Amplification of multiple modes in Er-doped multimode fibers


The Er-doped Multimode Fiber component was designed to allow the analysis of multiple modes amplification in large mode area fibers. The components are very similar to the original single-mode doped fiber amplifiers, however now the refractive index information and ion distribution profile can be defined by the user (see main tab parameters in the figure below).

Optical System - Figure 1 - Doped fiber parameters

Figure 1: Doped fiber parameters

Based on the parameters specified, the component’s mode solver calculates the modes supported for the signal, pump and ASE bands. The user can also define if all supported modes will be equally excited ( for pump and/or signal channels) or the power distribution ratio between the supported modes will be calculated based on coupling coefficients, in this case an initial optical excitation field has to be defined for pump and/or signal.

The following example shows an erbium-doped fiber (double clad fiber), where all signal modes supported are equally excited (MM EDFA ExampleAllModesEquallyExcited.osd).

Optical System - Figure 2 -  System layout.

Figure 2: System layout.

The refractive index profile (step index) and Er ion distribution (uniform) used are displayed in the figures below:

Optical System - Figure 3 - (a) Refractive index profile and (b) Ion distribution

Figure 3: (a) Refractive index profile and (b) Ion distribution.

After running the simulation, the following results were obtained:

Total Signal, Pump, and ASE power evolution along the fiber length.

Optical System - Figure 4 -  Total Signal Pump, and ASE power evolution along the fiber length

Figure 4: Total Signal, Pump, and ASE power evolution along the fiber length.

The fiber at 1550 nm (signal wavelength) supports 3 guided modes: LP01 and LP11 (two helical polarities).

The normalized radial intensity (azimuthal angle is 0) for LP01 (black line) and LP11 (red line) are displayed in the figure.

Optical System - Figure 5 - Radial profiles

Figure 5: Radial profiles.

The power evolution along the fiber length for LP01 (black line) and LP11 – sum of the sin and cos components – (red line) were also calculated.

Optical System - Figure 6 - Power evolution

Figure 6: Power evolution.

Based on the modes power distribution at the fiber output, the profile of the output beam is displayed:

Optical System - Figure 7 - Output beam

Figure 7: Output beam.