We describe a variable bandwidth tunable optical
spectral filtering device and associated method for selectively directing a portion of a
wavelength multiplexed input
signal, entering through one or more optical fibers, into one or more output signals provided to one or more optical fibers and / or electronic outputs. The optical filtering is accomplished using free-space diffractive
wavelength de-
multiplexing optics combined with a fixed (permanent) patterned structure located in the spectrally dispersed
image plane. The structure can direct a selected spectral portion of the optical
signal to one or more separate outputs, such as an
optical fiber or
power detector. A single active element in the
optical path is used to spatially shift, or steer, the entire input spectrum at the dispersed
spectral image plane, to control the portion of the input spectrum illuminating specific features on the permanent patterned structure. In one preferred embodiment, a device with a fixed selective area triangular shaped tilted reflective
facet on a flat reflective surface is constructed such that the light reflected off the flat reflective surface and off the triangular reflective
facet are selectively multiplexed back and directed to different output
fiber ports. Inputs at different angles of incidence on the reflective structures may be deflected by the same structures to different output port
fiber ports. A reconfigurable variable-bandwidth tunable optical add / drop
multiplexing device is constructed using such a filtering device and an application of such an add / drop
multiplexing in a
optical transport network is demonstrated.