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

Table of contents  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 P

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

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

States of polarization  Light is linearly polarized if the field components Ex and Ey oscillate in phase or 180° out of phase. P

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

Matrix representation of polarization states  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

Matrix representation of polarization states  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

Matrix representation of polarization states  The Stokes parameters  S 0 measures the total intensity of the beam  S 1 gives the extent by which the intensity of horizontal polarization exceeds the intensity of vertical polarization in the beam  S 2 determines the excess of the intensity of +45°- polarization over the intensity of -45°-polarization  S 3 estimates the excess of the intensity of right circularly polarized light of the intensity of left circularly polarized light P

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

Geometrical interpretation of Stokes parameters P

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

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

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

Measurement with Polarimeter  Result: P

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

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

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

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

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

Polarization maintaining fibers (PMF)  Measurement in the lab P

Polarization maintaining fibers (PMF)  Measurement in the lab P

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

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

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

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

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

Polarization controllers  The electro-optic waveguide approach  LiNbO 3 based high-speed polarization controllers  Two voltages and the electro-optic effect determine the effective optical axis of each wave plate P

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

Measurments on Polarization controllers  Polarisazation controller 1 (Thorlabs)  Based on the fiber coil approach  Consist of QWP, a HWP and a QWP  Measurement set-up: P

Measurments on Polarization controllers  Results:  You can create all type’s of polarizations P

Measurments on Polarization controllers  Polarisazation controller 2 (Fiberpro)  Based on the fiber coil approach  Consist of two QWP  You can create all type’s of polarizations P

Conclusion  Msc project is finished  Learned a lot about optics P

Thank you for your attention