An optical fiber made of silica glass includes a core having a maximum refractive index n1, a depressed portion surrounding the core and having an average refractive index n2, and cladding surrounding the depressed portion and having an average refractive index n3. In the optical fiber, n1>n3>n2. The optical fiber has a local maximum value of chromatic dispersion within a wavelength range of 1530 nm to 1610 nm, and the local maximum value is 2 ps/nm/km or greater and below 0 ps/nm/km. (86 words)

There are provided an optical receptacle having an optical fiber including a first portion on another end surface side, a third portion on one end surface side, and a second portion between the first portion and the third portion; a core diameter at the first portion is smaller than the core diameter at the third portion; the core diameter at the second portion increases from the first portion side toward the third portion side; a first elastic member is provided between the optical fiber and an inner wall of a through-hole; a holder holds the another end surface side of a fiber stub; and the sleeve holds the one end surface side of the fiber stub.

A fiber ring resonator having a relatively long loop of standard single-mode fiber with a short nanofiber segment. The evanescent mode of the nanofiber segment allows the cavity-enhanced field to interact with atoms in close proximity to the nanofiber surface.

An optical fiber with ultra-low attenuation and bend insensitivity includes a core layer and cladding layers. The cladding layers have an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary outer cladding layer. The core layer has a radius of 3.0-3.9 m, and a relative refractive index difference of 0.04% to 0.12%. The inner cladding layer has a radius of 8-14 m, and a relative refractive index difference of about 0.35% to 0.10%. The trench cladding layer has a radius of about 14-20 m, and a relative refractive index difference of about 0.6% to 0.2%. The auxiliary outer cladding layer has a radius of about 35-50 m, and a relative refractive index difference of about 0.4% to 0.15%. The outer cladding layer is a pure silicon-dioxide glass layer.

An optical fiber for efficient coupling of optical signals to photonic devices. The optical fiber includes a Cl doped tapered core region with a changing outer diameter and changing maximum core refractive index to provide improved coupling at wavelength of interest to photonic devices. The photonic devices may be, for example, silicon photonic devices with an operating wavelength at or near 1310 nm, or at or near 1550 nm.

An optical fiber with ultra-low attenuation and bend insensitivity includes a core layer and cladding layers. The cladding layers have an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary outer cladding layer. The core layer has a radius of 3.0-3.9 m, and a relative refractive index difference of 0.04% to 0.12%. The inner cladding layer has a radius of 8-14 m, and a relative refractive index difference of about 0.35% to 0.10%. The trench cladding layer has a radius of about 14-20 m, and a relative refractive index difference of about 0.6% to 0.2%. The auxiliary outer cladding layer has a radius of about 35-50 m, and a relative refractive index difference of about 0.4% to 0.15%. The outer cladding layer is a pure silicon-dioxide glass layer.

A distributed Brillouin sensor system comprising a pump laser, a Brillouin sensor fiber, and a detector system is described. The pump laser is arranged so as to send a pump signal into a first end of the Brillouin sensor fiber, and the detector system is arranged to detect Brillouin backscattering from the Brillouin sensor fiber. The Brillouin sensor fiber is characterized by having a negative dispersion, and further by an effective area of the sensor fiber being less than or equal to 50 m.sup.2.

The present invention is to provide a multi-core optical fiber that can expand its transmission wavelength band, and extend its transmission distance by reducing crosstalk, and also provide a method for designing the multi-core optical fiber. A multi-core optical fiber according to the present invention includes: four cores that are arranged in a square lattice pattern in a longitudinal direction; and a cladding region that is formed around the outer peripheral portions of the cores and has a lower refractive index than the cores, the absolute value of the relative refractive index difference between the cores and the cladding region being represented by A. In the multi-core optical fiber, the diameter of the cladding region is 125+1 m, the cutoff wavelength is 1.45 m or shorter, the mode field diameter MFD at a wavelength of 1.55 m is 9.5 to 10.0 m, the bending loss at a wavelength of 1.625 m and with a bending radius of 30 mm is 0.1 dB/100 turns or smaller, and the inter-core crosstalk at the wavelength of 1.625 m is 47 dB/km or smaller.

A distributed Brillouin sensor system comprising a pump laser, a Brillouin sensor fiber, and a detector system is described. The pump laser is arranged so as to send a pump signal into a first end of the Brillouin sensor fiber, and the detector system is arranged to detect Brillouin backscattering from the Brillouin sensor fiber. The Brillouin sensor fiber is characterized by having a negative dispersion, and further by an effective area of the sensor fiber being less than or equal to 50 m.sup.2.

A polarization maintaining fiber includes a core, paired stress applying parts disposed on both sides of the core, and a clad encompassing the core and the paired stress applying parts. When the polarization maintaining fiber has a fiber length of 2 m and a bend radius of 140 mm, the polarization maintaining fiber has a cut-off wavelength equal to or greater than 1.20 m and less than 1.31 m. When the polarization maintaining fiber has a bend radius of 5 mm and twists at a rate of one rotation per 31.4 mm of fiber length, the polarization maintaining fiber has a bending loss equal to or less than 6.6 dB at a wavelength of 1.31 m.