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    • Lectures >
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      • Day of Light 2019
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Student Lecture Oct 28 - KaiKai Liu and Jake Ewing

10/23/2021

 
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Join us at Henley Hall 1010 on 10/28 at 1pm! Free Pizza Provided! 

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Jake Ewing
DenBaars Group
Materials Dept, UCSB
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MicroLEDs for next-generation display technologies

Micro light-emitting diodes (µLEDs) are promising candidate many next-generation displays technologies including television screens and augmented reality (AR) glasses. Advantages of µLEDs include high efficiencies, self-emissivity, high brightness and long operating lifetimes. Current research focuses on improving growth methods and processing of µLEDs to achieve size-independent efficiency across the entire color spectrum. This talk will provide an overview of the progress of µLED technology as well as current research being conducted at UCSB

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KaiKai Liu
Blumenthal Group
ECE Dept, UCSB

Photonic integrated coil resonator for laser stabilization with ultra-low thermodynamic noise limit

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.

Student Lecture by KaiKai Liu on Milliwatt Threshold 0.5-Hz Linewidth Si3N4 Brillouin Laser

5/25/2021

 
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Friday May 28 at 1:00 pm 
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KaiKai Liu
Blumenthal Group
ECE Dept, UCSB

Milliwatt Threshold 0.5-Hz Linewidth Photonic Integrated Si3N4 Brillouin Laser

Narrow linewidth lasers are an essential component in a wide range of applications including coherent communications, atomic and optical clocks, and quantum communications and computation. Laser cavity Q factor plays the crucial role in semiconductor laser linewidth. Ultra-low loss SiN waveguide resonators are extremely advantageous for making Hz linewidth lasers.
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In this talk, I will introduce the unique linewidth property of Brillouin lasers and present our recent progress towards Billion Q photonics integrated SiN waveguide resonators and the demonstration of the milliwatt threshold Brillouin laser with 0.5 Hz Schawlow-Townes linewidth.

Student Lectures - Shubhra Pasayat and Chris Zollner

3/16/2021

 
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1:00 PM Friday, April 2nd

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Shubhra S. Pasayat
Mishra group 
ECE Dept, UCSB

III-Nitride Strain relaxation enabled by Porous GaN for optoelectronic applications 

In my talk, I will discuss the conceptualization, fabrication and optimization of the strain relaxed substrates followed by process optimizations which led to our demonstration of world’s first <10 µm sized red LED with measurable efficiency.

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Chris Zollner
Nakamura group 
 Materials Dept, UCSB

Ultraviolet LEDs for disinfection applications: efficiency bottlenecks and novel approaches  ​

In this talk, I will discuss why III-nitride based deep-UV LEDs remain less than 10% efficient, whereas blue and white GaN LEDs are now well over 60%. Next, I will summarize our approach to improving UV LED efficiency using improved material quality, device design, and fabrication technologies. Finally, I will suggest some possible future trends, and what it will take for UV LEDs to become the dominant UV light source.

Student Lecture Series - January 22, 2021

1/20/2021

 
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1:00 PM Friday, January 22nd
Zoom Meeting --– Meeting ID: 847 3105 9791 --- Password: 792878  --- Zoom Link


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Yahya Mohtashami
​Schuller group
ECE
Dept, UCSB



​Light-Emitting
Metasurfaces

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.

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Seamus O’Hara
Sherwin group
Physics
Dept, UCSB



​Optical Sensitivity to Wavefunctions of Electron-Hole Pairs in Semiconductors
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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.

Student Lecture Series - June 3, 2020 - Changyun Yoo

5/29/2020

 
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Changyun Yoo
Sherwin group
Physics Dept, UCSB
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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 Well 

We 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.
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Student Lecture Series: Feb. 21st 2020

2/19/2020

 
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12:00 - 1:00 PM Friday, February 21st in Engineering II 3519


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Haojun Zhang
​DenBaars group
ECE Dept, UCSB

Distributed feedback (DFB) laser diodes on GaN

I 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.

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Changyun Yoo
Sherwin group
Physics Dept, UCSB

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.

