Lasers operating at nanoscale Impact of quantum effects on coherence and dynamics

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

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

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

5. Cavity How to make such a laser Gain medium

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

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

8. What cavity 5 µm Micropillier Microdisques Cristaux photoniques sur membrane • Interferences in the pillar direction • Guided in plane • Guiding • Interferences in the membrane plane • Guiding effects in the perpendicular direction

9. Nanostructured laser cavities 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... Phys. Rev. Lett. 98, 043906 (2007) Univ Würzburg...

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

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

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

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

14. 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 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

15. 0,47 Pthres 1,0 0,69 Pthres 0,9 1,42 Pthres 0,8 1,9 Pthres Pumping Laser 4,76 Pthres 0,7 0,6 Normalised intensity (u.a.) 0,5 0,4 0,3 0,2 0,1 0 0 20 40 60 80 100 120 140 160 180 Time (ps) A threshold can still be defined even for =1 Threshold as change in the dynamics << Threshold >> Threshold X. Hachair et al, submitted

16. 5 µm Threshold as change in the dynamics Gain material Laser cavity InAs/GaAs QD Density ~ 1.5 x 1010 cm-2 Emission around 900 nm T ~ 4 K R. Braive et al. Opt. Lett. 34, 554 (2009)

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

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

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

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

21. Intensity (a.u.) 0 2 4 6 8 10 12 14 0 200 400 Time (ps) 600 800 10 GHz gain switched operation Long (movable) L Sample L S S  L  Short(Fixed) S Toward Streak camera Two pulses Two pulses First pump pulse Second pump pulse Intensity (a.u.) Intensity (a.u.) 0 2 4 6 8 10 12 0 2 4 6 8 10 12 14 14 0 0   200 200 400 400 Time (ps) Time (ps) 600 600 800 800 R. Braive et al. Opt. Lett. 34, 554 (2009)

22. 15 10 GHz 1rst excitation 2nd excitation 12,5 10 7,5 Intensity (u.a.) 19 dB 5 2,5 0 100 300 0 200 400 Time (ps) 10 GHz gain switched operation 104 103 102 Intensity (u.a.) 10 GHz 10 3 GHz 100 0 200 400 600 800 Time (ps) 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/cm2 per excitation pulse R. Braive et al. Opt. Lett. 34, 554 (2009)

23. 0 ps 400 ps 10 GHz gain switched operation 15 0,20 0,15 12.5 0,10 10 0,05 7.5 0,00 Intensity (a.u.) 5 -0,05 -0,10 2.5 -0,15 0 -0,20 0 100 200 300 400 Time (ps) R. Braive et al. Opt. Lett. 34, 554 (2009)

24. 0 ps 0 ps 0 ps 400 ps 400 ps 400 ps 10 GHz gain switched operation 15 0,20 0,15 12.5 0,10 10 0,05 7.5 Intensity (a.u.) 0,00 5 -0,05 -0,10 2.5 -0,15 0 -0,20 0 100 200 300 400 Time (ps) R. Braive et al. Opt. Lett. 34, 554 (2009)

25. 0 ps 400 ps 10 GHz gain switched operation 15 0,20 0,15 12.5 0,10 10 0,05 7.5 0,00 Intensity (a.u.) Relative wavelength shift (nm) 5 -0,05 -0,10 2.5 -0,15 0 -0,20 0 100 200 300 400 Time (ps) 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) R. Braive et al. Opt. Lett. 34, 554 (2009)

26. 15 10 GHz 1rst excitation 2nd excitation 12,5 10 7,5 Intensity (u.a.) 19 dB 5 2,5 0 100 300 0 200 400 Time (ps) 10 GHz gain switched operation QD lasing QW lasing (100GHz) QD lasing High quantum yield QW lasing Low quantum yield R. Braive et al. Opt. Lett. 34, 554 (2009) H. Altug et al. Nature 2, 484 (2006)

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

28. Going to 1.55µm. Everything must be re-designed Gain material Laser cavity InAsP/InP QD Density ~ 1.5 x 1010 cm-2 Emission around 1.55 µm Inhomogeneous ~ 145 nm T ~ 300 K R. Hostein et al.Appl. Phys. Lett94, 123101(2009)

29. Going to 1.55µm. Everything must be re-designed 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 7x107 to 3x1010 QDs/cm2 A. Michon et.al.J. Appl. Phys. 104, 043504 2008 D. Elvira et al.Appl. Phys. Lett 97, 131907 (2010)

30. Going to 1.55µm. Everything must be re-designed Quality factor Q  50000 <=> Photon lifetime  30 ps R. Hostein et al.Appl. Phys. Lett94, 123101(2009)

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

32. 8 10 7 10 6 10 5 10 4 10 3 10 2 10 1 10 0 10 -1 10 -2 10 How to define the threshold now ? Classical definition Gain = Loss Quantum definition Mean number of photons In the laser mode <n>=1 Statistical definition Second order coherence g(2)(0) Fano Factor F = <n>(g(2)(0)-1)+1 Sp emission 2 g(2)(0) Light-Out <n> St emission 1 0.0 0.5 1.0 1.5 2.0 0.1 1 10 0.1 1 10 Light-In Light-In Light-In Do these definitions always coincide ? Light-Out F N.J. Van Druten et al, Phys. Rev. A 62, 05308 (2000) 0.1 1 10 0.0 0.5 1.0 1.5 2.0 Light-In Light-In

33. How to define the threshold now ? g(2)(0) -1 Sp emission Light-Out St emission Class B 0.0 0.5 1.0 1.5 2.0 Light-In Class A 2 g(2)(0) 1 0.1 1 10 Light-In N.J. Van Druten et al, Phys. Rev. A 62, 05308 (2000)

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

35. 2ond order autocorrelation function g//=400 ps Gc=30 ps b=0.012

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

37. 2ond order autocorrelation function hand waving explanation gn=Gc/(n0+1) photonic damping (net damping rate of the loaded cavity) gN=g// (1+ b n0) atomic damping (net stabilisation of the inversion of the laser dynamics) High-b laser => lasing with a small number of photons => gn > gN => Non poissonian statistics even above threshold => Mesoscopic Laser Van Druten et.al. PRA 62, 053808 (2000) D. Elvira et.al. to be submitted

38. 15 10 GHz 1rst excitation 2nd excitation 12,5 10 7,5 Intensity (u.a.) 19 dB 5 2,5 0 100 300 0 200 400 Time (ps) Conclusion Defining the laser threshold as change in the dynamics High-speed modulation Room temperature telecom nanolaser, Defining lasing as g(2)(0)=1

39. Quelle cavité? Ingénierie de la courbe de dispersion dans un cristal photonique bi-dimensionnel a1 a2 0.255 0.245 Zone I a/ Zone I II Zone I 0.235 M M Confinement optique Zone II 0.225 Transmission 0.3 0.5 0.34 0.38 0.42 0.46 k Fréquence c/a2 From Ph. Lalanne et al Gap Espace réel • 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 ...