Method and apparatus for measuring the polarization mode dispersion of an optical fiber
The present invention relates to a new model for interpreting interferometric measurements, able to lead to a new method, system ( 10 ) and device ( 27 ) for measuring the PMD (Polarisation Mode Dispersion) of an optical fibre ( 11 ). The model, which is based on the theory of propagation of the optical signal as can be determined according to the socalled Prindpal States of Polarisation (PSPs) of the fibre, leads to a new interpretation of the interferogram generated with the interferometric measurements and is characterized in that it identifies in said interferogram a central peak and two side lobes. Thanks to this new model, it is possible to determine the PMD of the fibre based on the information content associated to at least one of the two side lobes identified in the interferogram.
1. A method for measuring the polarization mode dispersion of an optical fiber, the method comprising the steps of:
applying an optical signal to a first end of the fiber,
coupling a second end of the fiber to an interferometer;
generating by means of said interferometer at least one interferogram comprising at least a central peak and two side lobes having a determined information content;
processing said interferogram in such a way as to measure the information content of at least one of said two side lobes;
determining the polarization mode dispersion of the fiber and associating with the measurement of said information content a probability density function representative of the polarization mode dispersion of the fiber in the form of differential group delay by computing the deconvolution of the one side lobe with the central peak so that the deconvolution corresponds to the probability density of the differential group delay determined by the PMD of the fiber; and
outputting the determined polarization mode dispersion.
2. The method as claimed in claim 1 , further comprising the step of
determining an average of measurements of said information content to which said probability density is to be associated.
3. The method as claimed claim 1 , wherein said information content comprises a single numeric value determined by the position of said at least one side lobe in the interferogram.
4. The method as claimed in claim 1 wherein said information content comprises a plurality of values determined by the position of said at least one side lobe in the interferogram.
5. A computer program product able to be directly loaded in the internal memory of an electronic measuring device and comprising portions of software code to implement the method as claimed in claim 1 when the product is run on said electronic device.
6. The method as claimed in claim 1 wherein the determined polarization mode is outputted by displaying it.
7. A system for measuring the polarization mode dispersion of an optical fiber, the system comprising:
an optical source able to generate an optical signal to be injected into the fiber;
an interferometer associated with the fiber and able to generate an interferogram comprising at least a central peak and two side lobes having a determined information content;
control means connected to said interferometer for
processing said interferogram in such a way as to measure the information content of at least one of said side lobes;
determining the polarization mode dispersion of the fiber and associating with the measurement of said information content a probability density function representative of the polarization mode dispersion of the fiber in the form of differential group delay; and
computing the deconvolution of the one side lobe with the central peak so that the deconvolution corresponds to the probability density of the differential group delay determined by the PMD of the fiber.
8. The system as claimed in claim 7 , wherein the control means further serves for
determining an average of measurements of said information content to which said probability density is to be associated.
9. A device for measuring the polarization mode dispersion of an optical fiber into which optical signals have been injected, the device comprising
an optoelectronic module able to convert the optical signals into electrical signals;
means for generating an interferogram comprising at least a central peak and two side lobes a having a determined information content;
control means for
measuring the information content of at least one of said two side lobes;
determining the polarization mode dispersion of the fiber and associating with the measurement of said information content a probability density function representative of the polarization mode dispersion of the fiber in the form of differential group delay; and
computing the deconvolution of the one side lobe with the central veak so that the deconvolution corresponds to the probability density of the differential group delay determined by the PND of the fiber.
10. The device as claimed in claim 9 , wherein the control means further serves for
determining an average of measurements of said information content to which said probability density is to be associated.