High power and single frequency quantum cascade lasers for chemical sensing

Transcription

1 High power and single frequency quantum cascade lasers for chemical sensing Stéphane Blaser final version: Page 1 of 51 Collaborators Yargo Bonetti Lubos Hvozdara Antoine Muller Guillaume Vandeputte Hege Andersen This work was done in collaboration with the University of Neuchâtel Marcella Giovannini Nicolas Hoyler Mattias Beck Jérome Faist Page 2 of 51

2 Outline Company profile Introduction - state of the art High power Fabry-Pérot devices Applications Distributed-feedback lasers High power pulsed DFB devices >77K operating continuous-wave DFB devices Reliability Production Page 3 of 51 Company profile Founded August 1998 as a spin-off company from the University of Neuchâtel incorporated as a SA under swiss law with a capital of 1 kchf) Founders Jérôme Faist Antoine Muller Mattias Beck Employees (September 23) 8 persons (6 full-time) Installed at Maximilien-de-Meuron 1-3, 2 Neuchâtel since April 22 Page 4 of 51

3 Company profile > 3 man-years experience 7 patents on QCL technologies > 15 devices sold > 5 customers turnover 23: > 1.3 MCHF average growth rate: 1% / year Page 5 of 51 Quantum cascade lasers Page 6 of 51

4 Interband vs intersubband E E E f E 12 E 12 E f k k Interband transition - bipolar - photon energy limited by bandgap E g of material - Telecom, CD, DVD, Intersubband transition - unipolar, narrow gain - photon energy depends on layer thickness and can be tailored Page 7 of 51 Quantum cascade lasers Cascade - each e- emits N photons Active region / injector - active region population inversion which must be engineered - injector avoid fields domains and cools down the electrons MBE - growth of thin layers - sharp interfaces T e >>T l 3 τ 32 τ 32 > τ τ 21 T e ~T l active region relaxation / injection Page 8 of 51

5 State of the art: QCL performances Atmospheric windows Temperature [K] LN 2 Reststrahlen band Peltier Wavelength [μm] CW pulsed CW pulsed InP GaAs - Good Mid-IR coverage - Terahertz promising Data: MIR FIR Uni Neuchâtel NEST Pisa Alpes Lasers MIT Bell Labs Uni Neuchâtel Thales TU Vienna Northwestern Uni W. Schottky/TU Munich Page 9 of 51 Designs Double-phonon resonance: (patent n wo 2/23686A1) 4QW active region with 3 coupled lower state lower states separated by one phonon energy each keeps good injection efficiency of the 3QW design Hofstetter et al. APL 78, 396 (21). Bound-to-continuum: (patent n wo 2/19485A1) transition from a bound state to a miniband combines injection and extraction efficiency broad gain curve -> good long-wavelength and high temperature operation J. Faist et al. APL 78, 147 (21). Double optical phonon resonance Bound-to-continuum Page 1 of 51

6 Two-phonon structure at 8 m Based on two-phonon resonances design injection barrier arrow QW/barrier pair extraction barrier InGaAs/InAlAs-based heterostructure with E c =.52eV Grown by MBE on InP substrate 35 periods n-doped 4 QW active region one period 41, 16, 8, 53, 1, 52, 11, 45, 21, 29, 15, 28, 16, 28, 17, 27, 18, 25, 21, 25, 26, 24, 29, 24 Page 11 of 51 High average power FP QCL RT-HP-FP Voltage [V] K, 6% K, 2% mm-long μm-wide back-facet coated Current [A] Average power [W] Characteristics λ = 7.9 Average power: P = 15 mw threshold current: I th = 2.1A (j th =3. ka/cm 2 : P =.82 W (6% dc) I th =.51A (j th =.75 ka/cm 2 ) CW: P = 3mW (j th =.78 ka/cm 2 ) Page 12 of 51

7 Array of lasers DUAL-RT-HP-FP DC voltage fed to LDD [V] T = -25 C duty-cycle = 1% laser up laser dn array of 2 lasers Current [A] Average power [mw] Characteristics both lasers: 1.5 mm-long, 28 μm-wide λ 7.9 μm T = -25 C, duty-cyle = 1% laser Average power I th [A] j th [ka/cm 2 ] up 25.4 mw dn 22.6 mw array 44.9 mw Total power 9% (P 1 +P 2 ) Total threshold current I 1 +I 2 Page 13 of 51 Applications Page 14 of 51

