Abstract: A travelling wave-type optical modulator has a substrate made of an electro-optic material, optical waveguides fabricated on the top surface of the substrate, and electrodes for modulating an optical wave through the optical waveguide. The substrate is partially thinned from the bottom surface of the substrate to form a first thinned portion and a second thinned portion so that the thickness of the first thinned portion is set to be larger than the thickness of the second thinned portion, and the optical waveguide is positioned in the first thinned portion.

Abstract: A traveling wave optical modulator includes an optical waveguide substrate made of an electro-optic and ferrodielectric single crystal in the form of an X- or Y-orientation plate_and comprising a thicker portion having a larger thickness and a thinner portion having a smaller thickness; first and second branched optical waveguide portions formed at least on the thinner portion of the optical waveguide substrate; a set of electrodes provided on at least the thinner portion of the substrate and adapted for applying voltage to the first and second optical waveguide portions to modulate a light propagating the optical waveguide portions; and a buffer layer provided to cover a part of the optical waveguide portions at the thinner portion of the substrate, the electrodes crossing on the buffer layer.

Abstract: An optical waveguide device 1A has an optical waveguide substrate 15A and a supporting body 8 for supporting the substrate 15A. The substrate 15A has a main body 2 made of an electrooptic material and having a main face 2a and an opposing face 2b, optical waveguides 4A, 4B, and electrodes 3A, 3B, 3C for applying an electrical signal on the optical waveguides. At least a part of the opposing face 8a of the supporting body 8 opposing the substrate 15A is covered with a conductive layer 7A. It is thus possible to reduce the resonance due to substrate radiation of microwave into the whole of the optical waveguide substrate and supporting body.

Abstract: An optical waveguide device 1A has an optical waveguide substrate 10A and a supporting substrate 6 supporting the substrate 10A. The substrate 10A has a main body 4 made of an electrooptic material and having first main face 4a and a second main face 4b, an optical waveguide 3 formed in or on the main body 4 and an electrode 2A, 2B or 2C formed on the side of the first main face 4a of the main body 4. The supporting substrate 6 is joined with the second main face 4b of the main body 4. A low dielectric portion 11 with a dielectric constant lower than that of the electrooptic material is formed in the supporting substrate 6.

Abstract: A travelling wave-type optical modulator has a substrate made of an electro-optic material, optical waveguides fabricated on the top surface of the substrate, and electrodes for modulating an optical wave through the optical waveguide. The substrate is partially thinned from the bottom surface of the substrate to form a first thinned portion and a second thinned portion so that the thickness of the first thinned portion is set to be larger than the thickness of the second thinned portion, and the optical waveguide is positioned in the first thinned portion.

Abstract: A traveling wave optical modulator comprising a substrate made of a ferrodielectric electro-optic single crystal and having a pair of opposing main planes, an optical waveguide formed on a side of one of the main planes of the substrate, and a pair of electrode films which apply a voltage for modulating a light transmitting through the optical waveguide and between which the optical waveguide is located, wherein the thickness of each of the electrode films is not less than 20 &mgr;m and a width of a gap between a pair of the electrode films is not less than 25 &mgr;m.

Abstract: A travelling wave-type optical modulator has a supporting substrate and a ferroelectric single crystalline layer on the supporting substrate. The ferroelectric single crystalline layer has thicker parts and thinner parts within the modulating region of the travelling wave-type optical modulator as viewed in the cross section of the modulating region. Then, an optical waveguide is formed in the thicker part of the ferroelectric single crystalline layer, and electrodes for modulation are provided on the thinner part of the ferroelectric single crystalline layer in between the adjacent thicker parts.

Abstract: An optical waveguide element has a substrate made of a lithium tantalate single crystal or a lithium niobate-lithium tantalate solid solution single crystal and a bulky optical waveguide made of a lithium niobate single crystal directly joined the substrate. The c-axis of the single crystal to constitute the substrate is tilted from the surface of the substrate to be joined preferably by 17-37 degrees.

Abstract: A traveling wave optical modulator includes an optical waveguide substrate made of an electro-optic and ferrodielectric single crystal in the form of an X- or Y-orientation plate_and comprising a thicker portion having a larger thickness and a thinner portion having a smaller thickness; first and second branched optical waveguide portions formed at least on the thinner portion of the optical waveguide substrate; a set of electrodes provided on at least the thinner portion of the substrate and adapted for applying voltage to the first and second optical waveguide portions to modulate a light propagating the optical waveguide portions; and a buffer layer provided to cover a part of the optical waveguide portions at the thinner portion of the substrate, the electrodes crossing on the buffer layer.

Abstract: A traveling wave optical modulator including an optical waveguide substrate made of a ferrodielectric electro-optic single crystal and having a pair of opposed main planes, an optical waveguide formed on one of the main planes, at least one pair of electrodes provided on the other main plane of the optical waveguide to apply a voltage for modulating a light propagating the optical waveguide, a fixing substrate bonded to said one of the main planes of the optical waveguide via an adhesive layer, said adhesive layer covering the optical waveguide and made of an adhering agent having a refractive index lower than that of the electro-optic single waveguide.

Abstract: An optical waveguide device includes an LiNbO.sub.3 substrate and an optical waveguide disposed on the LiNbO.sub.3 substrate by diffusing Ti therein. The LiNbO.sub.3 substrate has a step on a surface thereof which corresponds to the area in which Ti is diffused. The step has opposite side edges and a central area therebetween, the side edges having a height greater than a height of the central area, whereby the side edges are raised higher than the central area. The optical waveguide device has a relatively small coupling loss with respect to an optical fiber having a small light beam mode shape, thus eliminating optical device loss faults.

Abstract: In a method of forming an assembly of an optical waveguide substrate and an optical fiber aligning substrate by adjoining an end face of a main body of the optical waveguide substrate and an end face of a main body of the optical fiber aligning substrate, a starting block formed by a flat rectangular plate is divided along a dividing surface which intersects perpendicularly to a side wall as well as a bottom wall of the starting block which are selected as a reference surface to obtain the main bodies of the optical waveguide substrate and optical fiber aligning substrate, optical waveguides are formed on the main body of the optical waveguide substrate by using the side wall and bottom wall as a positional reference, V-shaped guide grooves are formed in the main body of the optical fiber aligning substrate by using the side wall and bottom wall as a positional reference, and optical fibers are inserted into the guide grooves.