Abstract: The present invention makes it possible to prevent an optical loss in association with mode field diameter conversion and to prevent deformation in a mode field converter. The present invention includes: (a) temporarily fixing an end surface of an optical fiber (1) to an end surface of a core part (8) via a highly-viscous resin (3); and (b) after the step (a), while butting the end surface of the optical fiber (1) against the end surface of the core part (8) through the highly-viscous resin (3), fixing the optical fiber (1) to a semiconductor optical device (100) at a place away from the end surface of the optical fiber (1).

Abstract: An optical waveguide element includes a core and a cladding that is made of SiO2. When ng_i_TE is a group refractive index of a TE0 polarized wave in the i-th waveguide counted from a light incidence plane of the core and ng_i_TM is a group refractive index of a TM0 polarized wave in the i-th waveguide, the length L—i[m] of the i-th waveguide satisfies a predetermined relation.

Abstract: An optical modulation device configured of a planar optical waveguide, includes: a light incidence unit which allows light to be incident on the planar optical waveguide; a Mach-Zehnder interferometer which includes a first optical splitter section branching the light incident on the light incidence unit, two arm portions guiding the light branched by the first optical splitter section, a phase modulation unit linearly disposed on each of the two arm portions, and a first optical coupler section combining the light guided from the two arm portions; a light launching unit which launches the light combined by the first optical coupler section from the planar optical waveguide; and a traveling-wave electrode which includes an input unit and an output unit, and applies a voltage to the phase modulation unit.

Abstract: An optical waveguide element includes a core and a cladding that is made of SiO2. When ng_i_TE is a group refractive index of a TE0 polarized wave in the i-th waveguide counted from a light incidence plane of the core and ng_i_TM is a group refractive index of a TM0 polarized wave in the i-th waveguide, the length L_i[m] of the i-th waveguide satisfies a predetermined relation.

Abstract: The present invention makes it possible to prevent an optical loss in association with mode field diameter conversion and to prevent deformation in a mode field converter. The present invention includes: (a) temporarily fixing an end surface of an optical fiber (1) to an end surface of a core part (8) via a highly-viscous resin (3); and (b) after the step (a), while butting the end surface of the optical fiber (1) against the end surface of the core part (8) through the highly-viscous resin (3), fixing the optical fiber (1) to a semiconductor optical device (100) at a place away from the end surface of the optical fiber (1).

Abstract: A method includes: an optical component installation process P1 in which an optical component 23 is formed on one face of a component installation substrate 10 using a thin film process, the optical component 23 having an end portion 25 to be optically coupled to an optical fiber 40; an optical fiber fixing process P2 in which a V-shaped groove 35 is formed on one face of an optical fiber fixing substrate 30 and the optical fiber 40 is fixed to the V-shaped groove 35; and a contacting process P3 in which the surface of the component installation substrate 10 on which the optical component 23 is provided is contacted with the surface of the optical fiber fixing substrate 30 to which the optical fiber 40 is fixed.

Abstract: A high-frequency circuit 10 includes: a termination resistor 12a embedded to a surface of a substrate 21; and a signal line 11a formed on the surface of the substrate 21, the signal line having a junction segment CJ, the junction segment CJ covering a portion of an upper surface of the termination resistor 12a so that at least a portion along a width of the junction segment CJ that extends from the start position to the end position is connected to the termination resistor 12a. A width WS of the signal line 11a at the start position of the junction segment CJ is equal to or greater than a width WT of the upper surface of the termination resistor 12a at the start position.

Abstract: A high-frequency circuit 10 includes: a termination resistor 12a embedded to a surface of a substrate 21; and a signal line 11a formed on the surface of the substrate 21, the signal line having a junction segment CJ, the junction segment CJ covering a portion of an upper surface of the termination resistor 12a so that at least a portion along a width of the junction segment CJ that extends from the start position to the end position is connected to the termination resistor 12a. A width WS of the signal line 11a at the start position of the junction segment CJ is equal to or greater than a width WT of the upper surface of the termination resistor 12a at the start position.

Abstract: An optical modulation device configured of a planar optical waveguide, includes: a light incidence unit which allows light to be incident on the planar optical waveguide; a Mach-Zehnder interferometer which includes a first optical splitter section branching the light incident on the light incidence unit, two arm portions guiding the light branched by the first optical splitter section, a phase modulation unit linearly disposed on each of the two arm portions, and a first optical coupler section combining the light guided from the two arm portions; a light launching unit which launches the light combined by the first optical coupler section from the planar optical waveguide; and a traveling-wave electrode which includes an input unit and an output unit, and applies a voltage to the phase modulation unit.

Abstract: An optical fiber coupler is comprised of a fusion-elongated portion 15 in which an optical fiber 11 which is designed and fabricated for use at a wavelength in the vicinity of 1.55 ?m and an optical fiber 12 which is designed and fabricated for use at a wavelength in the vicinity of 0.98 ?m are fused and elongated. The propagation constant difference between optical fibers 11 and 12 is 10?4 rad/?m or smaller.

Abstract: A polarization-maintaining optical fiber component which suppresses coupling of propagating light to a high-order mode at the optical coupling section of the polarization-maintaining optical fiber component, caused by different refractive indexes between the stress applying sections and the cladding, thus reducing excess loss, is constructed by using a polarization-maintaining optical fiber having stress applying sections arranged symmetrically to each other with respect to a core in a cladding surrounding the core, wherein the largest one of those concentric circles of the core or the said cladding which do not reach the stress applying sections and do not include the stress applying sections within has a diameter of 20 ?m or greater.

Abstract: An optical fiber coupler is comprised of a fusion-elongated portion 15 in which an optical fiber 11 which is designed and fabricated for use at a wavelength in the vicinity of 1.55 &mgr;m and an optical fiber 12 which is designed and fabricated for use at a wavelength in the vicinity of 0.98 &mgr;m are fused and elongated. The propagation constant difference between optical fibers 11 and 12 is 10−4 rad/&mgr;m or smaller.

Abstract: In a method of manufacturing a polarization-maintaining optical fiber coupler by heating lengthwise portions of two polarization-maintaining optical fibers extending side by side, and elongating the heated portions to thereby form a fused-elongated section, elongation is terminated when the cyclic changes in a coupling ratio of two polarized waves according to an elongation length at a wavelength in use are both within first two cycles, so that the coupling ratio of one of the polarized waves is equal to or less than 10% and the coupling ratio of the other one of the polarized waves is equal to or greater than 90%. This method can provide a polarization-maintaining optical fiber coupler whose coupling ratio has a large dependency on polarization with a short elongation length.