Ultra-stable optical wavelength division multiplexer/demultiplexer

An optical wavelength division multiplexer or demultiplexer comprising a plurality of unbalanced Mach-Zehnder interferometers located in a plurality of stages of a cascading arrangement, each unbalanced Mach-Zehnder interferometer comprising:

• a first fused tapered coupler responsive to the reception of at least one of first and second optical input signals for generating separate predetermined first and second optical output signals for transmission via first and second optical waveguides, respectively;
• a second fused tapered coupler responsive to the reception of the first and second optical output signals from the first fused tapered coupler which are received at first and second optical inputs, respectively, from the respective first and second optical waveguides, for generating separate predetermined first and second optical output signals from the unbalanced Mach-Zehnder interferometer;
• and
• variable delay providing means coupled in one of the first and second waveguides coupling the output signals from the first fused tapered coupler to the first and second optical inputs of the second fused tapered coupler for introducing a predetermined variable delay into the associated optical output signal from the first fused tapered coupler passing therethrough for maintaining a relative delay between the first and second waveguides at a constant value.

A method of providing an unbalanced Mach-Zehnder interferometer that compensates for signal drift comprising the steps of:

• (a) receiving at least one of first and second optical input signals at a first fused tapered coupler and generating separate predetermined first and second optical output signals for transmission via first and second optical waveguides, respectively;
• (b) receiving the first and second optical output signals generated by the first fused tapered coupler instep (a) at first and second optical inputs, respectively, of a second fused tapered coupler from the respective first and second optical waveguides, and generating separate predetermined first and second optical output signals from the unbalanced Mach-Zehnder interferometer;
• and
• (c) introducing a predetermined variable delay into one of the first and second optical output signal from the first fused tapered coupler generated in step (a) in a variable delay providing means for maintaining a relative delay between the first and second waveguides coupling the first and second output signals from the first fused tapered coupler to the first and second optical inputs of the second fused tapered coupler at a constant value.