Join us at Henley Hall 1010 on 10/28 at 1pm! Free Pizza Provided!
Student Lecture by KaiKai Liu on Milliwatt Threshold 0.5-Hz Linewidth Si3N4 Brillouin Laser5/25/2021
Friday May 28 at 1:00 pm
1:00 PM Friday, April 2nd
1:00 PM Friday, January 22nd |
Yahya Mohtashami Schuller group ECE Dept, UCSB | In this talk, we show that we can increase the light extraction efficiency of, impart directionality upon, collimate, and focus the spontaneous emission from InGaN/GaN quantum wells, using phased-array metasurfaces. |
Strong THz laser fields can explore non-linear, non-equilibrium phenomena in matter. The talk will focus on photons emitted by electron/hole re-collisions, and how the polarization of these photons carries information about the semiconductor. |
Schematic for the cross-section of a TACIT mixer (right); Optical image of a TACIT mixer with an SEM image of the active region (top) | Terahertz Heterodyne Detector Based on the Intersubband Transition of a GaAs/AlGaAs Quantum WellWe are developing a new type of THz heterodyne detector based on a high-mobility 2-dimensional electron gas (2DEG) in a GaAs/AlGaAs quantum well for spectroscopic applications in deep-space and planetary missions. Named as Tunable Antenna-Coupled Intersubband Terahertz (TACIT) mixer, the detector is a four-terminal hot-electron bolometer (HEB) mixer that uses intersubband transition for efficient absorption of THz radiation in a 2DEG. The dual gate structure of TACIT mixers, necessary for the precise control of the intersubband absorption characteristics, enables a high coupling efficiency at THz frequencies and tunability in the detection frequency, but also poses challenges in the fabrication, modelling, and operation of the device. In this talk, I will discuss our recent experimental results with a prototype TACIT mixer that we have fabricated with a flip-chip process that enables dual-side processing of a sub-micron thick quantum well membrane. |
12:00 - 1:00 PM Friday, February 21st in Engineering II 3519
Haojun Zhang DenBaars group ECE Dept, UCSB | Distributed feedback (DFB) laser diodes on GaNI will first talk about the recent work on blue III-Nitride LDs grown on semipolar GaN substrates. Then I will analyze the main hurdles that impeded its performance, focusing on improving the operating voltage, lifetime and mode quality, and discuss the efforts and approaches to further improve the efficiency and high-speed performance. |
Terahertz Heterodyne Detector Based on the Intersubband Transition of a GaAs/AlGaAs Quantum Well We are developing a new type of THz heterodyne detector based on a high-mobility 2DEG in a GaAs/AlGaAs quantum well for spectroscopic applications in deep-space and planetary missions. Named as Tunable Antenna-Coupled Intersubband Terahertz (TACIT) mixer, the detector uses intersubband transition for efficient absorption of THz radiation in a 2DEG. The dual gate structure of TACIT mixers, necessary for the precise control of the intersubband absorption characteristics, enables a high coupling efficiency at THz frequencies and tunability in the detection frequency, but also poses challenges in the fabrication, modelling, and operation of the device. In this talk, I will discuss our recent experimental results with a prototype TACIT mixer that we have fabricated with a flip-chip process that enables dual-side processing of a sub-micron thick quantum well membrane. |
Friday, Feb 14th from 12:00 - 1:00 pm in Elings 1601
Ring-Assisted Mach-Zehnder Interferometer Switch with Multiple Rings per Switch ElementWavelength-selective switches have been propsed for datacenter use to help meet ever-increasing traffic demands. We present a 4-port silicon photonic ring-assisted Mach-Zehnder interferometer (RAMZI) switch, fabricated in the AIM Photonics process, with multiple-sized rings per switching element in a Benes network configuration to reduce the number of electrical pads required compared to a crossbar switch. Another advantage the RAMZI switch has over the crossbar switch is that the loss through the switch is not path-dependent due to its balanced path configuration. Finally, we present results from the fabricated switch co-packaged with a custom driver for control and discuss the outlook for further scaling of the switch architecture. |
Characterization of InGaN quatum dots grown by metal organic chemical vapor deposition (MOCVD)InGaN quantum dots were grown by metal organic chemical vapor deposition and shown to exhibit a bimodal size distribution. Atom probe tomography was used to characterize the dots in conjunction with atomic force microscopy (AFM), photoluminescence (PL), and x-ray diffraction (XRD). Small dots with low indium contents were found to coexist with larger, very high indium composition dots. The dots showed abrupt interfaces with the surrounding GaN, verifying the ability to cap the dots without causing intermixing for extremely high indium content dots. |
Blue Semipolar III-Nitride Vertical-Cavity Surface-Emitting Lasers
Blue semipolar (20-2-1) vertical-cavity surface-emitting lasers with ion-implanted apertures and buried tunnel junction apertures (BTJ) are fabricated and compared to show that the BTJ's reduced absorption improves device performance. The effect of changing the out-coupling mirror reflectivity is calculated to project the potential of these devices with minor structural changes. |
Pizza will be provided!
