Jake Ewing
DenBaars Group
Materials Dept, UCSB​

Stable lasers and reference cavities provide the frequency standards and precision measurement references and are an essential component in a wide range of applications including coherent communications, atomic and optical clocks, and quantum communications and computation. On-chip laser frequency reference cavities have been drawing attention and interests, as on-chip optical ultra-low loss waveguide resonators are able to achieve Q factors above 100 Million.
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In this talk, I will introduce the landscape of table-top stable lasers and bulk optical reference cavities and move on to our recent progress towards on-chip ultra-high Q reference resonator and the resonator design and engineering to mitigate the thermodynamically driven noise. We demonstrate the stabilized laser reaches the resonator intrinsic thermorefractive noise limit.

Matthew Wong
DenBaars group
Materials Dept, UCSB
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In this talk, we report a monolithically-integrated photoreceiver with a pseudo-differential Cherry-Hooper trans-impedance amplifier (TIA) in a 250 nm BiCMOS process. High sensitivity 50 Gbps operation is demonstrated, and the TIA architecture is analyzed. 

We demonstrate III-Nitride edge-emitting laser diodes (LDs) with tunnel junction contacts grown by MBE. Lower threshold current densities were observed in LDs with MBE-grown tunnel junctions than in control LDs with ITO contacts. LDs with tunnel junction contacts grown by MOCVD were also demonstrated. These LDs underwent a p-GaN activation scheme utilizing lateral diffusion of hydrogen through LD ridge sidewalls. Secondary ion mass spectroscopy measurements of the tunnel junction [Si] and [Mg] profiles were conducted to further investigate the results.

​An integrated solution for reducing the linewidth of widely tunable semiconductor diode lasers is presented.  Reducing the linewidth of tunable diode lasers enables lower cost, size, weight, and power (CSWaP) for many applications including LiDAR, sensing, and communication.  I will discuss the operating principles of the system, and show how it is realized in a photonic integrated circuit with characterization of the  components.  Utilizing this circuit to enable a photonic integrated transceiver for frequency modulated continuous wave LiDAR  is discussed.

​Optical metasurfaces --- strategically engineered subwavelength surface structures --- have emerged as an extremely versatile and compact means of manipulating the spatial and polarization structure of an incident beam of light. Critically, the functionality of such metasurfaces depends upon the existence of a well-defined input-phase, i.e., the incident beam. In this talk, I demonstrate the possibility of applying optical metasurface concepts to the spontaneous emission process, thereby generating unidirectional and variable emission from III-V quantum-well structures. 

​We investigate, both experimentally and theoretically, the gain characteristics of modulation p-doped 1.3 μm quantum dot lasers epitaxially grown on silicon. The inhomogeneous broadening is extracted to be 10 meV. A p-doped quantum dot active region has been found to show lower transparency current and higher material gain.