The physics of polarization optics
Polarized light propagation
Partially polarized light
Polarization Optics
N. Fressengeas
Laboratoire Mat´eriaux Optiques, Photonique et Syst`emes
Unit´e de Recherche commune `a l’Universit´e de Lorraine et `a Sup´elec
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N. Fressengeas
Polarization Optics, version 2.0, frame 1
The physics of polarization optics
Polarized light propagation
Partially polarized light
Further reading
A. Gerrard and J.M. Burch.
Introduction to matrix methods in optics.
Dover, 1994.
S. Huard.
Polarisation de la lumi`ere.
Masson, 1994.
N. Fressengeas
Polarization Optics, version 2.0, frame 2
The physics of polarization optics
Polarized light propagation
Partially polarized light
Course Outline
123
The physics of polarization optics
Polarization states Jones Calculus Stokes parameters and the Poincare Sphere
Polarized light propagation
Jones Matrices Examples Matrix, basis & eigen polarizations Jones Matrices Composition
Partially polarized light
Formalisms used Propagation through optical devices
N. Fressengeas
Polarization Optics, version 2.0, frame 3
The physics of polarization optics
Polarized light propagation
Partially polarized light
Jones Calculus Stokes parameters and the Poincare Sphere
The vector nature of light
Optical wave can be polarized, sound waves cannot
The scalar monochromatic plane wave
The electric field reads:
A cos (ωt − kz − ϕ)
A vector monochromatic plane wave
Electric field is orthogonal to wave and Poynting vectors Lies in the wave vector normal plane
Needs 2 components
Ex = Ax cos (ωt − kz − ϕx ) Ey = Ay cos (ωt − kz − ϕy )
N. Fressengeas
Polarization Optics, version 2.0, frame 4
The physics of polarization optics
Polarized light propagation
Partially polarized light
Jones Calculus Stokes parameters and the Poincare Sphere
Linear and circular polarization states
In phase components
ϕy = ϕx
π/2 shift
ϕy = ϕx π/2
π shift
ϕy = ϕx + π
Left or Right
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Polarization Optics, version 2.0, frame 5
The physics of polarization optics
Polarized light propagation
Partially polarized light
Jones Calculus Stokes parameters and the Poincare Sphere
The elliptic polarization state
The polarization state of ANY monochromatic wave
ϕy − ϕx = π/4
Electric field
Ex = Ax cos (ωt − kz − ϕx ) Ey = Ay cos (ωt − kz − ϕy )
4 real numbers
Ax ,ϕx Ay ,ϕy
2 complex numbers
Ax exp (ı˙ϕx ) Ay exp (ı˙ϕy )
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Polarization Optics, version 2.0, frame 6
The physics of polarization optics
Polarized light propagation
Partially polarized light
Stokes parameters and the Poincare Sphere
Polarization states are vectors
Monochromatic polarizations belong to a 2D vector space based on the Complex Ring
ANY elliptic polarization state
⇐⇒
Two complex numbers
A set of two ordered complex numbers is one 2D complex vector
Canonical Basis
ꢀꢁ ꢂ ꢁ ꢂꢃ
Polarization Basis
Two independent polarizations :
Crossed Linear
10
01
,
Reversed circular . . .
Link with optics ?
These two vectors represent two polarization states
YOUR choice
We must decide which ones !
