Quadrature phase shift technique for measurement of strain, optical power transmission, and length in optical fibers

A quadrature phase shift (QPS) technique is described that simultaneously measures the mechanical strain and optical power transmission on multimode and single-mode fibers. The principles of delay and power measurement are separately developed to derive the theoretical basis of the combined technique. The principles of the technique and its practical implementation are discussed. The technique is implemented using stabilized light-emitting diode sources which, unlike laser diodes, are insensitive to back reflections and allow any test wavelength in the usual wavebands to be chosen while being completely eye safe. Measurements on typical fiber and cable samples using a commercial QPS instrument are presented to demonstrate the versatility of the technique. The technique has applications such as cable tensile testing, temperature cycling, and installation monitoring. The technique is capable of state-of-the-art power/strain repeatability and long-term stability. Experimental results are given