Polarization mode dispersion(pmd)

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1. Polarization Mode Dispersion(PMD) Presented by: Md. Abdur Rahman ID:1402EEE00019 2 nd batch Dep't of EEE (MIU) 1

2. Content Polarization Mode Dispersion. Properties of PMD. The origins of PMD. Low PMD. High PMD. PMD test. 2

3. Polarization Mode Dispersion A form of dispersion in an optical fiber where two different polarization states of light travel at slightly different velocities. This is caused by imperfections and asymmetries in the glass fiber core itself and results in random spreading of the optical signal. 3

4. Single mode optical fiber consists of one propagation mode, which in turn, is comprised of two orthogonal polarization modes. Asymmetrical differences in the fiber introduce small refractive index variations between two states. This is known as birefringence or double refraction. Birefringence in turn causes slight slight differences in group velocity and phase which is referred to as PMD 4

5. Properties of polarized light Polarization is defined in terms of the electric field, which interacts more strongly with most devices. The electric field of a fully polarized, monochromatic light wave can be described as issuing from a point charge moving in an elliptical pattern in the plane of the source . 5

6. The origins of PMD The speed of propagation of a light wave depends on the index of refraction of the transmission medium in the direction of fluctuation of the electric field. Consider a short, straight length of single-mode fiber . Given an index difference between the X- and Y-directions, a Z-traveling wave decomposes into a pair of waves having X- and Y-directed electric fields. The two waves propagate at slightly different speeds, accumulating an optical phase shift and associated differential delay in proportion to distance. 6

7. Low PMD No Bit Errors In this illustrative example, the light signal exhibits no sign of PMD, and the subsequent digital signal shows no distortion and therefore no bit errors. 7

8. High PMD Multiple Bit Errors In this example, the dispersed light wave ultimately causes a distorted digital signal which leads to transmission errors. 8

9. Mathematically, PMD occurs as a statistically random measurement along the fiber . Which is to say that both polarized states exhibit some variable value of PMD at any point in time. 9

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