Transcript Dia 1 - wdm-vibrometry.pl

States of polarization of chosen
fiber elements
Supervisor: Prof K. Abramski
 Introduction
Table of contents
 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
Introduction
 Erasmusstudent from Belgium
 Finishing my studies Master in electronics
 Most interesting parts of my Msc project will be
explained
States of polarization
 Consider a monochromatic plane wave:
We describe the light by the transverse components of
its electric field:
States of polarization
 Light is linearly polarized if the field components Ex
and Ey oscillate in phase or 180° out of phase.
y
Ey
E
θ
Ex
x
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:
Ey
Ey
Ey
εy
εy E
εx
Ex
E
Ey
εx
Ex
Ex
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
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
Matrix representation of polarization states
 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
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
Geometrical interpretation of Stokes parameters
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
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
Measurement with Polarimeter
 Device that measures the state of polarization
 Test set-up:
Measurement with Polarimeter
 Result:
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
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
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.
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
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
Polarization maintaining fibers (PMF)
 Measurement in the lab
Polarization maintaining fibers (PMF)
 Measurement in the lab
Polarization controllers
 The free-space optics approach
A classic polarization controller consisting of three
rotatable wave plates
 This approach have produced respectable results.
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
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

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
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
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
Polarization controllers
 The electro-optic waveguide approach
 Disadvantages:
 High insertion loss
 High polarization-dependent loss
 High cost
 Expensive and complicated implementation
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:
Measurments on Polarization controllers
 Results:
 You can create all type’s of polarizations
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
Conclusion
 Msc project is finished
 Learned a lot about optics
Thank you for your attention