Nonuniform Bragg gratings for DWDM applications

The advent of the Dense Wavelength Division Multiplexing (DWDM) technology in Optical Fiber Networks (OFNs) has resulted in the necessity of developing advanced Optical Add/Drop Multiplexers (OADMs) on the basis of submicron Bragg gratings. The OADMs for dense multichannel OFNs with bit rates 10-40 Gbits/s per channel and channel spacing 200, 100 and 50 GHz must possess rectangular-shaped reflection/transmission spectra and linear phase characteristic within the stop/passband. These features can not be achieved using uniform Bragg gratings and therefore nonuniform gratings with space-modulated coupling coefficient and/or phase shifts π should be used. We present the recent advances in the design and fabrication of narrowband wavelength-selective filters for DWDM applications using submicron nonuniform Bragg gratings. The peculiarities of propagation, interaction and diffraction of electromagnetic waves in nonuniform grating structures are considered. Narrowband reflection filters using single-mode quartz fibers with side-polishing and relief gratings on dielectric and polymeric materials are designed and fabricated. The filters have nearly rectangular shape of the stopband with 0.4-1.6 nm width and peak reflectivity R > 99% in the 1.55 μm wavelength region. The architecture of multichannel OADMs for high-speed OFNs using planar polymer Integrated Photonic Circuits (IPCs) with biharmonic Bragg gratings, possessing phase shifts π, is discussed.