Research Advisor: Franko Kuepper, U of A

Abstract:
Channel capacity and transmission speeds have always been a prime factor in telecommunication network design. Multiplexing allows for higher transmission rates, but this normally increases signal impairments. To mitigate these impairments, the choice of modulation scheme is as important as signal correction and distortion compensation. Phase Shift Keying (PSK) modulation is a digital modulation scheme that encodes data on the phase of a carrier wave, therefore minimizing difficulties often experienced with conventional On-Off Keying (OOK). This paper presents the simulation methods and results of a back-to-back Polarization Multiplexed-Differential Quadrature PSK (PM-DQPSK) transmission system at 100 Gbps.

 

 

Research Advisor: Vitaly Lomakin, UCSD
Abstract:
The propagation of optical excitations along a chain of particles is affected in part by the materials, locations, and structures of those particles. Changing the scattering properties of each consecutive particle in the chain may be a method to make this type of wave propagation viable for various applications. This study involves optical wave transport on chains of resonant particles where the element's properties are tuned to result in a particular functionality. Chains with identical, closely spaced particles lead to waveguidance without radiation, which is mediated by strong interactions between particles and by constructive interference in a prescribed direction. Chains with a larger periodicity lead to radiation of a conical beam, which is mediated by leaky modes supported by such a chain. Chains with gradually tapered properties may lead to waveguidance with greatly enhanced fields at locations where slow group velocity is supported. In addition, controlling the resonant properties of the particles allows controlling the supported modal field’s transverse extent. These properties can be used to design optical couplers, radiating elements, and sensors.

 

Research Advisor: Ming Wu, Berkeley
Absract: Characterization of the coupling of a waveguide to a pseudo-disk resonator demonstrated effective infrared broadband signal filtration with a transmission spectrum bandwidth of approximately 3.5GHz. By altering phospho-silicate glass reflow conditions, roughness throughout the device was reduced. In turn, device quality factor (Q0) was increased and signal filtration optimization was observed.

Our micro-resonator bandwidth-tunable filters are uniquely intelligent, multi-functional optical devices that are capable of being tuned at very low voltage bias. We observed MEMS actuation at 35V with waveguide displacement of 8µm, which is well beyond the required tuning range. The mere fact that these devices can be successfully tuned beyond their tuning range at low applied voltage proposes an efficient optical device that will optimize internet use. Also, bandwidth-tunable filters may be used well beyond bandwidth tuning. These micro-devices have the capability of being used as sensors due to their unique optical response to different types of chemicals. Furthermore, our micro-devices are fabricated with the optical components composed of silica (SiO2). Silica offers a variety of benefits toward the progression of optical optimization of the devices while incurring new challenges. Silica inherently has lower optical absorption than silicon. Silica can also be PSG relowed, reducing sidewall roughness throughout the device. Thus, using pure silica for optical components improved output power and the quality factor of the resonator. Although silica is beneficial, new challenges arose. Silica cannot sit directly on the silicon substrate due to the large light absorption of silicon and, therefore, must be completely released. Also, silica is not electrically conductive. This presents a challenge for MEMS actuation because voltage bias applied does not get transferred to the MEMS

 

Research Advisor: Diana Huffaker, UCLA
Abstract:
This work devotes to develop high quality InAs QDs by Molecular Beam Epitaxy (MBE) with the help of Antimony (Sb) surfactant layer. An Sb flux (BEP=3ï‚´10-8 Torr) is exposed to the GaAs buffer layer for either 0, 15, 30, 45, 60 or 100 seconds before the growth of InAs QDs. Atomic Force Microscopy (AFM) images show a clear increase of QD density for longer Sb soak time. The photoluminescence (PL) measurements demonstrate the best soak time to be 30s as the QD PL intensity increase by over a magnitude. We also discuss the possible alteration of QD band structure after Sb incorporation into the QDs. In conclusion, we are able to see that the inclusion of a suitable Sb surfactant layer will produce an increase in the InAs QD density and subsequently PL intensity.

