PhD Defense: "Integrated True Time Delays and Optical Beamforming Networks for Wideband Wireless Communications"

Yuan Liu

March 19th (Tuesday), 1:00pm
Engineering Science Building (ESB), Rm 2001

Mobile data traffic is increasing dramatically in recent years. Currently, 34% of global data traffic is achieved by wireless and the global mobile data traffic has been projected to reach 77.49 exabytes per month by the year 2022. Given that the high spectral efficiency already been obtained, millimeter wave (mmW) frequencies at Ka-band, V-band and even W-band have been proposed for the 5th generation (5G) mobile cellular communication (expected in 2020) to achieve high bit rate links. Beamforming is inevitable in mmW communication systems as it provides a programmable antenna gain to overcome the high atmospheric loss of mmWs, reduces the signal interference and latency, and increases communication security. For wideband communications, true time delays (TTDs) is desirable for beamforming compared with phase shifters where the bandwidth could be limited by beam squinting. Integrated microwave photonics technology is more suitable for TTD beamforming due to the large bandwidth, low propagation loss, precise path length control, immunity to electromagnetic interference, lightweight, and low cost, comparing to its electrical counterpart. In this work, we studied integrated optical beamforming networks (OBFN) employing silicon nitride ultra-low loss waveguide technology based on optical ring resonators (ORRs) and switched delay lines (SDLs), respectively. A continuously tuning of 209ps with a bandwidth of 6.3GHz is achieved for ORR based delay lines, and a 172ps of continuously tuning range achieved for a bandwidth of 8.6GHz. A 22.5ps precise discrete delay tuning with a tuning resolution of 1.5ps is achieved over a bandwidth of 8nm for SDLs. A TTD beam steering experiment is also demonstrated with the SDL-OBFN. Beam angles of -51°, -33°, -17°, -2°, 14° and 31° are achieved for signal carriers from 85GHz to 100GHz.

About Yuan Liu:

photo of yuan liuYuan Liu received the B.S. degree from Harbin Institute of Technology in China, the M.S. degree in condensed matter physics the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, China, and the second M.S. degree in electrical and computer engineering from the University of California, Santa Barbara (UCSB), Santa Barbara, CA, USA in 2009, 2012, and 2014, respectively. He is currently working toward the Ph.D. degree at the UCSB with emphasis on photonic integrated circuits and microwave photonics.

Hosted by: Professor Jonathan Klamkin, Integrated Photonics Laboratory