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Applicazioni Fotonica 4: Photonic enhancement in emission

Applicazioni Fotonica 4: Photonic enhancement in emission. QDs light emitters: what next?. Increase the repetition rate Increse the emission efficiency Electrical injection GaAs QDs on Si subtrates. Photonics. Relazione NF e FF Diffrazione Kirchhoff. Different Diffraction Geometry.

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Applicazioni Fotonica 4: Photonic enhancement in emission

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  1. Applicazioni Fotonica 4: Photonic enhancement in emission

  2. QDs light emitters: what next? • Increase the repetition rate • Increse the emission efficiency • Electrical injection • GaAs QDs on Si subtrates Photonics

  3. Relazione NF e FF Diffrazione Kirchhoff

  4. Different Diffraction Geometry We wish to find the light electric field at large distance r after diffraction Observation sphere Near filed E(x,y) y1 y R P1 x x1 P r E(q,f) This region is assumed to be much smaller than this one. Incident wave What is E(q,f) at a distance r from the center of the plane of NF

  5. Diffraction Solution on a generic FF surface The field in the observation surface (x1,y1,z1), is given by where:

  6. Fresnel limit We have to approximate the phase where is a constant for a spherical surface The important point is that |x-x1|/z1, |y-y1|/z1are always smaller than 1. .

  7. Fraunhofer limit We have to approximate the phase where is a constant for a spherical surface where are the polar angles The important point is that x1/r, y1/r are always smaller than 1. To be more precise ka2/r<<2p or a2/lr<<1 (a2/lr is the Fresnel number) This formulation holds also for large angles.

  8. Fraunhofer limit Then We can write this result in terms of the off-axis k-vector components: and:

  9. a2/lr1 a2/lr>>1 a2/lr<1 r Far field=FT(NF) Fresnel diffraction Near field

  10. Aumento del rate radiativo In cavità Effetto Purcell Nel vuoto Fattore di Purcell Confronto

  11. Q factor in planar cavities

  12. Q factor in planar cavities R R dI dI dI dI Per massimizzare il Q factor si deve ridurre le perdite della cavità

  13. Photonic crystal heterostructures cavities PBG

  14. Photonic crystal heterostructures cavities

  15. Photonic crystal heterostructures cavities

  16. Efficienza di estrazione

  17. Predicting the FF from the NF Near field is localized within the photonic defect and it has a spatial modulation equal to the lattice constant

  18. d 2r0 a 2r Cosa stiamo facendo al LENS: Simultaneous engineering of Q & the angular pattern

  19. d 2r0 a 2r High extraction & directionality FF Best Q Engineering of Q r=109 nm d=28 nm

  20. d 2r0 a 2r High extraction & directionality FF Q=25000 h0.5=3 h0.3=1.6 Q=20000 h0.5=12 h0.3=6.5 Q=15000 h0.5=20 h0.3=10 Simultaneous engineering of Q & the angular pattern r=109 nm d=28 nm r=101 nm d=28 nm r=101 nm d=34 nm

  21. Vantaggi MC Microcavità 1. Controllo direzionalità di emissione, aumento efficienza di estrazione 2. Effetto Purcell, aumento rate di emissione

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