Dear Colleagues,

Nowadays, the laser-excited optical signal transmission technique over large-core silica optical fibers has found widespread use in various applications. When this technique is combined with special launching conditions, it provides a few-mode regime. Here, laser-excited optical emission is transferred over large-core optical fiber by some limited number of guided modes. Conversely, under the multimode regime, the transmitted optical signal contains almost all guided modes, satisfying the cut-off conditions. Since the ratification of the IEEE 802.3z standard in 1998, the laser-based optical signal transmission technique over MMFs started to find widespread use in short-range multi-gigabit solutions, and began to be in demand for on-board and industrial network applications, requiring 1 Gb/s and even greater bit rates. In this application, silica MMFs are utilized with extremely enlarged core diameters up to 100 mm as well as silica–polymer or polymer–polymer MMFs.

Today, MMFs and few-mode optical fibers (FMFs) are also considered as being an alternative solution to new-generation transport networks, providing extra-high bit rates of hundreds Tb/s and more. Here, the nonlinear effects occurring in standard silica singlemode optical fibers during the propagation of optical signals grouped by DWDM systems become the main issue and constitute a passage to enhancing the fiber-effective area by core diameter enlargement in combination with the use of the MIMO technique. This is one of the approaches to decreasing or even suppressing optical fiber nonlinearity for use in telecommunication system signals. At the present time, mode division multiplexing (MDM) is one of the new top trends in optical networking and applies spatial mode or optical angular moments (OAMs) multiplexing. Moreover, MMFs and FMFs have many applications outside telecommunications: fiber optic sensors, medicine, fiber optic lasers / laser delivery systems, light source for illumination, endoscopes, remote viewing, and other areas. A few-mode regime adds a new another dimension to the space of parameters: it is associated with guided modes of a particular order, which mostly limits the number (from two to a few dozens) transfer of optical signal power over the tested optical fiber. Therefore, the discovered new multi- and few-mode effects, as well as the utilization and customization of known multi- and few-mode regimes for specified applications in telecommunications, sensorics, medicine, fiber-optic lasers/laser delivery systems, light sources for illumination, endoscopes, remote viewing and other matters, are the key areas in the presented Special Issue. This publication will cover a large scope of research in the area of multi- and few-mode effects in optical fibers, including topics of:

• MMFs and FMFs for telecommunications;
• MDM / SDM technique for optical networking;
• MIMO technique for optical networks with MMFs and FMFs;
• laser optimized multimode optical fibers;
• FMFs / multicore FMFs;
• laser-based multi-Gigabit data transmission over large core optical fibers;
• fiber optic sensors based on a few-mode effects;
• extremely enlarged core optical fibers;
• MMFs and FMFs in medicine;
• MMFs and FMFs in lasers / laser delivery systems;
• image transmission over MMFs and FMFs;
• chiral MMFs and FMFs;
• microstructured and photonic crystal MMFs and FMFs;
• polymer optical fibers and microstructured polymer optical fibers.

Prof. Dr. Anton Bourdine
Dr. Ruslan Kutluyarov
Dr. Artem A. Kuznetsov
Prof. Dr. Manish Tiwari
Dr. Airat Zh. Sakhabutdinov
Guest Editors

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