wavelength of the thin film optical device.