Patent ID: 6229599
Filing Date: 2001-05-08
Classification: G01M,H04B

Abstract:
An apparatus for measuring characteristics of an optical fiber, at different positions along the length of the optical fiber, which apparatus comprises:tunable source means for providing optical pulses of light which have a variable wavelength and a narrow wavelength bandwidth;polarization selecting coupler means which comprises an input port, a bidirectional port and an output port, and which is for conveying light between the input port, the bi-directional port and the output port, such that a state of polarization of the optical pulses of light input at the input port becomes a particular launch state of polarization of light output from the bidirectional port, and such that one or more particular receive states of polarization of light input at the bi-directional port become one or more separate channels of light output from the output port;optical connector means for making an optical connection between the bidirectional port of the polarization selecting coupler means and one end of the optical fiber, so that the light output from the bi-directional port of the polarization selecting coupler means is launched into the optical fiber and the light backscattered within the optical fiber is received as the light input at the bi-directional port of the polarization selecting coupler means;photodetector means for converting the intensity of each of the one or more separate channels of light output form the output port of the polarization selecting coupler means into one or more separate electrical signals;launch controller means for controlling the timing, duration and wavelength of the optical pulses provided by the tunable source means, and for specifying the particular launch state of polarization of the light output from the bi-directional port of the polarization selecting coupler means;receive controller means for controlling the timing of measuring the electrical signals provided by the photodetector means, and for specifying the one or more particular receive states of polarization of light input at the bi-directional port of the polarization selecting coupler means; andprocessor means for measuring and processing the electrical signals provided by the photodetector means into measurements of the characteristics of the optical fiber, and wherein there is, only one separate channel of light output from the output port of the polarization selecting coupler means, such that the photodetector means converts the intensity of the said one separate channel of light; and in which the polarization selecting coupler means comprises:polarization independent coupler means which comprises an input port, a bi-directional port and an output port, and which is for conveying light between the input port, the bi-directional port and the output port, with negligible polarization dependent loss of the light, such that light input at the input port become light output from the bi-directional port, light input at the bi-directional port becomes light output from the output port, and the light is substantially unchanged as it passes in either direction between the bidirectional port of the (polarization) polarization selecting coupler means and the bi-directional port of the polarization independent coupler means;polarization controller means for converting the state of polarization of light input at the input port of the polarization selecting coupler means into a particular launch state of polarization of light input at the input port of the polarization independent coupler means, such that the particular launch state of polarization is selected as specified by the launch controller means; andpolarization analyzer means for selecting a particular receive state of polarization of the light output from the output port of the polarization independent coupler means to become the one separate channel of light output from the output port of the polarization selecting coupler means, such that the particular receive state of polarization is selected as specified by the receive controller means.