Abstract: A rare earth doped optical fiber consisting of a first core doped with a rare earth element and having a relative index difference ranging from about 0.76% to about 1.5%, a second core surrounding the first core and having a relative index difference of about 1.8% or more, and a clad surrounding the second core. The refractive index of the first core is set smaller than the refractive index of the second core, and only the first core is doped with a rare earth element, thereby suppressing the influence of concentration quenching.

Abstract: An optical fiber having a core for propagating light, where the core includes first, second and third regions. The first, second and third regions are concentrically arranged with the second region around the first region and the third region around the second region. The third region includes a dopant for increasing the refractive index of the third region. The first region includes a first dopant for providing an amplification band and a second dopant for expanding the amplification band. The second region has an impurity concentration which is lower than the concentration of the dopant in the third region and is lower than the concentrations of the first and second dopants in the first region. Upon production of the fiber, the second region acts as a barrier to prevent diffusion of dopants. As a result, the amplification band can be effectively expanded. Various other arrangements of core and clad regions and dopants are provided.

Abstract: An optical amplifier amplifies a wavelength division-multiplexed optical input signal composed of optical signals having different wavelengths such that the output level of each of the optical signal is always optimized and such that the difference between the gains of the amplifier on the optical signals is minimized when the number of optical signals is two. The output level of the amplifier is controlled according to the number of the optical signals, to optimize the output level of each of the optical signals.

Abstract: A method and apparatus for controlling gain differences between optical signals, and hence an output of each individual optical signal, in an optical amplifier including a rare-earth-doped fiber for optically amplifying a wavelength-division multiplexed signal. Pumping light is injected into an erbium-doped fiber that is also supplied with additional pumping light that gives a different gain characteristic to the erbium-doped fiber. The output of each signal light is detected by a photodetector and, based on the detected output, injection power is controlled individually for each pumping light.

Abstract: An optical fiber amplifier employs an optical fiber and an optical coupler. The optical fiber has a core and a clad. The core has an erbium-aluminum-doped center and an erbium-doped annular section. The optical coupler guides signal light and pump light to the optical fiber, which amplifies the signal light using the pump light. The center of the core corresponds to a section where the field diameter of the signal light overlaps that of the pump light. The annular section is outside the field diameter of the pump light. The amplifier provides a required gain without employing optical parts such as filters. The signal light has a wavelength in the 1.5-micrometer band, and the pump light has a wavelength, in the 1.45-micrometer band, corresponding to the absorption band of erbium. The present invention may further employ pump light having a wavelength in the 0.98-micrometer band.

Abstract: Disclosed is an optical amplifier, wherein efficient optical amplification of signal light of 1.3 .mu.m band is made achievable by optically exiting a doped fiber doped with Pr (praseodymium) alone, or together with other rare earth element, or a similar optical waveguide arrangement, and then supplying the optical waveguide arrangement with the signal light.

Abstract: A high-output optical transmitter including a rare earth-doped fiber. The optical transmitter includes a signal light source for outputting signal light having a first predetermined plane of polarization and a pumping light source for outputting pumping light having a second predetermined plane of polarization. The plane of polarization of the signal light from the signal light source is rotated 45 degrees by a Faraday rotator such that the plane of polarization of the signal light output from the Faraday rotator and the pumping light are perpendicular to each other. The signal light from the Faraday rotator and the pumping light from the pumping light source are polarization-coupled by a polarization coupler and the combined light is introduced into the rare earth-doped fiber.

Abstract: An apparatus for measuring characteristics of chromatic dispersion includes a Raman oscillator generating a laser pulse with wide band wavelength.The laser pulse generated by a Raman oscillation is transmitted through a selection and reflection film and then through a sample fiber.At an output end of the sample fiber, a reference wavelength light and an object wavelength light are received so that a delay time of the object wavelength light relative to the reference wavelength light is measured as a factor of a chromatic dispersion of the sample fiber.

