Abstract: [Problem] Provided is a diffraction grating element that allows the temperature control mechanism to be dispensed with or simplified.

Abstract: The present invention relates a diffraction grating element capable achieving a large angular dispersion and excellent diffraction characteristics. The diffraction grating element has a buried structure, and comprises: a first medium with a refractive index of n1; a second medium with lower refractive index of n2 than the first medium; and a diffraction grating formed at the interface between the first and second mediums. One of the first and second mediums is a solid, and the other thereof is a solid or a liquid. An anti-reflection film is formed on one surface of the first medium 11 on which the diffraction grating is not formed, and this anti-reflection film lies in contact with a medium with a refractive index no. Furthermore, an anti-reflection film is also formed on one surface of the second medium on which the diffraction grating is not formed, and this anti-reflection film lies in contact with the medium with the refractive index no.

Abstract: In this diffraction grating device manufacturing method, refractive-index-change-inducing light of a wavelength that induces a change in refractive index is irradiated onto an optical waveguide, thus forming a diffraction grating through refractive index modulation along the longitudinal direction of the optical waveguide. At this time, the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide is swung in a direction perpendicular to the longitudinal direction of the optical waveguide.

Abstract: An optical component is an optical fiber grating element having a grating formed in the core region of an optical fiber, and a cladding region is made of silica glass. An optical material for the core region is ladder-type silicone resin, whose refractive index is set to a desired value by appropriately adjusting the mixing ratio between SiO and a functional group and the mixing ratio of a phenyl group to a methyl group. The optical component has a desired thermal expansion coefficient and desired temperature characteristics as a whole.

Abstract: An optical fiber grating device 1 is a device in which a long period grating 14 is formed in a core region 11 of an optical fiber 10 consisting of the core region 11 having a refractive index n1 and an outside diameter 2a, a first cladding region 12 surrounding the core region 11 and having a refractive index n2 and an outside diameter 2b, and a second cladding region 13 surrounding the first cladding region 12 and having a refractive index n3 and an outside diameter 2c. There is a magnitude relation of n1>n2>n3 among the refractive index n1 of the core region 11, the refractive index n2 of the first cladding region 12, and the refractive index n3 of the second cladding region 13, a relative refractive index difference &Dgr;n2 of the first cladding region 12 to the second cladding region 13 is not less than 0.5%, and a thickness (c−b) of the second cladding region 13 with respect to a transmission loss peak wavelength &lgr; is in a range of not less than &lgr; nor more than 10&lgr;.

Abstract: The present invention relates to an optical fiber having a structure which allows further improvements to be made both in terms of lower reflectance and narrower bandwidth, and to a fiber grating type filter including the optical fiber. The optical fiber applied to the fiber grating type filter comprises a core region extending along a predetermined axis, and a cladding region provided on an outer periphery of the core region. The core region does not contain any photosensitive dopant which contributes to predetermined wavelength light photosensitivity as a glass property, but a part of the cladding region contain such a photosensitive dopant. By means of this composition, it is possible to form a grating, which has a grating plane slanted by a predetermined angle with respect to the optical axis, in a part of the cladding region surrounding the core region.

Abstract: The present invention relates to a branch line monitoring system and branch line monitoring method comprising a configuration which improves the S/N ratio of measurement information and can be realized inexpensively. This system is provided with optical filters which correspond to optical fiber lines to be monitored as branch lines. These optical filters each have such a cutoff characteristic as to cut of f respective one channel of monitor light but transmit therethrough the remaining monitor light and signal light. When the optical filters having such a cutoff characteristic are provided, each of the optical fiber lines is monitored by use of a plurality of channels of monitor light other than the one cut off by the optical filter provided so as to correspond thereto. Consequently, as compared with the case where one optical fiber line is monitored by its corresponding one channel of monitor light, the S/N ratio of measurement information is improved, whereby highly accurate monitoring is possible.

