An optical fiber comprising: (i) a chlorine doped silica based core comprising a core alpha ()>10, and maximum refractive index delta .sub.1max % and Cl concentration >1 wt %; (ii) a cladding surrounding the core, the cladding comprising: (a) an inner cladding region adjacent to and in contact with the core and having a refractive index delta .sub.2 and a minimum refractive index delta .sub.2min such that .sub.2min<.sub.1max, the inner cladding region comprising fluorine doped silica and the refractive index delta .sub.2 with region that decreases with radial position, and (b) an outer cladding region surrounding the inner cladding region and having refractive index delta .sub.3, such that .sub.2min<.sub.3. The fiber has mode field diameter MFD at 1310 nm of 9 microns, a cable cutoff of 1260 nm, zero dispersion wavelength of 1300 nmzero dispersion wavelength 1324 nm and bend loss at 1550 nm for a 20 mm mandrel of less than 0.5 dB/turn.

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.

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. An optical waveguide includes a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide also includes a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core varies angularly along a length of the propagation axis.

Disclosed is a small-diameter polarization maintaining optical fiber, which relates to the field of special optical fibers. The small-diameter polarization maintaining optical fiber comprises a quartz optical fiber (5); the periphery thereof is provided with an inner coating (6) and an outer coating (8); the interior of the quartz optical fiber (5) is provided with an optical fiber core layer (1) and a quartz cladding (2); two stress zones (4) are arranged between the optical fiber core layer (1) and the quartz cladding (2); a buffer coating (7) is arranged between the inner coating (6) and the outer coating (8); the periphery of each stress zone (4) is provided with a buffer layer (3) which is concentric with the stress zone (4); when a working wavelength of a small-diameter polarization maintaining optical fiber is 1310 nm, the attenuation thereof reaches less than 0.5 dB/km, and the crosstalk reaches 35 dB/km; and when the working wavelength of the small-diameter polarization maintaining optical fiber is 1550 nm, the attenuation thereof reaches less than 0.4 dB/km, and the crosstalk reaches 30 dB/km. The optical fiber not only has excellent stability characteristics of attenuation and crosstalk, but also has the excellent stability characteristic of long-term operation, and can provide a better optical fiber ring for research on a high-precision optical fiber gyroscope, thereby laying the foundation for the development directions of miniaturization and high precision of the optical fiber gyroscope.

Disclosed is a small-diameter polarization maintaining optical fiber, which relates to the field of special optical fibers. The small-diameter polarization maintaining optical fiber comprises a quartz optical fiber (5); the periphery thereof is provided with an inner coating (6) and an outer coating (8); the interior of the quartz optical fiber (5) is provided with an optical fiber core layer (1) and a quartz cladding (2); two stress zones (4) are arranged between the optical fiber core layer (1) and the quartz cladding (2); a buffer coating (7) is arranged between the inner coating (6) and the outer coating (8); the periphery of each stress zone (4) is provided with a buffer layer (3) which is concentric with the stress zone (4); when a working wavelength of a small-diameter polarization maintaining optical fiber is 1310 nm, the attenuation thereof reaches less than 0.5 dB/km, and the crosstalk reaches 35 dB/km; and when the working wavelength of the small-diameter polarization maintaining optical fiber is 1550 nm, the attenuation thereof reaches less than 0.4 dB/km, and the crosstalk reaches 30 dB/km. The optical fiber not only has excellent stability characteristics of attenuation and crosstalk, but also has the excellent stability characteristic of long-term operation, and can provide a better optical fiber ring for research on a high-precision optical fiber gyroscope, thereby laying the foundation for the development directions of miniaturization and high precision of the optical fiber gyroscope.

The optical fiber includes a core, the first cladding, and second cladding. The core is made of silica based glass containing Cl. The first cladding and the second cladding are made of silica based glass containing fluorine. The refractive index of the first cladding is lower than that of the core. The refractive index of the second cladding is lower than that of the core and higher than that of the first cladding. The second cladding is divided into an outer region having a uniform refractive index and an inner region having a refractive index higher than that of the outer region. The difference P between the maximum refractive index of the inner region and the refractive index of the outer region is 0.02% to 0.10% in terms of relative refractive index with respect to pure silica based glass. The radial thickness R of the inner region is 10 m to 25 m.

A multicore fiber includes six or more of core elements having a core, a first clad surrounding the outer circumferential surface of the core and a second clad surrounding the outer circumferential surface of the first clad, and includes a clad surrounding the core elements. All of expressions are satisfied: n.sub.1>n.sub.2>n.sub.3, n.sub.1>n.sub.4, n.sub.3<n.sub.4, wherein the refractive index of the core is n.sub.1, the refractive index of the first clad is n.sub.2, the refractive index of the second clad is n.sub.3, and the refractive index of the clad is n.sub.4. The core elements are disposed so that the inter-center pitch between the cores adjacent to each other is disposed at regular spacing and the centers of the cores are annularly disposed.

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. An optical waveguide includes a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide also includes a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core varies angularly along a length of the propagation axis.

There is provided a single mode optical fiber including a core layer, a first cladding layer, and a second cladding layer, in which when a refractive index of a center portion of the core layer is set as no, a radial position where a refractive index becomes n.sub.00.45 is set as r.sub.CORE, a minimum value of a refractive index of the first cladding layer is set as n.sub.3, and a radial position where a refractive index becomes the n.sub.3 is set as r.sub.3, a relative refractive index difference of the first cladding layer is reduced continuously and gently from the r.sub.CORE to the r.sub.3.

An optical fiber comprising: a core made of silica glass; and a cladding that is made of silica glass and that surrounds the core, wherein 1-20.02 is satisfied, where 1 represents the greatest value of the specific refractive index difference of the core in 0r/a0.3, and 2 represents the smallest value of the specific refractive index difference of the core in 0r/a0.9, where r represents the radial distance from the center axis of the core, and a represents the radius of the core.