Digital Broadband Linearization and Wideband High Speed Measurements in Optical Links
Sep 15, 2014
from 10:00 AM to 12:00 PM
|Where||Engr. IV Bldg., Tesla Room 53-125|
|Contact Name||Daniel Lam|
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Advisors: Professor Bahram Jalali and Professor Asad M. Madni
Optical fiber networks have been in use for many decades to transport large amounts of data across long distances. Internet traffic grows at an exponential rate and demand for increased bandwidth and faster data rates is higher than ever. Radio frequency over fiber is used for a plethora of applications such as providing wireless access to remote and rural areas, phased array radars, and cable television to name a few. As signals are transmitted over longer distances, nonlinearities are incurred which degrades the performance and sensitivity of the link. Moreover as the data rates increase, it becomes a challenge to measure and monitor the signal integrity.
This seminar will cover two main topics: digital broadband linearization and performing wideband high speed measurements using time-stretch technology. Over the last few years there has been considerable interest in reducing the intermodulation distortions in optical links. The intermodulation distortions are caused by the nonlinear transfer function of optical link. To reduce the nonlinearities in optical links, linearization of the optical link is performed. A novel digital post-processing algorithm has been developed to suppress nonlinearities and increase the dynamic range of the link. Digital Broadband Linearization Algorithm has been implemented and demonstrated a record 120 dB.Hz2/3 Spurious Free Dynamic Range (SFDR) over 6 GHz of bandwidth and is shown to suppress third order intermodulation products by 35 dB. By reducing the nonlinearities and improving SFDR, we have increased the sensitivity of the receiver. Afterwards, simulation of the real-time implementation of the Digital Broadband Linearization Algorithm onto a Field-Programmable Gate Array (FPGA) was performed by designing the architecture and translating the code into Verilog HDL. Simulations on collected data show comparable results in both MATLAB and iSim which were used to evaluate the performance.
In the second part of this seminar, two applications using time-stretch are demonstrated: ultra-wideband instantaneous frequency estimation and high speed signal analysis measurements. By combining time-stretch technology and windowing and quadratic interpolation, we demonstrate ultra-wideband frequency detection with improved frequency estimation. Moreover, multiple signal detection and measurement is performed, and the frequency resolution can be tuned easily. Lastly, we are able to use time-stretch to generate eye diagrams in real-time. We are able to perform high speed signal integrity measurements such as bit error rate, jitter, and rise and fall times by taking advantage of the high sampling throughput and analyzing the eye diagrams. In addition, we were able to integrate this technology into a testbed for agile optical networks and use it for real-time optical performance monitoring.
Daniel Lam is pursuing a Ph.D. degree in Electrical Engineering from the University of California, Los Angeles under the guidance of Professors Bahram Jalali and Asad M. Madni. He received a B.S. degree in Optical Sciences and Engineering from The University of Arizona in 2008, and a M.S. degree in Electrical Engineering from Stanford University in 2009. His research has been focused on digital broadband linearization of optical links and performing high speed measurements using time stretch technology. He is an engineer with Northrop Grumman Aerospace Systems since 2008. He is one of the recipients of the Northrop Grumman Aerospace Systems Fellowship.