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Polarization independent microsecond electro-optic switch Mohammad Mohammadimasoudi, Jungsoon Shin, Keechang Lee, Kristiaan Neyts,Jeroen Beeckman 18th Annual Workshop of the IEEE Photonics Benelux Chapter 1 of 17 Mohammad MohammadiMasoudi

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Mohammad MohammadiMasoudi 22/05/2015

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Polarization independent microsecond electro-optic switch

Mohammad Mohammadimasoudi, Jungsoon Shin, Keechang Lee, Kristiaan Neyts,Jeroen Beeckman

18th Annual Workshop of the IEEE Photonics Benelux Chapter

22 May 2015 - Mons, Belgium

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Content

  • Chiral nematic Liquid Crystals (CLCs)
  • Photonic band gap tuning
  • Partly Polymerized CLC
  • Electro-optic switch
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  • Chiral nematic Liquid Crystals
  • Nematic Liquid Crystal:

What are CLCs?

 Anisotropic: no & ne  Large electro-optic coeff.

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Chiral nematic LC?

Refractive index change period P/2

Distributed Bragg Reflector

Pitch Helix axis Director direction

Rotation of LC molecules like a screw 360° over pitch P

High reflection band- photonic bandgap or PBG

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Properties of CLC

  • High reflection for:

For circular polarized light

  • e

Pn Pn   

Pno Pne

½ Pitch Helix axis Director direction Left handedness Right handedness Left Right

Right handed CLC: Left handed CLC:

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Important for applications: change the wavelength of transmission/reflection/lasing devices

  • sensors
  • diffraction gratings
  • reflective displays
  • tunable lasers
  • Optical shutter

Useful for

  • photonic information technology
  • lab-on-a-chip devices

Why PBG tuning?

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History

1-*Huang, Y. H.; Zhou, Y.; Doyle, C.; Wu, S. T. Optics Express 2006, 14, 1236-1242

Significant efforts have been devoted using external stimuli such as:

  • Light [2]
  • Elasticity [4]
  • Electricity [3]
  • Heat [1]

2-White, T. J.; Bricker, R. L.; Natarajan, L. V.; Tondiglia, V. P.; Bailey, C.; Green, L.; Li, Q. A.; Bunning, T. J. Opt. Commun. 2010, 283, 3434-3436 3- Choi, S. S.; Morris, S. M.; Huck, W. T. S.; Coles, H. J. Adv. Mater. 2009, 21, 3915 4-Finkelmann, H.; Kim, S. T.; Munoz, A.; Palffy-Muhoray, P.; Taheri, B. Adv. Mater. 2001, 13, 1069

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History

Almost all CLC devices show: slow response (~ms) small tuning range Tuning by changing the pitch Direct electronic control of the PBG is relatively hard because:

  • Non-uniform deformation of the periodic structure
  • Disruption of The Bragg reflection
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Pattern with mixture of reactive LC, non-reactive LC, chiral dopant and photoinitiator

Our method for tuning PBG

Polymerized CLC with nanopores of LC

Nanopores: mixture ne, no Nanopores: only no

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A macroscopic photograph of the device with 1×1 cm active region

Good transmission for white light without scattering in the visible region which is usually not the case for polymer-CLC composites

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To control the size of pores:

1- Concentration of nematic LC 2- UV dose

Transmission spectra of the devices with 4 µm thickness

50 w% 40 w%

  • Threshold voltage : 90 V/µm
  • Blue shift : 141 nm
  • Threshold voltage : 65 V/µm
  • Blue shift : 114 nm
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Schematic drawing of the device operation to modulate unpolarized incident light.

Incident light

R

V

50%

L

50% 0% Detector PPCLC 1 PPCLC 2 λ/2-plate

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Transmission spectra of the device 4 µm thickness Contrast ratio: 5

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Transmission spectra of thicker device 8 µm thickness Contrast ratio: 20

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The response time

Block wave electric field: 150 V/µm amplitude and 1 kHz

 50 µs and 20 µs for on and off state

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Conclusions

Fast (20 µs) polarization-independent optical switch wavelength range of the switching is 50 nm High stability and reflectivity No degradation or disruption Reproducible switching Easy fabrication, low cost

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Acknowledgment

Jeroen Beeckman, KristiaanNeyts

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Mohammad MohammadiMasoudi 22/05/2015

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Than ank k yo you f u for

  • r yo

your ur atte tention ntion