Polarization independent microsecond electro-optic switch Mohammad - PowerPoint PPT Presentation

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 22/05/2015 22 May 2015 - Mons, Belgium

Content  Chiral nematic Liquid Crystals (CLCs)  Photonic band gap tuning  Partly Polymerized CLC  Electro-optic switch 2 of 17 Mohammad MohammadiMasoudi 22/05/2015

What are CLCs? • Chiral nematic Liquid Crystals • Nematic Liquid Crystal:  Anisotropic: n o & n e  Large electro-optic coeff. 3 of 17 Mohammad MohammadiMasoudi 22/05/2015

Chiral nematic LC? Director direction Rotation of LC molecules like a screw 360 ° over pitch P Helix axis Refractive index change period P/2 Pitch Distributed Bragg Reflector High reflection band- photonic bandgap or PBG 4 of 17 Mohammad MohammadiMasoudi 22/05/2015

Properties of CLC • High reflection for: Pn o Pn e    Pn Pn o e For circular polarized light Right handed CLC: Left handed CLC: Director direction Right handedness Helix axis ½ Pitch Left handedness Left Right 5 of 17 Mohammad MohammadiMasoudi 22/05/2015

Why PBG tuning? 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 6 of 17 Mohammad MohammadiMasoudi 22/05/2015

History Significant efforts have been devoted using external stimuli such as:  Elasticity [4]  Heat [1]  Electricity [3]  Light [2] 1-*Huang, Y. H.; Zhou, Y.; Doyle, C.; Wu, S. T. Optics Express 2006, 14 , 1236-1242 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 7 of 17 Mohammad MohammadiMasoudi 22/05/2015

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 8 of 17 Mohammad MohammadiMasoudi 22/05/2015

Our method for tuning PBG Polymerized CLC with nanopores of LC Nanopores: mixture ne, no Nanopores: only n o Pattern with mixture of reactive LC, non-reactive LC, chiral dopant and photoinitiator 9 of 17 Mohammad MohammadiMasoudi 22/05/2015

A macroscopic photograph of the device with 1 × 1 cm active region Good transmission for white light without scattering in the visible region 10 of 17 Mohammad MohammadiMasoudi 22/05/2015 which is usually not the case for polymer-CLC composites

To control the size of pores: Transmission spectra of the devices with 4 µm thickness 1- Concentration of nematic LC 2- UV dose 40 w% 50 w% • • Threshold voltage : 90 V/µm Threshold voltage : 65 V/µm • • Blue shift : 141 nm Blue shift : 114 nm 11 of 17 Mohammad MohammadiMasoudi 22/05/2015

Schematic drawing of the device operation to modulate unpolarized incident light. V L R 0% Incident light 50% 50% λ /2-plate PPCLC 1 PPCLC 2 Detector 12 of 17 Mohammad MohammadiMasoudi 22/05/2015

Transmission spectra of the device  4 µm thickness Contrast ratio: 5 13 of 17 Mohammad MohammadiMasoudi 22/05/2015

Transmission spectra of thicker device  8 µm thickness Contrast ratio: 20 14 of 17 Mohammad MohammadiMasoudi 22/05/2015

The response time Block wave electric field: 150 V/µm amplitude and 1 kHz  50 µs and 20 µs for on and off state 15 of 17 Mohammad MohammadiMasoudi 22/05/2015

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 16 of 17 Mohammad MohammadiMasoudi 22/05/2015

Acknowledgment Jeroen Beeckman, KristiaanNeyts 17 of 17 Mohammad MohammadiMasoudi 22/05/2015

Than ank k yo you f u for or yo your ur atte tention ntion 18 of 17 Mohammad MohammadiMasoudi 22/05/2015