Abstract: A width of a core in an optical waveguide is decreased in accordance with a value of a predetermined equation, as a distance of a position of the core to the center position thereof is decreased. Consequently, a rectangular spectrum property having no ripple is obtained on a lower wavelength side in a reflection grating. In addition, the width of the core is changed at the position Z in the direction of light propagation, while a UV light is radiated to the core, so that a periodically striated distribution of refractive indices having an envelope which is changed in accordance with a value of ".vertline.sin(C.multidot.Z).vertline./.vertline.C.multidot.Z.vertline." is formed in the core of the optical waveguide, and a phase of a light to be propagated in the direction of the light propagation is shifted at the position Z as defined below by .pi..Z=m.pi./C(m=. . . ,-3,-2,-1,1,2,3, . . )Thus, a rectangular spectrum property is obtained in a low reflection grating.

Abstract: A width of a core in an optical waveguide is decreased in accordance with a value of a predetermined equation, as a distance of a position of the core to the center position thereof is decreased. Consequently, a rectangular spectrum property having no ripple is obtained on a lower wavelength side in a reflection grating. In addition, the width of the core is changed at the position Z in the direction of light propagation, while a UV light is radiated to the core, so that a periodically striated distribution of refractive indices having an envelope which is changed in accordance with a value of ".vertline.sin (C.multidot.Z).vertline./.vertline.C.multidot.Z.vertline." is formed in the core of the optical waveguide, and a phase of a light to be propagated in the direction of the light propagation is shifted at the position Z as defined below by .pi.. Z=m.pi./C(m= - - - , -3,-2,-1,1,2,3, - - - ) Thus, a rectangular spectrum property is obtained in a low reflection grating.

Abstract: An optical device having a switching function has a waveguide filter for switching whether input signal light of including at least one specific wavelength should be transmitted or reflected. The input signal lights of wavelength of .lambda..sub.1 .about..lambda.n are transmitted to the input waveguide. When the waveguide filter is off, the signal lights of all wavelength are transmitted to the output port. When the waveguide filter is on, the signal light of wavelength of .lambda..sub.2 .about..lambda.n are transmitted, but the signal light of wavelength of .lambda..sub.2 is reversed and output to the drop port. If the thin film heaters are off, a signal light of wavelength of .lambda..sub.1 is output (dropped) from the drop port. If the thin film heaters are on, it is reversed and transmitted to the output port.

Abstract: A guided-wave optical multi/demultiplexer is capable of providing a wide wavelength band freely. Each of two directional couplers is constructed so that the coupling ratio of light intensity in the wavelength .lambda..sub.2 is at least 50% and the coupling ratio of light intensity in the wavelength .lambda..sub.3 having a wavelength band in close proximity to the wavelength .lambda..sub.1 is 0% or 100%, the light in the wave band containing the wavelength .lambda..sub.1 and the wavelength .lambda..sub.3 and the light in the wave band containing the wavelength .lambda..sub.2 being multiplexed and demultiplexed.

Abstract: A waveguide type light merging and branching device, in which a resistance layer is disposed on a surface of a substrate or at least on one side therein and a low refractive index layer (refractive index n.sub.b), a core waveguide layer (refractive index n.sub.c, n.sub.c >n.sub.b), and a cladding layer (refractive index n.sub.n, n.sub.n >n.sub.c) superposed thereon on each other, the resistance layer having electrode terminals at the two extremities thereof, to which a voltage is applied.

Abstract: A directional coupler for coupling two single-polarization optical fibers each comprising a core, a cladding, and an elliptic jacket having a major axis is made by preparing two quartz substrates each of which is formed with a channel on one major surface; embedding and bonding the jacketed single-polarization optical fibers in the channels in the substrates, respectively, such that the major axis of the elliptic jacket extends perpendicular to the substrate surface; abrading away the substrates together with the fiber embedded therein from the major surface to a depth where light traveling in the core of said fiber may leak out; placing one substrate on the other substrate with the abraded surfaces facing each other; and bonding the substrates to keep the cores in sufficiently close relation to establish evanescent wave coupling therebetween. A stress perpendicular to the major axis is preferably applied to the fiber.