Patent ID: 6842287

Claim:
An interference filter for introducing a relative delay between components of an input optical signal, the filter comprising: an input port for launching the input signal, an optical splitter, an optical combiner, a first optical path connecting an output of the optical splitter to an input of the optical combiner, a second optical path connecting a second output of the optical splitter to a second input of the optical combiner, a first photodetector for receiving light from a first output port of the optical combiner, a second photodetector for receiving light from a second output port of the optical combiner, wherein a) the optical propagation delay for light travelling from the first output port of the optical splitter to the first input port of the optical combiner differs from the optical propagation delay for light travelling from the second output port of the optical splitter to the second input port of the optical combiner by an integral number of bit periods of the input optical signal, b) the response of the first photodetector is combined with the response of the second photodetector in a negative linear combination, and c) at least one of the optical paths is unguided.