RP Fiber Power – Simulation and Design Software for Fiber Optics, Amplifiers and Fiber Lasers
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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.
Demo-Video
One of our case studies has been produced using the Power Form described here:
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:
Multi-step Profile
When you choose the profile type multiple steps, you can enter up to eight radial segments with different refractive indices:
Refractive Index Expression
For still more flexibility, you can define the refractive index vs. radial position r in the fiber core with an expression:
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:
For each mode, you get the following:
- mode name (according to the naming convention for LP modes)
- phase constant (imaginary part of the propagation constant, telling you how fast the optical phase changes during propagation
- effective refractive index: calculated from the phase constant
- effective mode area
- fraction (percentage) of optical power which propagates within the fiber core
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.
Diagrams
The form offers several diagrams for displaying 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:
Case Studies
The following case studies are available, where we used this Power Form:
Mode Structure of a Multimode Fiber
We explore various properties of guided modes of multimode fibers. We also test how the mode structure of such a fiber reacts to certain changes inthe index profile, e.g. to smoothening of the index step.
#modes
Number of Modes of a Highly Multimode Fiber
We seek a simple equation for estimating for the number of modes of a highly multimode fiber, which can be applied to fiber designs with arbitrary shapes of the refractive index profile. Instead of applying complicated mathematics, we build a hypothesis and subject that to multiple numerical tests.
#modes
The Numerical Aperture of a Fiber: a Strict Limit for the Acceptance Angle?
The requirement of total internal reflection would seem to set a strict limit for the angular distributions of fiber modes. However, some modes are found to exceed that limit significantly. We investigate that in detail for single-mode, few-mode and multimode fibers.
#modes#video
Dispersion Engineering for Telecom Fibers
We explore different ways of optimizing refractive index profile for specific chromatic dispersion properties of telecom fibers, resulting in dispersion-shifted or dispersion-flattened fibers. This also involves automatic optimizations.
#modes#dispersion#telecom#video
See also: overview on Power Forms