Main Optical Components for Fiber Laser/Amplifier Design

Abstract

The first reported theoretical analysis and prediction of laser action based on a semiconductor diode was published in 1959 in the USSR [1]. The first operation of a semiconductor laser (also called a ''diode laser'' or ''laser diode'') was reported in 1962 in the USA [2]. Semiconductor lasers play a very important role in the fiber laser field. Therefore, this section provides a detailed description of the physical processes that take place in these laser devices.Unlike isolated atoms and molecules (and even some laser optical centers in doped dielectrics), semiconductors demonstrate wide energy bands. These bands are separated by a bandgap (Fig. 9.1). Typical values of the bandgap of semiconductor materials for the most commonly used and commercially available diode lasers are on the order of a few electron volts. Under certain excitation conditions, such as injecting an electrical current, optical excitation, or heating, electrons from the valence band can move from the valence band to the conduction band after absorbing energy by an excitation process. As a result of this interband electron transition, a pair of charge carriers can be created (i.e., electrons in the conduction band and holes in the valence band), which is called an electron-hole pair. If an electron undergoes reverse transition (i.e., from the conduction band to the valence band), the process is called electron-hole recombination. The result of this interband recombination is usually an extraction of energy that was received during the excitation process.In equilibrium, electron-hole pairs can be created and recombined as a result of thermal diffusion and spontaneous emission of photons. Thermal equilibrium of electrons and holes, in this case, produces a certain concentration of electrons in the conduction band and holes in the valence band. Note that electrons are fermions (their spin equals 1/2) and thus follow so-called Fermi-Dirac statistics. Therefore, a probability of the electron occupying a certain level with energy E at V. Ter-Mikirtychev,

Quantum optical state comparison amplification of coherent states

“…Optical signals propagating through transmission media, such as an optical fiber, are affected by a loss which is dependent on the overall length of the communication channel. Commercially available all-optical amplifiers can counteract the loss by exploiting deterministic optical effects [11] allowing inter-continental transmissions. However, such amplifiers introduce noise levels [12] which destroy any quantum properties that the coherent states carry making it challenging to perform quantum communication protocols over long distances.…”