Shigeru Tanaka

Thermal characteristics of phase shift in jacketed optical fibers.

Frequency and pulse methods are applied to measure thermal characteristics of phase shift in bare and jacketed optical fibers. The thermal coefficient of phase shift in bare fibers is found to be 7 x 10(-6)/deg, which is in good agreement with the value predicted theoretically. It is also found that the coefficient is increased by four times after nylon jacketing due to the increase of the coefficient of linear expansion.

Measurement accuracy of chromatic dispersion by the modulation phase technique

A simple measuring method for the chromatic dispersion measurement is described. This technique uses group delay measurement by modulation phase of laser diodes with different wavelengths. An experiment showed that this technique is capable of measuring the chromatic dispersion of a 42.3-km single-mode fiber. The accuracy of measurement is discussed in view of fiber length, modulation frequency, and the number of employed laser diodes. The accuracy is improved when a higher modulation frequency is used and a longer fiber is measured since the detected phase fluctuation depends little on the modulation frequency and very little on the fiber length. The estimated measurement error of chromatic dispersion was 0.1 ps/km/nm for a four-laser diode system.

1.55-μm long-span fiber optic distributed temperature sensor

Distributed temperature sensors which utilize Raman scattering effects in optical fibers have been widely developed and used in actual applications [1] [2]. Possible applications include temperature monitoring for power cables or pipe lines. It is highly desirable to expand measurable distance with maintaining measurement accuracy.

Long-term reliability of layer-type tight structure cable

The long-term reliability of the optical-fiber strength in the tight structure cable is discussed from the viewpoint of residual fiber strain and prooftesting condition. The maximum fiber strain in the installed tight structure cable was evaluated as 0.05 percent experimentally as the summation of: 1) compressive strain induced by nylon jacketing; 2) added strain during cable; 3) residual strain by cable installation; and 4) thermal strain in the installed condition. Based on these measured residual strains on the typical 12-fiber cable with silicone resin and nylon-coated fiber, the required prooftest level was found to be 0.19 percent in order to guarantee the 10 000-km fiber for 25 years with failure probability less than 10-3.

Mode Field Diameter -- Measurement in Far Field Pattern Method and Characteristics --

Measurement accuracy of mode field diameter (M.F.D.) by far field pattern method and the characteristics of M.F.D. in viewpoint of its definition are examined. It is found that M.F.D. by second moment definition becomes larger than that by gaussian fit defini-tion with a decrease in normalized frequency V.