Broadband Mach–Zehnder interferometer design using microstructured optical fibers for multi-channel DPSK demodulation

Microstructured optical fibers (MOFs) are typically all silica optical fibers with air holes. Tremendous interest in these fibers has been generated because of potential applications in optical communications, remote sensing, frequency metrology and optical coherence tomography. A feature of MOFs is that waveguide dispersion can be modified significantly by means of geometrical parameters, namely, the positions and sizes of the different holes. We propose here an innovative MOF design whose waveguide dispersion inversely matches the material dispersion of silica to obtain broadband zero group velocity dispersion from 1400 to 1650 nm. One application of this fiber is in the demodulation of differential phase shift keying (DPSK) signals. We propose a novel Mach–Zehnder interferometer design using a small section of zero-dispersion fiber providing a wavelength-independent time delay and address all practical considerations. The constant free spectral range of the interferometer would allow the demodulation of multiple evenly spaced wavelength-multiplexed DPSK-encoded channels in a telecommunication link instead of one demodulator per channel.