Abstract: A diffraction optical element including an element body having a large number of grooves formed on its surface to form a grating, and a grating shape adjusting layer deposited on a grating surface of the element body by oblique incidence or material particles onto the grating surface, wherein the grating shape adjusting layer per se is made of a reflecting film material By the grating shape adjusting layer, the contour shape of the resulting grating surface in a section perpendicular to a lengthwise direction of the grooves is made not similar to the sectional shape of the element body. A reflecting film may be formed on a grating shape adjusting layer made of another material. A reflecting film may be provided on the element body before a grating shape adjusting layer made of a transparent dielectric material is provided on the reflecting film.

Abstract: An optical module according to the invention includes an optical fiber, a planar lens, and a flat plate-like transparent member for optically coupling the optical fiber and the planar lens to each other. The transparent member has a nearly spherical concave portion formed in a surface of the transparent member. An end surface of the optical fiber is inserted into the concave portion of the transparent member so as to abut thereon and bonded and fixed thereinto. Further, a surface of the transparent member opposite to the surface in which the concave portion is formed is joined to a surface of the planar lens to make an optical axis of the optical fiber coincident with an optical axis of the planar lens. The concave portion is filled with a filler material having a refractive index higher than that of the transparent member to thereby fix the optical fiber.

Abstract: As a feature of a glass substrate having at least one fine hole according to the invention, a side wall surface of the fine hole is connected to each surface of the glass substrate by a curved surface as a boundary portion between the two. As another feature of the glass substrate, a layer denatured by machining is removed from the inner wall surface of the fine hole and the boundary portion between the wall surface and each surface of the glass substrate. The fine hole is produced by: forming a fine hole in a glass substrate by machining or laser machining; and then applying liquid-phase chemical etching to surfaces of the glass substrate and the fine hole. On this occasion, it is desirable that the etching liquid used for the liquid-phase chemical etching is either of an aqueous solution of hydrofluoric acid and an aqueous mixture solution of hydrofluoric acid and ammonium fluoride.

Abstract: When an end surface of a silica optical fiber and another optical element are to be optically coupled to each other, according to the invention, the optical fiber is treated so that a core of the optical fiber is protruded from a clad of the optical fiber at an end portion of the optical fiber to form a protrusion shaped like a truncated cone or like a cone. On this occasion, the refractive index of the surrounding medium is selected to be in a range of from 1.35 to 1.60. Preferably, the area of the top surface of the truncated cone is not larger than ⅕ as large as the area of the bottom surface of the truncated cone. Further preferably, the side surface of the core protrusion is inclined at an angle of 30 degrees to 75 degrees, both inclusively, with respect to the central axis of the core.

Abstract: An optical module is provided in which any conjugate ratio in an optical axis direction may be easily realized, the time duration for alignment may be shortened by using a passive alignment technique, and a large degree of may be obtained for any optical design. The optical module comprises a planar microlens array, a transparent substrate for adjusting a conjugate ratio of the optical module, and a guide substrate for optical fibers. The planar microlens array consists of a planar transparent substrate, in one surface thereof a plurality of circular microlenses are formed and arrayed. The transparent substrate includes a plurality of micro fitting recesses formed and arrayed in one surface thereof. The guide plate includes a plurality of micro guide holes opened therethrough.