 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. |
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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. |
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Thursday, November 5th, 10 am (PST) via Zoom
Lithium niobate (LN), the workhorse of optoelectronics, is an excellent photonic material with large electro-optic coefficient, Kerr nonlinearity and piezoelectric response, and a wide optical transparency window. Recent advances in nanofabrication technology have allowed for the realization of ultra-low loss LN waveguides and are opening exciting opportunities for next-generation nonlinear photonic technologies with higher integration density and advanced functionalities. In this talk, I will review our recent developments of thin-film LN devices, including optical frequency combs, supercontinuum generation, optical frequency shifting, acousto-optic control. In addition, I will discuss the potential of LN platform for applications in nonlinear frequency conversion, frequency metrology, and microwave photonics.
Following the technical talk, I will give a short professional development talk, including networking and volunteering in the photonics community, and I will cover some career advice for graduate students.
Following the technical talk, I will give a short professional development talk, including networking and volunteering in the photonics community, and I will cover some career advice for graduate students.
Images from https://arxiv.org/pdf/2005.09621.pd
Monday, October 26th, 11 am (PDT) via Zoom
Fiber communications support a wide range of residential, mobile and enterprise services, within core, metro, and access optical networks. The 5G and beyond wireless is expected to have a dramatic impact on the fiber infrastructure, bringing new severe requirements such as higher data rates, ultra-high bandwidth, lower latency, accurate synchronization, network slicing, ultra-high reliability and massive connectivity for many devices. Adaptive, flexible and efficient optical resource management, as well as agile bit-rates are the key technologies to exploit the whole bandwidth of single-wavelength, single-core and single-mode fibers. All-optical orthogonal frequency division multiplexing (OFDM) and Nyquist-optical time division multiplexing (N-OTDM) are the two most suitable approaches to efficiently generate Tb/s superchannels, by optically multiplexing subcarriers or by time interleaving short sinc-shaped pulses. The superchannels are generated in the optical domain, in a power-efficient way, also overcoming the restrictions related to the bandwidth of modulators and digital signal processing devices. A planar arrayed waveguide grating (AWG) can be designed to implement the conventional or fractional Fourier transform and efficiently generate OFDM and Fr-OFDM superchannels, that are less sensitive to nonlinear distortion and chromatic dispersion effects. The ultimate efficiency in physical resource exploitation can be achieved only in a truly flexible system, where it is possible to switch from OFDM to N-OTDM and vice versa, through intermediate fractional grids. Starting from experimental results of a novel approach for hybrid time-frequency multiplexing, this talk will focus on additional multiplexing domains, such as polarization, space, wavelength and code. Suitable AWG configurations can be designed for simultaneous frequency and polarization or mode and frequency multiplexing, as well as for generating optical codes in asynchronous code division multiple access (CDMA) and optical packet switching systems.
Image from https://doi-org/0.1364/OE.25.00349
Gabriella Cincotti is a Full Professor at the Engineering Department, University Roma Tre, Rome Italy; she leads the Photonics Research Group and is in charge of the courses of Photonics and Biophotonics. She is a Fellow of the Optical Society of America (OSA), she was an elected member of the Board of Governors of the IEEE Photonics Society (2017-2019) and currently she is serving in the IEEE Photonics Publications Council. She was a technical program committee (TPC) member of the European Conference on Optical Communications (ECOC) (2010-2012), also serving as Chair of the Access Subcommittee. She was also TPC member of the Optical Fiber Communication Conference (OFC) (2016-2018). She served as an Associate Editor of Optics Letters (2008-2014) and she serves as Deputy Editor of Optica since 2017. She has authored or co-authored over 300 research papers in leading journals and conferences. Her main research interests are in the field of planar lightwave circuits, photonic devices and subsystems for high-speed optical signal processing. Recently, she moved part of her research interests toward super resolution imaging and point of care testing for biomedical and microbiological applications.
