Yasuji Murakami

Characteristics of a hemispherical microlens for coupling between a semiconductor laser and single-mode fiber

A hemispherical microlens is fabricated on the end of a single-mode fiber by an electric arc discharge technique. It improves coupling efficiency between InGaAsP lasers with buried heterostructure geometry and single-mode fiber. The lowest coupling loss of 2.9 dB is achieved with the optimum lens radius of 8.5 μm. This loss is 4.4 dB lower than that with a butt joint. Experimental results of coupling efficiency and alignment tolerances in coupling with different lens radii in the range of3.5-17 \mum are discussed in detail. The results are in good agreement with theoretical values derived by Gaussian beam and paraxial ray approximations.

Bending losses of coated single-mode optical fibers

Peaks appear in bending losses of coated single-mode fibers due to interference between the guided mode and rays which are radiated from the guided mode and are reflected at cladding-coating boundary. This paper reports derivation of bending loss formulas for coated slab waveguides and coated fibers. Plane wave concepts are also used to explain the appearance of the loss peaks. Measurements were performed by using two coated single-mode fibers. The agreement between theory and experimental results is found to be excellent. It is possible to obtain the refractive index difference from measured peak wavelengths.

Cut-off wavelength measurements for single-mode optical fibers

A new technique has been proposed for direct measurement of the cut-off wavelength, at which the first higher-order mode disappears. It uses a change of a near-field pattern of a fiber, which is excited by a variable wavelength source. The cut-off wavelength can be measured with +/-5-nm accuracy. The most suitable fiber length for precise measurement is 10-20 mm. It is found, furthermore, that the first higher-order mode under the condition near cut-off rapidly attenuates because of waveguide imperfections, in which the loss due to core-cladding boundary distortions is the most dominant.

Coupling characteristics measurements between curved waveguides using a two-core fiber coupler

Coupling characteristics between two curved waveguides are studied using a two-core fiber. A tunable monochromatic light source is used to measure the wavelength dependence of the coupling efficiency. Measured values of the coupling efficiency agree well with theory. It is found that (1) the coupling efficiency can be changed from 0 to 1 by changing the radius of curvature, for example, from 100 mm to infinity in the measured coupler; and (2) when phase shift due to curvature sbeta/2R exceeds the coupling coefficient K, where s is the center-to-center core separation, beta the propagation constant, and R the radius of curvature, coupling between the curved cores does not occur, and there is only the phase shift between the cores.

Studies on designing of submarine optical fiber cable

This paper describes important studies necessary to design submarine optical fiber cables. These include a study for deciding the optimum single-mode fiber parameters to suppress losses during cabling, cable laying, and so on. It also includes a study on the necessary fiber proof test conditions to prevent fiber breakage during cable handling, that is, during cable laying and recovery and to assure long-term fiber reliability. Submarine optical fiber cable sea trial results are also stated for cables designed applying these studies.

Raman scattering spectrum analyses for fluorine‐doped silica optical fibers

Raman scattering spectra for fluorine‐doped silica fibers are measured. A Raman scattering peak, assigned to be the Si–F bond in the fibers, is observed at a wave number of 930 cm−1. Heat tests in a hydrogen gas atmosphere are carried out. The result shows that the fiber loss due to the hydroxyl group, which is produced by the heat test, decreases by fluorine doping. These phenomena show that the Si–O–Si bond defects are filled with doped fluorine atoms, and oxygen atoms positioned at the defects are exchanged by the fluorine atoms.

Maximum measurable distances for a single-mode optical fiber fault locator using the stimulated Raman scattering (SRS) effect

Maximum measurable distances for a single-mode optical fiber fault locator using the stimulated Raman scattering effect were calculated. Calculations were carried out on the assumption that the light source is an Nd:YAG laser operating at 1.06 μm and the photodetector is a germanium avalanche photodiode (Ge-APD). The first to the seventh Stokes lights can be detected by the Ge-APD. Calculations show that a break can be measured in an up to 165 km long ultra-low-loss single-mode fiber.

Coupling between curved dielectric waveguides.

Coupling characteristics between two curved dielectric waveguides that lie in a plane and have the same center of curvature are discussed. Analysis is carried out by using the coupled-mode equations. It is found that (i) the maximum power transfer efficiency between two curved waveguides having the same propagation constant changes from 0 to 1 as the radius of curvature increases and (ii) complete power transfer between two waveguides having different propagation constants can be realized by bending the two guides with suitable radii of curvature.

Design and development of optical fiber joining techniques for efficient construction of aerial distribution cable systems

Two new optical fiber joining techniques have been developed for aerial distribution cables. One employs a compact mass-fusion splicer and the other involves a small mechanical splice. This paper describes their design and performance. These techniques are excellent for use in aerial sites and enable aerial distribution cable systems to be constructed efficiently. They will be useful for the economical construction of optical access networks for fiber-to-the-home.

Residual elongations of submarine optical-fiber cable laid on the sea bottom

Fiber elongations during laying and residual fiber-elongation strain after laying of submarine optical-fiber cables have been reported. The fiber elongations have been measured by the optical-pulse-delay method. It has been found that the residual fiber-elongation strains are closely related to cable slack and the cable tension at the sea bottom. Therefore, the residual strains can be minimized by controlling the slack and the tension. The relation between necessary proof-test strain and allowed residual strain has also been mentioned. If the proof-test strain is 1 percent, the allowed residual strain due to laying becomes 0.26 percent.