Abstract: An optical path conversion element includes a photonic crystal exhibiting periodicity of refractive index in one direction and using as an incident end face one of end faces substantially parallel with the periodicity direction of refractive index and an exit end face opposite the incident end face, an incident part for passing an incident light through the incident end face such that a propagation light is generated in the photonic crystal by a band on a Brillouin zone boundary, and a device for changing a photonic band structure of the photonic crystal and/or a device for changing a propagation optical path length that is a distance from the incident end face to the exit end face.

Abstract: A spectrometer using a diffraction grating includes a light-incident portion including an incident-side optical waveguide emitting a light beam that includes a plurality of wavelength components and that approximates a Gaussian beam, and a collimating lens that is arranged on an emission side of the incident-side optical waveguide and that converts the light beam approximating a Gaussian beam that is emitted from the incident-side optical waveguide into a substantially collimated light beam; a diffraction grating having grooves on its surface, on which the light beam that has been converted into the substantially collimated light beam by the collimating lens is incident, the diffraction grating spectrally separating the light beam by emitting light beams whose emission direction depends on their wavelength; and a light-emitting portion having a plurality of focusing lenses that respectively condense the light beams that have been spectrally separated by the diffraction grating.

Abstract: A photonic crystal waveguide and a homogeneous medium waveguide for enabling a steep bend and arrangement at an arbitrary angle with low propagation loss. A photonic crystal waveguide has a core formed by a photonic crystal having periodicity in the Y-direction. Electromagnetic wave is propagated by a band on the Brillouin zone boundary of the photonic band structure of the core. A side face of the core parallel to the Y-direction is in contact with a homogeneous medium having a refractive index of ns, and the condition of ?0/ns>a?/(?2/4+a2)0.5 is satisfied when the wavelength in vacuum of the electromagnetic wave is represented by ?0, the period of the photonic crystal is represented by a, and the period in the XZ-plane direction of the wave propagated through the core is represented by ?.

Abstract: A photonic crystal optical waveguide includes a optical waveguide portion having a core made of a photonic crystal with a structure having a periodic refractive index in at least one direction perpendicular to a propagation direction of guided light and having a uniform refractive index in the propagation direction of the guided light, and a cladding arranged in contact with the core, in order to confine the guided light in the core, and an incident-side phase modulation portion arranged in close proximity or in contact with an incident surface of the core.

Abstract: An optical element, composed of an one-dimensional photonic crystal of a triangular prism shape and a multilayer film and a phase modulation unit are used together, with the phase modulation unit adjacent or abutting to a light input end surface of the optical element. Input light is phase-modulated by the phase modulation unit in the same period and direction as those of photonic crystal so that only specific high-order band light can be propagated through the optical element. When this optical element is formed in an optical waveguide, a small-size spectroscopic device having high resolving power can be provided.

Abstract: In a waveguide element using a photonic crystal including a core formed of a photonic crystal having a refractive index periodicity in at least two directions perpendicular to a propagation direction of an electromagnetic wave and a cladding arranged in contact with the core in order to confine the electromagnetic wave in the core, an incident side phase modulation portion is provided for allowing an electromagnetic wave that is coupled to a band on or near a Brillouin zone boundary in a photonic band structure in the core and propagates in the core to enter the core.

Abstract: An optical imaging system is provided that includes a rod lens array and has the optimum refractive index distribution for achieving a high resolving power. The refractive index distribution of rod lenses can be expressed by n(r)2=n02·{1?(g·r)2+h4·(g·r)4+h619 (g·r)6+h8·(g·r)8}Eq. 45 where r is a radial distance from the optical axis of the rod lenses, n0 is a refractive index on the optical axis of the rod lenses, and g, h4, h6 and h8 are refractive index distribution coefficients. The refractive index distribution coefficients h4, h6 and h8 are set on a spheroid in a Cartesian coordinate system with h4 being x-axis, h6 being y-axis and h8 being z-axis. The spheroid is defined by a vector X* that is expressed by X*=(x, y, z)=O*+kAA*+kBB*+kCC*Eq.

Abstract: An optical element according to the invention constituted by a multilayer structure having a periodic structural portion as at least one region constituted by repetition of a predetermined period, wherein an end surface of the multilayer structure not parallel to layer surfaces of the multilayer structure is used as a light input surface whereas one or each of opposite surfaces of the multilayer structure parallel to the layer surfaces is used as a light output surface. There is an intermediate layer between a medium and a surface of the multilayer structure, the intermediate layer having a refractive index less than the refractive index of the medium. The periodic structural portion of the multilayer structure can be regarded as a one-dimensional photonic crystal. Refracted light from the one-dimensional photonic crystal has good directivity and the direction of the refracted light has strong dependence on wavelength.

Abstract: A spectrometer using a diffraction grating includes a light-incident portion including an incident-side optical waveguide emitting a light beam that includes a plurality of wavelength components and that approximates a Gaussian beam, and a collimating lens that is arranged on an emission side of the incident-side optical waveguide and that converts the light beam approximating a Gaussian beam that is emitted from the incident-side optical waveguide into a substantially collimated light beam; a diffraction grating having grooves on its surface, on which the light beam that has been converted into the substantially collimated light beam by the collimating lens is incident, the diffraction grating spectrally separating the light beam by emitting light beams whose emission direction depends on their wavelength; and a light-emitting portion having a plurality of focusing lenses that respectively condense the light beams that have been spectrally separated by the diffraction grating.

