PhD Defense: "Ph.D. Defense: Integrated Optical Phase-locked Loops"

Mingzhi Lu

April 22nd (Monday), 2:00pm
Engineering Science Building (ESB), Rm 2001

In modern communication and sensing devices, such as radios, cell phones, computers, and radar, phase-locked loop (PLL) technology is widely applied to enable coherent detection, which has a higher sensitivity and data capacitance compared to traditional envelope detection. However, historically the idea of extending this PLL concept into the optical domain proved difficult. The fundamental difficulty of building an optical phase-locked loop (OPLL) is due to the limited loop bandwidth relative to the laser linewidth and wavelength stability. In order to solve this problem, photonic and electronic integration needs to be applied as well as novel system design.

In this Ph.D. dissertation, homodyne and heterodyne OPLLs are designed, fabricated, and implemented based on advanced InGaAsP/InP photonic integration technology, as well as electronic integration. All the optic components that are needed in the OPLL are integrated monolithically, including a slave laser, a 90-degree hybrid, four high-speed photodetectors, and microstrip transmission lines.

The integration technology enables stable OPLLs with advanced functionalities. OPLL closed-loop bandwidth has been improved to 1.1~GHz, and based on this OPLL a synchronized homodyne receiver has been achieved, with a data rate up to 40 Gbit/s. Error free (bit error rate < 10E-12) is realized up to 35 Gbit/s. As for sensing and synthesis applications, two lasers are phase locked to each other with an offset frequency range of 40~GHz, and phase-locked frequency sweeping has been achieved. The residual phase noise is smaller than 0.03 rad^2, integrating from 100 Hz to 10 GHz. Utilizing the OPLLs demonstrated in this thesis, there are many potential applications. In the area of coherent communication, especial in short or mid distance range, where dispersion is not serious, OPLL-based homodyne receiver has the advantages of highest sensitivity, lower power consumption, smaller size and lower cost. On the other hand, in the area of optical sensing and synthesis, many novel coherent optical system can be established by using this OPLL as a key building block, including, but not limited to, light detection and ranging (LIDAR), fiber sensing, optical synthesis and terahertz wave generation.

About Mingzhi Lu:

photo of minghzi lu Mingzhi Lu received his B.S degree in Information Science and Technology from the Southeast University, China, in 2008, the M.S. degree in Electrical and Computer Engineering from UCSB, in 2009 and is currently pursuing Ph.D. under the guidance of Prof. Larry A. Coldren at the Optoelectronics Technology Center. His current research interests include photonic integration, optical phase-locked loops, coherent optical systems, and fiber-optic communications. He is a Peter J. Frenkel fellow of the Institute of Energy Efficiency. He has authored or co-authored more than 30 journal and conference papers.

His past research experience includes underwater acoustic signal processing, microwave and THz frequency selective surface, and metamaterials.

Hosted by: Professor Larry A. Coldren