ICHTHYOPLANKTON COMPOSITION, DISTRIBUTION AND ABUNDANCE ON THE SOUTHERN PATAGONIAN SHELF AND ADJACENT WATERS*

An unbalanced Mach-Zehnder interferometer is useable in an optical wavelength division multiplexer or demultiplexer to provide wavelength stability. First and second fused tapered couplers in the unbalanced Mach-Zehnder interferometer are each responsive to the reception of at least one first and second optical input signals for generating separate predetermined first and second optical output signals. The first and second output signals from the first fused tapered coupler are coupled via first and second optical waveguides, respectively, to respective first and second optical inputs of the second fused tapered coupler. First and second output signals from the second fused tapered coupler are provided as first and second output signals from the unbalanced Mach-Zehnder interferometer. A variable delay is coupled in one of the first and second waveguides coupling the first and second optical 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 an optical signal passing therethrough for maintaining a relative delay between the first and second waveguides at a constant value. A plurality of such Mach-Zehnder interferometers can be used to form cascaded stages of an optical wavelength division multiplexer or demultiplexer.