"UCSB Nanotech TECH Talks"

Dr. Garrett Cole, Crystalline Mirror Solutions and, Dr. Songtao Liu, UC Santa Barbara

September 5th (Thursday), 12:00pm
Engineering Science Building (ESB), Rm 1001

“Semiconductor Supermirrors”
Dr. Garrett Cole, Crystalline Mirror Solutions, Santa Barbara, CA

Substrate-transferred crystalline coatings are a groundbreaking new concept in optical interference coatings. Building upon fundamental research in cavity optomechanics, these “semiconductor supermirrors” were first demonstrated in 2013, with the key advantage being the ability to simultaneously achieve ultralow levels of optical and mechanical losses. With continuous refinement in epitaxial growth and layer transfer processes, we have now realized significant improvements in the limiting performance of these novel single-crystal multilayers. In the near-infrared (NIR), for center wavelengths spanning 1064 to 1560 nm, we have reduced the scatter + absorption losses to < 3 parts per million (ppm), enabling a cavity finesse exceeding 600,000 (equivalent to a reflectance > 99.9995%) at the telecom-relevant wavelength range near 1550 nm. Investigations in the mid-IR (MIR) spectral region also show exceptionally low levels of optical losses, with measurements yielding absorption below 50 ppm for wavelengths out to 4500 nm. Taken together, our NIR coatings are now fully competitive with ion beam sputtered films, while our prototype MIR optics have reached state-of-the-art performance levels. Looking ahead, we see a bright future for GaAs/AlGaAs-based crystalline coatings in applications requiring the ultimate levels of optomechanical performance.

“High Performance Lasers on Silicon”
Dr. Songtao Liu, University of California, Santa Barbara, CA

Efficient light generation on silicon has long-been a challenging topic because silicon is an indirect bandgap material. Many approaches have been proposed and demonstrated. We review our recent progress on high performance heterogeneously integrated and directly grown semiconductor light sources on silicon. One is a heterogeneously integrated sub-kilohertz narrow linewidth laser with 110 nm tunable bandwidth and <220 Hz lowest optical instantaneous linewidth, which is achieved by leveraging an ultra-low loss silicon waveguide platform developed at UCSB. The other is a directly grown quantum dot mode locked laser on silicon with wideband coherent comb generation. 80 coherent lines within 10 dB spectral bandwidth are demonstrated. By employing 64 wavelength channels with a 32 Gbaud PAM-4 transmission format, a total system level transmission capacity of 4.1 Tbit/s is achieved. The demonstrated performance makes these lasers appealing candidates for fully integrated large-scale silicon electronic and photonic integrated circuits with the lowest cost and highest functionality.

About Dr. Garrett Cole, Crystalline Mirror Solutions and:

Garrett D. Cole, Co-Founder of Crystalline Mirror Solutions (, obtained his PhD in Materials from UCSB in 2005. Since completing his doctorate, he has held positions ranging from the first employee of a high-tech startup (Aerius Photonics LLC, now FLIR Electro-Optical Components), to a postdoctoral position at Lawrence Livermore National Laboratory, a Marie Curie Fellow of the Austrian Academy of Sciences, and an assistant professor in the Faculty of Physics at the University of Vienna. Dr. Cole has co-authored 2 book chapters and published more than 50 journal articles and conference proceedings including papers in Science, Nature, Nature Physics, Nature Photonics, Nature Nanotechnology, Nature Communications, Physical Review Letters, and the Proceedings of the National Academy of Sciences. Leveraging his expertise in micro- and nanofabrication, tunable semiconductor lasers, and cavity optomechanics, Dr. Cole co-founded CMS in 2013 to commercialize high-performance single-crystal optical coatings for laser-based metrology and manufacturing systems.

Songtao Liu received the B.E. (Hons.) degree in electronic information science and technology from Henan University, Kaifeng, China, in 2012, and the Ph.D. degree in microelectronics and solid state electronics in 2017 from the University of Chinese Academy of Sciences, Beijing, China, where his Ph.D. dissertation was on monolithically integrated InP-based mode-locked lasers. He is currently a Postdoctoral Researcher with the University of California, Santa Barbara, Santa Barbara, CA, USA. His research interests are in the field of photonic integrated circuits, with an emphasis on monolithically integrated mode-locked lasers and tunable lasers both on InP and silicon platforms.

Hosted by: Professor Jonathan Klamkin