PhD Defense: "Ultra‑Narrow Bandwidth Optical Resonators for Integrated Low Frequency Noise Lasers"

Daryl Spencer

March 2nd (Wednesday), 4:00pm
Engineering Science Building (ESB), Room 1001

The development of narrowband resonators has far reaching applications in integrated optics. As a precise reference of wavelength, filters can be used in sensors, metrology, nonlinear optics, microwave photonics, and laser stabilization. In this work, we develop record high quality factor (Q) Si3N4 waveguide resonators, and utilize them to stabilize a heterogeneously integrated Si/III V laser.

To increase the Q factor of waveguide resonators, particular attention is given to loss mechanisms. Propagation loss of <0.1 dB/m is demonstrated on the ultra low loss waveguide platform, a low index contrast, high aspect ratio Si3N4 waveguide geometry fabricated with high quality materials and high temperature anneals. Ideality in the directional couplers used for coupling to the resonators is studied and losses are reduced such that 81 million intrinsic Q factor is achieved. Additional results include 1×16 resonant splitters, low κ narrowband gratings, and a dual layer waveguide technology for low loss and low bend radius in separate regions of the same device layer. We then implement an ultra-high Q resonator and a heterogeneous Si/III-V laser in a Pound-Drever-Hall (PDH) frequency stabilization system to yield narrow linewidth characteristics for a stable on chip laser reference. The high frequency noise filtering is performed with Si resonant mirrors in the laser cavity. A 30 million Q factor Si3N4 resonator is used with electrical feedback to reduce close in noise and frequency walk off. The laser shows high frequency noise levels of 60×10^3 Hz2/Hz corresponding to 160 kHz linewidth, and the low frequency noise is suppressed 33 dB to 10^3 Hz2/Hz with the PDH system.

About Daryl Spencer:

photo of Daryl SpencerDaryl Spencer received the B.S. in engineering physics from the University of Tulsa, in 2010, and the M.S. degree in electrical and computer engineering from the University of California, Santa Barbara, in 2012, where he is currently working towards the Ph.D. in electrical and computer engineering as an NSF Fellow. His research involves the active integration of ultra-high quality factor monolithic resonators for high performance microwave systems.

Hosted by: Professor John Bowers