A device for selectively increasing higher-order mode losses comprises an optical fiber taper executed on a multi-mode fiber of a selected wavelength, and the fiber taper has separated regions, i.e. non-tapered fiber regions which have a first diameter equal to that of the main fiber. The tapered regions can also include transition regions in which the fiber diameter is reduced/increased, respectively, and a taper waist region which has a reduced diameter, where the taper level ratio between the regular diameter and the narrowed diameter is at least 20%, and the length of the transition regions are at least 0.5 mm on one side and may be zero on the other side, and the length of the taper waist with the narrower diameter is at least 0.5 mm. Furthermore, the taper area is coated with a filtering substance with attenuating properties between the tapered section and the cladding.

In one example, an optical device may include a waveguide having a core index of refraction that decreases along a length of the waveguide and an edge index of refection of the waveguide that is constant along the length of the waveguide. The central rays of the optical signals travelling through the waveguide may be refracted towards higher radii while the outer rays propagate unaffected. The optical device may decrease dispersion of the optical signals travelling through an optical fiber.

A multimode optical fiber transmission system that employs an optical fiber with at least one modal-conditioning fiber is disclosed. The system includes a single-mode transmitter that generates modulated light having a wavelength between 800 nm and 1600 nm; an optical receiver configured to receive and detect the modulated light; a multimode optical fiber that defines an optical path between the single-mode transmitter and the optical receiver, the multimode optical fiber having a core with a diameter D.sub.40 and a refractive index profile configured to optimally transmit light at a nominal wavelength of 850 nm; and at least one modal-conditioning fiber operably disposed in the optical path to perform at least one of modal filtering and modal converting of the optical modulated light.

An optical coupling apparatus includes: a coupling and polarization beamsplitter, a phase shifter, a 22 adjustable beamsplitter, a photoelectric detector, and a microprocessor. Light in any polarization direction can be coupled from an optical fiber into a waveguide, an extra insertion loss is small, intrinsic insertion losses for light in different polarization directions are the same, a structure is simple, and miniaturization is easy to be implemented.

Some embodiments of the disclosure relate to an optical transmission system that operates at a wavelength in the range from 950 nm to 1600 nm and that employs a single-mode optical transmitter and an optical receiver optically coupled to respective ends of a multimode fiber designed for 850 nm multimode operation. The optical transmission system also employs at least one single mode fiber situated within the optical pathway between the optical transmitter and the receiver and coupled to the multimode fiber.

Apparatus for laser processing a material (11), comprising a laser (1), an optical fibre (2), and a coupler (125), wherein: the laser (1) is connected to the optical fibre (2); the optical fibre (2) is a multimode optical fibre having a first optical mode (21) having a first mode order (24), a second optical mode (22) having a second mode order (25), and a third optical mode (23) having a third mode order (26); the third mode order (26) is higher than the second mode order (25) which is higher than the first mode order (24); the coupler (125) switches laser radiation propagating in the first optical mode (21) to laser radiation propagating in the second optical mode (22); and the coupler (125) switches the laser radiation propagating in the second optical mode (22) to laser radiation propagating in the third optical mode (23).

Some embodiments of the disclosure relate to an optical transmission system that operates at a wavelength in the range from 950 nm to 1600 nm and that employs a single-mode optical transmitter and an optical receiver optically coupled to respective ends of a multimode fiber designed for 850 nm multimode operation. The optical transmission system also employs at least one single mode fiber situated within the optical pathway between the optical transmitter and the receiver and coupled to the multimode fiber.

A device for selectively increasing higher-order mode losses comprises an optical fiber taper executed on a multi-mode fiber of a selected wavelength, and the fiber taper has separated regions, i.e. non-tapered fiber regions which have a first diameter equal to that of the main fiber. The tapered regions can also include transition regions in which the fiber diameter is reduced/increased, respectively, and a taper waist region which has a reduced diameter, where the taper level ratio between the regular diameter and the narrowed diameter is at least 20%, and the length of the transition regions are at least 0.5 mm on one side and may be zero on the other side, and the length of the taper waist with the narrower diameter is at least 0.5 mm. Furthermore, the taper area is coated with a filtering substance with attenuating properties between the tapered section and the cladding.

Methods of selecting, from a set of like optical fibers, a subset of optical fibers that can meet both short-wavelength and target-wavelength bandwidth requirements are disclosed. The method includes obtaining short-wavelength bandwidth data from DMD measurements, and determining a peak wavelength for each optical fiber. A target-wavelength bandwidth is then calculated using the determined peak wavelengths. The calculated target bandwidth is then compared to the short-wavelength and target-wavelength bandwidth requirements to identify which of the optical fibers satisfy these requirements.

A super-mode selective optical unit that may include (i) a multicore fiber (MCF) that comprises one or more claddings, and multiple doped fiber cores located within one of the one or more claddings; and (ii) a multimode fiber (MMF) that comprises a first MMF end and a second MMF end; wherein the first MMF end is configured to receive optical signals from the MCF; wherein the MMF is configured to attenuate in-phase super-mode components of the optical signals of the MCF and to amplify out-of-phase components of the optical signals.