Fibre Properties

The package contains several utility functions determining properties of the fibre. If the core and cladding refractive indices are defined, for example:

n_core = 1.4
n_cladding = 1.38

then the fibre numerical aperture is given by:

na = lpmodes.fibre_na(n_core, n_cladding)

and the cut-off angle (largest coupled incident ray angle) by:

cut_off = lpmodes.acceptance_angle(n_core, n_cladding)

The V number of the fibre at a specific wavelength is given by, for example:

core_radius = 10  # microns
wavelength = 0.5 # microns
V = lpmodes.v_number(core_radius, n_core, n_cladding, wavelength)

An estimate of the number of modes supported (from the V number) is found using:

num_modes = lpmodes.est_num_modes(core_radius, n_core, n_cladding, wavelength)

This includes two linear polarization directions as well as the sine and cosine orientations of modes with l > 0. The number returned by est_num_modes should therefore be approximately twice the number of solved modes including rotations, i.e. that returned by num_rotated.modes().