Supervisor: Prof K. Abramski

1. States of polarization of chosen fiber elements Supervisor: Prof K. Abramski

2. Introduction • The Pointcaré sphere • States of polarization • Matrix interpretation of polarization states • Geometrical interpretation of Stokes parameters • The Pointcaré sphere • (Degree of polatization) • Measurement with Polarimeter • Polarization maintaining fibers • Optimized exctinction ratio measurement • Type’s of polarization controllers • Measurements on polarization controllers • Conclusion Table of contents P

3. Introduction • Erasmusstudent from Belgium • Finishing my studies Master in electronics • Most interesting parts of my Msc project will be explained P

4. States of polarization • Consider a monochromatic plane wave: • We describe the light by the transverse components of its electric field: P

5. States of polarization • Light is linearly polarized if the field components Ex and Eyoscillate in phase or 180° out of phase. P

6. States of polarization • For complex Exand Ey , the oscillations of the field components along the horizontal and vertical directions are generally not in phase, and we can write: P

7. Matrix representation of polarizationstates • Matrix approach to describe the polarization of light • The polarization changing characteristics of a device can be represented by a matrix • The Jones vectors • Useful to describe the polarization behavior of coherent light. The matrix form is • Disadvantage: Unpolarized light cannot be characterized in terms of the Jones vectors P

8. Matrix representation of polarizationstates • The Stokes parameters • Carries complete information on the intensity and state of polarization of a plane wave • For monochromatic light, the amplitude and phase factors are time independent and the Stokes parameters satisfy the condition P

9. Matrix representation of polarizationstates • The Stokes parameters • S0 measures the total intensity of the beam • S1 gives the extent by which the intensity of horizontal polarization exceeds the intensity of vertical polarization in the beam • S2 determines the excess of the intensity of +45°-polarization over the intensity of -45°-polarization • S3 estimates the excess of the intensity of right circularly polarized light of the intensity of left circularly polarized light P

10. Geometrical interpretation of Stokes parameters • The stokes parameters of completely polarized light can be expressed in a form that makes appear as the Cartesian components of , treated as a polar vector. • The above equations bear close resemblance to the relationships among the Cartesian and spherical polar components of the position vector P

11. Geometrical interpretation of Stokes parameters P

12. The Pointcaré sphere • It is a sphere of unit radius in a space spanned by the normalized Stokes parameters • Each point on the surface of the Pointcaré sphere represent a unique state of polarization P

13. The Pointcaré sphere • Points in the equator represent all possible states of linear polarized light • Unpolarized light can be represented by a point inside the sphere P

14. Measurement with Polarimeter • Device that measures the state of polarization • Test set-up: P

15. Measurement with Polarimeter • Result: P

16. Polarization maintaining fibers (PMF) • Manufactured with intentionally induced stress • The difference of the effective refractive indices for the two orthogonal field components is high •  small changes of the refractive indices can be neglected • Inportant: • Use linear polarized light • Correct azimuth orientation P

17. Polarization maintaining fibers (PMF) • The standard is to align the slow axis of the fiber with the connector key • There are also some other possibilities for alignment: • Slow axis • Fast axis • Specified by the costumer • Free P

18. Polarization maintaining fibers (PMF) • Extinction ratio • A PMF is only effective if linear polarized light is launched parallel to a main axis • A dimension for the quality of this coupling is the ER • If the ER is poor then either • The PMF has a poor polarization preserving capability • The alignment into the PMF is not optimal. P

19. Polarization maintaining fibers (PMF) • ER Measurement with Polarimeter • It uses an optimized algorithm • The recorded values during fiber stressing are used to fit a circle on the Poincaré sphere (Pancharatnam theorem) • The smaller the circle the higher is the ER P

20. Polarization maintaining fibers (PMF) • Measurement in the lab • I used a PMF from Optokon ER in datasheet: 25dB • How to stress the fiber? • By pulling the fiber -> unsuccessful • By heating the fiber -> successful P

21. Polarization maintaining fibers (PMF) • Measurement in the lab P

22. Polarization maintaining fibers (PMF) • Measurement in the lab P

23. Polarization controllers • The free-space optics approach • A classic polarization controller consisting of three rotatable wave plates • This approach have produced respectable results. P

24. Polarization controllers • The free-space optics approach • Disadvantages: • Collimating, aligning and refocusing are time consuming and labor intensive. • The wave plates and microlenses are expensive • High insertion loss • Sensitive to wavelength variations • Limited controller speed P

25. Polarization controllers • The fiber coil (mickey mouse ears) approach • An all-fiber controller based on this mechanism reduces the insertion loss and cost • Coiling the fiber induces stress, producing birefringence P

26. Polarization controllers • The fiber coil (mickey mouse ears) approach • The amount of birefringence is a function of: • The fiber cladding diameter • The spool diameter (fixed) • The number of fiber loops per spool • The wavelength of the light • Not a function of twisting the fiber paddles!! • The fast axis of the fiber is in the plane of the spool P

27. Polarization controllers • The fiber coil (mickey mouse ears) approach • Disadvantages: • Sensitive to wavelength variations • Limited controller speed • A bulky device (the fiber coils must remain large) • The use is primarily limited to laboratories P

28. Polarization controllers • The electro-optic waveguide approach • LiNbO3 based high-speed polarization controllers • Two voltages and the electro-optic effect determine the effective optical axis of each wave plate P

29. Polarization controllers • The electro-optic waveguide approach • Disadvantages: • High insertion loss • High polarization-dependent loss • High cost • Expensive and complicated implementation P

30. MeasurmentsonPolarization controllers • Polarisazation controller 1 (Thorlabs) • Based on the fiber coil approach • Consist of QWP, a HWP and a QWP • Measurement set-up: P

31. MeasurmentsonPolarization controllers • Results: • You can create all type’s of polarizations P

32. MeasurmentsonPolarization controllers • Polarisazation controller 2 (Fiberpro) • Based on the fiber coil approach • Consist of two QWP • You can create all type’s of polarizations P

33. Conclusion • Msc project is finished • Learned a lot about optics P

34. Thank you for your attention