fabry perot cavity based microspectrometer aamer mahmood donald p. butler ph.d. department of...
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Fabry Perot cavity based microspectrometer
Aamer MahmoodDonald P. Butler Ph.D.
Department of Electrical EngineeringUniversity of Texas at Arlington, TX 76019
Sponsored by the National Science Foundation
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Electromagnetic interference
• Electromagnetic energy from different sources will interfere when sharing the same space
101
jeEE
202
jeEE
)21(021
jtot eEEEE
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Electromagnetic interference
• Interference depends on the phase of each component
0 2 4 6 8 102
1
0
1
21.938
1.936
sin x( )
sin x .5( )
sin x( ) sin x 0.5( )
100 x
101
jeEE
202
jeEE
21 EEEtot
Constructive
interference
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A Fabry Perot cavity creates multiple sources with different phase from a single
source
)3(33
xxjeEE
x
jxeEE 0
Incident radiation
Transmitted radiation)( xnxj
nn eEE
Reflecting surface
Reflecting surface
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Interference due to a Fabry Perot cavity
• The inter-reflector spacing determines the phase of the transmitted energy
• For maximum constructive interference
• For maximum destructive interference
2)12(
nx...3,2,1,0n
nx ...3,2,1n
wavelength
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Fabry Perot cavity based spectrometer
• For an inter reflector spacing of , the transmitted radiation will add constructively at
Broadband incident radiation
Narrowband transmitted radiation
x
x
)12(
2
n
x ...3,2,1,0n
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Broadband incident radiation
Narrowband transmitted radiation wavelength
amplitude
λ0
Tunable Fabry Perot cavity based spectrometer
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Practical tunable Fabry Perot cavity
Support layer
Reflecting mirrorsMetal electrodes
•Provides mechanical support
•Transparent to incident radiation
•Effect electrostatic actuation•Form Fabry Perot cavity
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Design Considerations
• Optical transmission through support layer– Investigated by measurements
• Mechanical displacement of support layer– Investigated by multiphysics FEM simulations
• Mechanical strength of support layer– Investigated by multiphysics FEM simulations
• Flatness of reflecting mirror during deflection– Investigated by multiphysics FEM simulations
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Optical transmission through support layer
• Optical transmission through the support layer is to be measured
• The complex permittivity of the support material has been extracted using Variable angle spectrometery
0
1
2
3
4
5
6
-1
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40
'
"
Wavelength(m)
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Different designs
Corrugated support structure to improve flatness
Flat support structure
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Mechanical displacement of support layer
FEM multiphysics simulations
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Mechanical displacement of corrugated support layer
FEM multiphysics simulations
Top view of deflected top mirror
Top view of deflected support layer
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Flatness of displaced reflecting mirror
(corrugated structure)
-1.3
-1.28
-1.26
-1.24
-1.22
-1.2
-1.18
-1.16
0 50 100 150 200
radial distance from center (um)
def
lect
ion
(u
m)
bottom left-top right
bottom right_top left
-10123456789
0 50 100 150 200radial distance (um)
% d
efle
ctio
n
bottom left-top right
bottom right-top left
FEM multiphysics simulations
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Mechanical displacement of flat support layer
Top view of deflected top mirror
Top view of deflected support layer
FEM multiphysics simulations
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Flatness of displaced reflecting mirror
(flat structure)
-1.43-1.42-1.41-1.4
-1.39-1.38-1.37-1.36-1.35-1.34-1.33-1.32
0 50 100 150 200
radial distance from center (um)
def
lect
ion
(u
m)
bottom left-top right
bottom right_top left
-1
0
1
2
3
4
5
6
7
0 50 100 150 200
radial distancefrom center (um)%
de
fle
cti
on
bottom left-top right
bottom right-top left
FEM multiphysics simulations
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Tunable Fabry Perot cavity based microspectrometer
(computer generated model showing support layer)
Mechanical displacement Mises stresses due to displacement
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Tunable Fabry Perot cavity based microspectrometer
(computer generated model showing metal surfaces)