Selected applications of polarization interferometry · in which the state of polarization (SOP) of...
Transcript of Selected applications of polarization interferometry · in which the state of polarization (SOP) of...
Selected applications of polarization
interferometry
Faculty of Electronics, Telecommunication and Informatics
Paweł Wierzba
June 2nd, 2017
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Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
What is polarization interferometry
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One may read (or hear):
Polarization interferometers are ones in which the two
coherent beams required for interference are produced
from a single source by means of a birefringent beam-
splitter, i.e. use is made of the separation of the E and
O rays.
OR
Polarization interferometry is a branch of optical
interferometry investigating and using interferometers
in which the state of polarization (SOP) of interfering
beams is controlled and stable.
What is polarization interferometry
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Polarization interferometry is a branch of optical
interferometry investigating and using interferometers
in which additional information is obtained from the
state of polarization (SOP) of interfering beams.
What is polarization interferometry
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First polarization interferometer: Jamin 1868,
First polarization microinterferometer
or polarization microscope: Lebedeff 1930,
Jamin, M. J.; Sur un refracteur differentiel pour la lumiere
polarisee; Comptes Rendus Acad.Sc. Paris,
67, 814 (1868).
Lebedeff, M. A. A.; L’interferometre a polarisation at ses
applications; Revue d’Opt., 9, 385 (1930).
What is polarization interferometry
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Polarization interferometry has been the subject of
intense research.
Its scope of applications has steadily increased.
At present the research is concentrated on using
new materials and new states of polarization.
Polarization interferometers employ
several specific birefringent components
and use
dedicated detection setups.
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Components
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Specific birefringent components:
Waveplates (retarders)
Polarizers
Polarization BeamSplitters (PBS)
Prisms (e.g. Wollaston Prism)
... othersPBS
Components
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Wollaston Prism Can act as a polarizing beamsplitter (large ε)
Can produce interference fringe field (small ε)
WP
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Beware of Polarization
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Beware of Polarization? Why?
E2
E1
E2E1
E2
E1
Because interference depends on
the SOPs of interfering beams
Always check if there is any
potential for problems in your setup
Beware of Polarization
12A, B, Δ – Full description of the SOP
SOP – State Of
Polarization
Classical fully polarized wave
Beware of Polarization
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Poincare sphere for
visualization
Classical fully polarized wave – Poincare sphere
Beware of Polarization
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1) SOP changes slowly, compared to the optical
carrier frequency.
2) SOP is constant in the cross-section of a beam.
Classical fully polarized wave
Polarization modes in optical fibers
Vectorial vortex beams
Femtosecond lasers
Beware of Polarization
Fast-changing SOPLocal SOP fitting
Beware of Polarization
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Fast-changing SOP Local SOP fitting can
be performed
Beware of Polarization
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Fast-changing SOP Local SOP fitting cannot
be performed
Beware of Polarization
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Beams with SOP varying in the crossection
Generation of these beams – later
Beware of Polarization
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Laguerr-Gauss
vector beams
New Journal of Physics 9(2007) 78
(http://www.njp.org/)
Beware of Polarization
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‘Ultimate disaster’ – a full Poincare beam
A Full Poincare Beam,
contains in its cross-
section each SOP on the
Poincare sphere
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Liquid Crystals and Other Exotic Materials
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1) Liquid Crystals (LCs),
2) Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
3) Photo-alignment materials,
Liquid Crystals and Other Exotic Materials
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Liquid Crystals (LCs)
LCs consist of anisotropic molecules
electrical anisotropy
optical anisotropy
LCs can be aligned:
using electric or magnetic field
by confining them between pre-treated
surfaces
Liquid Crystals and Other Exotic Materials
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Liquid Crystals (LCs) – key textures
planar
homeotropic
splayed
tilted
Liquid Crystals and Other Exotic Materials
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LCs can be used to make birefringent optical
components
Waveplates
Wollaston prisms
Main problems
LCs remain liquid (must be confined)
Thicker layers (xx µm) are difficult to align
Liquid Crystal
Glass substrate
Liquid Crystals and Other Exotic Materials
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Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
Liquid Crystalline Polymers (LCPs) are Liquid
Crystals whose molecules have reactive
(polymerisable) group on both ends
LCPs can be aligned on a pre-treated surface
