1. Examen cours Cristaux Photoniques Mechanical tuning of Photonic Crystals July 23, 2009 Fabio Jutzi PhD student EDMI Ecole Polytechnique Fédérale de Lausanne Sensors, Actuators and Microsystems Laboratory EPFL STI IMT SAMLAB Rue Jaquet Droz 1 CH-2002 Neuchâtel, Switzerland Phone: +41 32 720 55 20 fabio.jutzi@epfl.ch

2. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 2 Outline Tuning of Photonic Crystals Mechanical Tuning concepts Examples: –Changing periodicity of crystal –Applications in Displays –Waveguide switch with switching slab –Wavelength-selective variable-reflection filter –Actuator inserting defects –Waveguide switch using evanescent interaction Conclusion

3. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 3 Tuning of photonic crystals (PhC) Electro-optic effect Thermo-optic effect Non-linear optic effect Index-modulation –Surface acoustic waves –Liquid crystals Mechanical tuning

4. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 4 Mechanical tuning concepts Changing the periodicity of the Photonic Cristal (PhC) Introducing defects Approaching material (evanescent coupling) Changes the PhCs optical transmission characteristic Using electrostatic actuated mechanics (e.g. MEMS) Applications: Optical switches Display systems Tunable filter Sensor (when measuring the change in transmission)

5. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 5 Changing periodicity of crystal Si pillars (white cylinders) embedded in flexible polymer (PDMS) Stretched using comb-drive actuators W. Park, J-B. Lee, Mechanically tunable photonic crystal structure, Appl. Phys. Lett., vol. 85, nr. 21, 2004, pp. 4845-4847 Numerical modeling using FDTD method No elongation 5% stretched 10% stretched

6. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 6 Applications for Displays (1) Self-assembled silica spheres on ITO electrode Polymer-solution infiltrated between spheres Increase of lattice constant with solven swelling red-shift of reflected light Solvent and ions are pushed electrolyticly into the lattice (fully reversible with reverse potential) A. Arsenault, D. Puzzo, I. Manners, G. Ozin, Photonic-crystal full-colour display, Nature photonics, vol. 1, 2007 pp. 468-472

7. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 7 Applications for Displays (2) A. Arsenault, D. Puzzo, I. Manners, G. Ozin, Photonic-crystal full-colour display, Nature photonics, vol. 1, 2007 pp. 468-472

8. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 8 Waveguide switch with switching slab (1) SOI-wafer: –203nm device layer = waveguide + beam thickness –3µm oxide layer = gap between substrate and electrode When potential is applied between electrodes, slab is pushed down and waveguide is interrupted K-I. Umemori, Y. Kanamori, K. Hane, Photonic crystal waveguide switch with a microelectromechanical actuator, Appl. Phys. Lett. 89, 021102 (2006) SEM picture

9. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 9 Waveguide switch with switching slab (2) Introducing holes in the slab lowers the transmission at off state Lowest transmission at ~400nm displacement higher transmission lower transmission

10. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 10 Wavelength-selective variable-reflection filter (1) For free-standing PhC-slab light is coupled by guided resonance (at resonance wavelength) giving 100% reflectance Evanescent coupling to substrate when moving the slab Y. Kanamori, T. Kitani, K. Hane, Control of guided resonance in a photonic crystal slab using microelectromechanical actuators, Appl. Phys. Lett. 90, 031911 (2007) Theoretical investigations: W. Suh, M. Yanik, O. Solgaard, S. Fan, Displacement-sensitive photonic crystal structures based on guided resonance in photonic crystal slabs, Appl. Phys. Lett., vol. 82, nr. 13, 2003, pp. 1999-2001

11. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 11 Wavelength-selective variable-reflection filter (2) Y. Kanamori, T. Kitani, K. Hane, Control of guided resonance in a photonic crystal slab using microelectromechanical actuators, Appl. Phys. Lett. 90, 031911 (2007) At gap > 5µm, resonant wavelength = 1545nm Reflective filter with a theoretical spectral bandwidth of 0.38nm can be obtained SOI-wafer with sputtered NiCr as bimorph actuator Decrease of reflectivity for gaps smaller than 500nm

12. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 12 Actuator inserting defects (1) PhC line-defect waveguide with air holes blocking incident light Actuator pulls rod (of same material as PhC) into holes incident light is transmitted Transmission efficiency depends on number of air holes Y. Kanamori, K. Inoue, K. Horie, K. Hane, Photonic crystal switch by inserting nano-crystal defects using MEMS actuator, Proceedings of the 2003 IEEE/LEOS International Conference on Optical MEMS Waikoloa, HI, USA, August 18–21 (2003), pp. 107–108

13. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 13 Actuator inserting defects (2) PhC on SOI-wafer LPCVD poly-Si cantilever with SiO2 as sacrificial spacer-layer Actuation by voltage between Cr-layer on cantilever and substrate No experimental measurements shown Y. Kanamori, K. Inoue, K. Horie, K. Hane, Photonic crystal switch by inserting nano-crystal defects using MEMS actuator, Proceedings of the 2003 IEEE/LEOS International Conference on Optical MEMS Waikoloa, HI, USA, August 18–21 (2003), pp. 107–108

14. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 14 Waveguide switch using evanescent interaction (1) Line-defect waveguide Dielectric plate above the waveguide interacts with evanescent field depending on distance S. Iwamoto, S. Ishida, Y. Arakawa, M. Tokushima, A. Gomyo, H. Yamada, A. Higo, H. Toshiyoshi, H. Fujita, Observation of micromechanically controlled tuning of photonic crystal line-defect waveguide, Appl. Phys. Lett. 88, 011104 (2006) SEM micrograph Microscope picture

15. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 15 Waveguide switch using evanescent interaction (2) SOI-wafer (200nm device layer, 600nm oxide) e-beam patterned 1µm poly-Si on 300nm sacrificial oxide patterned as moving plate In 5µm interaction length 10dB extinction is realized Compared to conventional waveguide: group velocity in PhC smaller (shorter interaction length needed) S. Iwamoto, S. Ishida, Y. Arakawa, M. Tokushima, A. Gomyo, H. Yamada, A. Higo, H. Toshiyoshi, H. Fujita, Observation of micromechanically controlled tuning of photonic crystal line-defect waveguide, Appl. Phys. Lett. 88, 011104 (2006) Wavelength of 1568nm with highest transmission chosen Response time ~1.5ms

16. Examen Photonic Crystals Course Fabio Jutzi – July 23, 2009 16 Conclusion Different concept studies for mechanical tuning of PhC were shown Not all are fabricated and completely measured There is still lot to be done and optimized Combining MEMS technology with PhC is very promising Different possible applications: –Optical switch –Optical switchable filter –Display systems