| Analog fiber optic links have been used in standard frequency distribution networks, phased array radars, fiber optic signal processors and sensors, and in a variety of other applications such as radar signal transmission on Naval shipboards. These systems typically employ fiber optic links to distribute precise reference signals from a standard frequency source to remote sights. There are several components, such as the laser source, photo-detector, and optical amplifier, which degrade the phase stability of the reference signals [1-3]. Shot noise and thermal noise are contributed to the link by the photo-detector. Environmental factors, temperature and pressure, for example, also impose noise on the link. Optical amplifiers (OA) affect the quality of the signal by adding amplified spontaneous emission (ASE) noise. The focus of this research is to determine the effect of ASE noise generated by an Erbium Doped Fiber Amplifier (EDFA) on the phase of an RF signal traveling through a WDM fiber optic link. The experimental set up includes a reference signal that is intensity modulated, transmitted through a fiber optic link, photo-detected, and compared to the original RF signal for phase detection. The EDFA is operated in the saturation region, where the gain decreases when the optical power increases. We are mainly interested in determining the additive phase noise levels with changes in EDFA gain. The set up includes a WDM laser source operating at wavelengths ranging from 1530 nm to 1560 nm, and the modulated 100 MHz reference signal is transmitted through a 9km fiber optic cable. The results indicate that for the wavelengths ranging from 1540 nm to 1560 nm, there exists a near-linear relationship between EDFA gain and additive phase noise. It is found that, on average, there is a 2-dBc/Hz increase in the phase noise for every 5dB increase in EDFA gain. This result is consistent for offset frequencies of 1 Hz to 1,000 Hz from the carrier frequency. In conclusion, the additive phase noise in a link with an EDFA is affected by the gain of the amplifier. In order to increase the phase stability of the link, the EDFA should be operated at higher optical input levels. These higher input power levels can be achieved by placing an EDFA as close as possible to the transmitter. |
| Dr. Mehdi Shadaram, Briscoe Distinguished Professor and Associate Dean of Engineering at the University of Texas at San Antonio has extensive experience in obtaining and successfully directing engineering grants. He has been either PI or Co-PI for numerous grants and contracts, totaling more than $6 million, in the past 10 years. NASA, Jet Propulsion Laboratory, National Science Foundation, Office of Naval Research, Department of Defense, Texas Instruments and Lucent Technologies have funded his research projects. His main area of research activity is in the broadband analog and digital fiber optic communication systems. He has published more than seventy articles in refereed journals and conference proceedings. He has extensive experience with mentoring minority and underrepresented groups. Under his supervision, seven PhD candidates and thirty-five Master’s students have finished their degree program in the past 20 years. He is a senior member of IEEE and member of OSA, SPIE, ASEE, and HKN. He received his Ph.D. in electrical engineering in 1984. |