Physics and technology of high power diode laser systems – key components in modern laser applications Katrin Paschke Ferdinand-Braun-Institut Berlin, September 22, 2014 German Soccer/Football Team won the world champion ship this year. 2 German Cars 3 Famous German Scientists Max Planck Max Born Gottfried Leibniz 4 Alexander von Humboldt Ferdinand Braun Ferdinand-Braun-Institut (FBH) – Innovation with microwaves and light FBH is situated in south/east of Berlin. 5 FBH: Facts & Figures Member of Forschungsverbund Berlin e.V., Leibniz Association Shareholders State of Berlin / Federal Republic of Germany Founded 1992 Staff 280 (incl. 140 scientists & PhD students) Budget / Turnover 22 M€ (incl. 11 M€ project revenues) Academic partners 6 Technische Universität Berlin Humboldt-Universität zu Berlin Goethe-Universität Frankfurt am Main FBH: semiconductors for new applications & markets Microwave & optoelectronic components – key devices for: Health & nutrition UV LEDs for water purification; diode lasers for dentistry, photodynamic therapy, fresh meat scanner … Climate & energy RF components: high-efficiency power amplifiers with novel amplifier architectures for efficient energy conversion Mobility Components for green car technologies Car safety (distance warning, parking assistance …) Security THz technologies for imaging systems for security applications Communications 7 Power amplifiers for mobile communications Unique feature: developments for highly specialized applications & markets Display technology Large-scale projections, flight simulators, holographic displays … Laser welding (e.g. in automotive industry) Production engineering Welding, cutting … Space technology Optical data transfer, high-precision measurements … Components for scientific applications … 8 Table-top X-ray laser, e.g. for analytics, laser-driven nuclear fusion for energy production of the future … © Trumpf Diode laser module for space applications FBH: Innovation with microwaves and light Applied research and development on III-V semiconductor devices, circuits and modules for microwave technology and optoelectronics Full value chain: International center for MMICs and high-power diode lasers covering all competencies Successful in knowledge and technology transfer by innovative product ideas and technologies: 9 Successful university cooperations (“joint labs”) Strategic partner of the industry Spin-offs FBH: Excellent in nano, micro and opto technology opto nano micro 10 application system FBH: Research program Microwave components & systems GaN high-power transistors & MMICs 100+ GHz: THz electronics (InP HBT) Microwave plasmas GaN power electronics FETs & diodes up to 1000 V GaAs diode lasers High-power diode lasers (0.63 - 1.2 µm) Hybrid diode laser systems (rgb) Laser sensors & metrology GaN Photonics UV & true blue III-V semiconductor technology 11 Epitaxy & process technology Mounting & packaging Outline Introduction Motivation: Laser diodes and systems Fabrication: Challenges and Solutions Beam shaping Mounting accuracy Examples Precision quantum optics experiments in space Material analytics Summary 12 Motivation: Diode lasers Key elements of laser technology in: Material processing Medicine photodynamic therapy surgery, dental, urology Communication (space applications, free space) Sensor systems material analytics, LIDAR Metrology atom interferometry, atomic clocks Entertainment / display Research / development (disk lasers, specific laser systems: X-ray, …) 24/09/2014 13 Motivation: Advantages of high power diode lasers High conversion efficiency Peak values >70% ; typically 50% At least a factor of two better than other lasers Extremly compactness Chip size 0.5 mm x 4 mm x 0.15 mm delivers up to 15 W Capability of mass production Full wafer processing Easy excitation 14 Motivation: Advantages of high power diode lasers Directly cover through conversion 630 nm … 1100 nm, VIS ... deep UV Large spectral tunability Up to many 100 GHz Provides wide bandwidth modulation capability Many MHz / GHz Narrow linewidth emission with advanced laser concepts Extremely robust Vibration, radiation, thermal