March 2000 Meeting

RF Photonics Technologies at SPAWAR

The Optical Society of San Diego is pleased to present Dr. Steve Pappert, who will describe on-going work in RF photonics-the use of light to perform microwave signal processing functions- performed within the Optoelectronics Branch at SPAWAR. Of special interest will be examples of fiber optics technologies that leverage strongly off commercial telecommunications and broadband technologies.

Abstract: The Optoelectronics Branch has been providing advanced fiber optic and integrated optic system solutions to the Navy for over 25 years. Challenging military requirements have fostered the development of RF photonic systems for a variety of applications such as high performance microwave-on-fiber photonic links and optical antenna control. For these and other applications, we have developed RF photonic subsystem technologies for RF signal distribution, antenna networking and antenna reconfiguration. Finally, we are developing the required components for these applications, including: semiconductor optoelectronic rf switches; optical signal processors and filters; high-speed A/D converters and passive fiber optic couplers for wavelength division multiplexing. In my talk, I will present a general overview of our ongoing research and development, that will be accessible to the non-specialist.

Biography: Dr. Steve Pappert has been with the Optoelectronics Branch at SPAWAR since 1983. He received the Ph.D. degree in electrical engineering from the University of California, San Diego in 1993. His research interests include microwave fiber optic links with application to optical signal processing and mixed signal networking. Dr. Pappert has published a total of more than 100 journal articles and conference proceeding papers, recently contributed a book chapter in RF Photonics, and holds a number of patents within the fiber optics and optoelectronics fields. Just last month, Pappert gave the invited paper at the plenary session of the DARPA Symposium on Photonic Systems for Antenna Applications (PSAA)-an important meeting in his specialty.

 

 

March Meeting Review:
by Jim Bechtel

"Optoelectronics at SPAWAR"

Dr. Steve Pappert of the SPAWAR Systems Center in San Diego was the featured speaker at the March Meeting of the Optical Society of San Diego. Dr. Pappert's topic was "Selected SPAWAR Optoelectronics Activities." For the last few years, he has been one of the Navy's principal advocates of the use of fiber optics and optoelectronics for naval applications.

After reviewing some of the history of the SPAWAR (previously NOSC, NRaD and NECL) optoelectronics effort, he described several topics of interest to the Navy. These include: 1) RF photonic link technology for antenna applications, 2) passive wavelength division multiplexing (WDM) components for analog and digital optoelectronic applications, and 3) optically controlled RF switching.

For the Navy, multi-ton weight reduction can be achieved by replacing shipboard copper transmission lines by fiber on current and future ships. Here multifunction RF photonic links have reduced size, weight, increased bandwidth, and EMI immunity. For broadband applications, Pappert described the challenges associated with noise figure, linearity, phase and amplitude stability, spurious free dynamic range as well as cost and reliability. He also discussed some recent success of fiber optic links that has been achieved for shipboard distribution of GPS signals.

His presentation also included recent research results to determine performance limits of both directly modulated and externally modulated links. Significant improvement was obtained in the dynamic range by the use of a 2-wavelength push-pull DFB laser system with the lasers biased for minimum 3rd order distortion and differential detection of the two wavelengths. Here the WDM passive components were developed at SPAWAR as polarization independent narrow channel (PINC) WDMs. One commercial application of these WDMs is to increase the pump power for fiber amplifiers and fiber lasers.

Other topics discussed were optical ADD/DROP multiplexers by writing a fiber grating in the coupling region of a fused coupler and the applications of these ADD/DROP multiplexers to wavelength routing in multi-wavelength networks.

As a final topic, Pappert discussed optical controlled RF switching. Here, applications include reconfigurable antenna and transmit-receive switches. The photonic control allows rapid switching and high reliability. In addition, the switch is electromagnetically isolated, no electrical bias is required, and the control lines are low-loss, broadband, and lightweight.

Pappert and his colleagues at SPAWAR are leading the way into the 21st century by applying modern optoelectronic technology to some technically interesting military applications for the US Navy.