N. Fressengeas
Polarization Optics, version 2.0, frame 7
The physics of polarization optics
Polarized light propagation
Partially polarized light
Stokes parameters and the Poincare Sphere
Examples : Linear Polarizations
Canonical Basis Choice
ꢁ ꢂ
10
: horizontal linear polarization
ꢁ ꢂ
0
: vertical linear polarization
1
Tilt
θ
- ꢁ
- ꢂ
cos (θ) sin (θ)
- Linear polarization Jones vector
- in a linear polarization basis
Linear Polarization : two in phase components
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Polarization Optics, version 2.0, frame 8
The physics of polarization optics
Polarized light propagation
Partially polarized light
Stokes parameters and the Poincare Sphere
Examples : Circular Polarizations
In the same canonical basis choice : linear polarizations
ϕy − ϕx = π/2
Electric field
Ex = Ax cos (ωt − kz − ϕx ) Ey = Ay cos (ωt − kz − ϕy )
Jones vector
- ꢁ
- ꢂ
1ı˙
1
2
√
N. Fressengeas
Polarization Optics, version 2.0, frame 9
The physics of polarization optics
Polarized light propagation
Partially polarized light
Stokes parameters and the Poincare Sphere
About changing basis
A polarization state Jones vector is basis dependent
Some elementary algebra
The polarization vector space dimension is 2 Therefore : two non colinear vectors form a basis Any polarization state can be expressed as the sum of two non colinear other states
Remark : two colinear polarization states are identical
Homework Find the transformation matrix between between the two following bases :
Horizontal and Vertical Linear Polarizations Right and Left Circular Polarizations
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Polarization Optics, version 2.0, frame 10
The physics of polarization optics
Polarized light propagation
Partially polarized light
Stokes parameters and the Poincare Sphere
Relationship between Jones and Poynting vectors
Jones vectors also provide information about intensity
- Choose an orthonormal basis
- (J1, J2)
Hermitian product is null : J1 · J2 = 0 Each vector norm is unity : J1 · J1 = J2 · J2 = 1
Hermitian Norm is Intensity
Simple calculations show that :
If each Jones component is one complex electric field component
The Hermitian norm is proportional to beam intensity
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Polarization Optics, version 2.0, frame 11
The physics of polarization optics
Polarized light propagation
Partially polarized light
Polarization states Jones Calculus
Stokes parameters and the Poincare Sphere
The Stokes parameters
A set of 4 dependent real parameters that can be measured
P0 P2
Overall Intensity
P0 = I
in a π/4 Tilted Basis
P2 = Iπ/4 − I
P1 P3
Intensity Diff´erence
P1 = Ix − Iy
in a Circular Basis
P3 = IL − IR
−π/4
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Polarization Optics, version 2.0, frame 12
The physics of polarization optics
Polarized light propagation
Partially polarized light
Polarization states Jones Calculus
Stokes parameters and the Poincare Sphere
Relationship between Jones and Stockes
Sample Jones Vector
ꢁ
4 dependent parameters
P02 = P12 + P22 + P32
ꢂ
Ax exp (+ı˙ϕ/2) Ay exp (−ı˙ϕ/2)
J =
P0 P2
Overall Intensity
P0 = I = A2x + A2y
P1
Intensity Difference
P1 = Ix − Iy = A2x − A2y
in a π/4 Tilted Basis
P3
in a Circular Basis
ꢂ
Jπ/4
=
ꢁ
Ax e+ı˙ϕ/2 − ı˙Ay e−ı˙ϕ/2
- ꢁ
- ꢂ
Ax e+ı˙ϕ/2 + Ay e−ı˙ϕ/2
−Ax e+ı˙ϕ/2 + Ay e−ı˙ϕ/2
π/4
1
2
√
√
JCir
=
Ax e+ı˙ϕ/2 + ı˙Ay e−ı˙ϕ/2
2
P3 = Jx · JCx ir − Jy · JCy ir
=
P2 = Jx · Jπx/4 − Jπy/4 · Jπy/4
=
- Cir
- Cir
2Ax Ay sin (ϕ)
2Ax Ay cos (ϕ)
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Polarization Optics, version 2.0, frame 13