Abstract: According to the present invention, a periodically perturbation part which serves as a refractive index modulated part is provided in a part of the optical waveguide of an optical fiber or the like in the longitudinal direction thereof, a line perpendicular to a level plane of this periodically perturbation part is tilted with respect to the optical axis X of the optical waveguide, and the plane defined by this optical axis X and a line A intersecting the optical axis X, that is, the deflection angle plane M is made, by twisting or the like, to include a portion that varies depending on the position of the optical waveguide in the longitudinal direction thereof.

Abstract: A transmitted type diffractive optical element comprises a transparent plate made of a material having a refractive index n2, whereas the transparent plate is in contact with a medium having a refractive index n1. A number of projections are arranged with a period L on the first surface side of the transparent plate. Each projection has a rectangular cross section with a height H and a width W. An antireflection layer is formed on the second surface of the transparent plate. When the light L1 having a wavelength &lgr; is incident on the first surface at an incident angle &thgr;, the transmitted type diffractive optical element satisfies (2n1L/&lgr;)sin &thgr;=1, and n2/n1≦3 sin &thgr;, whereas each of the diffraction efficiencies of transmitted first-order diffracted light L31 in TE and TM polarization modes is at least 0.8.

Abstract: The present invention is directed to a gain equalizer having a preferable equalization characteristic and a structure that can be easily fabricated. The gain equalizer flattens a spectrum of light in a predetermined wavelength range inputted through an input terminal and outputs the light from an output terminal, and comprises a coarse-tunable equalizing section and a fine-tunable equalizing section connected in series. The coarse-tunable equalizing section coarsely flattens the spectrum of the light in the predetermined wavelength range, and includes a plurality of filters each having a large loss and a small reflectance as compared with the fine-tunable equalizing section. The fine-tunable equalizing section flattens the spectrum of the light in a wavelength range where the coarse-tunable equalizing section can not flatten at a predetermined value or less among the predetermined wavelength range.

Abstract: The present invention relates to an optical filter and the like, applicable to a gain equalizer for equalizing the gain of an optical amplifier as well, comprising a structure enabling a repeater and the like to have a small-sized, inexpensive configuration. This optical filter 22 has such a transmission spectrum that a ripple of 1 dB or more exists with respect to light in a communication wavelength band. This transmission spectrum is designed so as to yield a transmissivity of −10 dB or less in both of a first blocking wavelength band having a bandwidth of 20 nm or more located on the shorter wavelength side than the communication wavelength band, and a second blocking wavelength band having a bandwidth of 20 nm or more located on the longer wavelength side than the communication wavelength band. The optical filter having such a transmission spectrum can function as a filter for blocking noise light and as a gain equalizer.

Abstract: An optical element comprises optical input/output means, polarization separating means, polarization plane rotating means, wavelength branching means, a condenser optical system, and reflecting means. The optical input/output means, for inputting and outputting light, has a plurality of ports. The polarization separating means separates the light into respective polarized light components (first and second light beams) having first and second directions orthogonal to each other. The polarization plane rotating means rotates a polarization direction of the received light beam to make the first and second light beams have the same polarization direction. The wavelength branching means spatially separates the light beams in terms of wavelength, and outputs thus separated wavelength light components. The condenser optical system converges the wavelength light components.

Abstract: An optical signal processor comprises optical input/output means, a first optical system, wavelength branching means, a second optical system, and reflecting means. The optical input/output means includes a plurality of input/output ports. The ports have respective light input/output directions, in parallel with each other, located on a first virtual plane. The optical input/output means inputs light into any of the ports and outputs the light from any of the ports. The first optical system collimates the light. The wavelength branching means spatially separates the light in terms of wavelength, and outputs thus obtained wavelength light components. The wavelength light components have respective optical axes located on a second virtual plane. The second optical system receives the wavelength light components and converges them. The reflecting means includes a mirror with a reflecting surface positioned at a light-converging point of the wavelength light components converged by the second optical system.

