This is my talk about "Picosecond VECSELs with Repetition Rates up to 50 GHz" which I gave at my Ph.D. defense at ETH Zurich

1. Dirk Lorenser Institute of Quantum Electronics ETH Zurich, Switzerland Picosecond VECSELs with repetition rates up to 50 GHz Ph.D defense presentation - December 5, 2005

5. Applications Optical clocking Telecommunications Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook Frequency doubling IR ->visible (RGB systems)

8. Gain Structure Design: GDD Subcavity resonances between R AR and R HR R HR > 99.9% R AR < 1% active region heat sink Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook Group-Delay Dispersion (GDD) GDD of gain structure is the dominating source of dispersion in the cavity of a ML VECSEL (up to several ±1000 fs 2 )

9. Processing # # : Häring et al., IEEE J. Quantum Electron., 38 (9), 1268 (2002) Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook (≈ 7 μ m thick)

10. Processing 2 mm 5 mm gain structure on copper heat spreader gain structure on CVD diamond heat spreader Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook

11. VECSEL Heating Temperature rise in center: Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook 1800 Diamond 400 Cu 45 GaAs  (WK -1 m -1 ) Material

12. Thermal lens: simple model Model thermal lens as a thin gradient-index lens of thickness d eff . Take the gain structure subcavity resonance as effective optical thickness: For gain structures on high-thermal-conductivity heat spreaders: Gaussian transverse temperature distribution with Δ T ≈ ΔT 1D which can be approximated with Taylor expansion to 2 nd order: Δ T = 40 K, w = 70 μ m n b = 3.54 (GaAs) dn/dT = 2·10 -4 K -1 Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook Δλ = 35 nm, λ = 960 nm, n = 3.54 (GaAs) -> d eff = 3.7 μ m

13. Thermal lens: simple model ray matrix for a GRIN duct of thickness d eff : for  d eff << 1 this is equivalent to a thin lens: ( single pass ) for double-pass and Gaussian profile: *measured: 3.2 ± 0.3 cm Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook 1.8* 17 f (cm) 45 30 Δ T 1D (K) Hi-Rep (50 GHz) w = 70 μ m d eff = 3.7 μ m dn/dT = 2·10 -4 Hi-Power (4 GHz) w = 175 μ m d eff = 3.7 μ m dn/dT = 2·10 -4

25. 50-GHz VECSEL folded cavity with L cav = 3 mm top-down pump under 45 º to maximize space in xy-plane Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook

26. 50-GHz VECSEL: cavity collimated-beam cavity with weakly curved or flat OC for 1:1 mode locking Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook

28. CW measurements copper heat spreader w p ≈ 65 μ m slope efficiency: ≈ 12% threshold: ≈ 556 mW max. TEM 00 output power: ≈ 115 mW Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook output coupler R = 200 mm , T out = 0.8%

29. CW measurements CVDD heat spreader w p ≈ 65 μ m slope efficiency: ≈ 14% threshold: ≈ 480 mW max. TEM 00 output power: ≈ 100 mW Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook output coupler R = 200 mm , T out = 0.8%

31. CW measurements flat OC gain structure on CVDD heat spreader w p ≈ 70 μ m T out = 1.6% slope efficiency: ≈ 22% extrap. threshold: ≈ 620 mW max. TEM 00 output power: ≈ 370 mW Motivation Optically-Pumped VECSELs Mode Locking VECSELs 1 - 10 GHz VECSELs up to 50 GHz Conclusion and Outlook

35. Acknowledgement FIRST Silke Schön Emilio Gini Dirk Ebling Martin Ebnöther Otte Homan Physics Department Hansruedi Scherrer Harald Hediger Jean-Pierre Stucki University of Southampton Anne C. Tropper ULP Group Ursula Keller Heiko Unold Rüdiger Paschotta Alex Aschwanden Deran Maas Aude-Reine Bellancourt Benjamin Rudin Rachel Grange Markus Haiml Reto Häring Industry Partners