Introduction to the Special Issue on Optical Fiber Sources and Amplifiers

Besides serving as transmission links, optical fibers have been used also to realize several types of photonic devices, namely optical amplifiers, lasers, and broadband sources. Ultrafast fiber lasers have the potential to make applications of ultrashort pulses widespread in different areas of science and technology. In particular, both stationary and pulsating dissipative ultrashort pulses as well as high energy dissipative soliton resonance pulses have attracted recently the attention of many researchers working with passively mode-locked fiber lasers. Supercontinuum fiber sources were found also to be very useful in several areas, such as optical communications, spectroscopy, optical coherence tomography, optical frequency metrology, etc. Concerning optical amplifiers, different kinds of specialty optical fibers have been developed as alternatives to conventional erbium-doped fibers (EDFs). In particular, extensive research has been done on EDFs using various glass host and co-dopant materials such as silica, fluorozirconate, chalcogenides, bismuth, aluminum, phosphorous, lanthanum, etc. Some of these materials have wider emission bandwidth that is suitable for wavelength-division multiplexing (WDM) systems. This Special Issue gathers several international experts to discuss the latest research advances and trends concerning the design, fabrication, and application of different types of optical fiber sources and amplifiers. Six papers have been submitted, which provide a nice perspective of this area. Two of them were already published in volume 39, issue 4 of this journal. One of these papers, by Yuri Barmenkov et al. (https://doi.org/10.1080/01468030.2020. 1826608), reports on the basic spectroscopic properties of a home-made holmium-aluminum-germanium co-doped silica fiber, designed for laser applications. The other paper, by Khurram Qureshi (https://doi.org/10.1080/ 01468030.2020.1829753), proposes and demonstrates a simple design of semiconductor fiber ring laser covering a broad tunable range, comprising L and extended L bands. A third paper submitted to this Special Issue provides a review of recent investigations on the behavior of a polarizationmaintaining passively mode-locked ytterbium-doped laser considering two different cavity configurations, namely fiber-ring (FR) and Fabry-Perot (FP) FIBER AND INTEGRATED OPTICS 2020, VOL. 39, NOS. 5–6, 213–214 https://doi.org/10.1080/01468030.2020.1860440