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Polarization-Insensitive Liquid-Crystal Fabry-Perot Tunable Optical Filter. T. Kataoka , S. E. Day, D. R. Selviah, A. Fern á ndez Department of Electronic and Electrical Engineering University College London, U.K. Content - PowerPoint PPT Presentation
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1
T. Kataoka, S. E. Day, D. R. Selviah, A. FernándezDepartment of Electronic and Electrical EngineeringUniversity College London, U.K.
Polarization-Insensitive Liquid-Crystal Fabry-Perot Tunable Optical Filter
Content
1. Motivation and Aim 2. LC-FPF with Extra Birefringent layers ● A Single Quarter-Wave Plate (QWP) ● A Pair of Quarter-Wave Plates (QWPs) 3. Conclusion
2
Dependence on Polarization States
LC-FPF for Optical Fiber Communication Systems
Electrically tunable filter with low voltage
Wide Tuning Range 60 nm ( = Free Spectral Range, FSR) (M. W. Maeda., et al, Bellcore, 1990)
Narrow Band (Full Width of Half Maximum, FWHM) 0.17 – 0.35 nm ( = 21.23 – 43.70 GHz) (K. Hirabayashi., et al, NTT, 1991)
Advantage
Problem
3
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
To
tal
tra
ns
mit
ted
in
ten
sit
y
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
Unpolarized incident light, 9 dielectric layer mirror, LC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm) design λ = 1550 nm
Transmission Spectra of a Conventional LC-FPF with Variable Birefringence of LC
S P P Sne
no ne none
4
Aim
LC-FPF Insensitive
to Input Polarization
Design & Optimization
Coinciding Two Sets of Orthogonal
Polarization Peaks
Attempt
Tuning PeaksAt the Same Rate
LC-FPF with Extra
BirefringentLayers
Solution
5
Two Types of LC-FPFs with Extra Birefringent Layers
Transmitted Intensity
Output PolarizationProperties
Calculation and Analysis
LC-FPF with A single QWP
LC-FPF with A pair of QWPs
Structure
LC is homogeneously aligned nematic
6
Structure of LC-FPF with a Single QWP in the Cavity
Incident light
Reflected light
Transmitted light
Polarization parallelto the optic axis of LC
Polarization normalto the optic axis of LC
Quarter-wave plate
The optic axis of LC
LC layer
Dielectric mirrors
ITOITO
Alignment layer
AR coatSubstrate
Y
XZ
~A.C
7
Transmission Spectra of LC-FPF with a Single QWP in the Cavity
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
Tota
l tra
nsm
itted
inte
nsity
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
Unpolarized incident light, 9 dielectric layer mirror QWP (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nmLC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm)
ne12 nm
8
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
Tra
ns
mit
ted
in
ten
sit
y
1.70(45)1.70(-45)1.69(45)1.69(-45)1.68(45)1.68(-45)1.67(45)1.67(-45)1.66(45)1.66(-45)1.65(45)1.65(-45)1.64(45)1.64(-45)1.63(45)1.63(-45)1.62(45)1.62(-45)1.61(45)1.61(-45)1.60(45)1.60(-45)
Polarized Transmission Spectra of LC-FPF with a Single QWP with a +45º / -45º Polariser
Unpolarized incident light, 9 dielectric layer mirrorQWP (no=1.50, ne=1.70, first-order), LC layer (HWP, no=1.50, ne=1.70, second-order)
+45º -45º +45º -45º +45º -45º
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
ne
9
Polarization parallel to the optic axis of LC
Polarization normal to the optic axis of LC
Structure of LC-FPF with a Pair of QWPs in the Cavity
Transmitted light
Incident light
Reflected light Crossed Quarter-wave plates
The optic axis of LC
Y
X Z
10
Transmission Spectra of LC-FPF with Two QWPs in the Cavity
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
Tota
l tra
nsm
itted
inte
nsity
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nmLC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm)
ne
11
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
Tra
ns
mit
ted
in
ten
isty 1.70(45)
1.70(-45)1.69(45)1.69(-45)1.68(45)1.68(-45)1.67(45)1.67(-45)1.66(45)1.66(-45)1.65(45)1.65(-45)1.64(45)1.64(-45)1.63(45)1.63(-45)1.62(45)1.62(-45)1.61(45)1.61(-45)1.60(45)1.60(-45)
Polarized Transmission Spectra of LC-FPF with a Pair of QWPs with a +45º / -45º Polariser
Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order), LC layer (HWP, no=1.50, ne=1.70, second-order)
+45º -45º +45º -45º -45º +45º+45º -45º ne
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
12
Transmitted light
Incident light
Reflected light Crossed Quarter-wave plates
The optic axis of first QWP
+45ºY
+45ºXZ
+45º / -45º Linearly Polarized Incident Beam Traveling Through LC-FPF Filter
LC layer (HWP)
The optic axis of second QWP
13
Cause for Splitting of Peaks of LC-FPF with a Pair of QWPs
+45º / -45º polarization encounters
only either the fast or the slow axis
of the QWPs
Two different sets of peaks
The optical path differencebetween the polarizations
the integral multiple to the incident wavelength
No splitting peakAt 1550 nm
No longer the integral multiple
when the birefringence of LC is changed
Started splitting
14
Transmission Spectra of LC-FPF with Two QWPs in the Cavity
0
0.5
1
1.5
2
2.5
3
1500 1510 1520 1530 1540 1550 1560 1570 1580
Wavelength (nm)
Tota
l tra
nsm
itted
inte
nsity
1.70
1.69
1.68
1.67
1.66
1.65
1.64
1.63
1.62
1.61
1.60
Unpolarized incident light, 9 dielectric layer mirror, QWPs (no=1.50, ne=1.70, first-order = 9.69 μm), design λ = 1550 nmLC layer (HWP, no=1.50, ne=1.70, second-order = 19.38 μm)
ne
15
Cause for Splitting of Peaks of LC-FPF with a Pair of QWPs
+45º / -45º polarization encounters
only either the fast or the slow axis
of the QWPs
Two different sets of peaks
The optical path differencebetween the polarizations
the integral multiple to the incident wavelength
No splitting peakAt 1550 nm
No longer the integral multiple
when the birefringence of LC is changed
Started splitting
16
Conclusion
Acknowledgements
LC-FPF with a single QWP
All peaks tuned by external electric field with unpolarized incident light
Spectrometer for Gas sensing systems.
LC-FPF with a pair of QWPs
Polarization-insensitive operation
A tuning range of 7 nm at near 1550 nm.
A Splitting of peaks caused by the birefringence of QWPs.
K. Wang in the Optical Devices and Systems Group, UCL.
SID, IEE, EPSRC, UCL Graduate School for Travel Grants.
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