Abstract: A manufacturing method for quasi phase matching (QPM) wavelength converter elements using crystal quartz as a base material in which twins are periodically induced, comprises a step of periodically inducing the twins by applying a stress onto a crystal quartz substrate as the base material so that an angle ? of a direction in which the stress is applied relative to a Z axis of the crystal quartz is 60°<?<90°.

Abstract: Rectangular protruding parts 2 are formed on the surface of one side of a quartz crystal substrate 1; these protruding parts 2 are formed as aggregates of rectangular protruding parts 4 of an even finer pattern. Recessed parts 5 which are lower than the surfaces of the protruding parts 4 are formed between the protruding parts 4; however, the width of these recessed parts 5 is narrow, so that when the protruding parts 4 are viewed on the macroscopic scale, numerous protruding parts 4 are aggregated, and appear to form single protruding parts 2. Such a quartz crystal substrate 1 is clamped between heater blocks from above and below, and the temperature of the quartz crystal substrate is elevated. At the point in time at which this temperature reaches a desired temperature, the substrate 1 is pressed by means of a press. Consequently, stress acts only on the portions corresponding to the protruding parts 4, so that the crystal axis components are inverted only in these portions.

Abstract: The present invention provides a highly-integrated and compact optical element and further provides an optical element having various functions such as lower driving voltage, chirping suppression and polarization-independency. The optical element has a substrate 1 formed of a material having an electrooptic effect, a plurality of optical waveguides formed on the substrate, and a modulating electrode for applying electric field into the optical waveguides, and is characterized in that the modulating electrode has at least two branching and confluence lines on the same line for applying the same modulating signal into different optical waveguides.

Abstract: A wavelength conversion element having multi-gratings free from damage propagation and a light generating apparatus using it, and a wavelength conversion element having multi-gratings to make a thermal distribution centrosymmetric, and being free from damage propagation, are provided. The wavelength conversion element is realized by comprising a holder and plural prismatic ferroelectric single crystals disposed in the holder, wherein plural prismatic ferroelectric single crystals have at least five planes; the aspect ratios of planes perpendicular to respective longitudinal directions of the plural prismatic ferroelectric single crystals are virtually unity; and each of the plural prismatic ferroelectric single crystals has a domain inversion structure with a predetermined period in the direction perpendicular to the polarization direction thereof, and is arranged in a way that said direction perpendicular to the polarization direction is the same as those of the other crystals.

Abstract: A wavelength converter that is used in an optical communication system utilizing wavelength multiplexing. The wavelength converter has a quasi-phase matched quartz crystal that has a second-order nonlinear effect, and a light coupling device that mixes the signal light and control light and inputs this mixed light into the quasi-phase matched quartz crystal. The wavelength converter also has quartz type optical fibers between the light coupling device and the quasi-phase matched quartz crystal. The mode diameter of the quartz type optical fibers is substantially the same as the mode diameter of the optical waveguide.

Abstract: A problem to be solved is to provide a method of forming domain inverted regions of short period in a ferroelectric single crystal in a controllable time period of application of voltage and an optical wavelength conversion element using the same. A solving means of it solves the problem by forming (i) a control layer having a larger defect density Dcont1 than the defect density Dferro of a ferroelectric single crystal (Dferro<Dcont1) or forming (ii) a control layer having a lower degree of order of lattice points than the degree of order of lattice points of the ferroelectric single crystal on a face perpendicular to the direction of polarization of the ferroelectric single crystal in the ferroelectric single crystal.

Abstract: Two grooves 10 are diced in parallel along the light passage direction in a quartz quasi-phase matching element 1. Consequently, as is shown in (b) and (c), a protruding part 11 which is positioned between the two grooves 10 is formed on the upper surface side (in the figures), and a ridge type waveguide 9 is formed inside this protruding part. Accordingly, if light is caused to pass through this ridge type waveguide 9, the light can be caused to pass through the portions with inverted crystal axes (polarization inversion regions) 4, and can be subjected to a wavelength conversion, in a state in which the light is confined into the ridge type wavelength guide 9. As a result, a state can be produced in which the energy of the light is high inside the wavelength conversion region, so that a high wavelength conversion efficiency can be obtained.

