Planar lightwave circuit based tunable 3 port filter

A tunable add/drop filter in a planar lightwave circuit (PLC) comprising:

• an input port for launching an input optical signal comprising a plurality of wavelength channels into the PLC;
• a demultiplexer with an input pupil and an output pupil for spatially separating the input optical signal into the wavelength channels;
• a slab waveguide region comprising a high-index core layer, surrounded above and below by lower-index cladding layers for transmitting the separated wavelength channels from the demultiplexer to an add/drop port;
• a lens system in the slab waveguide region for focusing the plurality of separated wavelength channels from the output pupil of the demultiplexer onto straight line at an edge of the PLC,
• a separate reflector adapted for transverse movement along the edge of the PLC for reflecting the separated wavelength channels;
• an add/drop port within a transmissive window within the reflector for receiving one or more of the separated wavelength channels as a drop port, or for inputting a new wavelength channel as an add port, the add/drop port being tunable as a function of transverse motion of the transmissive window along the separated wavelength channels focused at the edge of the PLC;
• a multiplexer with an input pupil optically coupled with the reflector and the add/drop port for receiving and multiplexing the one or more wavelength channels reflected by the reflector and any new wavelength channel input at the add port from the lens system in the slab waveguide region, and an output pupil;
• and
• an output port optically coupled to the output pupil of the multiplexer for outputting the multiplexed wavelength channels;
• wherein the output pupil of the demultiplexer is positioned with respect to the input pupil of the multiplexer, such that at least one wavelength channel focused on the reflector is optically coupled into the input pupil of the second demultiplexer.