8 Applications: telecom Telecommunications Free-space optical data transmission for the last mile (high speed with no need for licence and better operation in fog, compared to = 1.55 m) Bandwidth 1 Gbps 4 Gbps 1 Gbps 1 Gbps 622 Mbps 4 to 7 years 1 to 4 years Present 155 Mbps 1 Mbps Local Network Last Mile Metro Backbone Long-Haul Backbone R. Martini et al., IEE Elect. Lett. 37 (11), p. 129, 21. S. Blaser et al., IEE Elect. Lett. 37 (12), p. 778, 21. Page 15 of 51 Main application: chemical sensing by optical spectroscopy Detection techniques already demonstrated using QCL: photo-acoustic B. Paldus et al., Opt. Lett. 24 (3), p.178, D. Hofstetter et al., Opt. Lett. 26 (12), p. 887, 21. M. Nägele et al., Analytical Sciences 17 (4), p. 497, 21. TILDAS Some needs: M. Zahniser et al. (Aerodyne Research), TDLS 3. cavity ringdown high-power laser B. Paldus et al., Opt. Lett. 25 (9), p. 666, 2. absorption spectroscopy single mode A. Kosterev et al., Appl. Phys. B 75 (2-3), p. 351, 22. continuous-wave heterodyne detection scheme D. Weidmann et al., Opt. Lett. 29 (9), p. 74, 23. cavity enhanced spectroscopy D. Bear et al. (Los Gatos Research), TDLS 3. Page 16 of 51

9 Application fields Chemical sensing or trace gas measurements process development environmental science forensic science process gas control liquid detection spectroscopy Medical diagnostics breath analyzer glucose dosage Remote sensing leak detection exhaust plume measurement combat gas detection Page 17 of 51 Simultaneous 3-gas measurements with dual-laser QCL instrument 8 NH 3 (5 ppb) LASER 1: 967 cm N 2 O (31 ppb) LASER 2: 1271 cm -1 CH 4 (18 ppb) TRACTOR EXHAUST PLUME Two QC-lasers from Alpes: 2 to 6 gases (CH 4, N 2 O, NH 3 ) 56 m cell path length Detector options :45 PM 8/13/23 12:5 PM 12:55 PM 1: PM time M. Zahniser et al., Aerodyne Research Inc., Billerica (USA) Page 18 of 51

10 Spectrum covered by Alpes Lasers dfb QCLs radio 1 cm 1 cm 1 mm 1 μm 1 μm infrared.8 μm.4 μm UV RADAR NH 3 maser.1 THz QCL p-ge laser 1 THz CO 2 laser Wavelength [μm] CCl 2 O 2 C 2 H 4 O NH 3 F 4 Si O 3 N 2 O CH 4 C 2 H 4 C 5 H 1 O CCl 2 O CO N 2 O CO Wavenumber [cm -1 ] Page 19 of 51 Single-mode operation: distributed-feedback QCLs Page 2 of 51

11 How does a DFB work? Fabry-Pérot laser: gain Amplified light bounces in the cavity DFB: periodic grating => waves coupling => high wavelength selectivity gain Intensity [a.u.] Wavelength [μm] stopband Δν = 1.19 cm K 2 K complex-coupled DFB: lasing mode closest to the stopband stopband coupling strength Frequency [cm-1] 22 K Page 21 of 51 Distributed-feedback technologies D. Hofstetter et al., Appl. Phys. Lett., vol. 75, p.665, 1999) C. Gmachl et al. IEEE Photon. Technol. Lett., vol. 9, p.19, 1997) Grating on the surface (open-top) one MBE run (no MOCVD) high peak power (large stripes) but low average power optical losses due to metalization Grating close to active region lower thermal resistance (high duty / high temperature) high average power higher overlap, smaller losses jct dn mounting possible needs MOCVD regrowth Page 22 of 51

