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New Techniques for Transmitting Microwave Signals Over Optical Fiber

New Techniques for Transmitting Microwave Signals Over Optical Fiber. Thomas E. Murphy Dept. of Electrical and Computer Engineering Institute for Research in Applied Physics. ECE Research Revie w Day – October 9, 2009. Sponsors. Participants and Collaborators.

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New Techniques for Transmitting Microwave Signals Over Optical Fiber

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  1. New Techniques for Transmitting Microwave Signals Over Optical Fiber Thomas E. MurphyDept. of Electrical and Computer Engineering Institute for Research in Applied Physics ECE Research Review Day – October 9, 2009

  2. Sponsors

  3. Participants and Collaborators • Dr. Bryan Haas (Laboratory for Physical Sciences) • Dr. Timothy Horton (Laboratory for Physical Sciences)

  4. Coax vs. Fiber • High loss (750 dB/km at 5 GHz) • Large, heavy • Bandwidth: DC–20GHz (~ 5 mm diameter) http://www.phy.davidson.edu/stuhome/phstewart/ http://www.actewagl.com.au/ • Low loss(0.2 dB/km at l = 1.5 µm) • Thin, lightweight • Bandwidth: 187-230 THz (or l = 1.3–1.6 µm)

  5. Microwave Photonics:Using optical fiber to transmit microwave signals Advantages: • Negligible attenuation in fiber • Lightweight • Immune to EMI Disadvantages: • Requires high-fidelity modulation & demodulation • Total RF to RF loss can still be high

  6. Application: Antenna Relay • High-speed A/D conversion and signal processing is done remotely Problem: How to modulate and demodulate optical carrier without distortion

  7. Conventional Microwave Optical Link

  8. Optical Modulation

  9. Nonlinearity and Distortion

  10. Intermodulation Distortion • 3rd order intermodulation distortion products: (2f2-f1) and (2f1-f2) • Doesn’t matter how close together f1 and f2 are

  11. What About Phase Modulation?

  12. A Linearized Phase Modulator • TE and TM experience different degrees of phase modulation

  13. Linearization Condition • Third order nonlinearity can be cancelled, provided we choose a and q to satisfy: • g = ratio of TE/TM phase modulation

  14. Linearized Phase Modulator • For LiNbO3, TE and TMmodes experiencedifferent phase mod.r33 = 31 pm/Vr13 = 10 pm/V • Similar ratio is seen in EO polymers

  15. Experiment Lithium Niobate Phase Modulator

  16. Reduced Distortion • Third order nonlinearity can be cancelled, provided we choose a and q to satisfy: • g = ratio of TE/TM phase modulation

  17. Summary • Modulation nonlinearity can introduce distortion in microwave photonic transmission systems • New technique for linearization by using both polarization states in a phase modulator Future • Integrated polymer phase modulators, with built-in antenna • Applications in next-generation picocell wireless networks

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