category » Optics & Photonics

Figure 2: Final driver segments and 2.5 Gb/s eye diagram at 1.23 pJ/b and extinction ratio of 3 dB.  An off-chip tunable laser provides the incoming 1550-nm-band light.
A Monolithically-integrated Optical Carrier-injection Ring Modulator and All-digital Driver Circuit in Commercial 45-nm SOI
  • A monolithically integrated photonic modulator and driver circuit is a key building block toward realizing a dense and energy-efficient communication…


Figure 2: Optical response of the ring filter at minimum and maximum heater power settings (left) and tuning cost per gigahertz, with driver cost included, to reach a specific tuning offset (right).
Integrated Microring Tuning in Deep-trench Bulk CMOS
  • Wavelength-division multiplexed (WDM) silicon-photonic links form a promising alternative to traditional electrical interconnects. However, the essential component of these WDM…


Next-Generation Ultrafast Photo-Triggered Cathodes
  • State-of-the-art ultrafast cathodes are based on the photoelectric effect, where electrons are emitted from a flat surface using ultraviolet (UV)…


Figure 1: Brightfield image showing the patterned structure on a silicon substrate. The patterns were defined using ebeam lithography on SU8 resist followed by sputtering of 100 nm of silicon dioxide.
Nano-patterning of J-aggregate Thin Films
  • We show patterning of thin J-aggregate[1] films using nano-imprinting. Unlike the conventional microfabrication techniques, such as direct-write or lift-off processes,…


Figure 1: SEM of Au nanorod array.  The nanorod geometry was tuned to match a longitudinal surface plasmon mode of an Au nanorod, which was excited by 800-nm incident laser beam.
Nanostructured Photocathodes for Compact Coherent X-ray Sources
  • Nanostructured photocathode arrays can be used as the electron sources for the compact coherent X-ray source. Femtosecond laser pulses were…


Figure 1: The processor-DRAM interface platform, which consists of a DRAM memory chip and a processor chip with an on-chip Megacell structure and off-chip optical links.
Photonic Processor-DRAM Interface
  • Integrated photonic interconnects enable new possibilities for bandwidth and energy-efficiency driven VLSI applications, such as many-core processor systems, by removing…


Figure 1: A full-color device undergoing testing.
Light Modulators for Holographic Video Displays
  • In this research we seek to develop acousto-optic, guided-wave modulators in proton-exchanged lithium niobate[1] for use in holographic and other…


Figure 1: Artist’s impression of a tip-enhanced microscopy setup.
Spatially Resolved Exciton Dynamics in Quantum Dot Thin Films
  • The diffusion of excitonic energy from within the photosensitive layer of a photovoltaic cell towards the charge separation interface is…


Figure 1: Schematic of the planar STPV experimental layout. Incoming solar radiation is converted to heat at the absorber (MWCNT/W); heat is selectively radiated by the emitter (1D PhC) and converted to electrical power at the PV (InGaAsSb – 0.55 eV).
Optimizing Emitter-to-Absorber Area Ratio for Improved Efficiency in Planar Solar Thermophotovoltaics
  • Solar thermophotovoltaic (STPV) devices have the potential to overcome the Shockley-Queisser limit by converting solar radiation to a narrow-band thermal…


Figure 2: Energy of the plasmon peak (Ep) extracted from low-loss EELS data plotted as a function of scan position. The compositional variation corresponding to the observed changes in Ep is < 5.4%, which suggests that there are no large-scale In-rich clusters present.
Understanding the Light Emission Mechanisms in InGaN by Correlating its Structural and Optical Properties
  • Solid state light-emitting diodes (LEDs) containing InxGa1-xN (0 ≤ x ≤ 1)/GaN hetrostructures as active components are of particular importance…


Utilization of Doped-ZnO and Related Materials Systems for Transparent Conducting Electrodes
  • Efficient transparent electrode materials are vital for applications in smart window, LED display, and solar cell technologies.  These materials must…


