Abstract: A single mode fiber is provided which is suitable for high-speed, large-capacity optical communication and for optical wiring. The single mode fiber has a first cladding region with a uniform refractive index, a core region with a refractive index higher than that of the first cladding region, and a second cladding region including at least four air hole regions placed in the first cladding region. Optimization can be achieved by making the distance from the center of the core region to the air hole regions equal to 2–4.5 times the core radius, and the air hole radius equal to or greater than 0.2 times the core radius. It is preferable the core radius be 3.7–4.8 ?m, the relative index difference of the core region from the first cladding region be 0.3–0.55 %.

Abstract: A single mode fiber is provided which is suitable for high-speed, large-capacity optical communication and for optical wiring. The single mode fiber has a first cladding region with a uniform refractive index, a core region with a refractive index higher than that of the first cladding region, and a second cladding region including at least four air hole regions placed in the first cladding region. Optimization can be achieved by making the distance from the center of the core region to the air hole regions equal to 2-4.5 times the core radius, and the air hole radius equal to or greater than 0.2 times the core radius. It is preferable the core radius be 3.2-4.8 ?m, the relative index difference of the core region from the first cladding region be 0.3-0.55%.

Abstract: The present invention relates to an optical switch comprising a fiber arranging member having a substrate 1 with a plurality of fiber fixing grooves formed in an upper surface thereof, first optical fibers 2 fixed in the fiber fixing grooves, and a convey mechanism 5 for conveying a second optical fiber 6 to be connected to a corresponding first optical fiber 2 to a corresponding fiber fixing groove, wherein fiber introduction grooves 1h for guiding the end portion of the second optical fiber 6 are formed at the end portions of the fiber fixing grooves that fix the end portions of the first optical fibers 2.

Abstract: An optically active device comprising an optical fiber, a light source and an optical device is disclosed. The optical fiber comprises a core made of an optical functioning glass doped with Pr.sup.3+ as an active ion and transmits light at a first wavelength. The light source generates excitation light at a second wavelength shorter than the first wavelength. The optical device directs the excitation light from the light source into the optical fiber. Then, Pr.sup.3+ in the core of the optical fiber is stimulated to emit light at the second wavelength. As a result, an optical function such as optical amplification can be effected at the second wavelength.

Abstract: An object of this invention is to provide an optical filter which has higher mass-producibility and economy. This feature can be realized by doped a rare earth element into the region made of a glass material which can transmit light. In a case that Er and Tm are doped as the rare earth element into the region, a ratio .alpha..sub.Er /.alpha..sub.Tm between a contribution .alpha..sub.Er of Er to attenuation and a contribution .alpha..sub.Tm of Tm to attenuation is set in a range from about 1 to 1/25 for a 1.5 .mu.m band range, whereby attenuation in this wavelength range is retained above 50 dB/m to realize required cutoff function.

Abstract: An optical line monitoring method and an apparatus for locating a failure point in an optical communication system, wherein a plurality of types of inspection light rays having wavelengths which are determined by cut-off wavelengths, which differ from each other, of short-wavelength pass filters installed at a plurality of branched ports of an optical coupler/splitter of the communication system are sent from a light source having variable wavelengths into one or more corresponding optical fiber lines of the system in sequence via an optical directional coupler and the optical coupler/splitter. Each time reflected light, corresponding to the inspection light, from one or more optical fiber lines is received, an output representing the intensity level of the reflected light is sent from a light receiver to an arithmetic circuit and stored in the arithmetic circuit.

Abstract: A bi-directional optical communication system. A first optical fiber includes a plurality of pieces, each piece having a first and second end. An optical amplifier for amplifying optical signals transmitted in a first direction is coupled to first and second pieces of the first optical fiber. A second optical fiber is coupled to the first and second pieces, bypasses the optical amplifier and transmits optical signals in a second direction opposite to the first direction. A first optical signal generator apparatus coupled to the first piece of the first optical fiber provides optical signals propagating in the first direction to a optical receiver apparatus coupled to the second piece of the first optical fiber. A second optical signal generator in the optical receiver apparatus provides optical signals propagating in the second direction to the first optical signal generator apparatus.