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An Optical Fiber Mode-Locked Figure Eight Laser

K-State Physics REU Daniel Nickel Mentor: Brian Washburn. An Optical Fiber Mode-Locked Figure Eight Laser. Overview. Mode locked lasers Produce soliton-like pulses The soliton The optical soliton Dispersion Self-phase modulation The figure eight laser Description

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An Optical Fiber Mode-Locked Figure Eight Laser

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  1. K-State Physics REU Daniel Nickel Mentor: Brian Washburn An Optical Fiber Mode-Locked Figure Eight Laser

  2. Overview • Mode locked lasers • Produce soliton-like pulses • The soliton • The optical soliton • Dispersion • Self-phase modulation • The figure eight laser • Description • Principles of operation • Results

  3. Pulse Train from a Mode-Locked Laser Gain DC = Dispersion Compensation SA = Saturable Absorber S A D C

  4. The Soliton • First Observation • John Scott Russell, 1834 • Deemed the “Wave of Translation” Photos courtesy of www.amath.washington.edu/~bernard/kp/waterwaves

  5. The Optical Soliton sech2 • F8L produces soliton-like pulses • Balance between Self-Phase Modulation (SPM) and Dispersion

  6. Material Dispersion Characterized by the mode propagation constant: • Positive (normal) • High frequencies: slow • Low frequencies: fast • Negative (anomalous) • High frequencies: fast • Low frequencies: slow

  7. Temporal Spreading

  8. Self-Phase Modulation Net negative dispersion needed in F8L cavity to form solitons Arises from the Optical Kerr Effect Leading edge shifts to lower frequencies Trailing edge shifts to higher frequencies

  9. The Figure Eight Laser 980 nm pump 980 nm pump NALM PC PC Er fiber Er fiber isolator isolator PC PC PZT PZT NALM: nonlinear amplifying loop mirror 50/50 50/50 Output

  10. The Optical Coupler (50/50) Both 4 port devices Coupler needs a π phase difference between pulses to completely switch out of one port

  11. Nonlinear Loop Mirror: Linear Operation PC PC Linear Operation: No phase shift between interferometer arms

  12. Nonlinear Loop Mirror: Nonlinear Operation PC PC Nonlinear Operation:

  13. Building the Figure Eight Laser • Fiber length requirements • Net negative (anomalous) dispersion • NALM π phase shift • Fiber splicing using arc fusion splicer • Spliced fibers and components together • Spliced fiber that the polarization controllers broke • Mode-locking • Many days of manipulating the PC’s until sech2 shaped spectrum appeared

  14. Results Kelly Sidebands • Mode-locked Operation • Inherently Stable • Tunable Center Wavelength= 1567 nm Bandwidth (FWHM)= 12.9 nm Repetition Rate= 57.753 MHz Power = 10 mW

  15. Results Our pulses: Transform limited pulse: for sech2 pulses • Nearly transform-limited pulses • Shortest possible pulse with the given bandwidth • From the uncertainty principle

  16. What’s Next? Amplifier • Amplification and compression to < 70 fs pulses

  17. Thanks for your time. References: 1.I. Duling III, Opt. Lett. 16, 539 (1991) • M.E. Fermann, F. Haberl, M. Hofer, and H. Hochreiter, Opt. Lett. 15, 752 (1990)

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