12 High average power DFB QCL RT-HP-DFB-2-12 Distributed feedback QC laser at 8.35 m with InP top cladding Voltage [V] C 4 2 C 3 C Current [A] Average power [mw] Characteristics 3mm-long, 28μm-wide laser λ 8.35 C: Average power (2% dc): P = 32 mw (1.6 W peak power) threshold current: I th = 2.44 A (j th = 2.9 ka/cm 2 C : P = 25 mw (1.25W peak power) I th = 3.2 A (j th = 3.8 ka/cm 2 ) Page 23 of 51 High average power DFB QCL RT-HP-DFB-2-12 Voltage [V] C C 6 3 C Current [A] Average power [mw] 1 Characteristics Entire tuning range: Δν = 5.7 cm -1 at 1197 cm -1 (.47%) ( cm -1 (8.367 μm) at 3 C to 12.9 cm -1 (8.327 μm) at -3 C) C 3 C C, 14V 3 C, 12V 15 C, 14V 15 C, 12V C, 14V C, 12V 4 db (limited by the grating spectrometer) Wavelength [μm] Page 24 of 51

13 Long-wavelength ( 16.4 m) B2C DFB QCL RT-P-DFB-1-68 Laser based on a bound to continuum design, 16.4 m Rochat et al., APL 79, 4271 (21) DC voltage fed to LDD [V] C -15 C C 15 C 3 C 4 C 5 C Current [A] Average power [mw] Characteristics 3 mm-long, 44μm-wide laser λ 16.4 C: Average power (1.5% dc): P = 1.5 mw (1 mw peak power) Threshold current: Ith = 7.1 A (j th =5.4 ka/cm 2 C : P =.5 mw (33 mw peak power) Ith = 1.4 A (j th =7.9 ka/cm 2 ) Page 25 of 51 Long-wavelength ( 16.4 m) B2C DFB QCL RT-P-DFB-1-68 Normalized intensity Wavelength [μm] C, 21V -3 C, 27V -15 C, 21V -15 C, 27V C, 23V C, 28V 15 C, 24V 15 C, 29V 3 C, 26V 3 C, 3V 4 C, 27V 4 C, 32V 5 C, 28V 5 C, 32V Characteristics 3mm-long, 44μm-wide laser λ 16.4 μm Single-mode emission: Side Mode Suppression Ratio > 25 db (limited by the resolution of the FTIR) Tuning range: Δν = 4.5 cm -1 at 68 cm -1 (.7%) (65.76 cm -1 (16.51 μm) at 5 C to 61.3 cm -1 (16.38 μm) at -3 C) Wavenumbers [cm-1] Page 26 of 51

14 How does a DFB tune? Page 27 of 51 How does a DFB tune? Tuning always due to thermal drift (carrier effects can be neglected!) T act wavelength selection : λ = 2 n eff Λ grating n eff =n eff (T) T sub dλ λ = dn eff n eff Page 28 of 51

15 How does a DFB tune? T act Active region heating: T = T + I U δ R act sub th +I U R DC DC th ( ) T sub ΔT = T act T sub If T = 1 C 1% chance of laser-destruction (thermal stress) = 6 C depends of mounting / laser -> dangerous = 3 C OK substrate temperature additional bias current Different possibilities of thermal tuning: pulse length (chirping) pulse current {duty-cycle Page 29 of 51 Tuning by changing T sub (heatsink temperature) T act I T sub1 T sub2 t 1 t 2 I.5-5 A T sub t tuning coefficient : 1 Δλ = 1 Δn eff [ 6 7] 1 5 K 1 λ ΔT sub ΔT sub n eff L t 1 t 2 I T 6 C => Page 3 of 51

16 Tuning by DC bias-induced heating by DC bias-induced heating by changing T sub I t 2 T sub cst t 1 I.5-5 A I T sub1 T sub2 t 1 t 2 I DC ( 1-2 ma) I.5-5 A t t L ΔT R th = V device I DC L t 1 t 2 t 1 P opt cst I t 2 I T 3 C => >1kHz T 6 C => Page 31 of 51 Thermal chirping during pulse Intensity [arb. units] K I = 3.14 A gate width = 3 ns peak power = 5 mw + 8 ns + 2 ns + 1 ns drift with time:.3 cm -1 /ns (high dissipated power) 2 K temperature increase of during a 1-ns-long pulse Wavenumbers [cm -1 ] Faist et al., Appl. Phys. Lett. 7, p.267 (1997) Page 32 of 51

