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
Electromagnetic interference
• Electromagnetic energy from different sources will interfere when sharing the same space
101
jeEE
202
jeEE
)21(021
jtot eEEEE
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
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
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
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
Broadband incident radiation
Narrowband transmitted radiation wavelength
amplitude
λ0
Tunable Fabry Perot cavity based spectrometer
Practical tunable Fabry Perot cavity
Support layer
Reflecting mirrorsMetal electrodes
•Provides mechanical support
•Transparent to incident radiation
•Effect electrostatic actuation•Form Fabry Perot cavity
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
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)
Different designs
Corrugated support structure to improve flatness
Flat support structure
Mechanical displacement of support layer
FEM multiphysics simulations
Mechanical displacement of corrugated support layer
FEM multiphysics simulations
Top view of deflected top mirror
Top view of deflected support layer
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
Mechanical displacement of flat support layer
Top view of deflected top mirror
Top view of deflected support layer
FEM multiphysics simulations
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
Tunable Fabry Perot cavity based microspectrometer
(computer generated model showing support layer)
Mechanical displacement Mises stresses due to displacement
Tunable Fabry Perot cavity based microspectrometer
(computer generated model showing metal surfaces)