The document discusses femtosecond lasers and optical frequency combs and their applications. It describes how carrier envelope phase control allows generation of optical arbitrary waveforms. Frequency combs have enabled advances in optical clocks and precision sampling. Applications include spectroscopy, imaging, and communications. The author discusses using integrated modulators to generate complex waveforms spanning multiple octaves.

1. Clocks, Combs and OAWG Erich P. Ippen Massachusetts Institute of Technology Cambridge, MA 02139 [email_address] NEOSA September 15, 2011 MIT Optics and Quantum Electronics

2. Outline Femtosecond lasers – few cycle pulses Carrier envelope phase control Optical frequency combs Arbitrary optical waveforms Applications Clocks Precision sampling and timing MIT Optics and Quantum Electronics

3. The 5-fs Ti:sapphire Laser Kerr lens modelocking (KLM) Double-chirped mirrors All-solid state, prismless cavity 5 fs = less than 2 cycles Octave-spanning spectrum MIT Optics and Quantum Electronics

4. Under Each Pulse is a Short Waveform The electric field waveform slips under the envelope from pulse to pulse – if group delay and phase delay differ. Carrier-envelope phase slip  2n G L/c MIT Optics and Quantum Electronics BBO 570 nm filter PBS RF spectrum analyzer PMT Second harmonic generation

5. Control Over the Optical Phase Carrier-envelope phase stabilization An optical clockwork ! The optical frequency is an exact multiple of the pulse rep-rate. MIT Optics and Quantum Electronics

6. A Clock an oscillator a clockwork Pendulum - Christiaan Huygens 1656 Chronometer - John Harrison (H4) 1761 (10 -6 ~ 1 sec/ 9 days ) Quartz - W. Marrison, Bell Labs, 1928 (10 -8 ~ 1 sec/3yrs ) Cesium atom - 1955 (10 -10 ~ 1sec/300yrs) Hg ion – 5x10 -18 ~ 10sec since big bang Atomic fountain - NIST-F1 (1.7x10 -15 ~ 1sec/20Myrs) and MIT Optics and Quantum Electronics

7. Clockwork by Frequency Multiplication From the 9.192 GHz Cs frequency standard to the 456 THz (657nm) Ca transition 1999 10 -14 accuracy 10 lasers 8 phase-lock loops MIT Optics and Quantum Electronics

8. The Clockwork in the Frequency Domain 1f-to-2f frequency locking Octave-spanning frequency comb This locks the rep rate to the optical frequency. Still need an optical reference. MIT Optics and Quantum Electronics laser modes exact multiples of f rep 2 nd harmonics

9. Locking to the 3.39  m HeNe Reference via DFG He-Ne/CH 4 Laser 3.39  m Transportable Stability ~ 10 -14 Difference frequency generation in PPLN DFG MIT Optics and Quantum Electronics

10. A Portable Optical Frequency Reference Monolithic “ sitall / zerodur” resonator Compact Ultrastable (< 10 -14 ) Transportable Phase- locked He-Ne laser 3.39  m output Mikhail Gubin, Lebedev Institute Methane-stabilized He-Ne Laser:  = 3.39  m MIT Optics and Quantum Electronics

11. L 1GHz Ti:sapphire Laser Frequency Comb MIT Optics and Quantum Electronics CEO locked Frequency referenced 1f-to-2f in LBO CH 4 - stabilized HeNe

12. Optical Arbitrary Waveform Generation (OAWG) Amplitudes and phases of all these frequencies are now determined. How about: MIT Optics and Quantum Electronics

13. Completely Arbitrary Waveforms Fast modulator array Spectrum locked to “absolute” grid Arbitrary electrical field waveform ! Pulse-to-pulse AM & PM Arbitrary spectrum MIT Optics and Quantum Electronics f t

14. Optical Arbitrary Waveform Generation The basic idea (Heritage and Weiner) A grating disperses the broad spectrum of an ultrashort pulse. A phase and amplitude mask is inserted into the Fourier plane. A second grating recombines the modified spectrum into a “shaped” waveform. The advanced integrated version (UC Davis) In current technology, a small band of frequencies passes through each modulator element. Modulator array Arrayed Waveguide Grating MIT Optics and Quantum Electronics

15. InP Encoder: 10channel 14.2 mm UC Davis S.J. Ben Yoo et al. Trial output waveforms 10.7 mm PM AM MIT Optics and Quantum Electronics

16. Packaged InP OAWG (10 Ch AM+ 10 Ch PM) x 10 GHz InPhi & UC Davis MIT Optics and Quantum Electronics

17. Route to 10 GHz Precise dispersion compensation Gain flattening Optimized output mirror Tight focusing; low loss 1.5cm DCM11G 1% Inverse Gain OC DCM11G 1.5cm DCM11G 2.28mm Ti:Sa 5.5 GHz 1.5cm DCM11G 1% Inverse Gain OC DCM11G 1.5cm DCM11G 2.28mm Ti:Sa 3.3 GHz 10 GHz 0.75cm DCM11G 1% Inverse Gain OC DCM11G 0.75cm DCM11G 2.28mm Ti:Sa MIT Optics and Quantum Electronics

18. Alternate Route: 10 x Rep-Rate Multiplication by Filtering Mode Matching Optics Balanced Detector Brewster Plate PBS λ /4 4% BS Loop Filter Piezo Driver Output 10xf Piezo ML Laser Laser Rep Rate: f Super-invar Hänsch-Couillaud locking method F = 156 => 30dB sidemode suppression F = 2100 => 55 dB sidemode suppression J. Chen et al. Opt.Lett.32, 1556, 2007 10x F = 2100 MIT Optics and Quantum Electronics