17 Pulse length dependence of linewidth Linewidth [cm-1] Aerodyne measurements (diff. device!) FTIR spectrometer grating spectrometer calculation Pulse length [ns] Need for a good compromise: too long: limited by thermal chirping too short: limited by the time evolution of the lasing mode fundamental limits for narrower linewidth: cw operation Hofstetter et al., Opt. Lett. 26, p.887 (21) Page 33 of 51 CW operation at 6.73 m LN2-CW-DFB Characteristics Voltage [V] K 13K 12K 1K 8K Average power [W] 1.5 mm-long, 23 μm-wide laser CW operation at λ 6.73 K: Average power P =.2 W Threshold current: Ith =.35 A (j th = 1. ka/cm 2 ) I op <.8 A U op < 9 V Current [A] Page 34 of 51

18 CW operation at 6.73 m LN2-CW-DFB Wavelength [μm] Characteristics Normalized intensity K, 5mA 1K, 65mA 1K, 55mA 1K, 45mA 8K, 6mA 8K, 5mA 8K, 4mA 1.5 mm-long, 23 μm-wide laser CW operation at λ 6.73 μm Single-mode emission: Side Mode Suppression Ratio > 3 db (limited by the resolution of the FTIR) Tuning range: Δν = 4.9 cm -1 at 1485 cm -1 (.33%) Wavenumbers [cm -1 ] ( cm -1 (6.744 μm) at 12K to cm -1 (6.722 μm) at 8K) Page 35 of 51 CW operation at 4.6 m LN2-CW-DFB Voltage [V] K 9K 1K Average power [mw] Characteristics 1.5 mm-long, 21 μm-wide laser CW operation at λ 4.6 K: Average power P = 12 mw Threshold current density: Ith =.54 A (j th = 1.7 ka/cm 2 ) I op < 1.1 A U op < 8 V Current [A] Page 36 of 51

19 CW operation at 4.6 m LN2-CW-DFB Normalized intensity Wavelength [μm] K, 55mA 8K, 65mA 8K, 75mA 8K, 85mA 8K, 95mA 8K, 1.5A 9K, 1.A 9K, 1.1A Wavenumbers [cm-1] Characteristics 1.5 mm-long, 21 μm-wide laser CW operation at λ 4.6 μm Single-mode emission: Side Mode Suppression Ratio > 25 db (limited by the resolution of the FTIR) Tuning range: Δν = 8 cm -1 at 2171 cm -1 (.37%) ( cm -1 (4.613 μm) at 9K to cm -1 (4.596 μm) at 8K) Page 37 of 51 Future: continuous-wave and single-mode operation at room-temperature terahertz sources Page 38 of 51

20 Continuous-wave FP QCL on Peltier RT-CW-FP-5-18 Voltage [V] mm-long, 13 μm-wide λ 9.2 μm j th (-3 C) = 4.5 ka/cm 2-3 C -25 C -2 C -15 C -1 C -5 C C Current [A] Average power [W] I op < 1.2 A U op < 6 V Page 39 of 51 BH distributed-feedback QCLs grating Wavele ength [ μm] mA 23K 5mA n- InP i-inp 1 n-inp top cladding diamond Ti / Au 1.1 InGaAs waveguide layer Frequency [cm -1 ] Continuous-wave distributed-feedback quantum-cascade lasers on a Peltier cooler: T. Aellen, S. Blaser, M. Beck, D. Hofstetter, J.Faist, and E. Gini, Appl. Phys. Lett. 83, p.1929, 23. Page 4 of 51

