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www-g.eng.cam.ac.uk/cosmos COSMOS is a Basic Technology Research Grant funded by the EPSRC, EP/D04894X Photonic band gap tuning in chiral nematic LCs S. S. Choi 1 , S.M. Morris 1 , W.T.S. Huck 2 , H.J. Coles 1 1 Centre of Molecular Materials for Photonics and Electronics (CMMPE), Department of Engineering, University of Cambridge 2 Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge The Concept 0 5 10 15 20 0 10 20 30 40 A verage sw itching angle, av (D eg) E lectric F ield (V m -1 ) Further reading: S.S. Choi, S. M. Morris, W.T.S. Huck, H.J. Coles, Appl. Phys. Lett, 91 , pp.231110(1)-231110(3), (2007). L. Komitov, B. Helgee, J. Felix, A. Matharu, Appl. Phys. Lett. 86, 023502 (2005) The Command Surfaces Results – Bandgap tuning • Continuous control of the PBG due to the in-plane rotation of the command surfaces. • Fine tuning using both frequency and electric field strength variation. Fig.1. Schematic of the cell structure and the wavelength tuning mechanism using electrically commanded surface of an FLC Fig.2. Continuous gold stone mode switching of the FLC material. Fig.4. (Right) Tuning results of the photonic band gap (PBG) using electrically commanded FLC surfaces. (a) The PBG as a function of electric field strength at a constant frequency of 1 kHz; (b) The PBG as a function of frequency at a constant electric field amplitude of 20.8 Vμm -1 at 25 o C; (c) The long-photonic band edge ( L ) as a function of electric field strength at different frequencies; (d) Comparison of the shift of the PBG for no, single, and dual command surfaces with a constant electric field of 20.8Vμm -1 at 1kHz. Fig.3. (Above) Average switching angle as a function of electric field strength. E-O FF E-O N Rubbing direction Rubbing direction ITO Polyimide Polyimide ITO G lass G lass FLC surface Bulk N *LC ( ε<0) FLC surface E-O FF E-O N Rubbing direction Rubbing direction ITO Polyimide Polyimide ITO G lass G lass FLC surface Bulk N *LC ( ε<0) FLC surface 1 2 3 4 5 1 2 34 5 Increase E-field strength (c) (d) 500 550 600 650 40 50 60 70 80 90 100 T ransm ittance (% ) W avelength (nm ) 0 V m -1 7.5 V m -1 15.7 V m -1 20.8 V m -1 (a) 500 550 600 650 40 50 60 70 80 90 100 T ransm ittance (% ) W avelen gth (n m ) O FF 5 kH z 3 kH z 1 kH z 400 H z (b) 0 5 10 15 20 590 595 600 605 610 615 L ong-P B E (nm ) E lectric F ield (V m -1 ) 1 kH z 2 kH z 3 kH z 4 kH z 5 kH z 500 550 600 650 30 40 50 60 70 80 90 100 2 1 3 T ransm ittance (% ) W avelen gth (n m ) 1 O N :N o FLC surface 2 O N :S ingle FL C surface 3 O N :D ualFLC surfaces (c) (d) 500 550 600 650 40 50 60 70 80 90 100 T ransm ittance (% ) W avelength (nm ) 0 V m -1 7.5 V m -1 15.7 V m -1 20.8 V m -1 (a) 500 550 600 650 40 50 60 70 80 90 100 T ransm ittance (% ) W avelen gth (n m ) O FF 5 kH z 3 kH z 1 kH z 400 H z (b) 0 5 10 15 20 590 595 600 605 610 615 L ong-P B E (nm ) E lectric F ield (V m -1 ) 1 kH z 2 kH z 3 kH z 4 kH z 5 kH z 500 550 600 650 30 40 50 60 70 80 90 100 2 1 3 T ransm ittance (% ) W avelen gth (n m ) 1 O N :N o FLC surface 2 O N :S ingle FL C surface 3 O N :D ualFLC surfaces • Passive switching mechanism of the chiral nematic liquid crystal (N*LC). • Rotation of molecules at the surface generate a pitch contraction of the helix. • Continuous gold stone mode switching of a ferroelectric liquid crystal (FLC). • 100nm thick coated FLC layers at the glass substrates. • FLC layers respond to electric fields resulting in an in-plane rotation.
