Abstract: The refractive index of the first core portion 11a is higher than that of a clad 12, and the refractive index of the second core portion 11b is higher than that of the first core portion 11a. When light of the LP01 mode and light of the LP11 mode are standardized by power, in the core 11, an active element that stimulates to emit light of the predetermined wavelength is doped at a higher concentration in at least a part of an area where power of light of the LP01 mode is larger than that of light of the LP11 mode than at least a part of an area where the power of light of the LP11 mode is larger than that of light of the LP01 mode.

Abstract: The refractive index of the first core portion 11a is higher than that of a clad 12, and the refractive index of the second core portion 11b is higher than that of the first core portion 11a. When light of the LP01 mode and light of the LP11 mode are standardized by power, in the core 11, an active element that stimulates to emit light of the predetermined wavelength is doped at a higher concentration in at least a part of an area where power of light of the LP01 mode is larger than that of light of the LP11 mode than at least a part of an area where the power of light of the LP11 mode is larger than that of light of the LP01 mode.

Abstract: A photonic bandgap fiber includes a core of a solid material; a first cladding provided around the core; a low-refractive-index region provided in a part of a core vicinity portion of the first cladding and whose average refractive index is lower than that of the core; and a periodic structure region that is arranged in another part of the core vicinity portion of the first cladding which is made of a great many high-refractive-index portions whose refractive index is higher than that of the first cladding arranged in a periodic structure. According to the invention, it is possible to provide a photonic bandgap fiber which, when arranged in a double-clad structure, enables pump light to efficiently pump signal light.

Abstract: A photonic bandgap fiber includes a core and a cladding that surrounds the core. In this photonic bandgap fiber, high refractive index portions which have a refractive index higher than that of a medium of the cladding are provided in the cladding so as to form a triangular lattice structure with a lattice constant ?, and the refractive index of the core is higher than the refractive index of the medium of the cladding and lower than the refractive index of the high refractive index portion. The coupling length between the core and the high refractive index portion that is closest to the core is longer than the coupling length between adjacent high refractive index portions, or a periodic structure formed by the high refractive index portions is not provided around the entirely of the area along the circumference of the core.

Abstract: A photonic band-gap fiber comprises a first core having a refractive index that is not higher than a refractive index of a clad; a second core that is disposed so as to surround the first core and has a refractive index that is lower than the refractive index of the first core; a clad that surrounds the second core; and a periodic structure portion that is disposed in the clad in a vicinity of the second core and is constituted by high-refractive index portions that have a refractive index higher than that of clad and form the periodic structure, and the periodic-structure portion functions as a wave-length filter. By the function of the periodic structure portion as a wave-length filter, it is possible to reduce the propagation loss of the transmission wavelength and increase the propagation loss of the cutoff wavelength.

Abstract: A photonic bandgap fiber includes a first core having a refractive index equal to or smaller than a refractive index of a cladding, a second core that is provided to surround the first core and has a refractive index smaller than the refractive index of the first core, the cladding that surrounds the second core, and a periodic structure portion that is provided in the cladding around the second core, and in which high-refractive index portions having a refractive index larger than the refractive index of the cladding form a periodic structure. The periodic structure is configured such that at least the propagation constant of the fundamental mode at a wavelength to be used is in a photonic bandgap, and the propagation constant of a higher-order mode at the wavelength to be used is outside of the photonic bandgap.

Abstract: A photonic bandgap fiber of the present invention functions as a polarization maintaining fiber, and includes: a core made from a solid material; a cladding provided around the core; a periodic structure region which is provided in a part of the cladding in a vicinity of the core and in which a plurality of high refractive index parts with a refractive index higher than that of the cladding are arranged in a periodic structure; a low refractive index region which is provided in another part of the cladding in a vicinity of the core and has an average refractive index lower than that of the core; and stress applying parts which are provided in a part of the low refractive index region close to the periodic structure region and have a thermal expansion coefficient different from that of another part of the low refractive index region.

Abstract: A photonic band-gap fiber comprises a first core having a refractive index that is not higher than a refractive index of a clad; a second core that is disposed so as to surround the first core and has a refractive index that is lower than the refractive index of the first core; a clad that surrounds the second core; and a periodic structure portion that is disposed in the clad in a vicinity of the second core and is constituted by high-refractive index portions that have a refractive index higher than that of clad and form the periodic structure, and the periodic-structure portion functions as a wave-length filter. By the function of the periodic structure portion as a wave-length filter, it is possible to reduce the propagation loss of the transmission wavelength and increase the propagation loss of the cutoff wavelength.

