June 4 (Fri): "Photonic Integrated Circuits for Remote Sensing Lidar," Joseph Fridlander, ECE PhD Defense
To quantify and model current and future atmospheric compositions and to better understand tropospheric CO2 exchange with the land and oceans, accurate and precise measurements are required. Active sensing of CO2 can be accomplished with lidar. Unlike passive spectrometers that rely on sunlight, an active lidar provides significantly better wavelength and spatial resolution and can perform continuous sensing during the day and night.
Photonic integrated circuits (PICs) allow integration of complex optical systems on chip. In this work, an integrated path differential absorption (IPDA) lidar is designed for active sensing of CO2. All optical functions, with exception of a gas cell reference, are integrated onto a chip approximately 10 mm2.
First, using an integrated phase modulator, a master widely tunable SG-DBR laser is stabilized to a gas cell reference using a frequency modulation technique. Using an optical phase locked loop, a slave laser is locked to the master laser and stepped across multiple sampling points to map a CO2 absorption line at 1572 nm at offsets up to ±15 GHz. Before processing by the OPLL, the offset frequency between the lasers is detected with an on-chip high-speed photodiode in the form of a beat note. Finally, a pulse carver generates high extinction ratio pulses for transmission.
Using this PIC, we demonstrated a factor of 235 improvement in the master laser frequency stability over a 1-hr period using 1-second gate times. We also demonstrated slave laser locking to the master laser at offsets up to ±15 GHz, albeit we relied on an off-chip detector. Also demonstrated were pulses with more than 40 dB extinction ratio. Finally, we successfully demonstrated CW sensing of the 1572 nm CO2 absorption line. The work illustrated here shows that PICs are a very promising technology for earth science and sensing lidar at significantly reduced cost, size, weight, and power.
Joseph Fridlander is a fifth year PhD candidate at University of California, Santa Barbara, working under the supervision of Professor Jonathan Klamkin.
Hosted by: Professor Jonathan Klamkin
Submitted by: Joseph Fridlander <email@example.com>