cycling, … Reliable operation High brightness (spatial and spectral) main focus of current research 15 0 spectral density (dB) -10 -20 -30 -40 -50 -60 900 902 904 wavelength (nm) 906 908 Motivation: Why hybrid diode laser systems? Tailoring of diode laser characteristics Beam quality Spectral properties Wavelength Power Decoupling of light generation and amplification Avoiding complex monolithically process steps More degrees of freedom Thermal management Portable applications in situ sensors and analytics hand scanners for environmental research Goal: Small and compact 24/09/2014 16 Fabrication: Complete value chain … Design... T = 15°C Life test, 980 nm BA laser IRW / mA 100 150 200 250 300 5 Current / A 20 P = 10 W 1,0 P / a.u. P/W 10 0,5 976 977 978 / nm 0 5 10 12 W taging = 4300 h L = 4000 µm W = 100 µm POP = 12 - 15 W T = 25°C 10 0 Itaper / A Characterization... 17 15 W 15 15 Mounting Date: 17.01.2008 5 0,0 0 Processing… Epitaxy... 0 1000 2000 3000 4000 5000 Time / h Reliability Hybrid systems Applications Fabrication: Main research focus – GaAs DL Laser chip technology – limits of brilliance and power density Improvement of quality and extension of wavelength range New designs for edge emitters Resonators (RW, DFB, DBR, TA) Waveguide structures: Epitaxie III-V layer-structures MOVPE Monolithic integrated structures, processline Coating Surface emitting structures 10W/..kW CW/QCW/ ps-pulsed 18 n IRW Itaper SEM image Fabrication: Main research focus – GaAs DL Hybrid integrated laser sources Passive components Beam shaping with micro-optics (lenses, mirrors, polarization optics, gratings …) Micro-electronics (discrete components, TECs, modulators …) Sensors (temperature, …) Mounting technology No movable parts! Stability (mechanical, wavelength, reliable operation) Tolerances of adjustment Thermal optimisation Customize adapted Control system Housing with fiber output pole position of research institutions for diode laser chips and miniaturized hybrid integrated light sources 19 Fabrication: Beam shaping – Beam propagation parameter Beam parameters: • Diameter d • Waist position z0 d z d0 2 z z0 2 2 2 1 d 0 z z0 zR • Waist diameter d0 • Rayleigh length zR • Divergence • Beam propagation ratio M2 20 d0 M2 4 M2 1 Fabrication: Beam shaping – Propagation of simple astigmatic beams Independent sets of beam parameters for both principal axes: 21 2 d x z d0 x z z0 x 1 zRx 2 d y z d0 y z z0 y 1 z Ry Fabrication: Beam shaping – Lateral structure of diode lasers RW laser • Vertical and lateral single mode almost perfect beam quality (M2~1) • Very narrow spectral band possible (DBR, DFB) • Comparably low power (< 2 W) BA laser • Lateral multi mode (M2 > 50) • High power (> 10 W) • Good lateral beam quality (M2 <3) • High power (~10W) Tapered laser 22 Fabrication: Beam shaping – Lateral structure of diode lasers RW laser • Vertical and lateral single mode almost perfect beam quality • Very narrow spectral band possible (DBR, DFB) • Comparably low power BA laser • Lateral multi mode • High power • Good lateral beam quality • High power Tapered laser 23 Fabrication: Beam shaping – Lateral structure of diode lasers RW laser • Vertical and lateral single mode almost perfect beam quality • Very narrow spectral band possible (DBR, DFB) • Comparably low power BA laser • Lateral multi mode • High power • Good lateral beam quality • High power Tapered laser 24 Fabrication: Beam shaping – Lateral structure of diode lasers RW laser • Vertical and lateral single mode almost perfect beam quality • Very narrow spectral band possible (DBR, DFB) • Comparably low power BA laser • Lateral multi mode • High power • Good lateral beam quality • High power Tapered laser 25 Fabrication: Beam shaping – Transformation and coupling laser radiation The general problem of beam coupling/transformation incoming beam accepted beam Frequent problems: 26 Physical limitations (M2) Available focal lengths Impact of aberrations Space constraints Alignment accuracy vs. requirements Fabrication: Beam shaping – Microoptics and aberrations Uncorrected lens Corrected lens 27 Fabrication: Beam shaping – Simulation of propagation