19. Rep Rate Multiplication with Monolithically Integrated Interleavers M. Sander et al, CLEO 2011: CThY5 Thermal tuning for optimizing delays coupling coefficients Side-mode suppression limited by offsets in coupling coefficients waveguide dispersion

20. GHz Er:Fiber Laser Technology MIT Optics and Quantum Electronics

21. Wider Goal: Two Octaves of Frequency Comb Ti:sapphire Er/Yb glass/fiber 0.5  m 1.0  m 1.5  m 2.0  m 3.39  m /2 f-to-2f + DFG f-to-2f + DFG More power per comb line Facilitates demultiplexing via AWG HeNe-CH 4 3.39  m reference for DFG MIT Optics and Quantum Electronics

22. 1-GHz Er-doped Fiber Laser P output = 27.4 mW W intracav = 283 pJ P pump = 380 mW 187 fs pulses 17.5 nm BW MIT Optics and Quantum Electronics SBR Partial Reflector OC 10% Output Erbium Fiber (92mm) FC/PC connector WDM 977 nm SMF28e (11mm)

23. Integrated Femtosecond Waveguide Laser Integrated gain + dispersion compensation Integrated pump coupling Integrated loop mirror/output coupler Butt-coupled SBR 44x18 mm 2 400 MHz rep rate 440 fs pulse duraton MIT Optics and Quantum Electronics

24. High power femtosecond amplifier Octave-spanning continuum generation:  = 1  m - 2  m 1.55  m oscillator 1 GHz, 200fs, 20mW Output 100fs 2 W Positive dispersion high power amplifier 1 GHz Er-Fiber Comb D. Chao et al, to be published MIT Optics and Quantum Electronics PC SMF Pre-chirp Fiber HNLF ISO Pre-Amplifier PC ISO WDM 10W Raman Fiber Laser Liekki Er-doped Fiber SMF Post-chirp 1480nm PUMP Lens 980 nm Liekki Er-doped Fiber (83 mm) PUMP ISO 980 nm Collimator Dichroic Lens Lens SBR OC (5%) PZT AOM Lens Loop Filter ~ PD Amp BPF LO Feedback Control Electronics DFG HeNe SHG (f-2f) Loop Filter ~ PD Amp BPF LO Feedback Control Electronics

25. 1 GHz Octave-Spanning 1µm-2µm Continuum 1012nm 7.09mW 2024nm 65.37mW 1 GHz Source 1 GHz Supercontinuum 1082nm 8.56mW 1590nm 47.02mW 1f-2f DFG MIT Optics and Quantum Electronics

26. Some Applications High field and coherent control science Optical coherence tomography Ultrahigh-resolution 3-D LADAR imaging Multi-dimensional spectroscopic sensing Bistatic LADAR Novel coherent optical communications Impairment avoidance in fiber communications MIT Optics and Quantum Electronics

27. High Resolution Optical Sampling Application: Photonic analog –to- digital conversion Amplitude fluctuations of sampling pulse can be cancelled by balanced detection Resolution and dynamic range limited by timing jitter Modelocked lasers can achieve quantum-limited jitter Optical pulses sample analog signal on an electro-optical modulator voltage waveform MIT Optics and Quantum Electronics optical sampling pulse I(t) voltage waveform V(t) timing jitter V(t) E-O Modulator

28. Precision Sampling for ADC G.C. Valley, Opt.Exp. 15, 1955 (2007) R. H. Walden IEEE J.Sel.Areas in Comm 17, 539 (1999) ADC limited by timing jitter in sampler The Walden Wall MIT Optics and Quantum Electronics

29. 40 Gs/s 8-bit Optical Bit Interleaved ADC 4mm x 4mm chip 20 HIC ring filters with 8  m radius, 20 nm FSR SiGe detectors with 2 GHz BW, 100 nW NEP Analog Si modulator bandwidth 50 GHz Ultra Low-jitter direct optical sampling Kaertner, Ippen, Hoyt, Smith, Ram, MIT Lincoln Lab MIT Optics and Quantum Electronics

30. Synchronization of a Large Scale X-Ray FEL Kim et al., MIT/DESY MIT Optics and Quantum Electronics

31. Acknowledgments Andrew Benedick Hyunil Byun Jeff Chen David Chao Jonathan Morse Michelle Sander Jason Sickler Franz Kärtner Noah Chang Jung-Won Kim MIT Optics and Quantum Electronics

32. Linearly Chirped Waveform – 10 Modes 10 x 10GHz (10ps pulses) Supergaussian amplitude apodized 2  quadratic phase Chirp over timeslot - 100GHz/100ps Spectral domain Time domain – chirped pulse Phase vs. time Chirp Amplitude Initial vs. chirped pulse Theory MIT Optics and Quantum Electronics

33. Linearly Chirped Waveform – 100 Modes 100 x 10GHz (1ps pulses), Supergaussian amplitude apodized 27  quadratic phase Chirp over timeslot - 1THz/100ps Spectral domain Time domain – chirped pulse Phase vs. time Chirp Amplitude Initial vs. chirped pulse MIT Optics and Quantum Electronics

34. Linearly Chirped Waveform 10-Modes Blue Curve – Target Intensity Black Curve -- Measured Intensity Blue dots – Target Phase Red Curve – Measured Phase Circles – Target Intensity Black Stems -- Measured Intensity Blue X – Target Phase Red Dots – Measured Phase Experiment MIT Optics and Quantum Electronics