Abstract: A two-dimensional photonic crystal slab waveguide is provided in which a line defect is formed, wherein a first width which is a distance between centers of nearest two lattice points located on both sides of the line defect is different from a second width which is a corresponding distance in a normal two-dimensional photonic crystal slab waveguide. In addition, a two-dimensional photonic crystal slab waveguide is provided in which low refractive index columns in a optical waveguide part are placed at positions shifted from normal positions in a normal two-dimensional photonic crystal slab.

Abstract: A two-dimensional photonic crystal slab waveguide is provided in which a line defect is formed, wherein a first width which is a distance between centers of nearest two lattice points located on both sides of the line defect is different from a second width which is a corresponding distance in a normal two-dimensional photonic crystal slab waveguide. In addition, a two-dimensional photonic crystal slab waveguide is provided in which low refractive index columns in a optical waveguide part are placed at positions shifted from normal positions in a normal two-dimensional photonic crystal slab.

Abstract: Of hydrogen atoms constituting 2-adamantylamino-5-nitropyridine, at least hydrogen atom of N--H part is substituted with deuterium to obtain a deuterated AANP. An organic optical material is made from the deuterated AANP. Content of the deuterated AANP in this case is preferably more than 25%. With this method, an organic nonlinear optical material can be provided for devices having a large wavelength conversion efficiency in wavelength conversion relating to optical communications wavelength region, particularly at and around 1.55 .mu.m wavelength.

Abstract: According to the process of the present invention for producing a garnet single crystal fiber, a crystal is grown while the direction of a seed crystal, corresponding to the direction of growth, is set in a direction having angles of at least 10.degree. from a direction equivalent to the <100> orientation, at least 20.degree. from a direction equivalent to the <110> orientation and at least 20.degree. from a direction equivalent from the <211> orientation. The resulting garnet single crystal fiber does not include a core, which is formed due to facet formation, and has an excellent optical homogeneity necessary for use in an optical device such as a laser device or an isolator.

Abstract: A method of stabilizing the frequency of a semiconductor laser comprises stabilizing a time-dependent frequency fluctuation by utilizing an optical energy absorption medium including an isotope acetylene gas molecule. An apparatus for stabilizing the frequency of a semiconductor laser, comprises a semiconductor laser, an optical energy absorption medium, a photodetector and a control circuit as essential elements. The optical energy absorption medium includes an isotope acetylene molecule.

Abstract: A fiber coupler includes first and second optical fiber groups and a fused-elongated region. The first optical fiber group is obtained by parallelly arranging a plurality of optical fibers on a single plane, a coating of each of the optical fibers being removed throughout a predetermined portion at the same position as that of an adjacent optical fiber in a longitudinal direction. The second optical fiber group is obtained by parallelly arranging adjacent optical fibers on a predetermined plane parallel to an arrange plane of the first optical fiber group at the same pitch as that of the first optical fiber group, a coating of each of the optical fibers being removed throughout a predetermined portion at the same position as that of an adjacent optical fiber in a longitudinal direction as the first optical fiber group.