Jan 18 (Tue) @ 4:00pm: "Indium Phosphide Photonic Integrated Circuits for Remote Sensing," Fengqiao Sang, ECE PhD Defense
As the accelerating of global climate change that is caused by the greenhouse effect, many effects can be observable on our environment, including the shrinking of glaciers, early breaking up of the ice in the river and lakes, sooner flowering of trees, shifting of plants and animal ranges. In recent years, more attention and efforts have been made to monitor and decelerate the change of the greenhouse effect. NASA has launched the Orbiting Carbon Observatory (OCO) satellite missions in 2009 to remote sensing the change of carbon dioxide (CO2) level from low earth orbits using passive remote sensing technology. At the same time, the new active remote sensing system was also developed under the Active Sensing of CO2 Emissions over Nights, Days, & Seasons (ASCENDS) mission. However, those traditional remote sensing system is large, heavy, and power-hungry. To overcome those disadvantages of the remote sensing system, remote sensing system using photonic integrated circuits (PIC) technology becomes a promising solution for the future remote sensing application; especially the indium phosphide (InP) PIC technology, its capability of monolithic integrating high-quality lasers makes it an ideal technology for active remote sensing.
In this work, InP PICs using integrated path differential absorption lidar (IPDA) topology are designed for CO2 active remote sensing. The dimension of the fabricated PIC is within 1 mm × 10 mm, which integrated two lasers, a phase modulator, a pulse generator, a photodiode, many splitters, and optical amplifiers. The overall sensing system mainly consists of two parts, leader laser stabilization, and follower laser offset locking. The leader laser stabilization is achieved using a frequency modulation technique, where the leader laser is locked to a CO2 reference cell by modulating the phase of the laser output signal at 125 MHz. The follower laser offset locking is accomplished using the optical phase lock loop technique with the integrated photodiode. Over 2-hour measurements, with the leader laser stabilization enabled, the stability of the leader laser improved more than 20 dB; with the follower laser offset locking enabled, a more than 45 dB stability improvement is achieved for the follower laser. In addition, the CO2 active sensing is successfully demonstrated under continuous wave sampling and pulsed sampling in a lab environment using a CO2 Herriott testing cell. Under the continuous wave sampling, an 8.92 dBm fiber coupled output power is achieved. Under the pulsed sampling, the pulsed signal train achieved a more than 45 dB extinction ratio. In addition. under both sampling, the PIC successfully scanned over a 20 GHz range centered at 1572.335 nm and successfully recovered the CO2 absorption spectrum using Lorentzian fit. Overall, we have fundamentally and experimentally approved the possibility of using InP PIC technology for CO2 active remote sensing. Future efforts can be made towards the PIC packaging, and photonic-electronic integration to further reduce the size, weight, and power of the overall system.
Fengqiao Sang received his B.S. degree from Drexel University in 2015, and his M.S. degree from the University of California, Santa Barbara (UCSB) in 2017. Currently, He is a Ph.D. candidate in the Department of Electrical and Computer Engineering at UCSB under Prof. Klamkin. His research interests include semiconductor photonic integrated circuits and integrated Lidar for Remote Sensing applications.
Hosted by: Prof. Jonathan Klamkin
Submitted by: Fengqiao Sang <firstname.lastname@example.org>