Abstract: A position dependent strain measurement system detected strain as a function of position in an optical sensing fiber using an interferometer having an input coupled to the first end of the optical sensing fiber. An electronic phase measuring sub-system is coupled to an output of the interferometer. The electronic phase measuring sub-system defines a usable optical intensity range of input light of the interferometer, wherein the electronic phase measuring sub-system is capable of measuring the phase of the input light. An optically pumped optical fiber amplifier is coupled between the first end of the optical sensing fiber and the input of the interferometer in series with an electrically pumped semi-conductor optical amplifier. The electrically pumped semi-conductor optical amplifier having a non-linear intensity amplification range that overlaps with the usable optical intensity range.

Abstract: It is an object of the present invention to provide a rare earth doped fiber whose transient response is suppressed and an optical amplifier for optical packet communication having a good characteristic even if there is little traffic. The above-mentioned problem is solved by an optical amplifier for optical packet communication comprising a first rare earth doped fiber (EDFA) having an active region whose diameter is between 3.4 ?m and 10 ?m, inclusive, an intermediate gain equalizing filter, and a second EDF, wherein the first EDFA is shorter than the second EDFA, and wherein the intermediate gain equalizing filter adjusts the intensity of each wavelength channel so as to equalize the light intensity of each wavelength channel having transmitted through the second EDF.