Figure 2: Fitting experimental results of PS;DCM(II) peak energy shift as function of changed molecular packing density or dielectric susceptibility. Red dashed line indicate the OLM theory of DCM(II) with initial dielectric constant of 2.44 (x0 = 1.44) in polystyrene, and blue points indicate the fitted peak wavelength from the pressure experiment using elastic modulus as a fitting parameter. The plot shows good agreement for a PS elastic modulus of 1.2 0.6GPa.
Mechanical Pressure-induced Solid State Solvation in Organics Thin Films
  • Significant technological progress of organic semiconducting structures has led to their commercialization in the form of organic LED displays, solid…


Figure 1: Simulated extraction efficiency as a function of the QW placement for m-directional and c-directional axial heterostructures, with the solid line indicating the extraction efficiency for a 
c-directional radial heterostructure with the QW placed at 0.9 the distance from the center to the surface.
Efficiency Comparison of m- and c-directional GaN Nanowire-based LEDs on Si
  • III-nitride nanowire-based light-emitting diodes (LEDs) are promising alternatives to thin-film LEDs for solid-state lighting[1]. Facile strain relaxation in nanowires allows…


Figure 2: Confocal microscopic setup for quantum dot emission measurement.
Tunable Surface Plasmonics on Electric-gated Nanostructures and its Coupling with Quantum Dot Emission
  • The main goal of this work is to introduce functional natural materials into the design of surface plasmonic structures and…


Figure 2: Normalized integrated intensities of the 3.59-eV and 3.35- eV CL luminescence along the length of the nanorod shown in Figure 2(h). The positions of the nanorod coalescence in the n-GaN section and metallurgical junction are indicated. The squares and circles are experimental data and the dashed lines are fits based on an exponential decay model.
Correlation of Doping, Structure and Carrier Dynamics in a Single GaN Nanorod
  • GaN-based nanowires and nanorods are promising materials systems for optoelectronic applications such as high efficiency light emitting diodes[1],[2] or low…


Figure 1:  A scanning electron micrograph of six ten-probe line-ar arrays assembled into a six-by-ten two-dimensional array of probes.  The probes in this figure and in Figure 2 were fab-ricated for assembly studies and lack sense electrodes.  Each needle is 3.5 mm long and 40 µm wide at the tip.
Scalable 3-D Microelectrode Recording Architectures for Charac-terization of Optogenetically Modulated Neural Dynamics
  • Optogenetics is commonly used for precision modulation of the activity of specific neurons within neural circuits[1], but assessing the impact…


Figure 1:  (a) A photomicrograph of a linear array of five waveguide probes, each which has nine guides.  (b) An SEM micrograph of a 2-D probe array assembled from four linear arrays having five waveguide probes, each of which has twelve guides.  (c) A zoomed-in view of the 2-D array in Figure 1b showing the 45˚ mirrors and output ports.  The scale bars are all 100 µm long.
Waveguide Micro-probes for Optical Control of Excitable Cells
  • Optogenetics is the safe, effective delivery of light-gated membrane proteins to neurons and other excitable cells (e.g., muscle, immune cells,…


Figure 2. a) Image of the subwavelength 1D grating fabricated by GIL with the single exposure. During the exposure, the aperture plate moves to the left side of the sample (-x direction) at a constant speed. b) Cross-sectional micrographs of the grating with respect to the position from i to viii regions marked in Figure 2a.
Fabrication of Aperiodic Subwavelength Nanostructures by Grayscale Interference Lithography (GIL)
  • Interference lithography (IL) is one of the most effective and low-cost approaches for large-area nano-patterning and nanostructure fabrication; IL has…


Figure 1: a) Finite difference time domain (FDTD) simulation of an LRM resonator. b) Measured spectrum of the fabricated LRM filter, showing uncorrupted 4-THz FSR on through and drop ports. c) Temporal response of the thru and drop ports of the LRM filter, excited by 20kHz 0.15V square-wave drive, fit to a 2.6-µs exponential decay and a 1.6-µs rise thermal time constant (shown in red), the insertion loss (IL) of the LRM filter is
L-shaped Resonant Microring Filter with Integrated Thermal Tuner
  • Silicon photonics enables wavelength-division multiplexed (WDM) networks to be efficiently and cost effectively implemented on chip with potential for multi-terabit/s…


