Quantum- dot based nonlinear source of THz radia5on

Transcription

1 Quantum- dot based nonlinear source of THz radia5on A. Andronico a, J. Claudon b, M. Munsch b, I. Favero a, S. Ducci a, J. M. Gérard b, and G. Leo a a Univ Paris Diderot, MPQ Lab, CNRS- UMR 7162, Paris, France b CEA- CNRS, SP2M, Grenoble, France

2 Outline Mo5va5on Concept and design Fabrica5on and preliminary characteriza5on Conclusion 2

3 State of the art and mo5va5on Microwaves THz IR ν (Hz) λ (µm) Main THz CW sources today Photomixing: P max ~100 nw at 1 THz, 1 nw at 2 THz QCLs: Low- temperature opera5on (Coherent detec5on) Provide a cw electrically pumped THz emi8er opera9ng at 300K 3

4 THz NL sources based on GaAs waveguides K. L. Vodopyanov, Y. H. Ave5syan Op5cal THz wave genera5on in a planar GaAs waveguide Op5cs Le[ers 33, 2314 (2008) A. Marandi, T. E. Darcie, P. P. M. So Design of a cw tunable THz source using waveguide- phase- matched GaAs Opt. Expr. 16, (2008) Z. Ruan, G. Veronis, K. L. Vodopyanov, M. M. Fejer, S. Fan Enhancement of op5cs- to- THz conversion efficiency by metallic slot waveguides Opt. Express 17, (2009) Passive devices 4

5 An electrically pumped THz NLO source Intracavity DFG based on a dual- λ mid- IR QCL 33.7THz THz = 5.2THz 8.9 µm 10.5 µm 60 µm Belkin et al., Nature Photon. 1, 288 (2007) Belkin et al., APL 92, (2008) Pflügl et al., APL 93, (2008) Geiser et al., Opt. Express 18, 9900 (2010) Gain competition IR lasing on high-order lateral modes Pulsed operation 7µW at 80K 1µW at 250K 300nW at 300K Doping FCA in the THz High waveguide losses (250 cm -1 ) Short coherence length (50-80 µm) Surface emission 5

6 Outline Mo5va5on Concept and design Fabrica5on and preliminary characteriza5on Conclusion 6

7 DFG in an ac5ve WGM microcavity A. Andronico et al., Opt. LeY. 21, 2416 (2008) Relative Mode Intensity Au R Al x Ga 1-x As Al AlAs y Ga 1-y As GaAs w h Au m = 10 p = 1 Al AlAs y Ga 1-y As Embedded InAs QDs m = 10 p = 2 1 Q = 1 Q + 1 r Q + m x (µm) 0.9 µm h = 6 µm w = 0.3 µm R = 40 µm Al x Ga 1-x As 70 µm AlyGa1-yAs AlyGa1-yAs AlGaAs AlGaAs! 7

8 Former idea 4 µm diameter pillar T=14K Y.- R. Nowicki- Bringuier et al., OPEX 15, (2007) 8

9 WGM DFG in (100) GaAs: χ (2) and phase matching (2) d 14 " # xyz 2 TE and 1 TM fields! QD laser pumps ω 1 ω 2 TE x y THz DFG field ω 3 TM x y! 1) Automatic QPM in (100) GaAs WGMs Y. Dumeige et al., PRA, 74, (2006) z z 2) Anomalous dispersion V. Berger, C. Sirtori, Semicon. Sci. Technol. 19, 964 (2004)! ( 2 " ) eff # cos( 2$ ) Refractive index Reststrahlen band Wavelength (µm) 9

10 Design constraints TPA Limits max power at ω 1 and ω 2 Induces FCA Decreases when Al % increases χ (2) Goes to zero around 5.1 THz in GaAs Decreases when Al % increases α THz Avoid ternary AlGaAs alloys Stay away from Restrahlen band 10

11 Sample device (passive/ac5ve) Phase- matched DFG between 1 and 4 THz, with pump Pump wavelengths between 1280 and 1320 nm 2R 500nm 500nm 2.5 µm 400 nm 2.5 µm h 1 W h 2 Au AlGaAs 80% AlGaAs 32% AlGaAs 80% Au GaAs 11

12 Calculated performances - Q p = Q p = Q p = 10 4 R H W λ 1 m 1 λ µm 5 µm 400 nm 1293 nm nm Output m 2 λ µm (3.69 THz) m 3 η /W (for Q p = 10 5, before satura5on onset) 12

13 Outline Mo5va5on Concept and design Fabrica5on and preliminary characteriza5on Conclusion 13

14 Plasma etched high- Q WGM resonators Fabrication of high-q (~10 5 ), large diameter (> 10 µm) microresonators UV/Electron-beam lithography + plasma etching (ECR/ICP) (a) (b) 10 µm 5 µm 14

15 Characteriza5on of passive resonators Experimental setup sample λ 1 +λ 2 λ 1 λ 2 Near- IR injec9on THz/VIS op9cs λ 1, λ 2 InGaAs detector Removable mirror THz- VIS window Spli8er 50/50 Visible light source Bolometer CCD camera 15

16 Characteriza5on of passive resonators Preliminary results Diameter = 12.6 µm - experimental results - theoretical resonances 2.0 x x x x10 4 p=4 m=63 p=1 m=78 p=5 m=58 p=2 m=71 p=9 m=44 Taper normalized output power 16

17 WGM lasing under op5cal pumping P. Jaffrennou et. al. APL. 96, (2010) Emission and high-β lasing up to 100 K Excellent thermal stability Under way: RT operation 17

18 WGM lasing under electrical pumping F. Albert et al., APL 97, (2010) For a detuned gain spectrum: Pure WGM lasing in large- diameter µ- posts Depending on the specific detuning: 18

19 Conclusion and perspec5ves Strong points: Compact size, electrical pumping, RT operation, scalable output power in the µw range. Custom CW emission frequency from 2 to 4 THz. Key issues: WGM Q factor, FCA in the THz, heat sinking, and far-field pattern. Under way: Nonlinear characterization. Design optimization Multi-spectral emission Phased-array geometries THz! 1! 4!! 2! 5! 3! 6 Coherent detection schemes 19