 

Research Advisor: Galina Khitrova, U of A
Abstract:
We measure the quality factor (Q) of photonic crystal nanobeam cavities using resonant scattering and a fiber taper loop measurement. The fiber measurement is performed at both the edge and center of the nanobeam, to see which location results in the highest Q. Because it’s the area of weakest coupling, we observe the higher Q at the edge of the nanobeam for the fiber measurement. Overall, the highest Q is achieved by using the resonant scattering technique, but this measurement is more difficult to use than the fiber taper loop.

Research in cavity quantum electrodynamics focuses on understanding how light and matter interact with one another in the quantum regime. This involves studying light confined to a cavity and active emitters, such as quantum dots. To improve light-matter interactions, the Q of the cavity needs to be optimized. Having a higher Q means the cavity is confining the light better, which provides a longer photon lifetime and hence more opportunity for interaction. A higher Q also means higher field intensities, and hence stronger light-matter interactions. Therefore, our primary focus is on improving the Q of photonic crystal nanocavities.

In particular, we study 1D photonic crystal nanobeams that are fabricated in silicon-on-insulator, which confines light to the device in two dimensions by total internal reflection and in the third dimension by Bragg reflection as a result of its structure. The structure of a nanobeam has three main components, which include the mirror, taper, and cavity regions. In the mirror regions that are located at the ends of the nanobeam, air gaps, or holes, are periodically placed from one another. As a result, the holes act as Bragg reflectors, and define the photonic bandgap of the nanobeam. However, by modifying the size and spacing of the holes, we can introduce allowed states into the bandgap, which results in resonant wavelengths that define the mode of the cavity. The tapered sections of the nanobeam serve to select these resonant wavelengths, or the specific wavelengths of light, that are trapped in the cavity region [1]. For this experiment, we look at two methods for determining the Q of nanobeam cavities: resonant scattering and tapered fiber transmission.

Section II discusses the necessary apparatus and procedures needed to calculate the Q for both resonant scattering and the fiber taper measurement. Section III discusses the results from performing the tapered fiber transmission at two different contact locations along the nanobeam, and reports the Qs resulting from both the fiber taper and resonant scattering techniques. Section IV summarizes our conclusions from this experiment, which includes a brief comparison of the two methods.

 

Research Advisor: George Papen , UCSD
Abstract:
Optical 3D MEMS (micro-electromechanical systems) switches are being considered for data center application because of their low energy use and high port count. In order to effectively use a MEMS switch in a data center, the variability of the switching times needs to be characterized. There exist input/output port combinations that switch relatively slowly due to the mirrors’ mass-spring resonance and long port distances across the mirror array. Our objective is to determine which port combinations yield the longest signal switching times. Switch times are recorded on UCSD Calit2’s 3D MEMS Glimmerglass switch using single-shot oscilloscope triggering and data collection with LabVIEW Agilent 5460X virtual instrument. Our knowledge of the slowest switch times can help improve the performance of the data center.

 

Research Advisor: Shaya Fainman, UCSD
Abstract:
This presentation proposes a design for an efficient chip-scale germanium photodetector. The design is based on the optimization of modal characteristics to minimize transmission loss while maximizing the conversion efficiency between the optical and digital signals.

 

Research Advisor: Gil Zusman , Columbia
Abstract:
EnHANTS are tiny, supple and self-reliant (for energy) devices which can be used to track the normally non-networked materials [3]. The objective of this project is to use energy-harvesting sensors to emulate an automatic library shelving system. These mica2 mote networked tags can communicate with each other and with the librarian. Using the nes-C code in TinyOS platform these sensors nodes are programmed to find the misplaced items and report to the monitoring PC.

The system consists of 20 wireless motes, each mounted on an Ethernet programming board and fixed to the ceiling. All Ethernet programming boards are powered over Ethernet by a switch. The switch is also connected to a programming PC, which can program and monitor the Motes via Ethernet [2].

