Abstract: A measurement method for measuring an effective refractive index difference between two propagation modes of a multimode fiber is provided. The method includes: measuring a first Brillouin frequency shift ?1 by specifying a frequency having a lowest-frequency peak out of peaks in a first frequency spectrum of scattered light in a first propagation mode; measuring a second Brillouin frequency shift ?2 by specifying a frequency having a lowest-frequency peak out of peaks in a second frequency spectrum of scattered light in a second propagation mode; and calculating an effective refractive index difference ?neff in accordance with ?neff=(?1??2)/(2kVL) with use of the first Brillouin frequency shift ?1, the second Brillouin frequency shift ?2, a predetermined wave number k of light in a vacuum, and a predetermined constant VL.

Abstract: A measurement method for measuring an effective refractive index difference between two propagation modes of a multimode fiber is provided. The method includes: measuring a first Brillouin frequency shift v1 by specifying a frequency having a lowest-frequency peak out of peaks in a first frequency spectrum of scattered light in a first propagation mode; measuring a second Brillouin frequency shift v2 by specifying a frequency having a lowest-frequency peak out of peaks in a second frequency spectrum of scattered light in a second propagation mode; and calculating an effective refractive index difference ?neff in accordance with ?neff=(v1?v2)/(2kVL) with use of the first Brillouin frequency shift v1, the second Brillouin frequency shift v2, a predetermined wave number k of light in a vacuum, and a predetermined constant VL.

Abstract: An optical fiber alignment device includes an image-capturing device capturing images of end surfaces of two optical fibers; an image-analyzing device obtaining position coordinates of two or more cores in the end surfaces from the image captured by the image-capturing device for each of the two optical fibers; a calculation device substituting the position coordinates of the cores obtained for each of the optical fibers in a theoretical equation that represents a total sum of axial deviation losses at the time of splicing the cores to each other, the calculation device obtaining a positional relationship between the end surfaces of the optical fibers from the theoretical equation such that the total sum of the axial deviation losses becomes a minimum; and a driving device arranging the optical fibers such that the end surfaces of the optical fibers satisfy the positional relationship obtained by the calculation device.

Abstract: An optical fiber which allows propagation of two or more modes, and in a case where a mode coupling coefficient between at least two modes among the two or more modes is h [1/km], the length of the optical fiber is z [km], and the amount XT of coupling between the two modes is represented by XT=10·log10(zh) [dB], the amount XT of coupling satisfies Expression (A) described below.

Abstract: Optical fibers Fp, Fn, included in a light transmission path, are two-mode optical fibers for propagating an LP01 mode component and an LP11 mode component contained in signal light, and a gradient d??/d? of a mode dispersion ?? with respect to a wavelength ? in a wavelength band of 1530 nm to 1625 nm is |0.5| ps/km/nm or less. Symbols of mode dispersions ?? of the optical fibers Fp, Fn are opposite to each other. The light transmission path can satisfactorily compensate the mode dispersion in a wide wavelength band.

Abstract: An optical fiber alignment device includes an image-capturing device capturing images of end surfaces of two optical fibers; an image-analyzing device obtaining position coordinates of two or more cores in the end surfaces from the image captured by the image-capturing device for each of the two optical fibers; a calculation device substituting the position coordinates of the cores obtained for each of the optical fibers in a theoretical equation that represents a total sum of axial deviation losses at the time of splicing the cores to each other, the calculation device obtaining a positional relationship between the end surfaces of the optical fibers from the theoretical equation such that the total sum of the axial deviation losses becomes a minimum; and a driving device arranging the optical fibers such that the end surfaces of the optical fibers satisfy the positional relationship obtained by the calculation device.

Abstract: An optical fiber, including (i) an inner core having an ?-power refractive index profile, (ii) an outer core having a refractive index of n1?, and (iii) a cladding having a refractive index of n2 (n1?<n2<n1), is configured such that a depth of a trench, defined by n2?n1?, is sufficiently increased.

