Lior Yaron 12.3.15

You are invited to attend a lecture

by

Lior Yaron

(PhD. student under the supervision of Prof. Moshe Tur)

School of Electrical Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel

Photonic True Time Delay

 Over the last fifty years, the engineering community recognized the need for True Time Delay (TTD) in phased array antennas.  However, the subject has become increasingly important in the last decade, as radar systems were required to achieve higher resolution, farther distances and wider scan angles. One of the preferred RF solutions is the Rotman lens, which uses RF guided waves in a specially designed geometrical structure to produce these delays for a number of discrete beams.  However, the need for smaller volume and lower weight, as well as for still wider bandwidth, has made this option less attractive. Alternatively, TTD may be implemented digitally, using fast (many Giga-Samples/sec) Analog to Digital converters on every element.  This power-hungry technology, though, has not yet reached maturity but may become a viable solution in the future.  This leaves photonic technology as a mid-term feasible option.

In this seminar we will discuss the need for TTD in modern radar systems and the possibility to implement it using a photonic sub-system. We will present a photonic delays network for antenna array receiver employing multiple scanning beams and discuss the main design considerations. We will also present measurements results of a single TTD module with 4 independent beams and 8 different delays showing extremely smooth RF response in the X-band, fast switching capabilities and negligible crosstalk.

In the second part of this seminar we will discuss Brillouin Dynamic Gratings (BDGs), which have been recently suggested to realize tunable photonic delay elements with large delay-bandwidth product. A fundamental feature of Brillouin scattering that might present a limitation is the inevitable presence of spontaneous Brillouin scattering, generated by the scattering of the optical signal from thermally excited acoustic waves. In this talk we will show theoretically and experimentally how the undesired scattering of the signal can be considerably enhanced in BDG through interaction with the scattering of the orthogonally polarized pump which writes the grating. For a strong enough pump and even moderate signal power levels, the observed scattering is dominated by the pump, exhibiting an average power more than 30 dB stronger than that of the signal alone.

Thursday, March 12, 2015, at 12:00

Room 011, EE- KITOT building