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

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 http://www.phy.davidson.edu/stuhome/phstewart/http://www.actewagl.com.au/ Low loss (0.2 dB/km at = 1.5 µm) Thin, lightweight Bandwidth: 187-230 THz (or = 1.3–1.6 µm) (~ 5 mm diameter)

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 3 rd order intermodulation distortion products: (2f 2 -f 1 ) and (2f 1 -f 2 ) Doesn’t matter how close together f 1 and f 2 are

11. What About Phase Modulation?

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

13. Linearization Condition Third order nonlinearity can be cancelled, provided we choose  and  to satisfy:  = ratio of TE/TM phase modulation

14. Linearized Phase Modulator For LiNbO 3, TE and TM modes experience different phase mod. r 33 = 31 pm/V r 13 = 10 pm/V Similar ratio is seen in EO polymers

15. Lithium Niobate Phase Modulator Experiment

16. Reduced Distortion Third order nonlinearity can be cancelled, provided we choose  and  to satisfy:  = 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