Abstract: An optical fiber (1) includes (i) an inner core (111) whose refractive index distribution has an ? profile, (ii) an outer core (112) which surrounds the inner core (111), and (iii) a clad (12) which surrounds the outer core (112). In the optical fiber (1), Rd is set to not less than 0.15, where Rd is a ratio of a refractive index difference between the outer core (112) and the clad (12) to a refractive index difference between a center part of the inner core (111) and the clad (12).

Abstract: Optical fibers Fp, Fn, included in a light transmission path, are two-mode optical fibers for propagating an LP01 mode component and an LP11 mode component contained in signal light, and a gradient d??/d? of a mode dispersion ?? with respect to a wavelength ? in a wavelength band of 1530 nm to 1625 nm is |0.5| ps/km/nm or less. Symbols of mode dispersions ?? of the optical fibers Fp, Fn are opposite to each other. The light transmission path can satisfactorily compensate the mode dispersion in a wide wavelength band.

Abstract: An optical fiber, including (i) an inner core having an ?-power refractive index profile, (ii) an outer core having a refractive index of n1?, and (iii) a cladding having a refractive index of n2 (n1?<n2<n1), is configured such that a depth of a trench, defined by n2?n1?, is sufficiently increased.

Abstract: An optical fiber (1) includes (i) an inner core (111) whose refractive index distribution has an a profile, (ii) an outer core (112) which surrounds the inner core (111), and (iii) a clad (12) which surrounds the outer core (112). In the optical fiber (1), Rd is set to not less than 0.15, where Rd is a ratio of a refractive index difference between the outer core (112) and the clad (12) to a refractive index difference between a center part of the inner core (111) and the clad (12).

Abstract: An optical modulation method operable in an optical transmission path using an optical fiber, wherein an optical fiber bending region is formed by bending a portion of the optical fiber into a U shape having a predetermined bending width. A bending width set point is set in correspondence with a predetermined inclined portion of a characteristic curve representing a dependency ratio of insertion loss of light propagating in said optical fiber bending region relative to the bending width thereof, said predetermined inclined portion of said characteristic curve being located between a predetermined maximum and minimum portion thereof. Intensity modulation of light propagating in the optical fiber is performed using a signal to be transmitted by adjusting the bending width of the optical fiber bending region in correspondence with the signal to be transmitted with reference to the bending width set point as a center.

Abstract: An optical modulation method operable in an optical transmission path using an optical fiber, wherein an optical fiber bending region is formed by bending a portion of the optical fiber into a U shape having a predetermined bending width. A bending width set point is set in correspondence with a predetermined inclined portion of a characteristic curve representing a dependency ratio of insertion loss of light propagating in said optical fiber bending region relative to the bending width thereof, said predetermined inclined portion of said characteristic curve being located between a predetermined maximum and minimum portion thereof. Intensity modulation of light propagating in the optical fiber is performed using a signal to be transmitted by adjusting the bending width of the optical fiber bending region in correspondence with the signal to be transmitted with reference to the bending width set point as a center.

Abstract: A single-polarization optical fiber comprising a core, an inner cladding surrounding the core, an outer cladding surrounding the inner cladding and at least one pair of stress-applying portions each of which are partially extended into both the inner and outer claddings and which are symmetrical about the axis of the core and having thermal expansion coefficient higher than those of both the inner and outer claddings. When the refractive index of the stress-applying portions is lower than that of the core and higher than that of the inner cladding and further not higher than that of the outer cladding, one of orthogonally polarized mode is cutoff and only one polarized mode can propagate in the optical fiber.

Abstract: A 1.5 .mu.m zero dispersion single mode optical fiber comprising a center core, a side core disposed on an outer side of the center core and having a refractive index lower than that of the center core, and a cladding portion disposed on an outer side of the side core. Each of the refractive indices of the center core and the side core has a step-like profile in the direction of the radius of the optical fiber. The bending loss is low. The mode field diameter can be increased without deteriorating the bending loss, and the splice loss can be reduced. The chromatic dispersion varies only to a small extent with respect to changes in the core diameter, so that the zero dispersion wavelength can be well controlled.