of beam parameters 28 Useful method for very quick and easy first order system design Identification of alignment problems Aberrations and diffraction neglected Simulation by proprietary software (WinABCD) Fabrication: Beam shaping – Simulation of propagation of beam parameters Useful method for very quick and easy first order system design Identification of alignment problems Aberrations and diffraction neglected Simulation by proprietary software (WinABCD) Paraxial and non-paraxial propagation can be approximated by raytracing (e.g. non-sequential mode in ZEMAX) 29 Fabrication: Mounting accuracy – Challenges of integration High precision bonding mounting tolerances down to ± 1 µm laser diodes, package, … laser diode Microbench High precision bonding allows high precision optics mounting. High precision optics mounting optics mounting tolerances < 1 µm FAC (vertical), SAC (lateral) 24/09/2014 30 Microbench Fabrication: Mounting accuracy – Flip-Chip bonder for high precision mounting Flip-Chip bonder FC 150 direct bonding accuracy: x,y: ± 1 µm ; θ ± 9 µrad travel distance > 50 mm programming & monitoring of process parameters for soldering gluing 24/09/2014 can be used to build 3D structures high precision mounting and alignment of different materials in one package part of the hybrid integration 31 Fabrication: Mounting accuracy – Hexapod for higher precision mounting Hexapod F-206.S smallest step size x,y,z: 0.1 µm ; θ: ± 2 µrad max. travel distance < 10 mm 24/09/2014 32 high precision mounting of optics part of the hybrid integration Outline Introduction Motivation: Laser diodes and systems Fabrication: Challenges and Solutions Beam shaping Mounting accuracy Examples Precision quantum optics experiments in space Material analytics Summary 33 Hybrid integrated laser sources: Topics Display and pumping of compact solid-state and fibre lasers (NIR/red/SHG: 1W...10W, M² < 3, < 5MHz) Highly coherent sources for holographic displays (rgb) Integration of nonlinear frequency conversion High power modules including with SMF and LMF coupling © LG 34 Hybrid integrated laser sources: Topics Display and pumping of compact solid-state and fibre lasers (NIR/red/SHG: 1W...10W, M² < 3, < 5MHz) Highly coherent sources for holographic displays (rgb) Integration of nonlinear frequency conversion High power modules including with SMF and LMF coupling Material processing, LIDAR, and coherent communication (0,01W...1 W, < 1MHz) Gain-switched diode lasers for pulse width 2-100ns Q-switched diode lasers for pulsed widths around 100ps 35 © LG Hybrid integrated laser sources: Topics Precision quantum optics experiments in space (0,01W...1 W, < 1MHz) Miniaturized tunable laser sources with very narrow line-width Rb- and K- ultrahigh precision spectroscopy & atom interferometry, local oscillators for optical clocks Integration of GaAs based modulators & complex PICs and SiO2-based PICs Space qualified housing Material analytics (0,001W...1 W, < 1GHz) Raman spectroscopy (SERDS and DUV excitation) Fluorescent spectroscopy 36 Yellow spectral range Spatial resolved ps-pulse excitation Absorption spectroscopy (DIAL) Monolithic Single Frequency Diode Lasers - Concepts advantages of monolithic lasers: - compact - robust - low system complexity / high reliability Fabry – Perot resonator: many longitudinal modes require frequency selective element (built-in surface or buried grating) Bragg equation: 2·L·sin = n· distributed Bragg reflector (DBR) Laser = 90°, n = 3, = 940nm L = 156nm reflector section grating active layer 24/09/2014 37 gain section distributed feedback (DFB) Laser Monolithic Single Frequency Diode Lasers - Results DBR – Ridge waveguide laser (0.62 – 1.18 µm) linewidth < 500kHz, power (cw) 10 mW…100 mW linewidth < 500kHz, power (cw) …1000 mW linewidth < 100kHz, power (cw) 50 mW…100 mW 626 nm*, 628 nm, 632.8 nm**, 647 nm 976 nm*** 1064 nm 647 nm 1064 nm measurement 15°C Voigt fit 15°C measurement 25°C Voigt fit 25°C 0.1 25°C linewidth / kHz power spectral density 1 0.01 976 nm 1E-3 15°C 1E-4 50 60 70 80 90 frequency / MHz 100 110 1600 1600 1400 1400 1200 1000 400 Lorentzian part 15°C Gaussian part 15°C Lorentzian part 25°C Gaussian part 25°C 1200 976 nm 200 1000 400 200 650 700 750 800 850 900 950 1000 1050 1100 optical output power / mW * Diode-laser-based system for 9Be+ cooling and manipulation at 313 nm, F.M.J. Cozijn1, G. Blume2, K. Paschke2, and J.C.J. Koeleme (2014) ** Narrow linewidth of 633 nm DBR ridge-waveguide lasers, G. Blume, M. Schiemangk, J. Pohl, D. Feise, P. Ressel, B. Sumpf, A. Wicht and K. Paschke ***High-power distributed Bragg reflector ridge-waveguide diode laser with very small spectral linewidthij1, K. Paschke...