 

Research Advisor: Bahram Jalali, UCLA
Abstract:
As technology has progressed and image-taking techniques become more sophisticated, image-processing skills have grown more important for scientists and engineers. Acharya and Ray (2005) discuss many useful applications of image processing in both industry and research. Some examples are inspection, analysis, and feature and object detection, which can be used in a large variety of areas. A biomedical use of image processing would be the images that are made using several different types of scans of the human body, such as MRIs, CT-Scans, and X-Rays. If a doctor or some other personnel is looking for cancer in a scan of someone’s chest, it must be distinguishable from the ribs, the lungs, the heart, and other body tissue that will also be in the image. In industry, product inspection can be a key factor in being a successful company. General Electric Corporation is one of many companies that use an automatic visual inspection system to check the filaments in the incandescent lamps that they sell (Ray, 2005).

Small errors in the filaments can be problematic in a lamp so it is important that there be a system in place to check for such errors. With mass production it would be nearly impossible for someone to check each one by examining it, but with the help of image processing a computer can easily check for abnormalities in all of the filaments that are produced. The problem being addressed here is the application of imaging techniques and processing of human cells to be able to compare normal blood cells to abnormal cells, such as cancer cells. The problem is that when the images of cells are created, they have a lot of noise, which is caused by an outside source of alteration to the image by interference in the sensors or camera and also by other sources. To be able to accurately analyze the cell images it is important to remove or reduce the noise so that other image processing techniques can be used to be able to identify key identifying information from the cells.

 

Research Advisor: Keren Bergman, Columbia
Abstract:

We experimentally characterize the intermodulation crosstalk incurred by w avelength-parallel optical signals using a silicon microring resonator electro-optic modulator. We measure corresp onding bit-error-rates and record eye diagrams, observi ng signal integrity degradation for varying wavelength channel spacing.

The continuing scalability trend associa ted with increasing the number of processing cores in chip multiprocessors has fostered the requirement for high-perform ance networks-on-chip, directing on-chip communication b etween processing cores, as well as off-chip communication for memory access. The resulting bandwidth requirements are quickly exceeding the capabilities of traditional electronics, g enerally limited by power dissipation, as well as electrical pin count and packaging constraints. Photonic networks-on-chip have the potential to alleviate the bandwidth bottleneck, and i mprove the overall power consumption. Here, silicon pho tonic components required for modulating, transmitting, routing, and receiving optical signals have all been individually demonstrated on a silicon-on-insulator (SOI) platform compatible with complementary metal-oxide-semiconductor (CMOS) [1–6].

The silicon microring resonator electro-optic modulator offers a small footprint (Fig. 1a), low powe r consumption, and high modulation rate. Using this device, error-free operation of up to 12.5- Gb/s modulation rates have been demonstrated [5]. Leveraging these devices in systems that m aximize bandwidth using wavelength division multiplexing (WDM), multiple microring modulators can be cascaded along the same waveguide [6]. The wavelength selectivity of each modulator can be controlled by varying the radius of each microring during the fabrication process. Since each modulator in the cascade affects a single target wavelength channel, this alleviates the need for spectrally demultiplexing and multiplexing each wavelength channel for independent modulation. However, since the microring modulator encodes the optical data by shifting its resonance in and out of the target wavelength channel, neighboring wavele ngth channels will suffer from intermodulation crosstalk for sufficiently small wavelength channel spacing. A wavelength spectrum of the modulator presented in this work, in its passive and modulated states, is shown in Fig. 1b. When modulated, thermal dissipation from the electrical current yieldds a stable red shift of the resonance wavelength; carrier injection blue shifts the resonance wavelength, resulting in optical m odulation

 

Research Advisor: Robert Norwood , U of A
Abstract:
The purpose of the research performed this summer was to test the environmental and photo stability of polymer based waveguides while becoming familiar with Telcordia Standards 1209 and 1221.

The tests used were based off of Telcordia Standards 1209 and 1221, but were slightly modified to coincide with the amount of time allotted. A Series F4 environmental chamber was used to conduct thermal soaking and thermal cycling on the waveguide. For the thermal soaking test, the sample was placed into the chamber at 85°C for twenty-four hours and two hundred and ninety hours. The first soak was short in order to become familiar with the environmental chamber and gain initial data. The thermal cycling required the parameters of the experiment to be programmed into the chamber. The program ran for ninety hours and soaked the waveguide for two hours at 75°C. The temperature was then ramped down to -40°C at a rate of 1°C per minute where the waveguide then soaked for two hours before the temperature was ramped back up to 75°C at the same rate. This cycle was set to repeat twenty four times in order to run for about a week but, due to time constraints, was cut short.

