Quasi-Phase-Matched Gallium Arsenide for Mid Infrared Frequency Conversion E. Lallier, A. Grisard Research & Technology Thales Research & Technology, France B. Gerard Alcatel-Thales 3-5 Lab, France
2 Mid-IR sources requirements and OPOs Military Environment Medical Industrial Tunability, multi-spectral t l Mid-IR laser sources High energy /peak power CW to short pulses Narrow or broad linewidth Optical Parametric Oscillator (OPO) Pump Multi-wavelength capability NL Cristal χ (2) Wide tunability Suitable MIR nonlinear crystal?
3 MWIR quasi-phase-matched crystal Desirable properties for the NL crystal: High nonlinear coefficient Low absorption loss High laser damage threshold Low thermal lensing Non-critical phase matching Transmission (µm) Nonlinear Coefficient (pm/v) PPLN ZGP GaAs 0.35-5 1-12 1-16 27 75 96 QPM vs BPM: High nonlinearities Non-critical interactions Engineering flexibility Thermal Conductivity (W/m.K) α (cm -1 ) (> 2 µm) 5 35 52 -- 0,025 0,02 PPLN-like crystal for the mid-ir?
Quasi-Phasematching (QPM) in GaAs Periods under 100 µm for near-infrared pump lasers 16000 15000 14000 13000 12000 11000 10000 OP-GaAs 60 µm OP-GaAs 50 µm d eff -d eff d eff -d eff d eff Λ = 2π / Δk wavelength (nm) 9000 8000 7000 6000 5000 OP-GaAs 40 µm OP-GaAs 30 µm Output The informatio 4 4000 3000 PPLN 30 µm 2000 1500 1600 1700 1800 1900 2000 Pump wavelength (nm)
5 Quasi-Phasematching (QPM) in GaAs Following Armstrong et al. (1962) π + χ (2) - χ (2) + χ (2) (19 GaAs plates) [110] [-110] [110] ( p ) π π Boyd et al. (1966) Thompson et al. (1976) 0,5 mm (95 GaAs plates) - χ (2) - χ (2) - χ (2) + χ (2) + χ (2) + χ (2) + χ (2) 8 mm kg 9 mm 7 mm GaAs substrate Gordon et al. (1993) Thales/ Stanford (1999)
Thales prior written approval. THALES 2008. Template trtp 6 Fabrication of Thick Orientation-Patterned GaAs 1) [001] + [001] 2) [001] 0.1 µm [001] 2 GaAs wafer 2 GaAs wafer + etch-stop layer + 0.1 µm GaAs layer regrowth Crystallographic inversion by wafer bonding process 5) - χ (2) 4) 3) - χ (2) [00-1] [001] Lc [00-1] - χ (2) + χ (2) - χ (2) - χ (2) + χ (2) - χ (2) >500 µm - χ (2) - χ (2) - χ (2) + χ (2) + χ (2) 0,1 µm HVPE regrowth Gratings defined by photolithographic process Mechanical & chemical etching
7 Growth techniques on QPM GaAs samples 100 µm 100 µm DB GaAs DB GaAs CSVT growth on 212 µm DB-GaAs sample HVPE growth on 212 µm DB-GaAs sample 500 µm 500 µm OP-GaAs template OP-GaAs template HVPE growth on 60 µm 2 OP-GaAs template (Thales) HVPE growth on 60 µm OP-GaAs sample (Stanford/Thales)
Hydride Vapour Phase Epitaxy (HVPE) Physics of GaAs growth : GaCl g + ¼ As 4g + ½ H 2g GaAs + HCl g Oven HCl + H 2 H 2 + HCl add AsH 3 Quartz HCl GaCl HCl Gallium source As 2 / As 4 H 2 GaAs substrate Growth Characteristics : Perfect growth selectivity (preserve initial orientations) GaAs growth with low impurity concentration (residual 10 14 cm 3 ) High frequency desorption of As/GaCl precursors on surface Growth rate up to 35 µm/h 8
9 Influences of HVPE growth parameters Examples of HVPE growth anisotropy of GaAs crystal: III/V= 9, T=760 C T= 780 C, III/V = 3 GaAs band // [-110] III/V = 3 T= 760 C GaAs band // [110], III/V = 3,T= 760 C Due to χ (2) /-χ (2) orientations on OP-GaAs template: OP-GaAs template Apparition of a morphology conflict during HVPE regrowth
10 HVPE regrowth on OP-GaAs template (1) Gratings period ~30 µm HVPE film 380 µm 100 µm L C OP-GaAs 30 µm Gratings period ~ 60 µm HVPE film 380 µm 200 µm L C OP-GaAs 60 µm Gratings period ~ 212 µm HVPE film 380 µm L C OP-GaAs L C 212 µm