Abstract: The present invention provides a highly-integrated and compact optical element and further provides an optical element having various functions such as lower driving voltage, chirping suppression and polarization-independency. The optical element comprising a substrate 1 consisting of a material having an electrooptic effect, top optical waveguides 2-1 an 2-2 formed on the top face of said substrate, bottom optical waveguides formed on the bottom face of said substrate, a top modulating electrode for controlling the phase of a light wave being propagated through said top optical waveguide, and a bottom modulating electrode for controlling the phase of a light wave being propagated through said bottom optical waveguide, is characterized in that at least one side edge of said substrate comprises output and input of said optical waveguides formed on said top and bottom faces, and a turnback element is located adjacent to said one side edge to guide the light wave from said output to said input.

Abstract: An object of the present invention is to provide an optical device having high quality, excellent productivity and optical characteristics, and capable of suppressing a refractive index of a substrate surface from increasing when a dopant is thermally diffused into, or a heat treatment is performed in order to compensate of process distortion in stoichiometric lithium niobate crystal or a crystal substrate in which Mg is doped into the crystal, and a method of manufacturing the same. According to the present invention, there is provided a method of manufacturing an optical device including the steps of: forming a dopant layer on a substantial stoichiometric lithium niobate single crystal substrate; and diffusing a dopant in the dopant layer into at least a portion of the substantial stoichiometric lithium niobate single crystal substrate, wherein, in the diffusing step, a heat treatment is performed at a diffusion temperature of 1000° C. to 1200° C.

Abstract: The present invention provides a highly-integrated and compact optical element and further provides an optical element having various functions such as lower driving voltage, chirping suppression and polarization-independency. The optical element has a substrate 1 formed of a material having an electrooptic effect, a plurality of optical waveguides formed on the substrate, and a modulating electrode for applying electric field into the optical waveguides, and is characterized in that the modulating electrode has at least two branching and confluence lines on the same line for applying the same modulating signal into different optical waveguides.

Abstract: When forming a periodically-poled structure on a nonlinear optical crystal 1 that permits wavelength conversion and/or optical computing, the group velocity matching conditions are determined to synchronize the group velocity of the incident light L1 with that of the outgoing light L2, and the polarization reversal period of the periodically-poled structure is determined to satisfy quasi-phase matching conditions for the aforementioned wavelength conversion and/or optical computing. As a result, the problems associated with wavelength conversion of the pulsed light due to a difference in the group velocity are suppressed.

Abstract: The present invention provides a method for forming a ferroelectric spontaneous polarization reversal capable of forming a ferroelectric spontaneous polarization reversal condition homogeneously within the ferroelectric spontaneous polarization reversal region even across a large region of 50 ?m and over in width of a ferroelectric spontaneous polarization reversal. Also, it provides a method for forming a ferroelectric spontaneous polarization reversal where a ferroelectric substrate has convexo-concave structure, such as ridge structure and the like, on its surface and the polarity of the region including one portion of said convex part is reversed with accuracy.

Abstract: The present invention provides a highly-integrated and compact optical element and further provides an optical element having various functions such as lower driving voltage, chirping suppression and polarization-independency. The optical element comprising a substrate 1 consisting of a material having an electrooptic effect, top optical waveguides 2-1 an 2-2 formed on the top face of said substrate, bottom optical waveguides formed on the bottom face of said substrate, a top modulating electrode for controlling the phase of a light wave being propagated through said top optical waveguide, and a bottom modulating electrode for controlling the phase of a light wave being propagated through said bottom optical waveguide, is characterized in that at least one side edge of said substrate comprises output and input of said optical waveguides formed on said top and bottom faces, and a turnback element is located adjacent to said one side edge to guide the light wave from said output to said input.