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Friday, October 23rd, 11 am (PDT) via Zoom
Dr. Christian Reimer is a physicist and entrepreneur working in the fields of nonlinear optics, integrated photonics and quantum optics. He received graduate degrees from the Karlsruhe Institute of Technology in Germany, Heriot-Watt University in Scotland, and the National Institute of Scientific Research in Canada. He then worked as a postdoctoral fellow at Harvard University, before becoming Co-Founder and Head of Product of HyperLight Corporation. HyperLight, a Venture-Capital funded start-up out of Harvard University, is specialized on integrated lithium niobate technologies for ultra-high performance photonic solutions.
In the scientific part of his talk, Christian will introduce the field of integrated photonics based on thin-film lithium niobate, with a focus on electro-optic applications, as well as recent progress on transforming the field from chip-based proof-of-concept realizations for wafer-scale production. In the professional development section, he will then share his experience transitioning from academia to a start-up company. He will talk about differences and similarities in the work environment, what to expect in terms of tasks and responsibilities, and explain how salaries at start-ups can include combinations of equity and incentives.
In the scientific part of his talk, Christian will introduce the field of integrated photonics based on thin-film lithium niobate, with a focus on electro-optic applications, as well as recent progress on transforming the field from chip-based proof-of-concept realizations for wafer-scale production. In the professional development section, he will then share his experience transitioning from academia to a start-up company. He will talk about differences and similarities in the work environment, what to expect in terms of tasks and responsibilities, and explain how salaries at start-ups can include combinations of equity and incentives.
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Images from hyperlightcorp.com
 | On Henley Hall Prof. John Bowers |  |
Friday, Oct. 16th, 4 pm (PDT) via Zoom
Henley Hall will hold state-of-the-art research facilities for developing energy-efficient technologies. Prof. Bowers will present the research capabilities and expected research ramp-up timeline for the new building.
Thursday, Oct. 8, 1-2 pm (PDT) via Zoom
Meeting ID: 819 4601 6935, Password: 597044
Meeting ID: 819 4601 6935, Password: 597044
Entanglement and encoding in discrete frequency bins – a quantum analogue of wavelength-division multiplexing – represents a relatively new degree of freedom for quantum information with photons. Potential advantages include generation of high-dimensional units of quantum information called qudits, which can carry multiple qubits per photon; robust transmission over fiber; frequency parallelism and routing; and compatibility with on-chip implementations, as well as hyperentanglement with other photonic degrees of freedom. In this talk I first give an overview of manipulating and measuring quantum states encoded and entangled in the photonic frequency degree of freedom. I will then discuss our recent experiments that focus on high-dimensional entanglement and mixing of multiple frequency bins in a single operation, going well beyond nearest neighbor “interactions.
Tuesday, September 8th, 10 am (PDT) via Zoom
Meeting ID: 978 3569 2970 Passcode: 468555
Meeting ID: 978 3569 2970 Passcode: 468555
Infectious diseases and water are some of the greatest, most urgent challenges of the 21st century. III-nitride ultraviolet (UV) light sources, including light emitting diodes (LEDs) and lasers, are the only alternative technology to replace conventional power-hungry, hazardous mercury lamps for disinfection and water purification. Recent studies showed that AlGaN-based UV-C LEDs can readily shred genetic material of viruses and bacterial and achieve 99.9% sterilization of SARS-COV-2. In this talk, I will present the recent advances of AlGaN and BN nanostructures and heterostructures and their applications in UV optoelectronics, including the first demonstration of mid and deep UV laser diodes and tunnel junction UV-C LEDs with significantly improved performance. The recent development of far-UV-C LEDs, in the wavelength range of 207-222 nm, will also be presented, which has shown to be faster and far more effective than traditional UV-C light (~265 nm) in preventing the transmission of microbial diseases, while causing virtually no harm to mammalian skin or eye.
  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.  |
Wednesday, May 20, 2020, 1 p.m.
Sustainability applied to networking is about treating professional support and assistance like a resource, and creating more of it than you take. Dr. Willis will discuss principles and applications of sustainable professional networking, and how to use it to generate success through mutually beneficial professional relationships. She will also discuss her own career path, citing examples that illustrate the value of sustainable networking.