11 HVPE regrowth on the OP-GaAs (2) HVPE regrowth on an OP-GaAs template with intentional Si doping : Gratings period: 60 µm zoom OP-GaAs GA 30 µm [001] [00-1] [001] [00-1] [001] [00-1] [001] [00-1] [001] V(113) V(-112) Intentional GaAs doping 25 35 OP-GaAs 30 µm L C No GaAs doping The informatio Growth parameters verify the condition: v(113) * sin 55 = v(-112) * sin 65
12 Full wafer growth 2 multigrating 500 µm thick OP-GaAs 500 µm Growth characteristics: Growth rates: v(113)= 33 µm/h v(-112)= 30 µm/h 4 growth interruptions P=63.8 µm 500 µm 0 16,6 mm 500 µm 33,3 mm Cross section of a 3 cm-long OP-GaAs sample (63 µm grating period)
13 Towards thicker samples Old growth conditions with shorts cycles: 0.5 mm thickness (prior art) 0.8 mm thickness (summer 2009) 1.3 mm thickness (summer 2010) New growth conditions with long cycles: Thickness is limited it by parasitic nucleation Thicker samples will require a new reactor 1.5 mm thickness (winter 2011)
Optical transmission 1,2 1 Air 0,8 Transmission (mw) 0,6 Probe 0,4 HVPE Substrate 1 2 λ =1.5 µm ω 0 =50 µm 0,2 0 1cm 0 150 300 390 450 510 570 630 690 750 810 870 930 990 1050 1110 1170 1230 1290 0,08 Déplacement vertical (µm) 0,07 006 0,06 0,05 0,04 0,03 1 2 α < 0.03 cm -1 pertes cm-1 The informatio 0,02 0,01 0 490 510 530 550 570 590 610 630 650 670 690 710 730 750 770 790 810 830 850 870 890 14 Lowest loss measured 0.016 cm -1 at 2 µm (in resonant cavity)
15 Optical Parametric Oscillation First demonstration of GaAs OPO (2004): Stanford University & Thales (K.L Vodopyanov et al., Optics Letters, Vol 29, 16 (2004)) 500 µm HVPE film OP-GaAs sample length: 13 mm HVPE layer thickness: 500 µm PPLN OPO pump
Difference Frequency Generation DFG at around 7.8 µm from Er and Tm CW fiber lasers : UoDusseldorf (S. Vasilyev et al., Opt. Lett., 33, 13, 2008, pp. 1413-15) 33 mm GaAs optional Isolator Er source l th 1.55 μ m 10 W mid-ir detector wavelength measurement and control optional λ/2 mid-ir DFG output Theorical fit Tm source μ 1.93 m 0.25 W Isolator λ/2 L1 Λ= 38.6 μm t=25-175 O C L2 L3 DM OP-GaAs Beam separation 120 100 80 60 DFG output, % The informatio 16 40 20 Theorical fit 0 00 0.0 05 0.5 10 1.0 15 1.5 20 2.0 25 2.5 30 3.0 35 3.5 40 4.0 X, mm
17 High power OPO High power GaAs OPO (2008): Institut t St. Louis (ISL) (C. Kieleck et al., Optics Letters, Vol 34, 3 (2009)) 2.09 µm high rep.rate Ho:YAG pump, 3-5 µm emission. Up to 60% slope efficiency and 2.85 W output Efficiency comparable to ZnGeP 2 0.5 mm OP-GaAs 20 mm long 200 µm pump diameter 50% OC (s+i)
18 DIRCM module 20 W Tm fiber laser 10 W Q-switched Ho:YAG 3.0 W MWIR at 40 khz M 2 = 1.4 Portable demo A. Grisard et al., Proc SPIE 7836-06 (2010)
Parametric amplification of a DFB QCL 3 mw 4.5 µm CW DFB QCL 2.09 µm Ho:YAG 30 ns pulsed pump p at 20 khz 53 db gain with 41 mm long GaAs crystal 600 W peak power M 2 = 1.3, Δλ < 0.5 nm (instr. limited) 60 55 41 mm GaAs Tm Fiber Pump Stage 1.9µm AO Ho:YAG 450 µm OP-GaAs 50 45 40 35 Signal Gain (db) The informatio 19 DFB-QCL 4.5µm 2.09µm Pump : 2.09µm Idler : 3.9µm 30 32 mm GaAs OP-GaAs Signal : 4.5µm 25 20 0 1 2 3 4 Average Pump Power (W) G. Bloom et al., Optics Letters, Vol.35, N 4, (2010).
20 Recent results using OP-GaAs 7.7 W average power ns OPO (ISL) Fiber laser pumped ns OPO (ISL) Intracavity ps DFG for THz generation (Stanford) Fs MIR frequency comb (Stanford) CW OPO (BAE US) CLEO 2012
21 Aknowledgments C. Kieleck, M. Eichhorn, and A. Hildenbrand (ISL) S. Vasilyev and S. Shiller (UoDusseldorf) Part of this work was supported by the French MoD DGA/UM-TER/CGN Part of this work was/is supported by the European Comission: i VILLAGE (http://www.neo.no/village) MIRSURG (http://www.mirsurg.eu) IMPROV (http://www.fp7project-improv.eu)