Figure 1: a) 3D sketch of the LRM modulator showing size, doping, and metal connections. b) Spur-free single mode operation of the LRM modulator with an FSR of 5.3 THz. c) Spectral response of the LRM modulator with respect to voltage dropped and current passing through the device. d) High speed measured optical eye diagrams at 15-, 20-, 25-, and 30-Gb/s data rates of the LRM modulator, driven by a PRBS data of 2.2Vpp with a -0.6V DC bias. Dynamic insertion loss and extinction ratio are denoted below the eye diagrams.
L-shaped Resonant Microring Modulator
  • On- and off-chip bandwidth and energy scaling are pushing the limits of CMOS and VCSEL technology, which allow only a…


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Adiabatic Resonant Microring Modulators with Integrated Thermal Tuner
  • Wavelength division multiplexed systems can achieve high bandwidth by utilizing many channels on a single fiber as opposed to current…


Figure 1: a) 3D sketch of the microdisk modulator with integrated heater showing size, doping and contacts. b) Measured DC spectral response of the integrated heater inside the microdisk modulator with an applied bias voltage to heater pins. c) High-speed optical eye diagrams at a data rate of 13-Gb/s with an ac-coupled 1.5Vpp drive and 2V applied across heater contacts. The  extinction ratio is 5.8dB and insertion loss is 1.22dB. d) Measured spectral response of the microdisk modulator with applied DC bias voltage to modulator pins from -3V to 0.5V.
Vertical Junction Silicon Microdisk Modulator with Integrated Thermal Tuner
  • Silicon photonics, because it enables wavelength division multiplexed (WDM) systems, will help to minimize the number of fibers required in…


Figure 1: a) Top-view of the 6-µm-diameter microdisk modulator, which utilizes circular inner contacts. b) 2D cross-section showing the doping profile with p-n vertical junction, p+and n+ overlapping regions. c) Spectral response of the microdisk modulator with respect to voltage dropped and current passing through the microdisk modulator. d) High-speed measured optical eye diagrams at 10-, 15-, 20-, and 25-Gb/s data rates of the microdisk modulator, driven by AC coupled 1.2Vpp. The eye diagrams are shown with the true zero (gray line) at each data rate.
Vertical Junction Silicon Microdisk Modulators at 25Gb/s
  • High-performance computing systems require high bandwidth, low power, and scalable optical interconnects to maintain balanced communications in future exascale machines….


Fig. 1. (a) SEM of a SiNx membrane (~ 350-nm thick) with SNSPD on top. (b) Optical micrograph of a membrane-SNSPD that was transferred and aligned to a Si waveguide on a PIC chip. (c) Instrument response function (IRF) of a membrane-SNSPD transferred onto a secondary substrate. The IRF was measured using a mode-locked fiber-coupled laser with sub-ps-pulse-width and 1550-nm wavelength. We measured sub-35-ps timing jitter for detectors with IC > 13 μA.
Membrane-integrated Superconducting Nanowire Single-photon Detectors
  • Superconducting nanowire single-photon detectors (SNSPDs)[1] based on niobium nitride (NbN) nanowires have shown high speed (< 3ns dead time[2] )…


Figure 1. Passive phased arrays. (a) A schematic of the large-scale optical phased array. Inset, a scanning electron micrograph (SEM) of a part of the phased array fabricated with the state-of-the-art CMOS technology. (b) Near-field emission of a 64×64 phased array. (c) Simulated and (d) measured far-field interference pattern of a 64×64 phased array to generate an MIT-logo. (e) Simulated and (f) measured far-field interference pattern of a 32×32 phased array to generate multiple beams. The white/red lines separate the interference orders while the green circle depicts the edge of the objective lens.
Large-scale Nanophotonic Phased Array
  • Electromagnetic phased arrays at radio frequencies (RFs) are well known and have enabled applications from communications to radar, broadcasting, and…


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Wide-field Multispectral Super-resolution Imaging Using Spin-dependent Fluorescence in Nanodiamonds
  • Recent advances in fluorescence microscopy have enabled spatial resolution below the diffraction limit by localizing multiple temporally or spectrally distinguishable…


