How can I get the waveguide and material dispersion of a step-index single-mode fiber at the operating wavelength if I know its core size and NA?
You can get the theoretical waveguide and materical dispersion values if you have the accurate refractive index profile of the fiber. The fiber designing software OptiFiber is available for guidance.
You can estimate them provided you have idea about the refractive index profile. Even the V parameter can also be helpful while estimating that. I would like you to go through some fundamental papers related to simulation.
- Thank you very much for all your helpful answers indeed. It seems using numerical methods to estimate the effective refactive index is then enough to further get the dispertion value if the core size and the refractive index difference are known. But I'm still wondering if there are some analytical and simple formulas to do that.
What accuracy do you need?
For material dispersion, you need to make some assumptions about the composition of the fibre core and cladding.
J. W. Fleming, “Material dispersion in lightguide glasses”, Electron. Lett., vol. 14, pp. 326-328, (1978) reports refractive index measurements for pure silica, GeO2, P2O5 and Fluorine-doped glasses. For a binary glass (SiO2-GeO2) you can estimate the composition by linear interpolation from Fleming's values if you know the core/clad refractive index difference at a particular wavelength, then use his Sellmeier coefficients to calculate the refractive index and its derivative at any other wavelength. With more than one dopant, if you don't know the ratios, then some guesswork is required. For the same index difference, material dispersion depends on the exact chemical composition of the glass.
For an ideal step-index fibre there are good analytic approximations for waveguide dispersion in the weakly guiding limit, which apply to typical single mode fibres. Allan W. Snyder & J. D. Love, “Optical Waveguide Theory”, Chapman Hall, 1983, ISBN 0 412 09950 0, present a decent overview with analytic, graphical and tabular results for step (and other) profiles.
Strictly speaking, you can't simply add the material and waveguide dispersion components together. The field distribution changes as the normalised frequency (V-number) varies, and there may be second order terms, for instance associated with the change of index difference with wavelength (referred to as profile dispersion). These effects may be small enough to ignore, but I don't recall how small for typical single mode fibres. I do know that profile dispersion can be significant for multimode graded index fibre dispersion.
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity