1:00 PM Friday, March 5th Zoom Meeting --– Meeting ID: 847 3105 9791 --- Password: 792878 --- Zoom Link
Thursday, February 25th, 10 am (PST) via Zoom Meeting ID: 854 2977 2482 Passcode: 230903 Both human vision and imaging systems have limited capability to separate spatial features, and this information can only be extracted from a limited range in depth. These limitations arise from diffraction, i.e., the finite dimensions of the imaging optics and the geometry of the sensor. In this talk, I will present novel photonic approaches to exceed the resolution limitations of geometric optics. I will show how those concepts can be adapted to micro endoscopy as well as to microscopy-related configurations, including ophthalmic devices for correcting visual deficiencies.
Friday, January 29th, 10 am (PST) Infrared detectors and imaging systems are becoming increasingly important in a diverse range of astronomic, military, and civilian applications. This field has gained significant attention while incorporating various materials and architectures into detector designs with a strong focus on applicability into clinical domains. Dr. Perera will discuss recent detector structures, and his latest work on disease detection. Biomedical applications of infrared include an exploration of an Affordable, Sensitive, Specific, User-friendly, Rapid, Equipment-free, and Deliverable (ASSURED) diagnostic regimen and testing its clinical feasibility for inflammatory bowel diseases (IBDs) and cancer screening. A study using Fourier transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) sampling mode analyzed body fluids in order to identify reproducible, stable, and statistically significant differences in spectral signatures of the IR absorbance spectra between the control and disease samples. These results show that serum samples can be used to detect the biochemical changes induced by these diseases.
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. |
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.
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.
Meeting ID: 819 4601 6935, Password: 597044
Meeting ID: 978 3569 2970 Passcode: 468555
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. |
Advanced Semiconductor Lasers: Ultra-low Operating Energy and Hetergeneous Integration with Si Photonics Devices |
![]() 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 |
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!
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