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symmetry breaking in a periodically layered medium Artur Hermans 1,2 - - PowerPoint PPT Presentation

Jul 24, 2023 414 likes •560 views

P HOTONICS R ESEARCH G ROUP InSpectra Second-harmonic generation based on symmetry breaking in a periodically layered medium Artur Hermans 1,2 , S. Clemmen 1,2 , E. Solano 3 , J. Dendooven 3 , E. Brainis 2,4 , C. Detavernier 3 and R. Baets 1,2 1

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SLIDE 1

PHOTONICS RESEARCH GROUP 1

PHOTONICS RESEARCH GROUP

Second-harmonic generation based on symmetry breaking in a periodically layered medium

Artur Hermans1,2, S. Clemmen1,2, E. Solano3, J. Dendooven3,

  • E. Brainis2,4, C. Detavernier3 and R. Baets1,2

1Photonics Research Group, UGent 2Center for Nano- and Biophotonics, UGent 3Conformal Coating of Nanomaterials Research Group, UGent 4Physics and Chemistry of Nanostructures Group, UGent

InSpectra

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SLIDE 2

PHOTONICS RESEARCH GROUP 2

Second order nonlinear optical effects

In linear optics: 𝐐 = ε0χ 1 𝐅 In nonlinear optics: 𝐐 = ε0χ 1 𝐅 + ε0χ 2 𝐅𝐅 + ε0χ 3 𝐅𝐅𝐅 + ⋯

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SLIDE 3

PHOTONICS RESEARCH GROUP 3

Second order nonlinear optical effects

In linear optics: 𝐐 = ε0χ 1 𝐅 In nonlinear optics: 𝐐 = ε0χ 1 𝐅 + ε0χ 2 𝐅𝐅 + ε0χ 3 𝐅𝐅𝐅 + ⋯

Second-harmonic generation (SHG), sum frequency generation (SFG), difference frequency generation (DFG), Pockels effect, ...

SHG SFG DFG

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SLIDE 4

PHOTONICS RESEARCH GROUP 4

Why do we need 2nd order nonlinear effects?

  • Wavelength conversion

E.g. optical parametric amplifiers/oscillators, frequency doubling in green laser pointers

  • Pockels effect → electro-optic modulator

http://www.armlaser.com/200mw-green-laser-light-match-p-44.html http://www.thorlabs.com/navigation.cfm?guide_id=2090 http://www.coherent.com/products/?930/Mira-OPO

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SLIDE 5

PHOTONICS RESEARCH GROUP 5

Research goal

Integrating 2nd order nonlinear devices on a silicon chip

http://www2.imec.be/be_nl/pers/persberichten/archief-2012/imecgenalyte.html

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SLIDE 6

PHOTONICS RESEARCH GROUP 6

BUT silicon and silicon nitride are not 2nd order materials

χ(2) = 0 in materials having inversion symmetry Solution? Break inversion symmetry

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SLIDE 7

PHOTONICS RESEARCH GROUP 7

BUT silicon and silicon nitride are not 2nd order materials

χ(2) = 0 in materials having inversion symmetry Solution? Break inversion symmetry

  • Inhomogeneous strain

in Si waveguides

  • Unknown symmetry breaking mechanism in SiN gives χ(2) ≠ 0

R S Jacobsen et al, Nature 441, 199 (2006) χ(2) ≈ 15 pm/V M Cazzanelli et al, Nat Mater 11, 148 (2012) χ(2) ≈ 40 pm/V

  • J S Levy et al, Opt Express 19, 11415 (2011): χ(2) ≈ 0.04 pm/V
  • T Ning et al, Appl Phys Lett 100, 161902 (2012): χ(2) ≈ 2.5 pm/V
  • A Kitao et al, J Phys D: Appl Phys 47, 215101 (2014): χ(2) ≈ 11.8 pm/V
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SLIDE 8

PHOTONICS RESEARCH GROUP 8

Interfaces break the inversion symmetry

Surface second-harmonic generation is used in surface science e.g. to study molecular adsorption

Y R Shen, Appl Phys B 68, 295 (1999)

Problem to use this in Si or SiN waveguides: weak effect, only close to interfaces

http://en.wikipedia.org/wiki/Second-harmonic_generation

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SLIDE 9

PHOTONICS RESEARCH GROUP 9

Use multiple interfaces to enhance χ(2) effects

Thin layers (~1 nm) fabricated by atomic layer deposition (ALD)

A Khanna et al, “Impact of ALD grown passivation layers on silicon nitride based integrated optic devices for very-near-infrared wavelengths,” Opt Express 22, 5684 (2014)

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SLIDE 10

PHOTONICS RESEARCH GROUP 10

First take a step back

  • 3 materials A = TiO2,

B = Al2O3 and C = In2O3 deposited sequentially: ABCABC...

  • Individual layer

thickness = 0.7 nm

  • ABAB... will not work

because of destructive interference

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SLIDE 11

PHOTONICS RESEARCH GROUP 11

First take a step back

  • C∞v symmetry
  • Nonvanishing tensor

components: χxxz = χxzx = χyyz = χyzy, χzxx = χzyy, χzzz

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SLIDE 12

PHOTONICS RESEARCH GROUP 12

Experimental setup for second-harmonic generation

fs laser

λ/2 longpass Rotation stage sample shortpass bandpass @490 nm Detector

V

980 nm, 100 fs, 80 MHz, 1.11 W average Parabolic mirror, f = 50.8 mm p polarization

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SLIDE 13

PHOTONICS RESEARCH GROUP 13

Experimental results

100 200 300 400 500 20 40 60 80

SH power (a.u.) Incidence angle (°)

0 nm 2.1 nm 25 nm 50 nm 75 nm χ 2

eff = sin 2φ cos Φ χxxz + cos φ 2 sin Φ χzxx + sin φ 2 sin Φ χzzz

Estimate main tensor component χzzz ≈ 0.4 pm/V

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SLIDE 14

PHOTONICS RESEARCH GROUP 14

Conclusions and future

  • Interfaces break the inversion symmetry
  • An ABCABC... layer sequence allows the second-harmonic

contributions generated at each of the interfaces to add up

  • Main tensor component χzzz of our TiO2-Al2O3-In2O3 composite

≈ 0.4 pm/V

  • Future work: second-harmonic generation in waveguides,

electro-optic modulation

We acknowledge K. Koskinen and M. Kauranen from Tampere University of Technology for their helpful advice