Liquid Crystals and Other Exotic Materials
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Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
The same textures as LCs
Under UV illumination polymerization takes place
and a solid birefringent layer is formed
Liquid Crystals and Other Exotic Materials
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Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
λ/4 Waveplate made from RM
AR Coating
Beamsplitter
No need for confinement
= simpler components
Better integration
of optical setups
is possible
ReactiveMesogen
Glass substrate
Liquid Crystals and Other Exotic Materials
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Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
Retardation control:
Birefringence adjustment (temperature)
Process adjustment (composition, ω)
Liquid Crystals and Other Exotic Materials
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Liquid Crystalline Polymers (LCPs),
Reactive Mesogens (RMs)
Quarter-wave plate
between
crossed polarizers
Liquid Crystals and Other Exotic Materials
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Photo-alignment materials (for LCs and LCPs)
Direction of
orientation
corresponds to the
direction of the UV
radiation polarization
Liquid Crystals and Other Exotic Materials
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Vector Vortex Waveplates
N. Murakami, Opt. Expr. Vol. 21, no. 6 pp. 7400-7410
Liquid Crystals and Other Exotic Materials
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Vector Vortex Waveplates
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Polarization interferometers
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Displacement measurement interferometer
BS – Beamsplitter, WP – Wollaston Prism, L1, L2 – Lens,
DS – detection setup, M1 – Measurement Mirror,
M2 – Reference Mirror.
Beam displacer
can be used
instead of the
Wollaston prism
Polarization interferometers
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Displacement measurement interferometer
Twice as sensitive as Michelson interferometer
Can be used for pressure measurement
Polarization interferometers
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Wavelength measurement
Problem:
Fast high-resolution measurement of wavelength emitted by
a tunable semiconductor laser
The wavelength is known to some accuracy,
The laser linewidth is narrow,
High absolute accuracy is not always needed,
Polarization interferometers
38Juncar P and Pinard J, Rev. Sci. Instrum. 53, 939 (1982)
Wavelength measurement: solution
Polarization interferometers
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lN 0
0
212
l
2
lN
0
0
22
Wavelength measurement: solution
Polarization interferometers
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Wavelength measurement: solution
Polarization interferometers
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Problem: λ/8 waveplate
We can make it from LCP
Polarization interferometers
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Phase contrast microscopy
Polarization interferometers
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Phase contrast microscopy
CCD/
CMOS
detector
array
M. Pluta. Advanced Light Microscopy. Vol. 1-3, Elsevier 1989-93
Polarization interferometers
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Phase contrast microscopy
Image of an
LED surface
Laser as a
light source?
Polarization interferometers
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… Qualitative Phase Measurement techniques
Polarization interferometers
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Vector Vortex coronagraph
N. Murakami, Opt. Expr. Vol. 21, no. 6 pp. 7400-7410
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Detection setups
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Detection Setups
Detection setups convert phase difference of output
beams into one or more intensity signals
Photodetectors convert these signals to electric domain
Electric signals are processed and fed to the output(s)
Detection setups
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In many instances we can select
‘the best’ detection setup
Detection Setups or ‘Mix and Match’
Detection setups
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BS
w2
WP1
D2
D4
i -D4 iD3
WP2
QWPHWP
i -D2 iD1
D1
D3
wi
w1
wd1 wd2
wd3
wd4
cos2
12 rtSPii WPiDD
sin2
34 ttSPii WPiDD
Detection setups
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Detectors
Fringe pattern on detectors
AnalyserA
Beams frominterferometer
Nomarski prismNP
Beam expander
BE
α
This setup can work also with a broadband source
Detection setups
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Phase measurement range can cover 100s fringes
Detectors
Fringe pattern on detectors
AnalyserA
Beams frominterferometer
Nomarski prismNP
Beam expander
BE
α
Outline
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Introduction,
What is polarization interferometry?
Components,
Beware of Polarization,
Liquid Crystals and Other Exotic Materials,
Polarization interferometers,
Detection setups,
Conclusions,
Conclusions
Some components, e.g. waveplates, can be reliably
and inexpensively made from Liquid Crystal Polymers
Its scope of application has been expanding, due to
important that this technique provides
Polarization interferometry is a measurement
technique providing high performance solutions
Further research on materials, components and
setups will result in new devices and applications.
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Price of components specific to this technique limits
its scope of applications
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