Abstract: The upper block 12 contacts the bearing block 20, and the bearing block 20 is coupled to the upper plate 21. The upper block 12 has a protruding part 22 on the upper surface that is worked into a convex surface with a radius of R1, and the bearing block 20 has a recessed part 23 in the undersurface that is worked into a concave surface with a radius of R2 (R2>R1). As a result of such a construction being used, the pressing surface of the upper pressing plate 15 always conforms to the surface of the quartz crystal substrate 11 during pressing, so that a uniform load is applied to the quartz crystal substrate 11. As a result, the surface of the quartz crystal can be uniformly pressed in the hot pressing method.

Abstract: Rectangular protruding parts 2 are formed on the surface of one side of a quartz crystal substrate 1; these protruding parts 2 are formed as aggregates of rectangular protruding parts 4 of an even finer pattern. Recessed parts 5 which are lower than the surfaces of the protruding parts 4 are formed between the protruding parts 4; however, the width of these recessed parts 5 is narrow, so that when the protruding parts 4 are viewed on the macroscopic scale, numerous protruding parts 4 are aggregated, and appear to form single protruding parts 2. Such a quartz crystal substrate 1 is clamped between heater blocks from above and below, and the temperature of the quartz crystal substrate is elevated. At the point in time at which this temperature reaches a desired temperature, the substrate 1 is pressed by means of a press. Consequently, stress acts only on the portions corresponding to the protruding parts 4, so that the crystal axis components are inverted only in these portions.

Abstract: The signal light is coupled with control light that is emitted from a laser diode 3 by a WDM coupling device 2. The optical fiber 4 on one end of the WDM coupling device is mode-matched with the optical waveguide of the quasi-phase matched quartz crystal 1 by a V groove 1a. The output light generated by the difference frequency generation of the signal light and control light is again guided to the optical fiber 5 from the quasi-phase matched quartz crystal 1 by the other V groove 1a. Then, this light is incident on the optical filter 7, so that the signal light and control light are cut. The optical fiber 9 is connected to a fiber amplifier 10. In cases where a quasi-phase matched quartz crystal is used as the wavelength conversion element, the wavelength conversion efficiency drops compared to lithium niobate as a result of the nonlinear constants being small. The fiber amplifier 10 is installed in order to compensate for this.

Abstract: Two grooves 10 are diced in parallel along the light passage direction in a quartz quasi-phase matching element 1. Consequently, as is shown in (b) and (c), a protruding part 11 which is positioned between the two grooves 10 is formed on the upper surface side (in the figures), and a ridge type waveguide 9 is formed inside this protruding part. Accordingly, if light is caused to pass through this ridge type waveguide 9, the light can be caused to pass through the portions with inverted crystal axes (polarization inversion regions) 4, and can be subjected to a wavelength conversion, in a state in which the light is confined into the ridge type wavelength guide 9. As a result, a state can be produced in which the energy of the light is high inside the wavelength conversion region, so that a high wavelength conversion efficiency can be obtained.

Abstract: When forming a periodically-poled structure on a nonlinear optical crystal 1 that permits wavelength conversion and/or optical computing, the group velocity matching conditions are determined to synchronize the group velocity of the incident light L1 with that of the outgoing light L2, and the polarization reversal period of the periodically-poled structure is determined to satisfy quasi-phase matching conditions for the aforementioned wavelength conversion and/or optical computing. As a result, the problems associated with wavelength conversion of the pulsed light due to difference in the group velocity are suppressed pulsed light and a preferable element for wavelength conversion and optical computing can be provided.

Abstract: A method for treating a photorefractive effect of an optical device, which comprises irradiating an optical device comprising a lithium niobate single crystal or a lithium tantalate single crystal with an ultraviolet light having a wavelength of at least 300 nm and at most 400 nm so as to suppress and control a photo-induced refractive index change (photorefractive effect) caused on the device.

Abstract: A manufacturing method for quasi phase matching (QPM) wavelength converter elements using crystal quartz as a base material in which twins are periodically induced, comprises a step of periodically inducing the twins by applying a stress onto a crystal quartz substrate as the base material so that an angle e of a direction in which the stress is applied relative to a Z axis of the crystal quartz is 60°<&thgr;<90°.