To test the photo stability, a laser would be connected to a ninety-ten splitter, in which ninety percent of the laser’s power would be channeled to the waveguide then to a detector while ten percent of the laser’s power would be channeled straight to a detector. This allowed for monitoring of the laser’s power without disassembling the setup. Unfortunately, due to lack of available time and resources, the experiment to test the photo stability is still in the preparation stage.

 

Research Advisor: Supapan Seraphin , U of A
Abstract:
Coming soon !

 

Abstract:
The purpose of this research is to characterize the quality of semiconductor nanostructure devices. The two structures that we characterize are quantum dots and nanocavities. Quantum dots are semiconductor structures that trap electrons and holes. One reason why quantum dots are interesting for fundamental physics research is that they have discrete energy levels. For this reason quantum dots are sometimes referred to as “artificial atoms.� Nanocavities are structures that confine light. Our nanocavities are slab photonic crystal devices that confine light in the plane of a semiconductor slab. The focus of our investigations is the interaction between the quantum dots and the nanocavities. The characterization parameters include the structural quality of the samples, the density, wavelength, and efficiency of the quantum dots, the linewidth of the nanocavity modes, the Purcell enhancement factor of the dots in the cavities, and whether a single quantum dot is strongly enhanced or coupled to a nanocavity mode. These characteristics are attractive to basic physicists because such devices would enable ultralow threshold lasers, single photon sources, and quantum information processing, which are potential building blocks for the next generation of telecom.

Abstract:
A fiber optic transmission line is a non-linear system due to the Index of Refraction vs. Power relationship. On the one hand, as light travels a fiber, the chromatic dispersion causes a broadening of the pulses due to the different velocities of the different spectral components. In high-speed transmission, this broadening can result in overlap of signal pulses and corruption of bit information. On the other hand, the differences in Index of Refraction along the temporal shape of the pulses has the potential to create pulse compression. The soliton effect occurs when the non-linearity of a transmission line exactly compensates for the chromatic dispersion of that same line creating an undistorted signal for high-speed transmission over very long distances. This work has been part of a project where the soliton effect will be used to synchronize high speed data streams in the time division multiplexing systems.

Absract: Magneto-optic (MO) materials employing novel conjugated polymers and commercial rare-earth garnets like bismuth iron garnet (BIG) with in-plane magnetization have opened the door to compact, low-power telecom modulators as well as high performance 6 magnetic field sensors and optical isolators. The Faraday effect is the rotation of the polarization vector of linearly polarized light when the light travels through a MO material having a length L with a uniform magnetic field B applied parallel to the direction of the light propagation. The motivation in this study was to improve performance of the existing MO setup used at the University. The current setup which uses a small solenoid has a narrow frequency response and spatial properties of the existing solenoid make alignment of the optics and placement of the MO material both very tedious. Our new approach is to create a wideband Helmholtz coil (HC)-based magnetic field delivery system along with driver electronics integrated into a differential polarimetric MO measurement setup. Due to the frequency limitations of existing lab gaussmeters, the spatial and frequency response of the magnetic field is to be characterized using an optical approach. The sensitivity limitations of the resulting MO sensor setup are to be determined using an experimental approach based upon previous work

Abstract:
This article presents the synthesis and characterization of carbon nanotubes (CNTs) on silicon substrates by chemical vapor deposition (CVD) at 900ºC using methane and hydrogen flow rates. The variation of H2 gas concentration and a set growth time of 15 minutes, have a significant effect on distribution, morphology, internal structure and electronic properties of the nanotubes. The transmission electron microscope (TEM) and state-of-the-art scanning electron microscope (SEM), equipped with Raman spectrometer allowed us to obtain critical information on the morphology and chemical and electronic structures of the CNTs. The results revealed substantial quantity trends as hydrogen flow rate increased from 100 to 700 standard cubic centimeter per minute (sccm). At a constant CH4 flow rate of 700 sccm and varied H2 of 100 and 200 sccm, we observed that few CNTs were produced. Between H2 flow rates of 300 and 400 sccm, the highest density of CNTs were grown; therefore, suggesting optimum growth conditions within that range. Increasing H2 to 700 sccm, the amount of CNTs decreased. The results from this study will guide a production process to obtain high quantity and quality CNTs with desired properties.

