Abstract: In an optical module such as an optical branching and multiplexing device used in an optical communication system, optical waveguides are formed on a surface of an optical waveguide substrate and optical fibers are held by arranging guide grooves on an optical fiber arranging substrate. The optical waveguide substrate has positioning guide grooves which can engage with the arranging guide grooves. The pitch of the optical waveguides on end faces of the optical waveguide substrate coincide with the pitch of the arranging guide grooves, so that the optical fibers and the optical waveguides are coupled accurately without any adjustment.

Abstract: In an optical module such as an optical branching and multiplexing device used in an optical communication system, optical waveguides are formed on a surface of an optical waveguide substrate and optical fibers are held by arranging guide grooves on an optical fiber arranging substrate. The optical waveguide substrate has positioning guide grooves which can engage with the arranging guide grooves. The pitch of the optical waveguides on end faces of the optical waveguide substrate coincide with the pitch of the arranging guide grooves, so that the optical fibers and the optical waveguides are coupled accurately without any adjustment.

Abstract: In the forward direction, the light from an input fiber is polarized and separated in a polarized light separating and combining element, the separated polarized light is rotated by a polarized light rotating element, dispersed according to wavelength by a wavelength dispersing element, rotated again by the polarized light rotating element, and is further rotated by a phase plate, thereby combining the polarized lights in the polarized light separating and combining element, so that only the light of a desired wavelength is coupled with the optical fiber. In the reverse direction, the light from the output fiber is not coupled with the input fiber, and hence the light propagation direction is defined in one direction in the disclosed optical circuit. A light transmission system and method using this optical circuit is also presented.

Abstract: On one end side of a converging rod lens are provided a first and second input optical fibers and a first and second output optical fibers. On the other end side of the converging rod lens is provided a reflecting mirror. Between the converging lens and the first and second input and output optical fibers is provided a birefringent element for resolving a ray which passes therethrough into an ordinary ray and an extraordinary ray. In the optical paths of the first and second output optical fibers between the converging rod lens and birefringent element is placed a compensator for rotating 45 degrees the plane of polarization of a ray which passes therethrough. The reflecting mirror reflects incident rays from the first and second input optical fibers to the first and second output optical fibers. Between the converging rod lens and the reflecting mirror is provided a magneto-optical element for rotating 22.5 degrees the plane of polarization of a ray which passes therethrough.

Abstract: According to the present invention, a diffraction element comprising a transparent substrate having a first face and a second face; periodic grooves engraved on the first face; a reflective film provided on the first face having the periodic grooves; and a antireflection film provided on the second face, wherein the periodic grooves and the reflective film constitute a diffraction grating.

Abstract: A diffraction grating unit includes a reflection type diffraction grating; a transparent medium; and a filter which is formed on the diffraction grating through the transparent medium so as to be disposed on an incident surface of the diffraction grating unit; wherein the filter transmits therethrough a ray having a specific wavelength but reflects a further ray having a wavelength equal to a half of the specific wavelength of the ray, and a second-harmonic generator employing the diffraction grating unit.

Abstract: An input light beam is applied to a diffraction element. The diffraction element is moved relative to a path of the input light beam while the input light beam is diffracted by the diffraction element and is thereby made into a diffracted light beam traveling from the diffraction element. A portion of the diffracted light beam is detected, and an intensity of the received diffracted light beam is also detected. In addition, a peak of the detected intensity of the received diffracted light beam is detected while the diffraction element is moved relative to the path of the input light beam. A position of the diffraction element is detected at which the detected peak of the detected intensity occurs. The position of the diffraction element is controlled on the basis of the detected position at which the detected peak of the detected intensity occurs.

Abstract: An optical fiber array is disclosed, including a pair of blocks having respective cutouts which, when the blocks are combined together, cooperate together to define a cavity, and a plurality of optical fibers having respective end portions accommodated within the cavity in a linear array. Neighboring end faces of the blocks adjacent end faces of the optical fibers are ground slantwise relative to a common plane in which the linear array of that end portions of the optical fibers lie and also relative to an optical axis of each of the optical fibers. A method of making the optical fiber array and a wavelength selecting device utilizing the optical fiber array are also disclosed.

Abstract: An optical fiber array includes a pair of blocks having respective recesses which, when the blocks are combined together, cooperate together to define a cavity, and a plurality of optical fibers having respective end portions accommodated within the cavity in a linear array. Neighboring end faces of the blocks adjacent end faces of the optical fibers are ground at an inclination relative to a common plane in which the linear array of the end portions of the optical fibers lie and also relative to an optical axis of each of the optical fibers. A method of making the optical fiber array and a wavelength selecting device utilizing the optical fiber array are also disclosed.

Abstract: In an optical filter to be used for signal selection, removal of noise, equalizing the wavelength of signal light, etc. in an optical communication system, optical measurement device or the like, and in an optical amplifier employing such optical filter, signal light is dispersed at different angles according to each wavelength by a diffraction grating and the dispersed light is selectively transmitted or reflected by a transmission type spatial filter or reflection type spatial filter, and is then coupled with an output fiber bundle as non-dispersed light by the diffraction grating. Thus, the optical filter has variable wavelength pass band characteristics and the optical amplifier possesses a uniform wavelength amplification factor.

Abstract: A diffraction grating has a reflection film formed on a photosensitive layer disposed on a substrate through exposure followed by development and the groove profile thus formed has a configuration distorted from a sinusoidal form because the sensitivity curve of the photosensitive layer is of the second order non-linearity to the exposure amount. With the groove pitch expressed by d, K=2 .pi./d, the coordinate perpendicular to the groove direction taken as x, and the groove profile .eta.(x) expressed as .eta.(x)=h [sin (Kx)+.gamma.sin (2Kz-90.degree.)], the parameters h, .gamma. and .phi. satisfy as follows:0.26.ltoreq.2h/d.ltoreq.0.520.05.ltoreq..gamma..ltoreq.0.32.The wavelength region to be used is normalized by the groove pitch d as 0.67.ltoreq..lambda./d.ltoreq.1.15. When an incident angle is expressed by .theta. and the first order Littrow angle is expressed by .theta..sub.L, the mount to be used is carried out in such a region that satisfies the following expression:.theta..sub.L -5.degree..ltoreq..