The physics of polarization optics
Polarized light propagation
Partially polarized light
Polarization states Jones Calculus
Stokes parameters and the Poincare Sphere
The Poincare Sphere
Polarization states can be described geometrically on a sphere
Normalized Stokes parameters
(S1, S2, S3) on a unit radius sphere
Si = Pi /P0
Unit Radius Sphere
P
General Polarisation
3
i=1 Si2 = 1
Figures from [Hua94]
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Polarization Optics, version 2.0, frame 14
The physics of polarization optics
Matrix, basis & eigen polarizations Jones Matrices Composition
A polarizer lets one component through
Polarizer aligned with x : its action on two orthogonal polarizations
- ꢁ ꢂ
- ꢁ ꢂ
10
10
Lets through the linear polarization along x:
−→
- ꢁ ꢂ
- ꢁ ꢂ
01
00
Blocks the linear polarization along y :
−→
- x polarizer Jones matrix
- in this basis
- ꢁ
- ꢂ
1 0 0 0
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Polarization Optics, version 2.0, frame 15
The physics of polarization optics
Matrix, basis & eigen polarizations Jones Matrices Composition
A quarter wave plate adds a π/2 phase shift
- Birefringent material: n1 along x and n2 along y
- thickness e
Linear polarization along x: phase shift is ke = k0n1e Linear polarization along y: phase shift is ke = k0n2e
Jones matrix
ꢁ
in this basis
- ꢂ
- ꢂ
- ꢁ
- ꢂ
- ꢁ
eı˙k n e
0
0
10
0ı˙
10
0ı˙
- 0
- 1
= eı˙k n e
≈
- 0
- 1
eı˙k n e
2
0
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Polarization Optics, version 2.0, frame 16
The physics of polarization optics
Matrix, basis & eigen polarizations
Eigen Polarizations
Eigen polarization are polarizations that do not change upon propagation
Polarization unchanged
Eigen Vectors
λ ∈ C
v is an eigen vector
J and λJ describe the same polarization
M · v = λv ⇔
λ is its eigen value
Intensity changes
Handy basis
A matrix is diagonal in its eigen basis
Polarizer eigen basis is along its axes Bi-refringent plate eigen basis is along its axes
Homework Find the eigen polarizations for an optically active material that rotates any linear polarisation by an angle φ
N. Fressengeas
Polarization Optics, version 2.0, frame 17
The physics of polarization optics
Matrix, basis & eigen polarizations
A polarizer in a rotated basis
In its eigen basis
- ꢁ
- ꢂ
1 0 0 0
Eigen basis Jones matrix : Px =
When transmitted polarization is θ tilted
Change base through −θ rotation Transformation Matrix
- ꢁ
- ꢂ
cos (θ) − sin (θ)
R (θ) = sin (θ) cos (θ)
- ꢁ
- ꢂ
- ꢁ
- ꢂ
1 0 0 0 cos2 (θ) sin (θ) cos (θ) sin (θ) cos (θ) sin2 (θ)
- P (θ) = R (θ)
- R (−θ) =
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Polarization Optics, version 2.0, frame 18
The physics of polarization optics
Matrix, basis & eigen polarizations
Changing basis in the general case
Using the Transformation Matrix
If basis B1 is deduded from basis B0 by transformation P :
B1 = P B0
Jones Matrix is transformed using J1 = P−1 J0 P
- From linear to circular
- example
Optically Active media in a linear basis : cos (φ) sin (φ)
- ꢁ
- ꢂ
J =
− sin (φ) cos (φ)
- ꢁ
- ꢂ
1
I
1
−ı˙
Transformation Matrix to a circular basis P =
- ꢁ
- ꢂ
eı˙φ
0
e−ı˙φ
P
−1MP =
0
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Polarization Optics, version 2.0, frame 19
The physics of polarization optics
Matrix, basis & eigen polarizations
Anisotropy can be linear and circular
Linear Anisotropy
Orthogonal eigen linear polarizations
Circular Anisotropy
Orthogonal eigen Circular polarizations
- Different index n1 & n2
- Different index n1 & n2
Eigen Jones Matrix
ꢁ
Eigen Jones Matrix
- ꢁ
- ꢂ
- ꢂ
- 1
- 0
- 1
- 0
- 0 eı˙θ
- 0 eı˙θ