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Engineering robust solid-state quantum systems is amongst the most pressing challenges to realize scalable quantum photonic circuitry. While several 3D systems (such as diamond or silicon carbide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy. In this presentation I will discuss single defects in an emerging 2D material – hexagonal boron nitride (hBN), that is promising as qubits for quantum photonic applications. In particular, I will focus on ways to engineer these defects deterministically using either chemical vapour deposition growth or ion implantation, and show results on strain tuning of these ultra-bright quantum emitters. I will then highlight promising avenues to integrate the single defects with photonic cavities, as a first step towards integrated quantum photonics with 2D materials. I will summarize by outlining challenges and promising directions in the field of quantum emitters and nanophotonics with 2D materials.
Watch the recorded lecture from April 23, 2020:
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. |
 | Advanced Semiconductor Lasers: Ultra-low Operating Energy and Hetergeneous Integration with Si Photonics Devices
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Friday, February 7th from 12:00 - 1:00 pm in ESB 2001
The electrical power consumed in data transmission systems is now hampering efforts to further increase speed and capacity at various scales, ranging from data centers to microprocessors. Optical interconnects employing ultra-low-energy directly-modulated lasers will play a key role in reducing the power consumption. Since a laser's operating energy is proportional to the size of its active volume, developing high-performance laser with a small cavity is important. For this purpose, we have developed DFB and photonic crystal (PhC) lasers, in which active regions are buried with an InP layer. Thanks to the reduction of cavity size and the increase in optical confinement factor, we have achieved an extremely small operating energy of 4.4 fJ/bit by employing a wavelength-scale PhC cavity. Cost reduction is also an important issue because a larger number of transmitters are required for short-distance optical links. For this purpose, Si photonics technology is expected to be a potential solution because it can provide large-scale photonic integrated circuits (PICs). Therefore, heterogeneous integration of III-V compound semiconductors and Si has attracted much attention. To fabricate these devices, we have developed wafer-scale fabrication that employs regrowth of III-V compound semiconductors on directly-bonded thin InP templates on an SiO2/Si substrate.
Dr. Matsuo discusses some of the equations related to semiconductor lasers.
 |  Nanoscale Engineered Silicon Imagers Reaching Theoretical Limit of Performance and their Applications in Space Exploration and Synergistic Fields Dr. Shouleh Nikzad NASA Jet Propulsion Laboratory |
Thursday, January 30th, 11 am, Elings 1605
NASA’s trend toward less costly missions has created a need for smaller and more capable instruments for in situ planetary applications, space weather, and Earth Observations. The rise of cubesats has created a new powerful platform that if enabled with powerful sensing technology can be an instrument of discovery. At the same time, large aperture UV/visible/Near Infrared space telescope are being planned for cosmology and astrophysics studies that will need high performance yet affordable detectors to populate their very large focal plane arrays. In nearly all these facets of space exploration, there is a strong need for high signal to noise ultraviolet detection technology. This is due to the fact that the ultraviolet part of the spectrum is rich in spectral information that are key to study exo-solar planets, protoplanets, intergalactic medium, supernovae, electromagnetic counterpart of gravitational wave, star formation, galaxy evolution, and more. Semiconductor detectors offer a rich spectral range, tailorable spectral response, high resolution, and sensitivity; however, these capabilities are not available in a single material or class of material. For example, while silicon imagers have reached high performance levels in format, pixel size, and signal to noise, they are naturally insensitive to ultraviolet light. Using non-equilibrium processes, we can manipulate materials at nanometer scale, form unusual and quantum structures, and alter bandstructures. Through nanoscale surface and interface engineering of 2D doping (superlattice doping and delta doping) high performance silicon-based imagers are produced with record high quantum efficiency in the ultraviolet. Furthermore, the response of silicon imagers can be tailored for out of band rejection through nano-scale interface engineering. In this talk we will discuss the underlying physics of the ultraviolet silicon detectors, their performance, their integration in systems, and their application in cubesats and space flagship missions. We will also discuss the synergy between the requirements for instruments in NASA space applications and medical applications and show how space technologies can and have been used for medical applications.