Abstract:
The goal of this research project is the design and implementation of a method for generation of multilevel optical signals operating at a symbol rate of 10Gs/s (gigasymbols per second). By using an FPGA (Field Programmable Gate Array) processor and time division multiplexers, different composite signals corresponding to different signal constellations can be generated. The electrical signals are then used to drive optical modulators which, when properly combined, generate multilevel optical signals for high spectral efficiency data transmission. The 7 main objective of this summer research was to test a method that could increase spectral efficiency. Maximizing the spectral efficiency involves the use of multilevel modulation formats for optical transmission where multiple orthogonal optical signals are modulated separately and mixed together in a proper fashion, then transmitted over the optical fiber channel. The graphical representation of the composite signal is a space where a constellation of possible values (points) exist for every combination of the number of bits carried by the optical pulse. Upon reception, the signal is decomposed and several detectors working in parallel determine the signal parameters of interest. This results in locating a point in the constellation space that corresponds to the transmitted pulse and subsequently, in detecting the sequence of bits carried by this pulse.

Abstract:
Development of a high powered, narrow linewidth, tunable VECSEL (Vertical External Cavity Surface Emitting Laser) holds promise for stimulating advances in a great many other fields of research. A specific application is the creation of a sodium guide star laser capable of creating an artificial star in the earth’s mesosphere which would aid adaptive optical telescopes in the creation of clearer pictures. This 589.159 nm yellow laser with over 10 Watts of output power and a linewidth of less than 1 GHz is the predominant goal of the research mentioned within this paper. A VECSEL was chosen for this task because of the potential for high power, high brightness, and access to the cavity allows for frequency doubling, and linewidth narrowing. Additionally, creation of a 589 nm output by a laser is traditionally very difficult with any other method due to the lack of gain materials that produce this wavelength. Thermally induced wavelength shift and wide linewidth are among the drawbacks of VECSELs. Thus, being able to tune and narrow the linewidth of the VECSEL output is an important feature. This narrowing and tuning is possible with the use of a birefringent filter (BF) within the VECSEL cavity. The specific goals of this research have been to determine a relationship between the thickness of the BF placed within a VECSEL cavity and the linewidth and output power that that VECSEL produces. The main goal is to reduce the VECSEL’s linewidth to 1GHz and increase the output power to the 10W range, so understanding how the BF’s thickness affects these characteristics will enable us to maximize our output power and minimize our linewidth

Abstract:
The "nano-texturing" of chloro-indium phthalocyanine (ClInPc) donor layers for use in "Type II Heterojunction" organic photovoltaics (OPV) has been investigated. A central problem in OPV optimization is that exciton diffusion lengths in donor and acceptor layers are on the order of 20nm, requiring the use of extremely thin, nearly transparent films of these materials. 8 Our goal is to create "textured" features, 20-40nm in size on the surface of a promising donor material, ClInPc using solvent vapor annealing. This improves OPV device efficiency by increasing the effective interaction volume for a ClInPc/C60 heterojunction, as well as allowing us to utilize thicker, more light absorbing donor layers, leading to higher short circuit currents, JSC, than from a planar heterojunction. The aim of this research has been to quantitatively compare the Phase I to Phase II surface morphology and absorption spectrum transformations of solvent vapor annealed thin films of ClInPc.
See Brittany talk about her research here

Abstract:
There are two digitizers/oscilloscopes that have been widely in use: equivalent-time digitizers, also known as sampling oscilloscopes, and real-time digitizers. Equivalent time oscilloscopes rely on continuous repetitive signals in order to be sampled. This is because equivalent time sampling collects samples at rates that are above the Nyquist sampling frequency (half of the sample rate); the oscilloscope constructs the signal by collecting more and more samples at each repetition and then “stitching� together the resulting repetitive waveform. Non-repetitve signals and rare events cannot be captured using the sampling oscilloscope. Also, it takes a long time to construct the repetitive signal. The electrical signal that is captured by real-time digitizers on the other hand have small bandwidths in comparison to equivalent-time digitizers, but differ in that they collect samples continuously. TiSER is a new sampling oscilloscope that combines the real time capabilities of the real time oscilloscope and the high bandwidth of the equivalent time oscilloscope to achieve the high sample rate needed to record transient events, which are impossible to record with the aforementioned methods.