21 THz applications New sources: R. Köhler et al., Nature 417, p.156, 22. M. Rochat et al., Appl. Phys. Lett. 81 (8), p.1381, 22. Terahertz applications: Astronomy Medical imaging Chemical detection Telecommunications for local area network (LAN) Page 41 of 51 Terahertz sources THz QC laser based on a bound to continuum design, 87 m Structure grown at University of Neuchâtel (G. Scalari, L. Ajili, M. Beck and M. Giovannini) j [A/cm 2 ] k 15 Characteristics Voltage [V] Emission energy [mev] 5k 7k 78k 1 5 Peak power [mw] THz QC laser: λ 87 μm 2.7mm-long, 2μm-wide laser back-facet K: Peak power (2.5% dc): P = 14 mw threshold current density: j th = 267 A/cm Current[A] pulsed operation up to 78K CW operation up to 3 K Page 42 of 51

22 Reliability of the devices Page 43 of 51 Reliability of the devices: ageing T measure = 3 C Pulser QCL 1 QCL 2 Voltage [V] 3 C Current [A] Power [mw] Temperature controller QCL 3 T ageing = 13 C 1 Detectors 1 Slots Page 44 of 51

23 Ageing: theory Conversion of lifetime using Arrhenius type relation: t ~ exp[e/(kt)] where: t is lifetime T temperature E=.7 ev activation energy [H. Ishikawa et al., J. Appl. Phys. 5, 1979] (needs to be evaluated for QCL) The room temperature lifetime t 1 (at T 1 = 2 C and 7% of initial power) can be extrapolated by : E k t 1 = t e 1 1 T 1 T with t is the measured lifetime at the ageing temperature T (here 13 C = 43K). (using 1 C for example it will take 5 times longer) 8 C 17 Page 45 of 51 Ageing at 13 C: results Normalized output power (measured at 3 C) Extrapolated 2 C lifetime t 1 [years] (HR) c1 (HR) c11 (HR) c13 c14 c Ageing Time at 13 C [hours] (cooling and heating time needed for measurement (cycles of about 2h) already subtracted) Page 46 of 51

24 Production Page 47 of 51 Production line Delivery time - 2 weeks 1-4 weeks 2-5 months 4-6 months 5-9 months Stocks in stock fully tested in stock need mounting and/or testing growth in stock need gratings and process design done need growth completely new wavelength asked need design Operations laser cleaving laser mounting facet coating laser testing mounting / testing DFB gratings regrowth MOCVD SiO PECVD/RIE mesa etching λ MBE growth X-Ray measure wafer cleaning growth design lateral regrowth MOCVD top contact process re-fabrication / feedback thinning back contact Page 48 of 51

25 Production - lasers off the shelf Possible Need customization process Multimodes off the shelf DFB off the shelf Wavelength [μm] Wavenumber [cm -1 ] for an up to date wavelength listing, contact us at: Page 49 of 51 List of products - prices Type Dutycycle Operating temp. Product name Power Linewidth Tunability Off the shelf Built to order 1+ DFB pulsed RT RT-HP-DFB-2-X > 2 mw < 33 MHz.4% 11 keur 28 keur RT-HP-DFB-5-X > 5 mw 13.5 keur cw LN2 LN2-CW-DFB-2-X > 2 mw < 3.5 MHz.4% 23.5 keur 5 keur cw RT RT-CW-DFB-2-X > 2 mw < 3.5 MHz.4% available end 24 FP pulsed RT RT-HP-FP-1-X > 1 mw 1-4 % N/A 6 keur pulsed LN2 LN2-HP-FP-15-X > 15 mw 1-4 % N/A 2 keur cw RT RT-CW-FP-5-X (only at 9.1 μm) > 5 mw 1-4 % N/A 17 keur Page 5 of 51

26 Conclusion / outlook Available products pulsed DFB QCL on Peltier cooler in the range of 4.3 m to 16.5 m LN 2 continuous-wave DFB QCL in the range of 4.6 m to 1 m continuous-wave FP on Peltier cooler at 9.1 m Soon available THz sources (LN 2 ) Available end 24 continuous-wave DFB on Peltier cooler (already demonstrated: T. Aellen, S. Blaser, M. Beck, D. Hofstetter, J.Faist, and E. Gini, Appl. Phys. Lett. 83, p.1929, 23) Page 51 of 51