Coffee provided!
Dr. Nikzad introduces here work at NASA on Si-based UV detectors applications on cubesats.
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. |
Friday, January 24th | 12:00 pm | ESB 2001
Pizza will be provided!
Pizza will be provided!
Come and mingle for any sessions during the first all-online photonics conference, the Photonics Online Meetup (POM). The event will be continuously live-streamed between 11am and 4pm in Elings 1605. Refreshments will be served.
The conference will feature internationally renowned scientists as plenary speakers:
https://sites.usc.edu/pom/program/
The conference will feature internationally renowned scientists as plenary speakers:
- Prof. Mete Atature (University of Cambridge, UK)
- Prof. Nader Engheta (University of Pennsylvania, USA)
- Prof. Mercedeh Khajavikhan (CREOL-University of Central Florida, USA)
https://sites.usc.edu/pom/program/
 | Dr. Volker J. Sorger Associate Professor ECE Dept. - George Washington University Volker J. Sorger is an Associate Professor in the Department of Electrical and Computer Engineering, and the leader of the Integrated Nanophotonics lab at the George Washington University. He received his PhD from the University of California Berkeley and MS from UT Austin. His research focuses on integrated photonics and plasmonics, and analog information processing such as programmable photonic circuits and neuromorphic computing. His work was recognized by Presidential Early Career Award for Scientists and Engineers (PECASE), the Emil Wolf prize from the Optical Society of America, the AFOSR Young Investigator (YIP) award, the Hegarty Innovation prize, the National Academy of Sciences paper-of-the-year award, and both the Early Career and Outstanding Research awards at GWU. He is the editor-in-chief of the Nanophotonics and the OSA division chair for Optoelectronics-and-Photonics. He serves at the boards of OSA and SPIE, and is a senior member of IEEE, OSA & SPIE. Further details at sorger.seas.gwu.edu. |
Thurs. Nov 14, 2019 | 12:00 - 1:00 pm | ESB 2001
Photonic technologies are at the forefront of the ongoing 4th industrial revolution of digitalization supporting applications such as virtual reality, autonomous vehicles, and electronic warfare. The development of integrated photonics in recent years enabled functional devices and circuits through miniaturization. However, fundamental challenges such as the weak light-matter integration can limited silicon and III-Vbased devices to millimeter-scale footprints demanding about one million photons-per-bit. Overcoming these challenges, in the first part of this talk I will show how nanoscale photonics together with heterogeneous integration of emerging materials into foundry-based photonic chips enables strong nonlinearity, which we use to demonstrate attojoule and compact optoelectronics. Here I will discuss our recent devices demonstrating ITO-based MZI modulators, 2D-material excitonic photodetectors, and exotic epsilon-near-zero modes empowering record-efficient phase shifters for applications in data-comm, LiDAR, and photonic neural networks (NN). Further, I will show that the usually parasitic Kramers-Kronig relations of altering the optical index can be synergistically exploited delivering new modulator operations. With Moore’s law and Dennard scaling now being limited by fundamental physics, the trend in processor heterogeneity suggests the possibility for special-purpose photonic processors such as NNs or RF-signal & image filtering. Here unique opportunities exist, for example, given by algorithmic parallelism of analog computing enabling non-iterative O(1) processors, thus opening prospects for distributed nonvan Neumann architectures. In the second part of this talk, I will share our latest work on analog photonic processors to include a) a feed-forward fully-connected NN, b) mirror symmetry perception via coincidence detection of spiking NNs, c) a Fourier-optics based convolutional processor with 1 PMAC/s throughputs at nanosecond-short delays for real-time processing, d) a photonic residue arithmetic adder, and e) meshbased reconfigurable photonic & metatronic PDE solvers. In summary, heterogeneous photonics connects the worlds of electronics and optics, thus enabling new classes of efficient optoelectronics and analog processors by employing the distinctive properties of light.
Pizza will be provided!
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