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RP Fiber Power – Simulation and Design Software
for Fiber Optics, Amplifiers and Fiber Lasers

Power Form: Mode Properties of a Fiber

This Power Form allows to conveniently calculate properties of guided modes of an optical fiber with a given refractive index profile.

graphic for this Power Form

Defining the Refractive Index Profiles

You have three options:

Simple Step-index Profile

When you choose the profile type single step, you can simply enter core diameter, cladding index and numerical aperture:

defining a single-step profile

Multi-step Profile

When you choose the profile type multiple steps, you can enter up to eight radial segments with different refractive indices:

defining a multi-step profile

Refractive Index Expression

For still more flexibility, you can define the refractive index vs. radial position r in the fiber core with an expression:

enter expression for refractive index

In this example, we have a parabolic index profile, as it may be used for a typical graded-index fiber.

Display of Mode Properties

Below the index definition area, the form displays a table with calculated mode properties for a given wavelength:

table with mode properties

For each mode, you get the following:

Besides, the M2 factor of the fundamental mode is displayed. It is often close to 1, but in some cases with deformed mode profile it may also be substantially higher.

Note that chromatic dispersion properties cannot be calculated, since for that we would need wavelength-dependent refractive indices as inputs. That, however, is possible in our form for germanosilicate fibers.


The form offers several diagrams for displaying mode properties:

diagrams for mode properties

Just select those which you need, and (in the right column) select certain options.

The following screenshots show you for our last example case (parabolic index profile) what you can get from this form:

example diagram
example diagram
example diagram
example diagram
example diagram

See also: overview on Power Forms