Abstract: A gain flattening filter includes a first optical fiber that has a core, a first cladding, and a second cladding and that has a uniform composition in a length direction; and a pair of second optical fibers fused to both ends of the first optical fiber. The first optical fiber has a first section in which a slanted refractive index grating is formed and a pair of second sections connecting both ends of the first section to the pair of second optical fibers. The first cladding contains a photosensitive material whose refractive index increases upon irradiation with light having a specific wavelength. In the core, a tensile stress remains in the first section. An average MFD of the second sections is larger than an average MFD of the second optical fibers and smaller than an average MFD of the first section.

Abstract: One embodiment of the present disclosure relates to an SFG (slanted fiber grating) that can easily realize a high-performance gain equalizer. The SFG includes an optical fiber comprised of silica-based glass and including a core, a first cladding containing a photosensitive material, and a second cladding. A specific section between two different points arranged along a fiber axis in the optical fiber is configured with a first region, a pair of second regions, and a third region. The first region includes a slanted Bragg grating provided in a region as the first cladding. The pair of second regions are arranged to sandwich the first region. The third region is disposed to sandwich both the first region and the pair of second regions. An MFD at a wavelength of 1.55 ?m in the third region is smaller than an MFD at a wavelength of 1.55 ?m in the first region.

Abstract: An optical fiber includes a silica-based glass. The optical fiber includes a core, an optical cladding surrounding the core, and a physical cladding surrounding the optical cladding. The optical cladding includes a first region in contact with the core and surrounding the core. A photosensitive material is added to the core and the first region. A concentration of the photosensitive material in the first region is 30% or more of a concentration of the photosensitive material in the core. A value obtained by integrating a light intensity of an LP01 mode at a wavelength of 1310 nm in a region added with the photosensitive material is 87% or more of a value obtained by integrating the light intensity in an entire region of the optical fiber.

Abstract: The present embodiment relates to an optical amplifier and the like having a structure for enabling efficient use of pumping light while avoiding complication of a device structure. In such an optical amplifier, since pumping light from a pumping light source is supplied to each core of an amplification MCF, a coupling MCF in which adjacent cores form a coupled core is arranged between the amplification MCF and the pumping light source. The pumping light source is optically connected to a specific core of the coupling MCF, and pumping light is coupled from the specific core to remaining cores except the specific core in the coupling MCF before pumping light is supplied to each core of the amplification MCF. This enables coupling of pumping light between optically connected cores between the amplification MCF and the coupling MCF.

Abstract: An object is to provide, for example, an optical wavelength conversion device capable of highly efficient wavelength conversion on the surface of, or inside, the main body of any of various shapes, such as a bulky shape and a fiber shape. The optical wavelength conversion device includes a main body configured to allow light to propagate therein, and a plurality of crystal regions arranged inside the main body along a propagation direction of the light. The plurality of crystal regions each have a spontaneous polarization oriented along the propagation direction (i.e., spontaneous polarization having a polarization orientation coinciding with the propagation direction).

Abstract: One embodiment of the present disclosure relates to an SFG (slanted fiber grating) that can easily realize a high-performance gain equalizer. The SFG includes an optical fiber comprised of silica-based glass and including a core, a first cladding containing a photosensitive material, and a second cladding. A specific section between two different points arranged along a fiber axis in the optical fiber is configured with a first region, a pair of second regions, and a third region. The first region includes a slanted Bragg grating provided in a region as the first cladding. The pair of second regions are arranged to sandwich the first region. The third region is disposed to sandwich both the first region and the pair of second regions. An MFD at a wavelength of 1.55 ?m in the third region is smaller than an MFD at a wavelength of 1.55 ?m in the first region.

Abstract: An optical fiber according to an embodiment includes a core having a single-peaked and graded refractive index profile, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding. The inner and outer claddings have refractive indices lower than the maximum refractive index of the core. A photosensitive region constituted by the core and the inner cladding contains a photosensitive material. The inner cladding has an outer diameter one time or more and two times or less the MFD of an LP01 mode in a 1310-nm wavelength band.

Abstract: A method for manufacturing an optical device includes a hydrogen-loading step, a laser irradiation step, and a light condensing point movement step. A continuous refractive index changed region is formed in a glass member by alternately repeating the laser irradiation step and the light condensing point movement step or performing the laser irradiation step and the light condensing point movement step in parallel. In the hydrogen-loading step, hydrogen is loaded into the glass member containing P2O5 as a main component. In the laser irradiation step, a femtosecond laser beam having a repetition frequency of 10 kHz or higher is condensed in the hydrogen-loaded glass member, and a light-induced change in refractive index is caused in the glass member. In the light condensing point movement step, a light condensing point position of the femtosecond laser beam is moved relative to the glass member.

Abstract: A method for manufacturing an optical device includes a hydrogen-loading step, a laser irradiation step, and a light condensing point movement step. The laser irradiation step and the light condensing point movement step are alternately repeated, or are performed in parallel. In the hydrogen-loading step, hydrogen is loaded into a glass member containing B2O3 and has a content of GeO2 less than 10% by mass fraction based on an oxide. In the laser irradiation step, a femtosecond laser beam having a repetition frequency of 10 kHz or higher is condensed and emitted into the glass member into which the hydrogen is loaded, and a light-induced change in refractive index is caused in the glass member. In the light condensing point movement step, a light condensing point position of the femtosecond laser beam is moved relative to the glass member.

Abstract: A method for manufacturing an optical device includes: a laser irradiation step of condensing pulsed first laser light and pulsed second laser light to the inside of a glass member including germanium and titanium; and a condensing position movement step of moving condensing positions relatively to the glass member. Each of the first laser light and the second laser light has a repetition frequency of 10 kHz or greater. The first laser light is condensed to a dot-shaped condensing region, and the second laser light is condensed to an annular condensing region surrounding the condensing region of the first laser light. A central wavelength of the first laser light is greater than 400 nm and equal to or less than 700 nm, and a central wavelength of the second laser light is equal to or greater than 800 nm and equal to or less than 1100 nm.

