Fiber Optic Tutorials

This is a continuation from the previous tutorial - rare-earth ion-doped fiber amplifiers.   There are a wide variety of lasers, covering a spectral range from the soft X-ray to the far infrared, delivering output powers from microwatts to terawatts, operating from continuous wave to femtosecond pulses, and having spectral linewidths from just a few hertz to many terahertz. The gain media utilized include plasma, free electrons, ions, atoms, molecules, gases, liquids, solids, and so on. The sizes range from microscopic, of the order of \(10\text{ μm}^3\), to gigantic, of an entire building, to stellar, of astronomical dimensions. An optical gain...

This is a continuation from the previous tutorial - laser amplifiers. Among the many different types of optical amplifiers, those that are guided-wave devices have many advantages over bulk devices. There are two important, but distinctly different, groups of guided-wave optical amplifiers: fiber devices and semiconductor devices. Fiber devices can be further subdivided into two categories: those based on active rare-earth ion-doped fibers and those based on the nonlinear optical processes in fibers. Therefore, there are three types of established guided-wave optical amplifiers: Rare-earth ion-doped fiber amplifiers Nonlinear Raman or Brillouin fiber amplifiers Semiconductor optical amplifiers Each type can be...

This is a continuation from the previous tutorial - population inversion and optical gain.   Any medium that has an optical gain can be used to amplify an optical signal. Depending on the physical mechanism responsible for the optical gain, there are two different categories of optical amplifiers: the nonlinear optical amplifiers and the laser amplifiers. The optical gain of a nonlinear optical amplifier is associated with a nonlinear optical process in a nonlinear medium, whereas the gain of a laser amplifier results for the population inversion in a medium. Important nonlinear optical amplifiers include the OPAs, discussed in the...

This is a continuation from the previous tutorial - optical absorption and amplification. From the discussions in the optical absorption and amplification tutorial, it is clear that population inversion is the basic condition for the presence of an optical gain. In the normal state of any system in thermal equilibrium, a low-energy state is always more populated than a high-energy state, hence no population inversion. Population inversion in a system can only be accomplished through a process called pumping by actively exciting the atoms in a low-energy state to a high-energy state. If left alone, the atoms in a system...

This is a continuation from the previous tutorial - optical transitions for laser amplifiers. Optical absorption results in attenuation of an optical field, while stimulated emission leads to amplification of an optical field. To quantify the net effect of a resonant transition on the attenuation or amplification of an optical field, we consider the interaction of a monochromatic plane optical field at a frequency \(\nu\) with a material that consists of electronic or atomic systems with population densities \(N_1\) and \(N_2\) in energy levels \(|1\rangle\) and \(|2\rangle\), respectively. Because the spectral intensity distribution of the monochromatic plane optical field that...