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Semiconductor lasers are ideally suited for mass production and widespread applications, because they are based on a wafer-scale technology with a high level of integration. Not surprisingly, the ...

Semiconductor lasers are ideally suited for mass production and widespread applications, because they are based on a wafer-scale technology with a high level of integration. Not surprisingly, the first lasers entering virtually every household were semiconductor lasers in compact disk players. A new ultrafast semiconductor laser concept has been introduced by Prof. Keller, which is power scalable, suitable for pulse repetition rate scaling in the 10 to 100 GHz regime, supports both optical and electrical pumping and allows for wafer-scale fabrication. This class of devices is referred to as the modelocked integrated external-cavity surface emitting laser (MIXSEL). The next step towards even lower-cost and more compact ultrafast lasers will be electrical pumping with both pico- and femtosecond pulses. This would result in devices ideally suited for many applications such as telecommunications, optical clocking, frequency metrology, high resolution nonlinear multiphoton microscopy, optical coherence tomography, laser display . anywhere where the current ultrafast laser technology is considered to be too bulky or expensive.

The project aims to demonstrate optically and electrically pumped MIXSELs in both the pico- and femtosecond regime. Picosecond MIXSELs are ideally suited for clocking applications whereas femtosecond MIXSELs are required for continuum generation and many biomedical applications. For both cases, average powers above 100 mW with electrical pumping and above 500 mW with optical pumping should be reached, which represent significant advances of ultrafast MIXSELs.

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    Mixsel Mixsel Presentation Transcript

    • Vertical integration of ultrafast semiconductor lasers for wafer-scale mass production Prof. Eli Kapon & Dr. Alexei Sirbu Institut de Photonique et d‘Electronique Quantiques, EPFL, Lausanne Prof. Bernd Witzigmann Computational Electronics and Photonics, University of Kassel (previously ETH Zurich)Prof. Pierre ThomannInstitut de Physique, Université de Neuchâtel Prof. Ursula Keller & Dr. Thomas Südmeyer Jan. 17, 2011 Laser Ultrafast Physics Department, ETH Zurich ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Compact ultrafast lasers for “real world application” Telecom & Datacom Interconnects Optical Clocking Multi-photon imaging Frequency comb Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • The first VECSELs conference at Photonics West Jan. 24 - 25, 2011 Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • CW Optically-Pumped VECSELs OP-VECSEL = Optically Pumped Vertical-External-Cavity Surface-Emitting Semiconductor Laser M. Kuznetsov et al., IEEE Photon. Technol. Lett. 9, 1063 (1997) • Semiconductor gain structure with reduced pump output coupler thickness laser IEEE JQE 38, 1268 (2002) gain structure • Pump: high power diode bar heat sink • External cavity Ultrafast Laser for diffraction-limited output ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • VECSEL gain structure heat gain structure sink pump output coupler pump energy laser gain structure heat sink ETH Zurich Ultrafast Laser Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Optically pumped semiconductor laser? • Maybe a bad idea coming from semiconductor diode lasers? • But for sure a good idea coming from diode-pumped solid-state lasers: - more flexibility in operation wavelengths - broad tunability - efficient mode conversion from low-beam-quality high-power diode lasers - modelocking possible with SESAMs - waferscale integration - cheaper ultrafast lasers in the GHz pulse repetition rate regime Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Semiconductor materials: bandgap engineering Wavelength of interest 960 nm, 1.3 µm, and 1.5 µm 1.5 µm Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • VECSELs: cw spectral coverage (Jennifer Hastie)• 2‐2.8 μm – GaInAsSb / AlGaAsSb • 1.5 μm – InGaAs / InGaAsP• 1.2‐1.5 μm – AlGaInAs / InP (fused)• 1.2‐1.3 μm – GaInNAs / GaAs• 1‐1.3 μm – InAs QDs• 0.9‐1.18 μm – InGaAs / GaAs• 850‐870 nm – GaAs / AlGaAs• 700‐750 nm – InP QDs• 640‐690 nm – InGaP / AlGaInP• Frequency‐doubled VECSELs have  been reported throughout the visible  and into the UV Infrared review: N. Schulz et al., Laser & Photonics Reviews 2, 160 (2008) Visible and UV review: S. Calvez et al., Laser & Photonics Reviews ETH Zurich Ultrafast Laser 3, 407 (2009) Physics updated by Jennifer Hastie, University of Strathclyde, group of Prof. Martin Dawsonnano-tera.ch Annual Meeting 12. 5. 11