Student Lecture Series: Feb. 14th 2020

2/12/2020

 
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Friday, Feb 14th from 12:00 - 1:00 pm in Elings 1601


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Takako Hirokawa
Schow group
ECE Dept, UCSB

Ring-Assisted Mach-Zehnder Interferometer Switch with Multiple Rings per Switch Element

Wavelength-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. 

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Caroline Reilly 
DenBaars Group
Materials Dept, UCSB

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. 

Student Lecture Series: January 24th 2020 - Jared Kearns

1/22/2020

 
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Blue Semipolar III-Nitride Vertical-Cavity Surface-Emitting Lasers

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Jared Kearns
Nakamura Group
​Materials Dept, UCSB
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​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. 
Friday, January 24th | 12:00 pm | ESB 2001
Pizza will be provided!

Student Lecture Series: June 7th 2019

6/5/2019

 
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Matthew Wong
DenBaars group
Materials Dept, UCSB

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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.
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Takako Hirokawa
Schow group
ECE Dept, UCSB

Energy Efficiency Analysis of Coherent Links for
Datacenters

We propose that coherent optical communication can offer energy-efficient operation in datacenters. Analysis and simulations determine optimal operating points for the laser and local oscillator (LO) and compare trade-offs in Silicon (Si) and Indium Phosphide (InP) Mach-Zehnder Modulators (MZMs) to reach pJ/b scale efficiency.
Friday, June 7th | 12:00pm | Elings 1605

Student Lecture Series: May 31st 2019

5/22/2019

 
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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.

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Chris Zollner
Nakamura group
Materials Dept, UCSB

MOCVD growth of AlN on SiC substrates for deep-UV optoelectronics: an inside the box approach

MOCVD 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.
Friday, May 31st | 12:00 pm | Elings 1605

Student Lecture Series: May 3rd 2019

5/2/2019

 
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Yating Wan
Bowers group
​ECE Dept, UCSB
Low Threshold 1.55 um Quantum Dash Microring Lasers 
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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 .

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Lei Wang
Klamkin group
​ECE Dept, UCSB
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. 
Friday, May 3 | 12:00pm | Elings 1605
Pizza will be provided!

Student Lecture Series: March 1st

2/26/2019

 
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Hector Andrade
Schow Group
​Electrical Engineering

​Monolithically-Integrated Photoreceiver with Cherry-Hooper TIA in BiCMOS Technology

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. 

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Songtao Liu
Bowers Group
​Electrical Engineering

A Low-noise High-channel-count 20 GHz Passively Mode Locked Quantum Dot Laser Grown on Si

Low 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.
12:00 PM Friday, March 1st in Elings 1605
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Pizza will be provided!

Student Lecture Series: Jan 25th

1/21/2019

 
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Joseph Fridlander
Integrated Photonics Lab
​Electrical Engineering, UCS
B

Photonic Integrated Transmitter for ​
​Space-Optical Communications

Abstract:  This talk provides an overview and demonstrates test results of a photonic integrated circuit transmitter for space optical communication utilizing an RZ-DPSK modulation format realized on an indium phosphide monolithic integration platform.
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Daniel Myers
Dr. James Speck’s
Group
​Materials, UCSB

Understanding the Limitations of LED Efficiency by Electron Emission Spectroscopy

Abstract:  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.
Friday, Jan. 25th at 12:00 PM in ESB 1001
Pizza will be provided

Student Lecture Series: Dec. 11th

12/8/2018

 
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Shereen Hamdy
Dr. Nakamura’s Group
Electrical Engineering

​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.
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​Brandon Isaac
Dr. Klamkin’s Group
Materials

​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.
Tuesday, Dec. 11th at 12:00 PM in Elings 3001
Pizza will be provided!

Student Lecture Series: Dec. 4th

11/29/2018

 
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Robert Zhang
Bowers Group
​
UCSB Electrical Engineering

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. 
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​​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. 
Tuesday Dec. 4th at 12:30 pm in ESB 1001
Pizza will be provided!
This is the start of the weekly student lecture series IEEE Photonics is hosting throughout Winter 2019!  Ryan DeCrescent and Robert Zhang will be presenting their talks.

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