An optical fiber having a small increase in loss at a wavelength of approximately 1400 nm involved in a deuterium treatment is provided, and an evaluation method to decide whether an optical fiber is that having such a loss increase, and a fabrication method of an optical fiber having a small increase in such a loss are also provided. Each device includes communication means for communicating with other ones of the plurality of devices when they are in range. A data acquisition system is connected to the controller and is capable of monitoring voltage and current output. The outside of the electrode core is covered with an insulation layer. The unitary shock absorber has circumferential notches engageable both by radial flanges 87) on the gear wheel and by elements for driving an output member, and chamfers are provided on the edges of the notches to ensure gradual torque-dependent angular deflection of the shock absorber and make it easier to mount the same automatically on the hub of the gear wheel. Further provided are compositions for use in recovering oil from an oil-bearing formation which comprise the sulfonated derivatives of one or more internal olefins having low amounts of tri-substitution on the olefin bond.