An Optical Fiber Mode-Locked Figure Eight Laser

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

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Pulse Train from a Mode-Locked Laser
D C
S A

• DC Dispersion Compensation
• SA Saturable Absorber

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The Soliton

• First Observation
• John Scott Russell, 1834
• Deemed the Wave of Translation

Photos courtesy of www.amath.washington.edu/berna
rd/kp/waterwaves
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The Optical Soliton

• F8L produces soliton-like pulses
• Balance between Self-Phase Modulation (SPM) and
  Dispersion

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Material Dispersion
Characterized by the mode propagation constant

• Positive (normal)
• High frequencies slow
• Low frequencies fast
• Negative (anomalous)
• High frequencies fast
• Low frequencies slow

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Temporal Spreading
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Self-Phase Modulation
Arises from the Optical Kerr Effect
Leading edge shifts to lower frequencies Trailing
edge shifts to higher frequencies
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The Figure Eight Laser
50/50
50/50
Output
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The Optical Coupler (50/50)
Both 4 port devices Coupler needs a p phase
difference between pulses to completely switch
out of one port
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Nonlinear Loop Mirror Linear Operation
PC
PC
Linear Operation No phase shift between
interferometer arms
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Nonlinear Loop Mirror Nonlinear Operation
PC
PC
Nonlinear Operation
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Building the Figure Eight Laser

• Fiber length requirements
• Net negative (anomalous) dispersion
• NALM p 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 PCs until sech2
  shaped spectrum appeared

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Results

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

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Results

• Nearly transform-limited pulses
• Shortest possible pulse with the given bandwidth
• From the uncertainty principle

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Whats Next?

• Amplification and compression to lt 70 fs pulses

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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)