Matthew Wong DenBaars group Materials Dept, UCSB | High Efficiency III-Nitride Mirco-Light-Emitting Diodes for Display Applications Micro-light-emitting diodes (µLEDs) with high energy efficiency are desired for a variety of display applications, including virtual reality (VR) and augmented reality (AR) near-eye displays. Although outstanding performances in different display aspects have been demonstrated with InGaN µLEDs, there are several challenges for commercialization. In this talk, two main issues, namely size-dependent efficiency and mass transfer of µLEDs, will be addressed and some promising solutions will be discussed. |
Takako Hirokawa Schow group ECE Dept, UCSB | Energy Efficiency Analysis of Coherent Links for |
Kristina Davis Mazin group Physics Dept, UCSB | Coherent Differential Imaging Techniques for MKID Detectors The field of direct imaging of exoplanetary systems allows astronomers to gain both photometric and spectroscopic analysis of these exoplanetary systems. I will present a technique I call Heterodyne Optical Phase Probe (HOPP) that measures the phase change of an incoming heterodyne signal incident on the kinetic inductance detector array as the deformable mirror is actuated. By measuring the phase response, we can improve our models of the DM surface shape under a variety of optical conditions, and have a better calibration of how to scale the offset positions we feed the DM when performing speckle nulling. |
Chris Zollner Nakamura group Materials Dept, UCSB | MOCVD growth of AlN on SiC substrates for deep-UV optoelectronics: an inside the box approachMOCVD growth of high-quality GaN on sapphire substrates is vital to today's blue LED industry, but the same methods cannot be applied to AlN/sapphire which is needed for deep-UV optoelectronics. We have developed a novel approach to MOCVD growth of AlN on SiC with quality comparable to industrial GaN/sapphire, and demonstrated UV-LEDs emitting at 280nm. |
Low Threshold 1.55 um Quantum Dash Microring Lasers We report the first room-temperature-continuous-wave (CW) operation of electrically-injected InAs quantum-dash microring lasers emitting at 1.55 µm telecom window. The microrings sustain CW lasing up to 55°C, while the lowest threshold current density is 528 A/cm2 . |
Quantum dot devices on silicon grown by MOCVD Direct heteroepitaxy of III-V quantum dots (QDs) is promising for achieving a monolithic laser source for silicon photonics. QDs are believed to be less sensitive to defects than quantum wells, and also offer desirable characteristics for high temperature operation and reduced sensitivity to reflection, because of the 3D carrier confinement of individual QDs. In this talk, I will introduce my research on growth of aluminium-free InAs/GaAs quantum dot laser structure on CMOS-compatible (001) by MOCVD, and some initial fabrication works for both electrically and optically devices. |
Pizza will be provided!
Monolithically-Integrated Photoreceiver with Cherry-Hooper TIA in BiCMOS TechnologyIn 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. |
A Low-noise High-channel-count 20 GHz Passively Mode Locked Quantum Dot Laser Grown on SiLow cost, small footprint, highly efficient and mass producible on-chip wavelength-division-multiplexing (WDM) light sources are key components in future silicon electronic and photonic integrated circuits (EPICs). We present here, for the first time, a low noise high-channel-count 20 GHz passively mode locked quantum dot laser grown on CMOS compatible on-axis (001) silicon substrate. The laser demonstrates a wide mode locking regime in the O-band. The 3 dB optical bandwidth of the comb is 6.1 nm (containing 58 lines, with 80 lines within the 10 dB bandwidth). Utilizing 64 channels, an aggregate total transmission capacity of 4.1 terabits per second is realized by employing a 32 Gbaud Nyquist four-level pulse amplitude modulation format. The demonstrated performance makes the laser a compelling on-chip WDM source for multi-terabit/s optical interconnects in future large scale silicon EPICs. |
Pizza will be provided!
Joseph Fridlander Integrated Photonics Lab Electrical Engineering, UCSB | Photonic Integrated Transmitter for |
Daniel Myers Dr. James Speck’s Group Materials, UCSB | Understanding the Limitations of LED Efficiency by Electron Emission SpectroscopyAbstract: The analysis of the energy distribution of electrons, emitted from the surface of an LED can provide an unambiguous measurement of efficiency loss mechanisms and transport phenomena. Previously this technique has been used to identify Auger recombination as the dominant efficiency loss mechanism for GaN LEDs operating at high current densities. My talk will focus on using this technique to improve the understanding of several other efficiency loss issues. Specifically, the loss of efficiency at elevated temperatures and the poor performance of long-wavelength (green) GaN LEDs. |
Pizza will be provided
Efficient Tunnel Junction Contacts for High-Power III-Nitride Edge-Emitting Laser Diodes 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. |
InP Photonic Integrated Circuit Transmitter with Integrated Linewidth Narrowing for Laser Communications and Sensing 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. |
Pizza will be provided!
Unidirectional spontaneous emission from emitting metasurfaces 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. |
Ryan DeCrescent Schuller Group UCSB Physics | Gain Characterization of p-doped 1.3 μm InAs Quantum Dot Lasers on Silicon 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. |
Pizza will be provided!
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