Methods, apparatus, and systems for modulation of a laser beam. An optical modulator may comprise an optical input to receive an optical beam, and one or more lengths of fiber between the optical input and an optical output. At least one of the lengths of fiber comprises a confinement region that is optically coupled to the output. The optical modulator may further comprise a perturbation device to modulate, through action upon the one or more lengths of fiber, a transmittance of the beam through the confinement region from a first transmittance level at a first time instance to a second transmittance level at a second time instance. The optical modulator may further comprise a controller input coupled to the perturbation device, wherein the perturbation device is to act upon the one or more lengths of fiber in response to a control signal received through the controller input.

Methods, apparatus, and systems for active saturable absorbance of an optical beam. An active saturable absorber may comprise an optical input to receive an optical beam, and one or more lengths of fiber between the optical input and an optical output. At least one of the lengths of fiber comprises a confinement region that is optically coupled to the output. The active saturable absorber may further comprise an optical detector to sense a characteristic of the optical beam, such as power. The active saturable absorber may further comprise a perturbation device to modulate, through action upon the one or more lengths of fiber, a transmittance of the beam through a fiber confinement region from a lower transmittance level to a higher transmittance level based on an indication of the characteristic sensed while the transmittance level is low.

An optical fiber includes (i) a chlorine doped silica based core having a core alpha (Core.sub.)4, a radius r.sub.1, and a maximum refractive index delta .sub.1max % and (ii) a cladding surrounding the core. The cladding surrounding the core includes a) a first inner cladding region adjacent to and in contact with the core and having a refractive index delta .sub.2, a radius r.sub.2, and a minimum refractive index delta .sub.2min such that .sub.2min<.sub.1max, b) a second inner cladding adjacent to and in contact with the first inner cladding having a refractive index .sub.3, a radius r.sub.3, and a minimum refractive index delta .sub.3min such that .sub.3min<.sub.2, and c) an outer cladding region surrounding the second inner cladding region and having a refractive index .sub.5, a radius r.sub.max, and a minimum refractive index delta .sub.3min such that .sub.3min<.sub.2. The optical fiber has a mode field diameter MFD at 1310 of 9 microns, a cable cutoff of 1260 nm, a zero dispersion wavelength of 1300 nmzero dispersion wavelength 1324 nm, and a macrobending loss at 1550 nm for a 20 mm mandrel of less than 0.75 dB/turn.

An optical fiber includes (i) a chlorine doped silica based core having a core alpha (Core.sub.)4, a radius r.sub.1, and a maximum refractive index delta .sub.1 max% and (ii) a cladding surrounding the core. The cladding surrounding the core includes a) a first inner cladding region adjacent to and in contact with the core and having a refractive index delta .sub.2, a radius r.sub.2, and a minimum refractive index delta .sub.2 min such that .sub.2 min<.sub.1 max, b) a second inner cladding adjacent to and in contact with the first inner cladding having a refractive index .sub.3, a radius r.sub.3, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2, and c) an outer cladding region surrounding the second inner cladding region and having a refractive index .sub.5, a radius r.sub.max, and a minimum refractive index delta .sub.3 min such that .sub.3 min<.sub.2. The optical fiber has a mode field diameter MFD at 1310 of 9 microns, a cable cutoff of 1260 nm, a zero dispersion wavelength of 1300 nmzero dispersion wavelength 1324 nm, and a macrobending loss at 1550 nm for a 20 mm mandrel of less than 0.75 dB/turn.

An optical fiber includes: a core; a cladding layer that is lower in refractive index than the core; and a depressed layer that lies between the core and the cladding layer and that is lower in refractive index than the cladding layer, wherein: the optical fiber has an effective core area Aeff that is equal to or greater than 100 m.sup.2 and equal to or less than 129 m.sup.2, the core has a radius r1 that is equal to or greater than 5.2 m and equal to or less than 7.4 m, the core has a refractive index volume Vcore that is equal to or greater than 8.5% m.sup.2 and equal to or less than 16.5% m.sup.2, the depressed layer has a refractive index volume Vdep that is equal to or greater than 40% m.sup.2 and less than 0% m.sup.2.

Provided are embodiments of an optical fiber cable. The optical fiber cable includes a cable jacket having an inner surface and an outer surface. The inner surface defines a central cable bore, and the outer surface defines an outermost surface of the optical fiber cable. The optical fiber cable also includes a cable core disposed in the central cable bore. The cable core includes a plurality of multicore optical fibers and a cross-sectional area. The plurality of multicore optical fibers fill at least 50% of the cross-sectional area of the cable core. Each multicore optical fiber of the plurality of multicore optical fibers has an inner glass region having a plurality of core regions surrounded by a common outer cladding. The cable core has a core region density that is at least 40 core regions/mm.sup.2.

A method of fabricating a multi-core polymer optical fibre comprises arranging optical fibre preforms in a stack, the optical fibre preforms each comprising a polymer core and polymer cladding surrounding the polymer core; and drawing and bonding the stack to form the multi-core polymer optical fibre. Any contaminants or impurities which collect on outer surfaces of the preforms may be confined to boundaries between the preforms, which may avoid attenuation of signals passed through the cores while at the same time reducing crosstalk between cores of the final manufactured fibre. Also provided is a multi-core polymer optical fibre obtainable by the method.

Single mode optical fibers with a chlorine doped core and a cladding having a fluorine doped trench region are disclosed. The optical fiber includes a chlorine doped silica core having a core alpha 10, a core radius r.sub.1 and maximum refractive index delta .sub.1max % and a Cl concentration0.9 wt %. The optical fiber also has a cladding surrounding the core, the cladding having an inner and an outer cladding. The inner cladding has first and second cladding regions. The optical fiber has mode field diameter at 1310 nm of larger than 9 microns, a cable cutoff wavelength of 1260 nm, a zero dispersion wavelength .sub.0, where 1300 nm.sub.01324 nm, and bend loss at 1550 nm for a 20 mm mandrel of less than 0.5 dB/turn.

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.

Optical waveguide cores having refractive index profiles that vary angularly about a propagation axis of the core can provide single-mode operation with larger core diameters than conventional waveguides. In one representative embodiment, an optical waveguide comprises a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide can also comprise a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core can vary angularly along a length of the propagation axis.