(2010) 38 Power Amplifier Chips tapered section 1 mm or 2 mm RW mode filter @ input necessary seed: few 10 mW Pre TA pre-amplifier up to several Watts output / up to 20 dB amp. spectral properties of seed maintained, PA-ASE background added optics Master-Oscillator-Power-Amplifier (MOPA) concept spectral properties of master maintained, power boosted monolithic DFB-MOPA / DBR-TPL 24/09/2014 39 hybrid DFB-RW-TA MOPA Power Amplifier Chips: Results DBR-TPL DBR - Tapered laser (0.65 – 1.18 µm) Ausgangsleistung P (W) P/W 14 920nm 976nm 1064nm 12 10 8 6 4 2 0 0 M² M² 2nd mom. Pmain lobe Astigmatism 5 10 15 Strom ITA (A) 1.0 1.0 1.0 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 0.0 0.0 0.0 919.5 920.0 920.5 975.0 975.5 976.0 1062.5 1063.0 1063.5 Wellenlänge (nm) 1.0 1/e² 1.2 1.2 1.1 1.1 1.1 1.1 1.1 5.5 1.9 4.6 6.8 8.0 7.0 14.5 12.8 14.7 90% 87% 83% 81% 82% 70% 72% 49% 1310µm 1350µm 1390µm 1430µm 1470µm 1510µm 1540µm 1570µm 0.8 intensity (a.u.) 1 2 4 6 8 10 11.4 12.0 < 10pm, power (cw)~ 2W < 10pm, power (cw)~10W 647 nm, 1178 nm 914 nm, 920 nm, 976nm, 981nm, 1030nm 1064nm, 1122nm: normierte Intensität (a.u.) 0.6 P=10W 2 M1/e²=1.2 2 M=5.0 0.4 0.2 0.0 -20 -10 0 10 beamwaist position (µm) * 12Whigh-brightness single-frequency DBR tapered diode laser, Electronics Letters 44(21): 1253-1255, Fiebig, Blume, Paschke (2008) **High-brightness distibuted-Bragg-reflector tapered diode lasers: pushing yout application to the next level, SPIE, High Power Diode Laser Technology and Application IX,7918:79180R, Fiebig et al., “ (2011) 40 20 Power Amplifier Chips tapered section 1 mm or 2 mm RW mode filter @ input necessary seed: few 10 mW Pre TA pre-amplifier up to several Watts output / up to 20 dB amp. spectral properties of seed maintained, PA-ASE background added optics Master-Oscillator-Power-Amplifier (MOPA) concept spectral properties of master maintained, power boosted monolithic DFB-MOPA / DBR-TPL 24/09/2014 41 hybrid DFB-RW-TA MOPA Master-Oscillator-Power-Amplifier (for Space Com) Technology (2nd generation) diode laser-based MasterOscillator-Power-Amplifier (MOPA) hybrid micro-integration with space-compatible technology DBR-master optical isolator micro-integration of two laser chips incl. optics for coupling & collimation Performance 42 P > 1 W @ 1060 nm dFWHM ~ 100 kHz (100 µs) / 4 kHz (intrinsic) continuous tuneability: up to 1 nm 25 gRMS vibration, 1500 g shock passed life time > 10.000 h demonstrated tapered amplifier beam forming optics AlN ceramic footprint: 50 x 10 mm2 Master-Oscillator-Power-Amplifier Technology (2nd generation) diode laser-based MasterOscillator-Power-Amplifier (MOPA) hybrid micro-integration with space-compatible technology DBR-master optical isolator micro-integration of two laser chips incl. optics for coupling & collimation Performance P > 10 W @ 1064 nm / up to 3 W @ 780 nm dFWHM ~ 1.2 MHz (FWHM) / 180 kHz (intrinsic) continuous tuneability: up to 1 nm tapered amplifier beam forming optics AlN ceramic footprint: 50 x 10 mm2 Transfer to other wavelength possible! Bottleneck: µ-isolator 43 Technology: Concepts (“3rd generation”) Master-Oscillator-Power-Amplifier Extended Cavity Diode Laser Technology Advancement for Sounding Rocket Deployment mechanical stability improved electronic interface, µ-TECs, µ-temperature sensor added (footprint: 80 25 mm2 ) Performance 44 P > 1 W @ 767 nm, 780 nm dFWHM ~ 1 MHz (100 µs) / < 100 kHz (intrinsic) 20 gRMS vibration passed for laser cooling and Bragg-pulses Performance P > 50 mW @ 767 nm, 780 nm dFWHM < 100 kHz (100 µs) / < 1 kHz (intrinsic) 29 gRMS vibration, 1500 g