Abstract: An optical fiber having a cladding region surrounding a core region having an elongate core hole, the inner or outer surface of the core hole having a surface roughness with a spatial period equal to or less than 5 ?m by a spectral power below 0.0017 nm2?m?1. A method of making an optical fiber including a cladding region having an arrangement of elongate cladding holes in a matrix material, surrounding an elongate core region having an elongate core hole, the method including the step of increasing the surface tension of the matrix material prior to or during the step of heating and drawing the fiber.

Abstract: An optical apparatus that lends itself to size reduction and mass production and enables detection of a return light beam by a pre-set operation irrespective of the state of the return light. The optical apparatus has a reflecting mirror 11 arranged in the vicinity of the focal point of the return light beam obtained on reflection by an illuminated object of the outgoing light from a laser light source 3, such as a semiconductor laser, and photodiodes PD.sub.1A, PD.sub.2A, PD.sub.3A, PD.sub.1B, PD.sub.2B and PD.sub.3B, as light receiving portions, arranged facing first and second reflecting surfaces M.sub.A and M.sub.B of the reflecting mirror 11. The reflecting surfaces M.sub.A and M.sub.B are arranged for reflecting a portion of the return light, while signal detection is performed by the light receiving portions.

Abstract: A triangular pyramidal semiconductor structure which precisely splits light is provided by preventing an unnecessary crystal plane from growing on the boundary of side surface crystal planes of the triangular pyramidal semiconductor structure. The triangular pyramidal semiconductor structure is formed of either one of a {111} A crystal plane and a {111} B crystal plane and two {110} crystal planes.