A multicore optical fiber includes two or more cores, a common interior cladding surrounding the two or more cores, and a common exterior cladding surrounding the common interior cladding. The common exterior cladding has a lower relative refractive index than the common interior cladding and reduces tunneling losses from the cores. The reduced tunneling loss allows placement of cores closer to the edge of the fiber, thus providing multicore optical fibers having higher core count for a given fiber diameter. Separation between cores is controlled to minimize crosstalk.

In various embodiments, the beam parameter product and/or numerical aperture of a laser beam is adjusted utilizing a step-clad optical fiber having a central core, a first cladding, an annular core, and a second cladding.

An optical fiber according to an embodiment includes a core, a cladding, and a coating layer. At the boundary between the core and the cladding, the local sound velocity decreases in the direction from the core side toward the cladding side. At least in the cladding, the local sound velocity changes continuously in a radial direction. Further, the line width of the Brillouin gain of the light beam guided by the fundamental mode is 60 MHz or more.

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 space-division multiplexed optical fiber includes a relatively high refractive index optical core region surrounded by alternating regions of relatively low and relative high refractive index material, forming concentric high index rings around the core. The optical core region supports propagation of light along at least a first radial mode associated with the optical core region and a high index ring region supports propagation of light along at least a second radial mode associated with the high index ring region. The second radial mode is different from the first radial mode.

A few mode optical fiber that includes an optical core and an optical cladding surrounding the optical core. The FMF has a step-index profile. The optical core has a core outer radius R.sub.17.5 m and a core refractive index difference n.sub.1 such that 14.510.sup.3<n.sub.1<2410.sup.3. The optical cladding comprises: an index ring with: a ring inner radius R.sub.r1 between 12 m and 19 m; a ring refractive index difference n.sub.r such that n.sub.1/n.sub.r is between 2 and 4; a ring volume V.sub.ring=n.sub.r(Rr.sub.2.sup.2Rr.sub.1.sup.2) between 1.8 m.sup.2 and 4.1 m.sup.2 where R.sub.r2 is the ring outer radius; an inner cladding between the optical core and the index ring, with an inner cladding inner radius R.sub.i1 and an inner cladding outer radius R.sub.i2, the inner cladding having an inner cladding refractive index difference n.sub.clad1 between 1.010.sup.3 and 1.010.sup.3.

An optical fiber according to an embodiment includes: a core; an inner cladding surrounding the core and having a refractive index smaller than a refractive index of the core; an outer cladding surrounding the inner cladding and having a smaller refractive index than the refractive index of the core and having a refractive index greater than the refractive index of the inner cladding, in which a ratio of a caustic radius to a MAC-value (caustic radius/MAC-value) at a bending radius of 10 mm at a wavelength of 1625 nm is 2.70 m or more.

In various embodiments, the beam parameter product and/or numerical aperture of a laser beam is adjusted utilizing a step-clad optical fiber having a central core, a first cladding, an annular core, and a second cladding.

A high bandwidth radiation-resistant multimode optical fiber includes a core and a cladding layer surrounding the core. The core is a fluorine-doped quartz glass layer with a graded refractive index distribution and a distribution power exponent of 1.7-2.2. The core has R1 of 15-35 m and 1%min of 0.8% to 1.2%. The cladding layer has an inner cladding layer having R2 of 15-38 m and 2% of 0.8% to 1.2% and/or a depressed inner cladding layer having R3 of 15-55 m and 3 of 1.0% to 1.4%, an intermediate cladding layer having R4 of 15.5-58 m and 4 of 0.7% to 0.2% a depressed cladding layer hasving R5 of 16-60 m and 5 of 0.8% to 1.2%, and an outer cladding layer sequentially formed from inside to outside. The outer cladding layer is a pure silica glass layer.

A vortex optical fiber for use in an illumination subsystem of an optical imaging system (e.g., a stimulated emission depletion (STED) microscopy system) includes an elongated optically transmissive medium having a set of regions including a core region, a trench region surrounding the core region, a ring region surrounding the trench region, and a cladding region, the set of regions having a doping profile providing a n.sub.eff for vector modes in an LP.sub.11 mode group of greater than 110.sup.4 in the visible spectral range so as to simultaneously guide stable Gaussian and orbital angular momentum (OAM) carrying modes at corresponding visible wavelengths.