    • Ultrafast VECSELs: Modelocking with SESAMs cw laser SESAM modelocked Semiconductor laser Saturable Absorber Mirror output pump coupler SESAM gain structure heat sinkReview articleUltrafast Laser for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006 ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Motivation for semiconductor lasers: Wafer scale integration D. Lorenser et al., Appl. Phys. B 79, 927, 2004 Passively modelocked VECSEL vertical external cavity surface emitting laser Review: Physics Reports 429, 67-120, 2006 SESAM MIXSEL modelocked integrated external-cavity surface emitting laser Ultrafast Laser D. J. H. C. Maas et al., Appl. Phys.ETH88, 493, 2007 B Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • MIXSEL wafer scale integrationA. R. Bellancourt et al., “Modelocked integrated external-cavity surface emitting laser” ETH Zurich Ultrafast LaserIET Optoelectronics, vol. 3, Iss. 2, pp. 61-72, 2009 (invited paper) Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Comparison of Ultrafast GHz LasersReview articleUltrafast Laser for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006 ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Optically pumped ultrafast VECSELs / MIXSELs B. Rudin, V. J. Wittwer, D. J. H. C. Maas, M. Hoffmann, O. D. Sieber, Y. Barbarin, M. Golling, T. Südmeyer, U. Keller, Opt. Express 18, 27582, 2010 Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Resonant vs. antiresonant MIXSEL design Initial MIXSEL demonstration had a resonant design: D. J. H. C. Maas et al., Appl. Phys. B 88, 493, 2007 • sensitive to growth errors • high GDD - long pulses growth error simulation: layer thickness variations < 1% Here: MIXSEL demonstration • tolerant to growth errors with Ultrafast Laser antiresonant design • low GDD - short pulses ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • MIXSEL: improved thermal management heat thermal estimated pump/ temp. rise heat sink output sink conductivity heating power laser (FE sim.) temperature power material (W m-1K-1) (pump power) mode radius GaAs 45 1.5 W (1.7 W) 80 µm 149 K -15 °C 41.5 mW copper 400 3.2 W (4.3 W) 80 µm 98 K +10 °C 660 mW diamond 1800 26.6 W (36.7 W) 215 µm 100 K -15 °C 6400 mW • exchange the copper with CVD diamond  reasonable temperatures • leads to highest output power from a ultrafast Finite Element (FE) temperature simulations Ultrafast Laser semiconductorZurich ETH laser Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • High power MIXSEL • Optical pumping 36.7 W at 808 nm • Cavity length: 60.8 mm  2.47 GHz • Pump / laser spot radius: ~215 m • Output coupling: 0.7% • Efficiency (opt-opt): 17.4 % • TBP: 1.35 (4.2 times sech2) B. Rudin, V. J. Wittwer,Laser H. C. Maas, M. Hoffmann, O. D. Sieber, Y. Barbarin, M. Golling, T. Südmeyer, U. Keller, Ultrafast D. J. ETH Zurich 18, 27582, 2010 Opt. Express Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Optically pumped ultrafast VECSELs / MIXSELs M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Kestnikov, D. A. Livshits, T. Südmeyer, U. Keller, Ultrafast Laser Opt. Express 19, 8108, 2011 ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Femtosecond all Quantum Dot VECSEL modelocked Separate pump mirror laser DBR separation tuning for maximum pump absorption  higher efficiency Active region chirped QD-layer positions output • each layer stack resonant for coupler QD-SESAM different laser wavelength • according to absorption intensity  broader gain QD-gain AR section CVD-diamond hybrid semiconductor / fused silica structure  reduction of the GDD Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Femtosecond QD-VECSEL modelocked laser heat sink: thinned QD gain structure on CVD substrate pump output coupler: 100 mm output coupler transmission: 2.5% output laser mode radius on QD-VECSEL: 115 µm coupler QD-SESAM laser mode radius on QD-SESAM: 115 µm heat sink temperature: -20°C CVD-diamond QD-gain structure pulse duration: 784 fs repetition rate: 5.4 GHz output power: 1.05 W TBP: 1.3 sech2 center wavelength: 970 nm peak power: 219 W Ultrafast Laser ETH Zurich M. Hoffmann, O. D. Sieber, V. J. Wittwer, I. L. Kestnikov, D. A. Livshits, T. Südmeyer, U. Keller, Opt. Express 19, 8108, 2011 Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • 2.62 W wafer fused VECSEL at 1550 nm • Combine advantages of InP-based active medium with GaAs/AlGaAs reflector • Intra-cavity diamond for good heat dissipation 2.62 W cw Ultrafast 21881-21886 (2008) Opt. Express 16, Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • First wafer-fused modelocked VECSEL at 1550 nm • First wafer-fused passively modelocked VECSEL at 1550 nm! • Combine advantages of InP-based active medium with GaAs/AlGaAs reflector • Intracavity diamond for good heat dissipation • Beam-spot diameters: 210 µm on gain chip; 50 µm on GaInNAs-based SESAM • 600 mW in 16 ps pulses at 1.29 GHz with 10 W pump power E. J. Saarinen, J. Puustinen, A. Sirbu, A. Mereuta, A. Caliman, E. Kapon, O. Okhotnikov, Ultrafast Laser ETH Zurich Optics Letters, 34, 3139 (2009) Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Electrical vs. optical pumping OP-VECSEL Output EP-VECSEL coupler Pump laser Top ring contact