Optical fibers are one of the latest additions to signal-link submillimeter-wavelength transmission line technology. Optical fibers are cylindrical waveguides with significantly low loss. Since frequencies of light are very high compared to that of microwaves, the bandwidth (BW) of an optical fiber is high, and high data rate transports can be delivered through it. The fundamental difference between a fiber and a coax is the material fiber versus metal and the nature of the signal: photons versus electrons. In coax, the information signal travels in the central conductor, whereas in the fiber, light travels in the core. In coax, the central conductor is surrounded by an insulation dielectric material and then by a conductive sleeve. In the fiber, the core is covered by a cladding, and the core refractive index and diameter define the type of the fiber. However, in both cases, the fiber and the coax can be used to transfer electromagnetic waves. Similar to circular or rectangular waveguides used in microwaves, the fiber is a circular waveguide. Hence, propagation modes depend on the dimensions of the fiber. These modes are marked as EHnp or HEnp, where n and p indices are the mode order of the Bessel equation solution. There are three main types of optical fibers.
Online access to SPIE eBooks is limited to subscribing institutions.