Abstract: A photonic bandgap fiber includes a first core having a refractive index equal to or smaller than a refractive index of a cladding, a second core that is provided to surround the first core and has a refractive index smaller than the refractive index of the first core, the cladding that surrounds the second core, and a periodic structure portion that is provided in the cladding around the second core, and in which high-refractive index portions having a refractive index larger than the refractive index of the cladding form a periodic structure. The periodic structure is configured such that at least the propagation constant of the fundamental mode at a wavelength to be used is in a photonic bandgap, and the propagation constant of a higher-order mode at the wavelength to be used is outside of the photonic bandgap.

Abstract: A photonic bandgap fiber includes a core and a cladding that surrounds the core. In this photonic bandgap fiber, high refractive index portions which have a refractive index higher than that of a medium of the cladding are provided in the cladding so as to form a triangular lattice structure with a lattice constant ?, and the refractive index of the core is higher than the refractive index of the medium of the cladding and lower than the refractive index of the high refractive index portion. The coupling length between the core and the high refractive index portion that is closest to the core is longer than the coupling length between adjacent high refractive index portions, or a periodic structure formed by the high refractive index portions is not provided around the entirely of the area along the circumference of the core.

Abstract: A photonic bandgap fiber includes a core of a solid material; a first cladding provided around the core; a low-refractive-index region provided in a part of a core vicinity portion of the first cladding and whose average refractive index is lower than that of the core; and a periodic structure region that is arranged in another part of the core vicinity portion of the first cladding which is made of a great many high-refractive-index portions whose refractive index is higher than that of the first cladding arranged in a periodic structure. According to the invention, it is possible to provide a photonic bandgap fiber which, when arranged in a double-clad structure, enables pump light to efficiently pump signal light.

Abstract: In a method of measurement of the birefringence of an optical fiber, the round-trip Jones matrix R(z) for a first interval (0, z) from a measurement starting point 0 in the optical fiber for measurement to a prescribed position z, and the round-trip Jones matrix R(z+?z) for a second interval (0, z+?z) from the measurement starting point 0 to a position z+?z differing from the position z, are acquired, the eigenvalues ?1, ?2 of the matrix R(z+?z)R(z)?1 are determined, and by computing the following equations (1) and (2), ? = arg ? ( ? 1 ? 2 ) 2 ( 1 ) ? ? ? n = ?? 2 ? ? · ? ? ? z ( 2 ) (where ? represents the phase difference between linear polarization components due to birefringence, ?n represents birefringence, and ? represents wavelength), the birefringence in the infinitesimal interval ?z from the position z to the position z+?z is obtained.

Abstract: In a method of measurement of the birefringence of an optical fiber, the round-trip Jones matrix R(z) for a first interval (0, z) from a measurement starting point 0 in the optical fiber for measurement to a prescribed position z, and the round-trip Jones matrix R(z+?z) for a second interval (0, z+?z) from the measurement starting point 0 to a position z+?z differing from the position z, are acquired, the eigenvalues ?1, ?2 of the matrix R(z+?z)R(z)?1 are determined, and by computing the following equations (1) and (2), ? = arg ? ( ? 1 ? 2 ) 2 ( 1 ) ? ? ? ? n = ?? 2 ? ? · ? ? ? ? z ( 2 ) (where ? represents the phase difference between linear polarization components due to birefringence, ?n represents birefringence, and ? represents wavelength), the birefringence in the infinitesimal interval ?z from the position z to the position z+?z is obtained.

Abstract: A method of measuring polarization mode dispersion (PMD) of an optical fiber, includes estimating PMD when an optical fiber is formed as an optical cable, from a beat length when the optical fiber is wound around a bobbin, and an average coupling length when the optical fiber is formed as the optical cable.

Abstract: A method of measuring polarization mode dispersion (PMD) of an optical fiber, includes estimating PMD when an optical fiber is formed as an optical cable, from a beat length when the optical fiber is wound around a bobbin, and an average coupling length when the optical fiber is formed as the optical cable.

Abstract: An optical head device having an optical element capable of transmitting without diffracting light having a wavelength emitted from a two-wavelength semiconductor laser and capable of diffracting light having another wavelength, to provide high utilization efficiency of light in a stable manner.

Abstract: An optical head device having an optical element capable of transmitting without diffracting light having a wavelength emitted from a two-wavelength semiconductor laser and capable of diffracting light having another wavelength, to provide high utilization efficiency of light in a stable manner.