Abstract: A wavelength separator includes a one-dimensional photonic crystal structure formed by providing a plurality of grooves in parallel with one another at uniform intervals in a homogeneous medium, and has an incident end face formed obliquely with respect to a direction in which the grooves extend, and an output end face formed approximately perpendicular to the incident end face.

Abstract: A diffraction device using a photonic crystal includes a diffraction grating, which has a period and periodically divides electromagnetic waves, and an input medium and an output medium, which contact the diffraction grating. The input medium is air, and the output medium is a one-dimensional layer having a periodic characteristic in a single direction (Z axis direction). The photonic crystal is formed by a periodic multilayer film having a period corresponding to the sum of the thickness of a first substance and the thickness of a second substance, which are superimposed. The diffraction device drastically decreases the resolution corresponding to the difference of the separated frequencies.

Abstract: A method of measuring a radial index distribution of a rod lens has the steps: (1) the rod lens is processed so that the length is approximately P/2 (where P is pitch length) or an integer multiple thereof and so end surfaces parallel, (2) a patterned surface is set as an object surface in the proximity of one end surface, and an image surface is formed in the proximity of the other end surface by irradiating the patterned surface with condensed monochromatic light, (3) the positions of paraxial focal points and the curves of curvature of field are obtained by observing the image surface, and (4) higher-order index distribution coefficients are calculated back by a fitting process on the basis of the positions of paraxial focal points and the curves of curvature of field.

Abstract: An optical element according to the invention uses a thin film-like two-dimensional photonic crystal having a structure of periodic repetition in two directions perpendicular to each other. When the two periodic directions are Y-axis and Z-axis directions, opposite surfaces of the photonic crystal structure perpendicular to the Z-axis direction and parallel to the Y-axis direction are used as a light input surface and a light output surface respectively. The direction of movement of light rays incident onto the light input surface is decided so that it is parallel to the YZ plane and inclined at a predetermined inclination angle to the Z-axis direction.

Abstract: Two lenses are used for forming a collimator parallel pair, in which the distance between the two lenses is substantially made coincident with the maximum distance allowing beam waists to be formed at equal distances from the two lenses respectively.

Abstract: An optical element of the present invention includes a structure having at least one convex portion and at least one concave portion formed so as to be adjacent to either one of the convex portions. At least one surface of the structure is covered, and the optical element has a hollow portion. At least one surface of the structure is covered with a covering layer formed by a deposition process.

Abstract: A lens function-including optical lens according to the present invention is constituted by: at least one step-index optical fiber; and at least one gradient index optical fiber having an outer diameter equal to that of the step-index optical fiber and having a periodic length exhibiting a lens function, the gradient index optical fiber being joined or attached to an end surface of the step-index optical fiber. The present invention is especially effective in a single mode optical fiber which is typical of the step-index optical fiber. The gradient index optical fiber can be produced by an ion exchange method.

Abstract: A diffraction device using a photonic crystal includes a diffraction grating, which has a period and periodically divides electromagnetic waves, and an input medium and an output medium, which contact the diffraction grating. The input medium is air, and the output medium is a one-dimensional layer having a periodic characteristic in a single direction (Z axis direction). The photonic crystal is formed by a periodic multilayer film having a period corresponding to the sum of the thickness of a first substance and the thickness of a second substance, which are superimposed. The diffraction device drastically decreases the resolution corresponding to the difference of the separated frequencies.

Abstract: In the invention, light incident onto an end surface of one-dimensional photonic crystal is phase-modulated in the same period and direction as those of the photonic crystal to thereby propagate only specific high-order band light in the photonic crystal. That is, a phase modulation unit for generating phase-modulated wave having the same period as that of the periodic structure is disposed adjacent or close to a light incident surface of the periodic structure.

Abstract: In an optical system in which light output from an optical fiber (11) is collimated into parallel light rays by a gradient index rod lens (13), reflected by a filter (4) and then converged again by the rod lens (13) so that the resulting light is coupled to an optical fiber (12), a principal beam component of the light output from the optical fiber (11) disagrees with an optical axis (32) of the optical fiber (12) to thereby cause a coupling loss. When W is the distance between optical axes (31 and 32) of optical fibers (11 and 12) and Z is the length of a rod lens (13) on an optical axis (33) of the rod lens, the optical fibers (11 and 12) and the rod lens (13) are disposed to satisfy the condition: W·g·(0.25−Z/P)2≦6×10−5 in which g is a gradient index distribution coefficient of the rod lens, and P is the periodic length of the rod lens (13).

Abstract: An optical module which satisfies a required insertion loss and can be easily assembled with high productivity. The optical module includes first optical fiber, a first lens, an optical device, a second lens, and second optical fiber. The first lens receives an incident light from the first optical fiber and converts the incident light into a parallel light. The optical device receives the parallel light and performs predetermined optical processing on the parallel light. The second lens receives a transmitted parallel light from the optical device and converge the transmitted parallel light to produce an outgoing light. The second optical fiber receives the outgoing light. An optical axis of the first lens and an optical axis of the second lens are substantially coincident with each other. An optical axis of the first optical fiber and an optical axis of the second optical fiber are substantially parallel with each other and substantially parallel to the optical axes of the first and the second lenses.