Electromagnetic Waves in Optical Fibers

Light or other electromagnetic waves can propagate through optical fibers. This Demonstration visualizes the field, energy distribution, and propagation of light in step index fibers. A step index fiber is composed of a core and cladding that have different refractive indices

n

1

and

n

2

, respectively. Many modes are possible, including the transverse magnetic (TM) and transverse electric (TE) waves, of which the zeroth modes

TM

0m

and

TE

0m

are chosen here.

In this Demonstration, the instantaneous fields, energy density, and power density are displayed for the designated time

ωt

for a given mode number

m

, core diameter

d

, and the frequency

f

. The maximum electric field is fixed at 1000 V/m for all conditions. The frequency has to be higher than the cut-off frequency

f

c

determined by

d

and

m

. Using cylindrical coordinates with the wave propagation direction as the

z

axis, the fields are a function of

r

,

z

, and

t

. Energy flows along the channel (along the positive

z

direction). The electric and magnetic fields are shown on a perpendicular plane by red and blue arrows, respectively. The energy density is displayed on two planes by coloring. The energy transport or power density

S

z

(

z

component) is shown. The fields proportional to the magnitudes are displayed, with their relations listed in the table.