The invention relates to a supercontinuum light source comprising a microstructured optical fiber and a pump light source. The microstructured optical fiber comprises a core and a cladding region surrounding the core, as well as a first fiber length section, a second fiber length section and an intermediate fiber length section between said first and second fiber length sections. The first fiber length section comprises a core with a first characteristic core diameter. The second fiber length section comprises a core with a second characteristic core diameter, smaller than said first characteristic core diameter, where said second characteristic core diameter is substantially constant along said second fiber length section. The intermediate length section of the optical fiber comprises a core which is tapered from said first characteristic core diameter to said second characteristic core diameter over a tapered length.

An optical module comprising a first optical fiber corresponding to an incidence side for laser light a second optical fiber corresponding to an emission side for the laser light; and a connection protecting portion that is provided and located so as to cover a connection site for optically connecting the first optical fiber and the second optical fiber, wherein the second optical fiber has a larger core diameter than the first optical fiber, the connection site is a site where a core portion of the first optical fiber and a core portion of the second optical fiber are connected to each other in a discontinuous shape, and the connection protecting portion is formed of a thermally conductive protective material and/or a photorefractive protective material includes refractive index that is equal to or higher than that of a clad portion of the first optical fiber.

A laser system based on nonlinear pulse compression and a LMA optical fiber therefor are provided. The LMA optical fiber is configured to amplify seed light pulses and promote the onset of nonlinear spectral broadening. The LMA optical fiber includes a first section having constant core and cladding diameters and receiving and supporting propagation of the light pulses in multiple transversal modes. The first section is configured to suppress high order modes propagating therealong. The LMA optical fiber further includes a tapered second section receiving the fundamental mode from the first section, the core and cladding diameters increasing gradually along said second section so as to provide an adiabatic transition of the fundamental mode. The LMA optical fiber further includes an optional third section having constant core and cladding diameters. Dispersive compression of the light pulses outputted by the LMA optical fiber provides excellent beam quality and high peak powers.

A random distributed Rayleigh feedback fiber laser based on a double-cladding weakly ytterbium-doped fiber includes: a pump laser source, a pump combiner, a cladding power stripper, and a double-cladding weakly ytterbium-doped fiber for simultaneously achieving distributed active gain and random distributed Rayleigh feedback. An output end of the pump combiner is connected with one end of the double-cladding weakly ytterbium-doped fiber, the other end of the double-cladding weakly ytterbium-doped fiber is connected with an input end of the cladding power stripper, and a concentration of ytterbium ions in the double-cladding weakly ytterbium-doped fiber is in a range of 0.510.sup.23 to 110.sup.27/m.sup.3. The laser provided by the present invention solves the problem that the existing random fiber lasers cannot simultaneously utilize distributed active gain and random distributed Rayleigh feedback with a single type of fiber.

An optical amplification transmission line of the present disclosure reduces a connection loss between an EDF located upstream of a signal light path and a SMF located downstream of the path, as compared with a conventional optical amplification transmission lines. The optical amplification transmission line includes an EDF and a SMF fusion-spliced to each other. The EDF has an Er-doped core and an F-doped cladding. A core of the SMF is doped with no Er. The ratio (MFD2/MFD1) of the MFD2 of a stationary section of the SMF to the MFD1 of a stationary section of the EDF falls within a range of 1.9 or more and 2.2 or less.

Provided is an optical coupler configured to cause an NA of light, which exits a taper fiber, to be smaller as compared with a conventional optical coupler. A taper fiber has a high refractive index part which is provided inside a core of the taper fiber and which has a refractive index smaller than a refractive index n.sub.core of the core. An exit end surface of each GI fiber is bonded to an entrance end surface of the taper fiber so that at least a part of the exit end surface of the each GI fiber overlaps with a section of the high refractive index part. A relative refractive index difference of the taper fiber is smaller than 0.076%.

Various embodiments include large cores fibers that can propagate few modes or a single mode while introducing loss to higher order modes. Some of these fibers are holey fibers that comprise cladding features such as air-holes. Additional embodiments described herein include holey rods. The rods and fibers may be used in many optical systems including optical amplification systems, lasers, short pulse generators, Q-switched lasers, etc. and may be used for example for micromachining.

The invention relates a power fiber laser system including at least one single-mode fiber laser, emitting at a signal wavelength, the fiber including at least one outer cladding and a core, in which the core of the fiber has a radially graded index. The fiber includes, at least over a part of its length, a geometrical section having a graded fiber-core radius that decreases between an input end of the section and an output end of the section, the core radius and the index variation between the cladding and the fiber at the input end being such that the normalized frequency at the signal wavelength is less than the normalized cutoff frequency at which the fiber becomes unimodal.

A bridge fiber includes a core layer and an outer layer which has an index of refraction higher than that of the core layer and covers the outer peripheral surface of the core layer. The outer layer is surrounded by a substance such as the atmosphere having an index of refraction lower than an index of refraction n.sub.2 of the outer layer. An area AR1 of the outer layer at one end face of the bridge fiber is an area that is to be optically coupled to an end face of a core of each of a plurality of pumping light inputting optical fibers, while an area AR2 of the core layer at another end face of the bridge fiber is an area that is to be optically coupled to an end face of a core of an amplification optical fiber.

A fiber optic cable including a first end and a second end, a core adapted to receive and transmit an optical signal and a cladding layer surrounding the core is disclosed. The fiber optic cable may include a ratio of an outside diameter of the cladding layer to a diameter of the core that decreases from the first end to the second end while the diameter of the core remains substantially uniform. The fiber optic cable may include a first portion of the cladding layer and a second portion of the cladding layer. A uniform outside diameter of the second portion may be less than a uniform outside diameter of the first portion. The fiber optic cable may further include a third portion of the cladding layer. A uniform outside diameter of the third portion may be less than a uniform outside diameter of the second portion.