Abstract: An optical fiber is made of silica-based glass and includes a core, a first cladding that surrounds the core and that has a refractive index lower than a refractive index of the core; and a second cladding that surrounds the first cladding and that has a refractive index lower than the refractive index of the core and higher than the refractive index of the first cladding. At least a part of the first cladding contains a photosensitive material whose refractive index increases by irradiation with light having a specific wavelength. A difference ?n between a refractive index of a portion of the first cladding, the portion being nearest to the core, and the refractive index of the core is in a range of 0.25% to 0.30%. The radius ra of the core is larger than 4.3 ?m and smaller than or equal to 5.0 ?m.

Abstract: A wavelength conversion optical device includes: a substrate having a virtual plane and first and second regions and including multiple first crystal regions and multiple second crystal regions. Each of the multiple first crystal regions includes a pair of portions arranged in a direction intersecting a first plane with the first plane interposed therebetween, the first plane being located in the first region, and directions of spontaneous polarizations of each of the pair of portions being directions away from the first plane. Each of the multiple second crystal regions includes a pair of portions arranged in a direction intersecting a second plane with the second plane interposed therebetween, the second plane being located in the second region. Directions of spontaneous polarizations of each of the pair of portions being directions away from the second plane.

Abstract: An optical fiber according to an embodiment includes a core having a single-peaked and graded refractive index profile, an inner cladding surrounding the core, and an outer cladding surrounding the inner cladding. The inner and outer claddings have refractive indices lower than the maximum refractive index of the core. A photosensitive region constituted by the core and the inner cladding contains a photosensitive material. The inner cladding has an outer diameter one time or more and two times or less the MFD of an LP01 mode in a 1310-nm wavelength band.

Abstract: An embodiment of the invention relates to an optical device which is capable of realizing a secondary nonlinear optical phenomenon. The optical device is a fiber-type optical device which is comprised of glass containing SiO2, and includes a core region, a first cladding region, and a second cladding region. At least a part of a glass region configured by the core region and the first cladding region has such a repetition structure that a first section serving as a poled crystal region and a second section serving as an amorphous region are alternately disposed along a longitudinal direction of the optical device.

Abstract: An optical wavelength converter of one embodiment comprises: a substrate comprised of a crystalline material or an amorphous material; plural first crystal regions each having a radial first polarization-ordered structure; and plural second crystal regions each having a radial second polarization-ordered structure. In the substrate, a first and second regions are defined to be directly adjacent to each other with a virtual axis therebetween when the substrate is viewed from a reference direction orthogonal to the virtual axis. Radial centers of the first polarization-ordered structures located in the first region and radial centers of the second polarization-ordered structures located in the second region are alternately arranged along the virtual axis. The plural first crystal regions partially protrude to the second region. The plural second crystal regions partially protrude to the first region.

Abstract: A method for manufacturing an optical device according to an embodiment comprises: loading hydrogen into a glass member containing Ge; irradiating a laser beam from a femtosecond laser into the glass member having the hydrogen loaded therein, the laser beam having an amount of energy causing a light-induced change in refractive index of the glass member and having a repetition frequency of 10 kHz or higher; and moving a light convergence point position of the laser beam relative to the glass member. A repetition of the irradiating and the moving forms a continuous refractive index changed region in the glass member.

Abstract: An object is to provide, for example, a method for manufacturing an optical wavelength conversion device having a structure that enables efficient formation of crystal regions on the surface of, or inside, an amorphous material. An amorphous main body is intermittently irradiated with a first laser beam for generating a high-density excited electron region inside the main body and a second laser beam for heating the high-density excited electron region, with respective focus regions of the first and second laser beams overlapping each other. During the intermittent irradiation with the first and second laser beams, the relative position of the main body and the overlapping focus region of the first and second laser beams are varied. This enables part of the main body where the overlapping focus region moves to serve as a heat source for forming a crystal region.

Abstract: An embodiment of the invention relates to an optical device which is capable of realizing a secondary nonlinear optical phenomenon. The optical device is a fiber-type optical device which is comprised of glass containing SiO2, and includes a core region, a first cladding region, and a second cladding region. At least a part of a glass region configured by the core region and the first cladding region has such a repetition structure that a first section serving as a poled crystal region and a second section serving as an amorphous region are alternately disposed along a longitudinal direction of the optical device.

Abstract: An object is to provide, for example, a method for manufacturing an optical wavelength conversion device having a structure that enables efficient formation of crystal regions on the surface of, or inside, an amorphous material. An amorphous main body is intermittently irradiated with a first laser beam for generating a high-density excited electron region inside the main body and a second laser beam for heating the high-density excited electron region, with respective focus regions of the first and second laser beams overlapping each other. During the intermittent irradiation with the first and second laser beams, the relative position of the main body and the overlapping focus region of the first and second laser beams are varied. This enables part of the main body where the overlapping focus region moves to serve as a heat source for forming a crystal region.

Abstract: An object is to provide, for example, a method for manufacturing an optical wavelength conversion device having a structure that enables efficient formation of crystal regions on the surface of, or inside, an amorphous material. An amorphous main body is intermittently irradiated with a first laser beam for generating a high-density excited electron region inside the main body and a second laser beam for heating the high-density excited electron region, with respective focus regions of the first and second laser beams overlapping each other. During the intermittent irradiation with the first and second laser beams, the relative position of the main body and the overlapping focus region of the first and second laser beams are varied. This enables part of the main body where the overlapping focus region moves to serve as a heat source for forming a crystal region.