Question

discuss modal propagation in optical fibers

Answer 1

Wave Model gives an accurate and complete description of light propagation inside an optical fibre. Depending upon the fiber radius, different number of modes propagates inside an optical fiber.wave equation is obtained by combining Maxwell's equations and the boundary conditions. Modes are the possible solutions of the wave equation.

When ray travels parallel to the length of the fiber, its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber and hence it is called transverse mode. If they do not have any magnetic field component in the direction of propagation(H_x = 0). We call this mode the Transverse Magnetic mode (TM mode). Similarly if electric field component in the direction of propagation is zero(E_x =0). We call this mode Transverse Electric mode (TE mode).If both the longitudinal components of the fields (E_x & H_x ) are non-zero then we call the mode Hybrid mode. This mode is a combination of TE and TM modes.So inside an optical fiber we have three types of modes.