1. Lasers operating at nanoscale Impact of quantum effects on coherence and dynamics PhD R. Hostein (now Paris 6) R. Braive (now LPN) D. Elvira A. Lebreton B. Fain Post-Doc X. Hachair (now industry) Permanent I. Robert-Philip I. Sagnes I. Abram A. Beveratos S. Barbay G. Beaudoin L. Le Gratiet JC Girard

2. P. 2 Moores Law of laser size ? O. Painter et.al. Science 284, 1819 (1999) Joannopoulos Research Group at MIT Optical interconnects Miniaturized lasers Physics of small lasers ? RT operation ? Telecoms operation ?

3. P. 3 Outline Introduction Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, coherence properties Conclusion

4. P. 4 What size ? Nano-world 0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm 100 µm Visible Infra-Red UltraViolet Miniature laser Microprocesseur Nanotransistor (CNRS/LPA) Transistor (Intel)

5. P. 5 How to make such a laser Gain medium Cavity

6. P. 6 What gain material Semiconductors Quantum Wells Quantum Dots Bulk material Dye molecules Wavelength (nm) Aborption/Emission (un. arb.) Aborption Emission QD InAs/GaAs – G. Patriarche (CNRS-LPN) 10 nm 3 – 50 nm -- -- Conduction band InAsPInP -- Energy x,y, z Valence band

7. P. 7 What cavity o Bragg Mirrors o Photonic Crystals cc Total internal reflexion Guiding effects Propagation in a periodic medium Interferences

8. P. 8 What cavity MicropillierMicrodisquesCristaux photoniques sur membrane Interferences in the pillar direction Guided in plane Guiding Interferences in the membrane plane Guiding effects in the perpendicular direction 5 µm

9. P. 9 Nanostructured laser cavities Phys. Rev. Lett. 98, 043906 (2007) Univ Würzburg... Phys. Rev. Lett. 96, 127404 (2006) Appl. Phys. Lett. 91 031108 (2007) Opt. Lett. 35, 1154 (2010) UCSB, Univ. Stanford, Caltech, Univ. Tokyo, Univ. Yokohama, CNRS-LPN...

10. P. 10 Plasmonic nanolasers Nature 461, 629 (2009) X. Zhang, Berkeley Nature 460, 1110 (2009) M. Noginov, Univ. Norfolk Nature 461, 604 (2009) Optics Express 17, 11107 (2009) Nature Photonics, (2010) Y. Fainman, Univ. San Diego

11. P. 11 Why so much fuss ?  factor of spontaneous emission in the laser mode β = Spontaneous emission in the laser mode Total spontaneous emission Laser mode Other modes In classical lasers  < 10 -5 and generally neglected In nanolasers lasers  > 10 -2 cannot be neglected In free space (emission rate  0 ) In a cavity (emission rate ) (Purcell factor)

12. P. 12 When  → 1 Yamamoto, Phys. Rev. A 50, 1675 (1992) Light-in (a.u.) Light-out (a.u.) Towards a thresholdless laser → ie does it always lase ? (and what does it mean)

13. P. 13 Outline Introduction Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, coherence properties Conclusion

14. P. 14 Threshold as change in the dynamics  No threshold = no difference between the 2 regimes in the number of photons, but different in the populations X. Hachair et al, submitted PRA Spontaneous only  photons are emited from the mode and N(t) slow Stimulated All photons are emitted from the laser mode And N(t) evolves quickly

15. P. 15 Threshold as change in the dynamics X. Hachair et al, submitted 020406080100120140160180 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 Normalised intensity (u.a.) Time (ps) 0,47 P thres 0,69 P thres 1,42 P thres 1,9 P thres 4,76 P thres Pumping Laser << Threshold>> Threshold A threshold can still be defined even for  =1

16. P. 16 Threshold as change in the dynamics Laser cavity Gain material InAs/GaAs QD Density ~ 1.5 x 10 10 cm -2 Emission around 900 nm T ~ 4 K R. Braive et al. Opt. Lett. 34, 554 (2009) 5 µm

