An optical fiber includes: a core that includes quartz glass doped with a core updopant; an inner cladding that includes quartz glass doped with a cladding updopant and a downdopant and that covers a circumferential surface of the core; and an outer cladding that includes quartz glass and that covers an outer circumferential surface of the inner cladding. A refractive index of the inner cladding is substantially equal to a refractive index of the outer cladding. The inner cladding contains the cladding updopant at a concentration such that a refractive index increase rate ascribed to the cladding updopant falls within a range of 0.25% to 0.5%.

According to some embodiments a fiber sensor comprises: an optical fiber configured for operation at a wavelength from about 300 nm to about 2000 nm, and further defined by a transmission end, another end, a fiber outer diameter and a fiber length, the fiber comprising: (a) a hybrid core comprising a single mode core portion and a multi-mode core portion; and (b) a cladding surrounding the hybrid core.

Optical fibers containing wet-spun multi-layer hydrogel cladding with ionic-crosslinked polysaccharides are provided. Optical fibers can be formed with step- or gradient-index architectures, fusion splicing, and facile rare-earth ion doping. Plasmonic nanoparticles, functionalized light-sensitive quantum dots, or particles can be incorporated into the fiber core to generate a resonance light shift upon the presence and binding of molecular biotargets for biosensor applications. The integration of plasmonic hydrogel fibers with medical swabs provides for rapid detection of pathogens such as severe acute respiratory syndrome coronavirus 2 (SARS-COV-2). The inclusion of living cells allows for the non-invasive digitalization and quantification of complex biological responses such as cancer proliferative invasion and discovery of anti-cancer drug susceptibility thresholds.

A single mode optical fiber including a germania doped silica central core region having outer radius r.sub.1 and refractive index .sub.1, a maximum refractive index .sub.1max, and 0.32%.sub.1max0.45%, and a core alpha profile (Core.sub.). In various embodiments, the optical fiber also contains a cladding region including: (i) a second inner cladding region or ring region surrounding the first inner cladding region; or (ii) an inner cladding region or pedestal region surrounding the germania doped silica central core region. The corresponding resultant optical fibers exhibit a 22 m cable cutoff less than or equal to 1260 nm, a macrobending loss at 1550 nm of 0.75 dB/turn on a 20 mm diameter mandrel, a zero dispersion wavelength, .sub.0, of 1300 nm.sub.01324 nm, and a mode field diameter at 1310 nm of 8.2 micronsMDF.sub.1310 nm9.6 microns.

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.

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.

According to embodiments, an optical fiber may include a core portion comprising an outer radius r.sub.C and a maximum relative refractive index .sub.Cmax. A cladding may surround the core portion and include a low-index trench and an outer cladding. The low index trench may surround the core portion and includes an outer radius r.sub.T and relative refractive index .sub.T. The outer cladding may surround and be in direct contact with the low-index trench. The outer cladding may be formed from silica-based glass comprising greater than 1.0 wt. % bromine and has a relative refractive index .sub.OC, wherein .sub.Cmax>.sub.OC>.sub.T. The optical fiber may have a cable cutoff of less than or equal to 1530 nm. An attenuation of the optical fiber may be less than or equal to 0.185 dB/km at a wavelength of 1550 nm.

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 wavelength1324 nm, and a macrobending loss at 1550 nm for a 20 mm mandrel of less than 0.75 dB/turn.

An optical fiber with low attenuation and methods of making same are disclosed. The optical fiber has a core, an inner cladding surround the core, and an outer cladding surrounding the inner cladding. The outer cladding is chlorine-doped such that the relative refractive index varies as a function of radius. The radially varying relative refractive index profile of the outer cladding reduces excess stress in the core and inner cladding, which helps lower fiber attenuation while also reducing macrobend and microbend loss. A process of fabricating the optical fiber includes doping an overclad soot layer of a soot preform with chlorine and then removing a portion of the chlorine dopant from an outermost region of the overclad soot layer. The soot preform with the modified chlorine dopant profile is then sintered to form a glass preform, which can then be used for drawing the optical fiber.

According to embodiments, an optical fiber may include a core portion comprising a radius r.sub.C, a centerline C.sub.L, a numerical aperture NA greater than or equal to 0.15 and less than or equal to 0.25, a graded relative refractive index profile having a maximum relative refractive index .sub.Cmax and an value greater than or equal to 1 and less than or equal to 3. The core portion may include an up-dopant with a graded concentration from the radius r.sub.C to the centerline C.sub.L and an attenuation dopant with a constant concentration from the centerline C.sub.L of the core portion to the radius r.sub.C of the core portion. The optical fiber is multi-moded for wavelengths of light within a range from 800 nm to 1350 nm and an attenuation of the optical fiber wavelengths between 800 nm and 1000 nm is greater than or equal to 0.5 dB/m.