Tailoring optical characteristics of dispersion-shifted lightguides for applications near 1.55 µm

Next-generation single-mode lightguides may be used in the 1.55-μm wavelength region where losses are a minimum for silica-based fibers. This paper discusses the basic fiber requirements of these new systems and provides design parameters for three types of dispersion-shifted fibers with various graded-index core profiles. The generic structural differences are that one type has a continuous cladding; the second has a depressed-cladding index relative to an outer substrate layer; and the third type has up to four cladding layers with different index values. The latter type includes a new lightguide structure that has a narrow depressed-index trench within its cladding. Results show how to choose lightguide parameters in order to tailor dispersion and mode-confinement properties.