17. P. 17 Threshold as change in the dynamics X. Hachair et al, submitted InAs/GaAS QD laser at 4K

18. P. 18 Outline Introduction Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, coherence properties Conclusion

19. P. 19 High-speed modulation Coldren & Corzine, Diode Lasers and Photonic Integrated Circuits, Wiley Series TransmitterReceiver …011010010… TbTb In optical communications High-speed modulation only possible with an important number of photons in the cavity

20. P. 20 Why nanolasers should be fast : A simple model  =10 -5  =10 -1 It takes time to have >1 photon in the mode >1 photon is obtained very rapidly Rapid Turn on In a cavity (emission rate ) Return to empty state, fast recovery

21. P. 21 10 GHz gain switched operation 0 200 400 600 800 024681012 14 Intensity (a.u.) Time (ps) 02468101214 Intensity (a.u.) 0 200 400 600 800 Time (ps)  Short (Fixed) Long (movable) LS S L  L S  Toward Streak camera Sample First pump pulseSecond pump pulse Two pulses  02468101214 Intensity (a.u.) 0 200 400 600 800 Time (ps) R. Braive et al. Opt. Lett. 34, 554 (2009)

22. P. 22 10 GHz gain switched operation Modulation rate of at least 10 GHz with quantum dots Build-up time of 50 ps, a maximum of 20 GHz rep rate expected 10 µJ/cm 2 per excitation pulse 0200400600800 Intensity (u.a.) Time (ps) 10 0 10 10 2 10 3 10 4 3 GHz 10 GHz 0200400 2,5 5 7,5 10 12,5 15 Intensity (u.a.) Time (ps) 10 GHz 19 dB 0 100 300 1 rst excitation 2 nd excitation R. Braive et al. Opt. Lett. 34, 554 (2009)

23. P. 23 10 GHz gain switched operation R. Braive et al. Opt. Lett. 34, 554 (2009) 0 ps 400 ps 0100200300400 0 2.5 5 7.5 10 12.5 15 -0,20 -0,15 -0,10 -0,05 0,00 0,05 0,10 0,15 0,20 Intensity (a.u.) Time (ps)

24. P. 24 10 GHz gain switched operation R. Braive et al. Opt. Lett. 34, 554 (2009) 0 ps 400 ps 0 ps 400 ps 0 ps 400 ps 0100200300400 0 2.5 5 7.5 10 12.5 15 -0,20 -0,15 -0,10 -0,05 0,00 0,05 0,10 0,15 0,20 Intensity (a.u.) Time (ps)

25. P. 25 10 GHz gain switched operation Same chirp behaviour as for single pulse excitation, even at high modulation  Recovery time faster than 100 ps  Same compensation for every pulse → possible down-to 11ps  100 Mhz/ps chirp →  H =3.5 (let's discuss after) 0 ps 400 ps 0100200300400 0 2.5 5 7.5 10 12.5 15 -0,20 -0,15 -0,10 -0,05 0,00 0,05 0,10 0,15 0,20 Intensity (a.u.) Time (ps) Relative wavelength shift (nm) R. Braive et al. Opt. Lett. 34, 554 (2009)

26. P. 26 10 GHz gain switched operation 0200400 2,5 5 7,5 10 12,5 15 Intensity (u.a.) Time (ps) 10 GHz 19 dB 0 100 300 1 rst excitation 2 nd excitation QD lasing QW lasing (100GHz) R. Braive et al. Opt. Lett. 34, 554 (2009) H. Altug et al. Nature 2, 484 (2006) QD lasing High quantum yield QW lasing Low quantum yield

