1. Radio-Frequency Characteristics of Ultraviolet Optical Links J. Deng, S. Halder, and J. C. M. Hwang, Lehigh University A. Osinsky, SVT Associates H. Seigneur, W. V. Schoenfeld, and L. Chernyak, University of Central Florida

2. Introduction Light-emitter diode (LED) characteristics Photo-detector (PD) characteristics LED-PD link DC characteristics LED-PD link RF characteristics Conclusion Outline

3. Non-Line-of-Sight Covert Links

4. Current UV Links Mercury lamp + photo-multiplier tube = bulky, inefficient and expensive

5. Proposed UV Links GaN light-emitting diode + photo-detector diode = compact, efficient, low cost 5µm PD2 100µm PD1 300µm LED

6. I (mA) 100 80 60 40 20 LED Emission Spectra

7. PD DC Characteristics Photo Response Dark Current Comparable between ( ■ ) PD1 & (▲) PD2

8. Distributive R-C Effect Both (symbol) measurement and (curve) simulation show larger dispersion in PD1 (▲) PD2 ( ■ ) PD1

9. DC LED-PD Link Comparable between ( ■ ) LED-PD1 & (▲) LED-PD2

10. (▲) LED-PD2 more wide- band than ( ■ ) LED-PD1 Small-Signal LED-PD Link

11. Bias Dependence of LED-PD1 Link Bandwidth and gain of LED-PD1 link increase with reverse bias of PD1 LED-PD2 link bandwidth independent of PD2 bias

12. Bias Dependence of LED-PD2 Link Bandwidth of LED-PD2 link increases with LED current Bandwidth of LED-PD1 link independent of LED current

13. Conclusion 370-nm link demonstrated at 60 MHz by using GaN LED and photo-detector Link bandwidth is orders-of-magnitude higher than that achieved by using lamp and tube Link bandwidth limited by LED instead of photo-detector Bandwidth improvement of solar-blind (<280nm) LED in progress

14. Acknowledgment LED supplied by Tekcore Co., Taiwan Research sponsored in part by the U.S. Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-06-2-0020. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government.