Active region ~ 50 μm DBR DBR Heat spreader Ultrafast Laser ETH Bottom Zurich disk contact Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • ETH Zurich EP-VECSEL design AR section Suitable for modelocking SiNx • Relatively low GDD: AR section top contact current spreading • Confined current injection for good beam profile • 6 µm current spreading layer layer • bottom p-doped, top n-doping n-DBR • small bottom disk p-contact p-DBR Power scalability bottom contact • Wafer removal active region • Large apertures possible SiNx Trade off between electrical and optical losses CuW wafer • Optimized doping profile • High doping → high free carrier absorption SEM • Low doping → high resistivity • Intermediate n-DBR for increased gain Design guidelines: P. Kreuter, B. Witzigmann, D.J.H.C. Maas, Y. Barbarin, T. Südmeyer and U. Keller, 14 µm Appl. Phys. B, 91, 257, 2008 Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11 11
    • First EP-VECSEL results  Growth, processing, and evaluation implemented  60 different EP-VECSEL lasing in cw  Output power up to 120 mW (cw) achieved  Good homogenous electroluminescence profiles measured for devices up to 100 µm (excellent agreement with our simulations) Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • EP-VECSEL cw results 40 EP-VECSELs with different bottom contact diameters Power scaling considerations • Output power should scale with area (P α Ø2) and current density (P α J ) • Ideal power scaling, ∆T independent of device size Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11 17
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • A key application: optical frequency combs offer - Phase stable link between optical (100s THz) and microwave frequencies (GHz) - Counting of arbitrary optical frequencies practicable for the first time impact - Fundamental physics - Optical clocks - Satellite navigation - Large bandwidth telecommunication - Spectroscopy - Medical applications, noninvasive diagnostics Ultrafast Laser Physics www.faszination-uhrwerk.de ETH Zurichnano-tera.ch Annual Meeting 12. 5. 11
    • Femtosecond Er:Yb:glass laser  Telecom center wavelength (1.55 µm)  Reliable telecom grade pump diode  Low power consumption (< 1.5 W electrical)  Clean soliton pulses  Polarized output  Total resonator losses below 3 %Stumpf, Zeller, Schlatter, Südmeyer, Okuno, Keller, Opt. Express 16, 10572 (2008) Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Moving of the laser from ETH to Neuchatel Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Noise performance of DPSSLs and VECSELs DPSSLs + high-Q cavity, low nonlinearities ⇒ extremely low intrinsic noise + convenient and robustExample excellent noise performance of DPSSLs: Optical ultra-stable microwave oscillator Compare 75 MHz 1.5-µm Er:Yb glass DPSSL with commercial 1.5-µm Er-fiber laser Relative frequency stability of the CEO frequency measured with the same feedback loop S.Schilt, M. C. Stumpf, L. Tombez, N. Bucalovic, V. Dolgovskiy, G. Di Domenico, D. Hofstetter, S. Pekarek, A. E. H. Oehler, T. Südmeyer, U. Keller, P. Thomann, “Phase noise characterization of a near-infrared solid-state laser optical frequency comb for ultra- stable microwave generation”, Optical Clock Workshop, Torino, Italy, December 1-3, 2010 (right scale: Ultrafast Laser relative frequency stability with respect to the optical carrier) ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • VECSELs for Frequency Comb Generation crucial for frequency comb stabilization: detection of the carrier envelope offset frequency (fCEO) fCEO detected with a DPSSL targeted VECSEL without pulse compression or amplification 278 fs p 200 fs 74 mW Pav 1W 75 MHz frep 1 GHz 3.1 kW Ppeak 4.4 kW 1550 nm λcenter 960 nm Stumpf, Pekarek, Oehler, Südmeyer, Dudley, Keller, Appl. Phys. B 99, 401 (2010) Femtosecond VECSEL: promising candidate for compact, low cost frequency comb generation Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Outline Motivation and research targets VECSELs and SESAMs MIXSEL concept Highlights • 6.4 W modelocked OP-MIXSEL chip at 960 nm. • 1 W femtosecond SESAM-modelocked OP-VECSEL at 960 nm. • 2.62 W cw average power from a 1550 nm OP-VECSEL realized with wafer fusion. First Modelocking result at 1550 nm. • 120 mW cw average power from an EP-VECSEL. • Full stabilization of a frequency comb (CEO beat and laser repetition rate) using a SESAM modelocked diode-pumped Er:Yb:glass Summary and outlook Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Optically pumped ultrafast VECSELs / MIXSELs Ultrafast Laser ETH Zurich Physicsnano-tera.ch Annual Meeting 12. 5. 11
    • Gantt chart• Excellent result of 960 nm MIXSEL => 1550 nm SESAM and MIXSEL delayed (Tasks 1.1, 1.2 and 2.1)• Femtosecond VECSEL demonstrated (Task 4.2) => high expectation for fs-MIXSEL (Task 4.3) Ultrafast Laser ETH Zurich Physics• First EP-VECSEL in a12. 5. 11nano-tera.ch Annual Meeting university,120 mW realized => 200 mW achievable in a next realization (Task 5.3)