27. P. 27 Outline Introduction Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, coherence properties Conclusion

28. P. 28 Going to 1.55µm. Everything must be re-designed Laser cavity Gain material InAsP/InP QD Density ~ 1.5 x 10 10 cm -2 Emission around 1.55 µm Inhomogeneous ~ 145 nm T ~ 300 K R. Hostein et al. Appl. Phys. Lett 94, 123101 (2009)

29. P. 29 Going to 1.55µm. Everything must be re-designed A. Michon et.al. J. Appl. Phys. 104, 043504 2008 D. Elvira et al. Appl. Phys. Lett 97, 131907 (2010) Stransky-Krastanov growth of InAsP/InP quantum dots Lattice mismatch : 3 % Wavelength emission : from 1.2 µm to 2.3 µm Quantum dots density : from 7x10 7 to 3x10 10 QDs/cm 2

30. P. 30 Going to 1.55µm. Everything must be re-designed R. Hostein et al. Appl. Phys. Lett 94, 123101 (2009) Quality factor Q  50000 Photon lifetime  30 ps

31. P. 31 Demonstration of room temperature operation R. Hostein et al. Opt. Lett. 35, 1154 (2010) CW RT operationPulsed RT operation

32. P. 32 How to define the threshold now ? Classical definition Gain = Loss Quantum definition Mean number of photons In the laser mode =1 Statistical definition Second order coherence g (2) (0) Fano Factor F = (g (2) (0)-1)+1 0.0 Light-Out 0.51.01.52.0 Light-In Sp emission St emission 0.1110 Light-In Light-Out 0.1110 Light-In 10 -2 10 10 0 1 2 3 4 5 6 7 8 0.1110 Light-In g (2) (0) 1 2 0.0 F 0.51.01.52.0 Light-In Do these definitions always coincide ? N.J. Van Druten et al, Phys. Rev. A 62, 05308 (2000)

33. P. 33 How to define the threshold now ? 0.0 Light-Out 0.51.01.52.0 Light-In Sp emission St emission N.J. Van Druten et al, Phys. Rev. A 62, 05308 (2000) Class A Class B g (2) (0) -1 0.1110 Light-In g (2) (0) 1 2

34. P. 34 2ond order autocorrelation function R. Hostein et al. Opt. Lett. 35, 1154 (2010) SNSPD (stop) SNSPD (start) Filter Sample N.A. 0,4; x20 SSPD : Superconducting single photon detector

35. P. 35 2ond order autocorrelation function  // =400 ps  c =30 ps  =0.012

36. P. 36 2ond order autocorrelation function hand waving explanation Spontaneous emission Stimulated emission Long transition region

37. P. 37 2ond order autocorrelation function hand waving explanation Van Druten et.al. PRA 62, 053808 (2000) D. Elvira et.al. to be submitted  n =  c /(n 0 +1) photonic damping (net damping rate of the loaded cavity)  N =  // (1+  n 0 ) atomic damping (net stabilisation of the inversion of the laser dynamics) High-  laser => lasing with a small number of photons =>  n >  N => Non poissonian statistics even above threshold => Mesoscopic Laser

38. P. 38 Conclusion Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, Defining lasing as g (2) (0)=1 0200400 2,5 5 7,5 10 12,5 15 Intensity (u.a.) Time (ps) 10 GHz 19 dB 0 100 300 1 rst excitation 2 nd excitation

39. P. 39 Quelle cavité? Ingénierie de la courbe de dispersion dans un cristal photonique bi- dimensionnel 0.255 0.245 0.235 0.225 0.3 0.34 0.380.420.46 0.5 k Zone I Zone II From Ph. Lalanne et al Fréquence c/a 2 a1a1 a2a2 Espace réel Gap Transmission Confinement optique Zone I II M M Sur Si : S. Noda et al, Nat. Mater 4, 207 (2005); T. Asano et al, Opt. Express} 14 (2006) 1996… Sur GaAs : E. Weidner et al, Appl. Phys. Lett. 89 (2006) 221104; R. Herrmann et al, Opt. Lett. 31 (2006) 1229... a/