Single-mode fiber

Suppose we have a fiber with the following characteristics:

Radius of the core	4.5 µm
Index of the core	1.4489
Index of cladding	1.4444

We want to know the effective index of the HE(1,1) mode.

First we import needed modules:

from fibermodes import FiberFactory, Mode, ModeFamily, Wavelength

We create a FiberFactory object. FiberFactory are used to create families of Fiber object. However, even in the case we only need a single fiber, we need to create it using a FiberFactory:

factory = FiberFactory()
factory.addLayer(name="core", radius=4.5e-6, material="Fixed", geometry="StepIndex", index=1.4489)
factory.addLayer(name="cladding", material="Fixed", index=1.4444)

We create an empty factory, and we add the two layers. When pos argument is not specified, layers are added to the end of the fiber. We do not need to specify radius for the cladding, as it is considered to be infinite. Cladding should always be StepIndex.

The FiberFactory is an iterator. Therefore, we could loop through generated Fibers within a for loop. We can also access generated fibers using index:

fiber = factory[0]

In this case, there is only one fiber generated. Therefore, specifying an index other than zero would raise an exception.

We can now solve for effective indices of this fiber. First, we create a Mode object:

he11 = Mode(ModeFamily.HE, 1, 1)

The constructor of Mode also accept a string to specify the family.

The effective index also depends on the Wavelength. We can explicitly build a Wavelength object:

wl = Wavelength(1550e-9)

Now we can compute the effective index:

neff = fiber.neff(he11, wl)

The wavelength parameter could also simply be given as a float number (in meters).

Suppose we want to be sure the designed fiber is really single mode. We could request the fiber to find all the modes at a given wavelength:

modes = fiber.findVmodes(wl)

You can now explore the documentation of the Fiber class to learn about other available functions.