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 Thomann
Institut 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
               Physics
nano-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
               Physics
nano-tera.ch Annual Meeting 12. 5. 11
The first VECSELs conference at Photonics West
                                        Jan. 24 - 25, 2011




               Ultrafast Laser                               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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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 Dawson
nano-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 sink

Review articleUltrafast Laser
               for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006
                                                                                      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
               Physics
nano-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
               Physics
nano-tera.ch Annual Meeting 12. 5. 11
MIXSEL wafer scale integration




A. R. Bellancourt et al., “Modelocked integrated external-cavity surface emitting laser” ETH Zurich
             Ultrafast Laser
IET Optoelectronics, vol. 3, Iss. 2, pp. 61-72, 2009 (invited paper)
             Physics
nano-tera.ch Annual Meeting 12. 5. 11
Comparison of Ultrafast GHz Lasers




Review articleUltrafast Laser
               for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006
                                                                                      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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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 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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               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
               Physics
nano-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
               Physics
nano-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)
             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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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
               Physics
nano-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 Zurich

nano-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
               Physics
nano-tera.ch Annual Meeting 12. 5. 11
Moving of the laser from ETH to Neuchatel




               Ultrafast Laser                ETH Zurich
               Physics
nano-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 robust

Example 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
               Physics
nano-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
               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
               Physics
nano-tera.ch Annual Meeting 12. 5. 11
Optically pumped ultrafast VECSELs / MIXSELs




               Ultrafast Laser          ETH Zurich
               Physics
nano-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. 11
nano-tera.ch Annual Meeting university,120 mW realized => 200 mW achievable in a next realization (Task 5.3)

Mixsel

  • 1.
    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 Thomann Institut 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
  • 2.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 3.
    Compact ultrafast lasersfor “real world application” Telecom & Datacom Interconnects Optical Clocking Multi-photon imaging Frequency comb Ultrafast Laser ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 4.
    The first VECSELsconference at Photonics West Jan. 24 - 25, 2011 Ultrafast Laser ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 5.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 6.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 7.
    VECSEL gain structure heat gain structure sink pump output coupler pump energy laser gain structure heat sink ETH Zurich Ultrafast Laser Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 8.
    Optically pumped semiconductorlaser? • 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 9.
    Semiconductor materials: bandgapengineering Wavelength of interest 960 nm, 1.3 µm, and 1.5 µm 1.5 µm Ultrafast Laser ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 10.
    VECSELs: cw spectralcoverage (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 Dawson nano-tera.ch Annual Meeting 12. 5. 11
  • 11.
    Ultrafast VECSELs: Modelockingwith SESAMs cw laser SESAM modelocked Semiconductor laser Saturable Absorber Mirror output pump coupler SESAM gain structure heat sink Review articleUltrafast Laser for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006 ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 12.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 13.
    Motivation for semiconductorlasers: 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 14.
    MIXSEL wafer scaleintegration A. R. Bellancourt et al., “Modelocked integrated external-cavity surface emitting laser” ETH Zurich Ultrafast Laser IET Optoelectronics, vol. 3, Iss. 2, pp. 61-72, 2009 (invited paper) Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 15.
    Comparison of UltrafastGHz Lasers Review articleUltrafast Laser for VECSELs: U. Keller and A. C. Tropper, Physics Reports, vol. 429, Nr. 2, pp. 67-120, 2006 ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 16.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 17.
    Optically pumped ultrafastVECSELs / 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 18.
    Resonant vs. antiresonantMIXSEL 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 19.
    MIXSEL: improved thermalmanagement 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 20.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 21.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 22.
    Optically pumped ultrafastVECSELs / 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 23.
    Femtosecond all QuantumDot 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 24.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 25.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 26.
    2.62 W waferfused 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 27.
    First wafer-fused modelockedVECSEL 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) Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 28.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 29.
    Electrical vs. opticalpumping 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 30.
    ETH Zurich EP-VECSELdesign 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 Physics nano-tera.ch Annual Meeting 12. 5. 11 11
  • 31.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 32.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11 17
  • 33.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 34.
    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 Zurich nano-tera.ch Annual Meeting 12. 5. 11
  • 35.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 36.
    Moving of thelaser from ETH to Neuchatel Ultrafast Laser ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 37.
    Noise performance ofDPSSLs and VECSELs DPSSLs + high-Q cavity, low nonlinearities ⇒ extremely low intrinsic noise + convenient and robust Example 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 38.
    VECSELs for FrequencyComb 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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 39.
    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 Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 40.
    Optically pumped ultrafastVECSELs / MIXSELs Ultrafast Laser ETH Zurich Physics nano-tera.ch Annual Meeting 12. 5. 11
  • 41.
    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. 11 nano-tera.ch Annual Meeting university,120 mW realized => 200 mW achievable in a next realization (Task 5.3)