Patent ID: 6891992

Claim:
An add-drop passive optical filter for subtracting a drop signal from a target wavelength channel of a multi-channel main input signal and adding an add signal into said target wavelength channel, comprising: an input line for receiving the main input signal, the main input signal comprising a plurality of input signals in a plurality of channels and the drop signal in the target wavelength channel; an add line for delivering the add signal at the target wavelength to the input signal; a drop line for receiving the drop signal in the target wavelength channel separate from the main input signal; a pair of passive chiral couplers, each said passive chiral coupler having a predetermined redirection hand and being optically connected to one another and to at least one of said input, add, and drop lines, said passive chiral coupler pair being operable to passively: a) separate the drop signal from the main input signal to generate a modified main signal; b) direct the drop signal into said drop line; c) add the add signal to said modified main signal to generate an output signal; and an output line for receiving and transmitting said output signal from said passive chiral coupler pair.