Figure 1: Top: dual disks of switches. Bottom: switching fabrics.
Compact Modeling for Silicon Photonic Wavelength Selective Switches
  • Silicon photonic wavelength selective switches have been recently demonstrated by the Photonic Microsystems Group, led by Prof. Watts, and hold…


Figure 2: Bending adapter consist of a 140-nm period nanograting (50% duty cycle) rotated 2.69° with respect to the horizon. The coupling grating deflects the light into a slab waveguide, and an impedance matching layer for reducing reflection at the boundary between the bending adapter and slab waveguide is created by a group of α-Si nanorods.
Design and Fabrication of Dielectric Nanostructured Bending Adapter for Optical Frequencies
  • Transformation optics has inspired numerous conceptual devices since the first theoretical model of invisibility cloaks[1],[2]. However, the transition of these…


Figure 2: The calculated absorptance in the in NbN device layer on a silicon nitride/silicon substrate with a SiOx cavity and gold mirror on top (red line) versus the cavity thickness. The blue line shows the absorptance for the NbN device on SiNx/Si without a cavity.
Optical Calculations for Enhancing the System Efficiency of Superconducting Nanowire Single-photon Detectors
  • Optical losses limit the system detection efficiency of systems using superconducting nanowire single-photon detectors (SNSPDs)[1]. SNSPDs are typically fabricated with…


Figure 2. (a) Simulated vertical emission for different structures, (b) Final structure with time integrated field box showing radiated field, (c) Free space far field pattern of same structure at λ=1550 nm.
Frequency-chirped Sub-wavelength Nanoantennas
  • Vertical coupling can be used in silicon on insulator-based optical phased arrays (OPA) to emit light traveling in a waveguide…


Figure 2. (a) Simulated vertical emission for structures with ground-plane: (blue dash-doted) single aperture, (dashed green) 3 apertures arranged laterally to waveguide direction, (solid cyan) 3x2 array design to emit exactly to zenith, (magenta solid-w-dots) 3x2 array design for 10º backward emission, (red dashed-line-w-dots) 3x6 array design for 5º backward emission, and (black line-w-Xs) ohmic losses of 3x6 array, (b) simulated 3x6 structure with time Fourier integrated field box showing emitted fields. (c) Far field pattern of same structure at λ=1550nm.
Vertical Emitting Aperture Nanoantennas
  • Vertical input/output coupling in the telecom C-band (1535 nm << 1565 nm) has been extensively investigated for coupling to or…


Figure 1: a) Beam waist (w) propagation of three beams initially separated by 4 mm propagating in a 4-lens optical system. The first four vertical red lines represent the position of the 4 lenses. The last red line is a fictitious end plane. b) Separation between the center of a beam initially shifted 4 mm from the optical axis and the optical axis itself as a function of position (d) on the optical axis.
Free space Coupled Superconducting Nanowire Single photon Detectors
  • Superconducting nanowire single‑photon detectors (SNSPDs)[1] are a technology that combines single‑photon sensitivity, high speed, and high time resolution in the…


Band diagram and subband wave functions of a THz quantum-cascade laser based on resonant-phonon design.
Development of Terahertz Quantum-cascade Lasers
  • The terahertz frequency range (1-10 THz) has long remained undeveloped, mainly due to the lack of compact, coherent radiation sources….


Figure 1:  An SEM image of an integrated platelet laser (upper left) with inserts showing the fit along the lower edge (lower left), and the lateral alignment and gap (1.02 µm) at the output end of the laser (right).
Co-axial Recess-integration of 1.55-µm Edge-emitting Laser Diodes with SiOxNy Waveguides on Silicon
  • We have demonstrated for the first time in-plane InGaAs/InP laser diodes that are recess-integrated with SiON waveguides on silicon substrates…


Figure 1: Schematic of absorption and fluorescence enhancement using the J-aggregate excitonic antenna.
Absorption and Fluorescence Enhancement of Single Molecules and Quantum Dots Using an Excitonic Antenna
  • Nature presents us with a fundamental mismatch between the “size” of visible light (~250 nm in free space) and the…