description
1. 5. 2. 3. 4. 5. 4. 3. 1. 2. Increase E-field strength. Photonic band gap tuning in chiral nematic LCs S. S. Choi 1 , S.M. Morris 1 , W.T.S. Huck 2 , H.J. Coles 1 - PowerPoint PPT Presentation
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www-g.eng.cam.ac.uk/cosmos
COSMOS is a Basic Technology Research Grant funded by the EPSRC, EP/D04894X
Photonic band gap tuning in chiral nematic LCsS. S. Choi 1, S.M. Morris 1, W.T.S. Huck 2, H.J. Coles 1
1 Centre of Molecular Materials for Photonics and Electronics (CMMPE),Department of Engineering, University of Cambridge
2 Melville Laboratory for Polymer Synthesis, Department of Chemistry, University of Cambridge
The Concept
0 5 10 15 200
10
20
30
40
Ave
rage
switc
hing
ang
le, av
(Deg
)Electric Field (Vm-1)
Further reading: S.S. Choi, S. M. Morris, W.T.S. Huck, H.J. Coles, Appl. Phys. Lett, 91 , pp.231110(1)-231110(3), (2007).L. Komitov, B. Helgee, J. Felix, A. Matharu, Appl. Phys. Lett. 86, 023502 (2005)
The Command Surfaces
Results – Bandgap tuning• Continuous control of the PBG due to the in-plane rotation of the command surfaces.
• Fine tuning using both frequency and electric field strength variation.
Fig.1. Schematic of the cell structure and the wavelength tuning mechanism using electrically commanded surface of an FLC
Fig.2. Continuous gold stone mode switching of the FLC material.
Fig.4. (Right) Tuning results of the photonic band gap (PBG) using electrically commanded FLC surfaces.
(a) The PBG as a function of electric field strength at a constant frequency of 1 kHz;
(b) The PBG as a function of frequency at a constant electric field amplitude of 20.8 Vμm-1 at 25oC;
(c) The long-photonic band edge (L) as a function of electric field strength at different frequencies;
(d) Comparison of the shift of the PBG for no, single, and dual command surfaces with a constant electric field of 20.8Vμm-1 at 1kHz.
Fig.3. (Above) Average switching angle as a function of electric field strength.
E-OFF E-ON
Rubbing direction
Rubbing direction
ITOPolyimide
Polyimide
ITOGlass
Glass
FLC surface
Bulk N*LC(ε<0)
FLC surface
E-OFF E-ON
Rubbing direction
Rubbing direction
ITOPolyimide
Polyimide
ITOGlass
Glass
FLC surface
Bulk N*LC(ε<0)
FLC surface
1 2 3 4 5
12 3 4
5
Increase E-field strength
(c) (d)
500 550 600 65040
50
60
70
80
90
100
Tran
smitt
ance
(%)
Wavelength (nm)
0 Vm-1
7.5 Vm-1
15.7 Vm-1
20.8 Vm-1
(a)
500 550 600 65040
50
60
70
80
90
100
T
rans
mitt
ance
(%)
Wavelength (nm)
OFF 5 kHz 3 kHz 1 kHz 400 Hz
(b)
0 5 10 15 20590
595
600
605
610
615
Lon
g-PB
E (n
m)
Electric Field (V m-1)
1 kHz 2 kHz 3 kHz 4 kHz 5 kHz
500 550 600 65030
40
50
60
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100
2 13
Tra
nsm
ittan
ce (%
)
Wavelength (nm)
1 ON:No FLC surface 2 ON:Single FLC surface 3 ON:Dual FLC surfaces
(c) (d)
500 550 600 65040
50
60
70
80
90
100
Tran
smitt
ance
(%)
Wavelength (nm)
0 Vm-1
7.5 Vm-1
15.7 Vm-1
20.8 Vm-1
(a)
500 550 600 65040
50
60
70
80
90
100
T
rans
mitt
ance
(%)
Wavelength (nm)
OFF 5 kHz 3 kHz 1 kHz 400 Hz
(b)
0 5 10 15 20590
595
600
605
610
615
Lon
g-PB
E (n
m)
Electric Field (V m-1)
1 kHz 2 kHz 3 kHz 4 kHz 5 kHz
500 550 600 65030
40
50
60
70
80
90
100
2 13
Tra
nsm
ittan
ce (%
)
Wavelength (nm)
1 ON:No FLC surface 2 ON:Single FLC surface 3 ON:Dual FLC surfaces
• Passive switching mechanism of the chiral nematic liquid crystal (N*LC).
• Rotation of molecules at the surface generate a pitch contraction of the helix.
• Continuous gold stone mode switching of a ferroelectric liquid crystal (FLC).
• 100nm thick coated FLC layers at the glass substrates.
• FLC layers respond to electric fields resulting in an in-plane rotation.
