Appliance for measuring polarization mode dispersion and corresponding measuring process

Appliance for measuring the polarization mode dispersion (PMD) of a waveguide (2) comprising:

• a source (1, 6) of wide-band polarized light capable of sending a measuring light beam (21) into a first extremity (7) of waveguide (2),
• an interferometer (5, 51, 52, 53, 54) including an input (10) able to receive the measuring light beam (22) from the second extremity (8) of the waveguide (2), an output (11) capable of transmitting said light beam (25), and two arms (15, 16) diverging from the input (10) and converging at the output (11), said interferometer (5, 51, 52, 53, 54) dividing the measuring light beam (22) into two interference light beams (23, 24) crossing respectively the two arms (15, 16) and combining at the output (11) of interferometer (5, 51, 52, 53, 54) by producing interferences,
• a detector (3) capable of detecting the measuring light beam (25) from the interferometer (5, 51, 52, 53, 54),
• an electronic processing unit (4) linked to detector (3), capable of extracting a value (.tau.) representative of the polarization mode dispersion of the waveguide (2) from the detected measuring light beam (25),
• characterized in that it comprises at least one birefringent element (17, 18, 19, 46, 47, 59), having two independent modes of polarization, placed on at least one of the arms (15, 16) of the interferometer (5, 51, 52, 53, 54), the independent modes of the birefringent elements (17, 18, 19, 46, 47, 59) being identical, the algebraic sum of the elementary phase shifts produced by the birefringent elements respectively in each of the arms (15, 16) being equal to a relative phase shift and the algebraic difference of the two relative phase shifts having a value of .pi..