Abstract: An optical fiber amplifier in which light generated within an Er doped optical fiber by spontaneous emission is eliminated or suppressed. By inserting a wavelength demultiplexer in the Er doped optical fiber, the light generated within the optical fiber by spontaneous emission can be effectively eliminated. As an alternative, the Er doped optical fiber is arranged in a coil form with a predetermined radius of curvature to thereby effectively eliminate light due to spontaneous emission on the longer wavelength side than the signal light. Further, by doping the center portion of the core of an optical fiber with aluminum and the whole body of the core uniformly with erbium, it is made possible to suppress the generation of light by spontaneous emission without causing an adverse effect on the amplification performance of the signal light.

Abstract: An optical fiber doped with Er is provided at its both end portions with a pair of 1.25 .mu.m band reflecting filters such that the distance therebetween becomes the resonator length for a light beam of 1.25 .mu.m band. When a pumping light beam of a wavelength of 0.8 .mu.m band is introduced into the optical fiber, laser oscillation at 1.25 .mu.m band is produced, whereby the energy level of Er in an excited state is lowered and a signal light beam of a wavelength of 1.55 .mu.m band can be optically amplified with high efficiency. Another fiber optic amplifier in which a pair of 0.98 .mu.m band reflecting filters are disposed at both end portions of an optical fiber doped with Yb and Er such that the distance therebetween becomes the resonator length for a light beam of 0.98 .mu.m band is also disclosed.

Abstract: An optical fiber amplifier is disclosed wherein pumping light and signal light are introduced into an optical fiber doped with a rare-earth element to directly amplify the signal light. The optical fiber amplifier of the invention comprises means constituted from a reflecting film, a fiber loop or the like for causing pumping light to pass by a plurality of times in the doped fiber. Due to the provision of the reflective film or the fiber loop, pumping light can be utilized efficiently, and the amplification factor of the optical fiber amplifier is improved.

Abstract: The present invention relates to an optical fiber cable. In view of narrowing optical fiber cables, the spiral grooves to accommodate optical fiber cables are formed in the core loading material, in the longitudinal direction, by bundling high tensile strength synthetic resin fibers and covering the external circumference of the bundled material with a synthetic resin covering layer. Moreover, a method is disclosed for manufacturing an optical fiber cable which stably loads the optical fibers by holding the core loading material in order to eliminate deviation generated in the rotating direction around the core loading material on the occasion of loading fibers in the spiral grooves of core loading material.

Abstract: An apparatus connects a single-mode optical fiber in a transmitting side to a multi-mode optical fiber in a receiving side without a deterioration of baseband transmission characteristics. The apparatus optically connects the single-mode fiber to the multi-mode fiber with an optical axes displacement therebetween, so that an optical signal to a multi-mode optical fiber from a single mode optical fiber is incident in a steady state mode including not only lower mode, but higher mode. In one embodiment, the optical axes displacement is achieved by axial displacement between the single-mode fiber and multi-mode fiber. In another embodiment, the optical axes displacement is achieved by an angle displacement between the single-mode fiber and multi-mode fiber.

Abstract: A constricted portion (14) is formed on an optical fiber (6) composed of a core (2) and a clad (4), and one or two belt-like conductive layers (20) elongated in a longitudinal direction of the optical fiber (6) are provided on a surface of the constricted portion (14). With the structure, the device functions as a polarizer which removes a polarized light component having a polarization plane perpendicular to the conductive layers (20). The optical fiber polarizer is suitably inserted in and used with an optical transmission line of an optical communication system and is also suitable for use as a component of an optical isolator.

Abstract: An optical waveguide having a first cross section is thinned to constitute a thinned portion having a second cross section, as long as a predetermined length. Surface of the thinned portion is contacted with a laser glass member doped with a rare earth element, such as Er. Due to the thinned diameter, the optical fiber is optically coupled with the laser glass member. A pumping light is input to either into the optical waveguide together with a signal light or directly into the laser glass member. Signal light coupled from the thinned portion to the laser glass member is amplified by stimulated emission of the laser glass. Thus amplified signal light is coupled back to the thinned portion so as to propagate along the optical waveguide. The thinned portion can be as short as several centi-meters compared with ten meters to more than one hundred meters of conventional optical amplifier.