Abstract:
Fabricating specific 3D nanostructures is a formidable challenge. Here we introduce a novel method for fabricating specific 3D nanophotonic structures. To do this, we take advantage of a previously practiced holographic lithography technique for fabricating relatively large arrays of periodic nanohole structures on polymer film. We demonstrate that these nanohole arrays can be integrated in a microfluidic platform, where we can effectively use the nanoholes as nanochannels—collectively, a nanochip. Nanoholes have previously been used as nanochannels for flow-through surface-plasmon resonance sensing. As we can control flow through these nanochannels, by creating pressure gradients, potential gradients, or concentration gradients, we are working to use them to align individual nanostructures to create functional 9 nanophotonic devices. In particular, we are working to produce specifically patterned nanosphere arrays that could be used as wave guides or for sensing purposes.

Abstract:
Several Gold nanohole arrays for a microfluidic sensor application were simulated, fabricated, and characterized to determine the effects of varying hole size, and periodic hole spacing on device performance. The samples were illuminated with 780nm laser light then rotated. At certain angles of incidence, a Surface Plasmon Polarition (SPP) is excited along the surface, which greatly enhances light transmission through the sub-wavelength sized holes. Changes in the refractive index surrounding the structure cause a measurable shift in the resonant incidence angle. The devices were fabricated by exposing SU-8 Negative Photoresist to the interference of two UV laser beams. A single exposure forms a grating. Rotating the sample 90 degrees then exposing again produces a grid of holes. Gold is sputtered on the developed SU-8 to a form a mushroom-like structure with holes at regular intervals. Hole size was calibrated by varying both exposure dosage, and gold deposition thickness. A hollow fluid chamber was cast is PDMS and bonded to the surface. Index of refraction was varied by injecting different fluids into the chamber. Device performance was then compared to simulated models.

Abstract:
This project deals with the design, fabrication and characterization of a laser at nanoscale, where laser’s physical dimensions are smaller than the vacuum wavelength of the light it emits. Characterization of optical gain of semiconductor materials is performed using variable-stripe method. In the experiment we use optical pump for the gain, and precise characterization of the pump beam profile is required. To achieve that we will use a razor blade mounted on programmed stages to incrementally cover portions of the beam, and use a power meter to measure the power in unblocked part of beam. This will be done in both horizontal and vertical direction. Using simple calculus one can calculate the beam profile from collected data. The experiment will be fully automated and controlled using MATLAB software

Abstract:
A major goal in the study of optoelectronics is the integration of high-quality III-V compounds onto inexpensive Silicon (Si) platforms supported by modern CMOS processes. A major advantage of the nanoneedle is its ability to grow on Si and serve as an optically active material. GaAs nanoneedles possess a single crystalline wurtzite structure and form without the assistance of catalysts. The sharp tips of nanoneedles may possess the advantage of enhanced electric fields at the tip. This strong electric field can then be used for field-enhanced applications such as surface enhanced Raman spectroscopy (SERS) and Terahertz generation. The focus of this particular research project is to characterize the optical properties of nanoneedles as a necessary step towards the ultimate goal of realizing nanoneedle nanolasers. The project consists of three primary objectives:
1. Optical characterization of an Aluminum Gallium Arsenide (AlGaAs) cladding on the surface of the nanoneedle to suppress non-radiative combination of electron hole pairs.
2. Characterization of nanoneedles grown on quartz and other new nanoneedle templates.
3. Characterization of effects of dopants added to nanoneedles to change the electrical properties. Tellurium (Te) will be investigated as the dopant because it is a good dopant at room temperature.