Abstract: An optical filter has a first long-period grating and a second long-period grating formed in a unitary optical fiber. A difference is not less than 100 nm between a wavelength at which optical coupling is maximum between core-mode light and cladding-mode light of a predetermined mode number in the first long-period grating and a wavelength at which optical coupling is maximum between core-mode light and cladding-mode light of the same mode number as the cladding-mode light of the predetermined mode number, in the second long-period grating. This optical filter can be constructed in compact size and can readily implement a desired transmission characteristic.

Abstract: In this diffraction grating device manufacturing method, refractive-index-change-inducing light of a wavelength that induces a change in refractive index is irradiated onto an optical waveguide, thus forming a diffraction grating through refractive index modulation along the longitudinal direction of the optical waveguide. At this time, the position of irradiation of the refractive-index-change-inducing light onto the optical waveguide is swung in a direction perpendicular to the longitudinal direction of the optical waveguide.

Abstract: In an optical waveguide grating in an optical fiber having a cladding region around a core region, a periodic refractive index distribution is existed in a predetermined area of the core region along the optical axis. The core region has a composition of GeO2—P2O5—SiO2 based glass, for example, whereas the cladding region is made of SiO2, and the co-doping ratio in the core region is adjusted, so as to lower the temperature dependence of characteristics. The doping amount of P2O5 in the core region is preferably {fraction (1/15)} to 1 times, more preferably 0.6 to 1 times that of GeO2.

Abstract: An optical fiber grating device 1 is a device in which a long period grating 14 is formed in a core region 11 of an optical fiber 10 consisting of the core region 11 having a refractive index n1 and an outside diameter 2a, a first cladding region 12 surrounding the core region 11 and having a refractive index n2 and an outside diameter 2b, and a second cladding region 13 surrounding the first cladding region 12 and having a refractive index n3 and an outside diameter 2c. There is a magnitude relation of n1>n2>n3 among the refractive index n1 of the core region 11, the refractive index n2 of the first cladding region 12, and the refractive index n3 of the second cladding region 13, a relative refractive index difference &Dgr;n2 of the first cladding region 12 to the second cladding region 13 is not less than 0.5%, and a thickness (c−b) of the second cladding region 13 with respect to a transmission loss peak wavelength &lgr; is in a range of not less than &lgr; nor more than 10&lgr;.

Abstract: The present invention relates to an optical amplifier (TDFA) having a configuration which enables to reduce temperature dependence of the gain with reduced power consumption and simple control. The optical amplifier includes, in the order from an input port to an output port, an optical isolator, an optical coupler, an optical amplification fiber, an optical coupler, an optical isolator, an optical gain equalizing filter, a variable optical attenuator, an optical isolator, an optical coupler, an amplification fiber, an optical coupler, and an optical isolator. At least a core region of the optical amplification fiber is doped with Tm element, and signal light in a predetermined wavelength range is amplified by supply of pumping light. The gain equalizing fiber has a loss spectrum which shifts toward the short wavelength side as the temperature of the optical waveguide is higher, thereby equalizing the optical amplification gain of the signal light in the optical amplification fiber.

Abstract: The present invention relates to a long-period grating device which eliminates only a desirable wavelength of core-mode light in a wavelength band in use from 1525 nm to 1610 nm. The long-period grating device according to the present invention comprises an optical fiber provided with a core region and a cladding region, whereas a long-period grating whose refractive index changes with a period &Lgr; in the advancing direction of light is provided in the core region, wherein the period &Lgr; is set such that the absolute value of a loss peak due to mode coupling concerning a refractive index modulation component with a period &Lgr;/(2n+1) (n=1, 2, 3, 4) is 0.2 dB or less in the wavelength band in use.

Abstract: The present invention relates to an optical multiplexer/demultiplexer. In the multiplexer/demultiplexer, a first grating receives to diffract a multi-wavelength light signal from a first port into light signals with different wavelengths. A second grating diffracts these light signals towards second ports. The second grating is disposed parallel with the first grating. The second grating has the same grating interval and grating direction as the first grating. The light signals diffracted by the second grating travel parallel with each other. Therefore, the light signals can efficiently enter the second ports without sophisticated lens design and adjustment of the optical system.