PMD emulation, measurement and compensation device
First Claim
1. An emulation device for emulating a polarization mode dispersion (PMD) of an optical transmission system comprisingan emulator input for an optical signal;
- at least one controllable birefringent polarization transformation element having a transformation element input and a transformation element output, which is designed for the polarization transformation of the optical signal;
at least one birefringent DGD element having a DGD input and a DGD output, the DGD element comprising a differential group delay time DGD between two mutually orthogonally polarized propagation modes of the DGD element; and
an emulator output for a PMD-modified optical output signal;
said polarization transformation element and DGD element being disposed in relation to each other in an optical signal path between the emulator input and the emulator output such that birefringent axes at the transformation element output are twisted by a torsional angle which is different from zero degrees in relation to the birefringent axes at the DGD input.
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Accused Products
Abstract
A PMD emulation, measurement and compensation device is based upon an emulation device having a piece of fiber having a fixed differential group delay (DGD) and another short piece of fiber (or double refracting crystal) having a variable differential group delay (T-DGD). The two pieces of fiber are coupled with a non-zero torsional angle between their respective double refractive axes, preferably 45°. A fiber squeezer/stretcher is used to provide the variable DGD for the short piece of fiber. Various serial couplings of DGD and T-DGD fiber may be added to provide greater control and accuracy, with the torsional angles preferably alternating. Such an emulation device may be incorporated into a measurement device to measure the PMD-related distortion of an optical signal. Further the measurement device may be used in a PMD compensator where an emulation device in series with the optical signal path is controlled until the measured PMD in the PMD-related distorted optical signal is minimized.
19 Citations
26 Claims
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1. An emulation device for emulating a polarization mode dispersion (PMD) of an optical transmission system comprising
an emulator input for an optical signal; -
at least one controllable birefringent polarization transformation element having a transformation element input and a transformation element output, which is designed for the polarization transformation of the optical signal;
at least one birefringent DGD element having a DGD input and a DGD output, the DGD element comprising a differential group delay time DGD between two mutually orthogonally polarized propagation modes of the DGD element; and
an emulator output for a PMD-modified optical output signal;
said polarization transformation element and DGD element being disposed in relation to each other in an optical signal path between the emulator input and the emulator output such that birefringent axes at the transformation element output are twisted by a torsional angle which is different from zero degrees in relation to the birefringent axes at the DGD input. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 26)
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18. A measurement device for measuring a polarization mode dispersion (PMD)-related distortion of an optical signal, comprising
a measurement input for the optical signal; -
at least one polarizer;
at least one polarization transformation element, which is designed for the polarization transformation of the optical signal and in which a signal path of the optical signal is arranged between the measurement input and the polarizer;
at least one photo detector for dectecting an intensity Ppol of the optical signal, which is arranged in the signal path of the optical signal behind the polarizer; and
a control and output device connected to the polarization transformation element and the photo detector, which controls the polarization transformation element such that the intensity Ppol is either at a minimum or maximum level and generates a measurement output signal, which corresponds to the minimum or maximum intensity Ppol,min or Ppol,max, respectively, as a measure of the PMD distortion of the optical signal. - View Dependent Claims (19, 20, 21, 22, 23)
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24. Compensation device for compensating polarization mode dispersion (PMD)-related distortions in an optical transmission system, comprising:
an emulation device with an emulator input to input a PMD-distorted optical signal and an emulator output to output an optical output signal, the emulation device comprising a plurality of controllable polarization transformation elements and a plurality of DGD elements;
a measurement device for measuring the PDM-related distortion of the optical signal and outputting a measurement output signal; and
a control device, which sees the measurement output signal and which controls the emulation device in such a way that the latter minimizes, and preferably fully compensates, the PMD-related distortion, the control device being designed to output an adjustment signal to the polarization transformation elements, which is superimposed with a periodic modulation signal, to detect, with a correct intensity and phase, corresponding modulation components in the measurement output signal, and to produce a new adjustment signal as a function of the modulation components detected.- View Dependent Claims (25)
Specification