shock passed for Raman beam generation Technology: cw-Laser, Results 2,5 IMO = 190 mA 2,0 optical power (W) frequency noise LSD [Hz/Hz ] TTA-MO = 1,7°C @ TMO= 35°C IRW = 200 mA 1,5 1,0 TMO = 15°C 25°C 35°C 0,5 150 mA 240 mA 3 10 2 10 0,0 0 MOPA.12 120123-16 500 1000 1500 2000 2500 TA injection current (mA) DFB-MOPA (780 nm) output power vs. injection current through tapered section of amplifier laser modules to be used onboard a sounding rocket in late 2014 45 3 10 4 10 5 10 6 10 7 10 frequency [Hz] ECDL (767 nm) single sided power spectral density of the laser frequency noise optical phase locked loop (OPLL) demonstrated with ~ 1 MHz servo BW laser modules to be used onboard a sounding rocket in late 2014 Technology (“4th generation”): Multi-Purpose Platform for Micro-Integration of Lasers Aim: portable Rb atom interferometer combination of any 2 chips fiber coupling chip 1 (e.g. RW) VHBG isolator 46 Chip 2 DFB amplifier DFB phase modulator ECDL amplifier ECDL phase modulator amplifier amplifier phase modulator amplifier technology advancement fiber coupling on-board µ-TECs to replace submounts for monolithic lasers UHF-modulation capability (10 GHz) hermetic housing thermal management (TECs) of ceramic body chip 2 (e.g. TPA) Chip 1 Sensoric: Introduction Raman spectroscopy gypsum (CaSO4 2H2O) Different effects can obscure the weak Raman lines Fluorescence Scattering Background lines Shifted excitation Raman difference spectroscopy (SERDS) 47 Sensoric: Shifted Excitation Raman difference spectroscopy (SERDS) Separate excitation with two emission lines - ∆𝝂 = 10 cm-1 ex-1 Difference spectrum ex-2 gypsum (CaSO4 2H2O) Reconstruction e.g. using integration SERDS-spectrum for gypsum (CaSO4 2H2O) Maiwald et.al. , Proc. SPIE 8935 Advanced Biomedical and Clinical Diagnostic Systems XII, 89350M (Feb. 2014); 48 Sensoric: Requirements for light sources for SERDS Target wavelengths in this work 671 nm (well-established for Raman spectroscopy) Spectral emission width: ∆𝜈 = 10 cm-1 typical width of Raman lines of solids and liquids (FWHM) Spectral stability 𝛿𝜈 = 1 cm-1 calibration free measurement over long times Spectral distance for SERDS ∆𝜈𝑆𝐸𝑅𝐷𝑆 = 10 cm-1 suitable for the separation of the Raman signals For in-situ experiments and portable systems Small size Low power consumption Robust Maiwald et.al. , Photonics Rev., vol. 7, no. 4, pp. L30-L33 (2013). 49 Sensoric: Solution- Light sources for SERDS Maiwald et.al. , Photonics Rev., vol. 7, no. 4, pp. L30-L33 (2013). 50 Sensoric: Power-voltage-current characteristics 671 nm: DBR Y-Branch Laser T = 25°C, Iout = 150 mA continuous wave operation Lasing starts around I1 = 85 mA I2 = 95 mA P400mA = 110 mW Variable optical power via injection current Pel. = 1.3 W at P = 100 mW Maiwald et.al. , Photonics Rev., vol. 7, no. 4, pp. L30-L33 (2013). 51 Sensoric: Spectra – 671 nm: DBR Y-Branch Laser Spectra at T = 25°C Laser starts at 1 = 670.42 nm, 2 = 670.87 nm Wavelength stabilized diode laser ∆𝜈 /I = 0.1 cm-1/mA ∆𝜈 /T = 0.9 cm-1/K Optical spectra at P = 100 mW Spectral width ≤ 0.6 cm-1 (95% optical power) Spectral distance 10 cm-1 Spectral properties suitable for SERDS see also Laser Photonics Rev., vol. 7, no. 4, pp. L30-L33 (2013). 52 Summary Laser chip technology Hybrid integrated laser sources Customized chips Design of subcarriers and micro bench and optical micro systems Mounting technology and Fibre coupling Examples CuW submount CW, T=25.0°C 15 986 0 0 spectral density (dB) 1.5 voltage U / V 0.5 5 0.5 0.4000 982 980 0.8000 edasloc, 4mm, 910nm edasloc, 6mm, 940nm asloc, 4mm, 940nm vendor A, 4mm, 970nm vendor B, 4mm, 940nm 0.0 [nm]nm 984 10 1.0 optical Power P / W 1.0 Metrology Sensoric conversion efficiency C 0 5 10 0 15 978 -20 -30 -40 -50 -60 1.000 5 0.0 -10 10 15 20 900 902 Current [A] current I / A pole position of research institutions for diode laser chips and miniaturized hybrid integrated light sources 53 904 wavelength (nm) 906 908 Acknowledgement Thanks to all my colleagues of FBH on departments about their work in high power diode laser and for your attention 24/09/2014 54 small
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