Examen cours Cristaux Photoniques

Mechanical tuning of Photonic Crystals

July 23, 2009

Fabio JutziPhD 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

Examen Photonic Crystals CourseFabio 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

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Tuning of photonic crystals (PhC)

• Electro-optic effect

• Thermo-optic effect

• Non-linear optic effect

• Index-modulation

– Surface acoustic waves

– Liquid crystals

• Mechanical tuning

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Mechanical tuning concepts

• Changing the periodicity of the Photonic Cristal (PhC)

• Introducing defects

• Approaching material (evanescent coupling)

Changes the PhC’s optical transmission characteristic Using electrostatic actuated mechanics (e.g. MEMS)

Applications:

• Optical switches

• Display systems

• Tunable filter

• Sensor (when measuring the change in transmission)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 micrographMicroscope picture

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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

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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