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Previous Events
| Thursday 17th September 2009 |
Playing with rare earth ions in a confocal microscope Dr. Daniel Jaque Abstract : Rare earth ions are nowadays regarded as one of the most versatile luminescent systems capable of producing light in a wide spectral range covering from the deep UV up to the medium infrared with a quantum efficiency almost reaching 100%. They, indeed, have been the basis of past solid state lasers that still play a relevant role in medicine, industry and science. During the last few years, rare earth ions, through their luminescence, are being used as optical probes capable of giving us information at the micro and sub-micrometric scale when combined with high resolution confocal fluorescence microscopy. In this talk I will briefly explain the basic principles and mechanisms of rare earth fluorescence, paying special attention to the information that fluorescence provides about the ion environment. Then I will show some very simple examples about how the presence of rare earth ions opens an unexplored window to understand and control the physics of micro luminescent systems. The examples I will show cover from material science (fluorescence imaging of ultrafast laser written waveguides in crystals, local control of spontaneous emission in photonic crystals and optical characterisation of rare earth doped micro-spheres) up to life sciences (cancer cell imaging). |
| Monday 31st August 2009 |
Wide Bandgap II-VI Compounds for Mid- and Near-IR Quantum Cascade Lasers Professor Maria Tamargo Abstract : Intersubband (ISB) devices have been the subject of intensive research over the past few years. These devices rely on electronic transitions between the energy levels of a quantum well (QW) within a single band (conduction band or valence band). They are particularly appealing because they promise a large degree of freedom from materials constraints, achieving their performance through bandstructure engineering. Some attractive properties are their fast temporal response and their unipolar nature. An ISB device that is receiving much attention is the Quantum Cascade (QC) laser. Currently, QC lasers operating in the 4-8μm range have been demonstrated. In view of their success, it is of interest to extend their operation further into the near-IR range. The short wavelength cut-off of QC lasers is determined by the conduction band offset (CBO) of the constituent QW materials. Thus, materials with larger CBO are needed to extend the operation wavelength of QC lasers to shorter wavelength. Our group has investigated the application of ZnCdMgSe/ZnCdSe heterostructures for the design and fabrication of QC lasers by MBE. Using the method of contactless electroreflectance (CER) we have measured the CBO for these materials to be as large as 1.12 eV, larger than the CBO of materials currently used for these devices. We have grown multi-quantum well structures with excellent crystalline quality and measured their intersubband absorption using FT-IR spectroscopy, demonstrating the ability to obtain transitions at wavelengths below 3μm. We have also grown and fabricated QC structures and observed electroluminescence in the mid-IR range. We are currently exploring the design of structures that incorporate waveguide layers in order to achieve lasing. Other experiments, such as the use of quantum dots for ISB devices, and the use of other IIVI heterostructures with larger CBO will also be presented. Speaker’s biography: Maria Tamargo conducts research on Molecular Beam Epitaxy (MBE) growth and characterization of semiconductor materials for photonic and electronic applications. Using a dual chamber MBE system, her group investigates III-V and II-VI semiconductor materials and their nanostructures. Characterization methods include photoluminescence, Hall effect, capacitance-voltage (C-V) and current-voltage (I-V) measurements, single and double crystal x-ray diffraction, Nomarski microscopy and scanning electron microscopy (SEM). Currently, the principal focus of the research is on wide bandgap II-VI compounds for visible light emitting devices. Her group at City College is investigating the growth and properties of a new family of wide bandgap II-VI semiconductors, ZnCdMgSe, grown lattice-matched to InP substrates by MBE. By optimizing the growth conditions they have reduced defect densities to the level of other more well-known II-VI compounds grown on GaAs. These new alloys and their heterostructures possess properties (band structures, lattice constants, band offsets and doping) that are attractive and offer advantages for the design of improved visible semiconductor lasers and LEDs. These devices are of interest for optical recording, displays and communications applications. Other areas of research include, saturable Bragg reflectors (SBR) made of III-V materials for laser mode locking, hexagonal II-VI structures for visible emitters, selective area epitaxy of CdTe detector array-like structures and hybrid semiconductor/molecular aggregates for photonic applications. Professor Tamargo joined the Chemistry department at City College in 1993 and is a member of the CUNY doctoral faculty in both Chemistry and Physics. She had previously been a Member of Technical Staff at Bellcore in Red Bank, NJ where she led a program on II-VI materials growth by MBE. Before that, she was at AT&T Bell Labs in Reading, PA and in Murray Hill, NJ, where she worked on Liquid Phase Epitaxy (LPE) of GaAlAs lasers and InGaAsP Avalanche Photodectors (APDs) for optical communications systems. She is a member of the CUNY Center for Advanced Technology (CAT) on Photonic Materials and Applications and of the Center for Analysis of Structures and Interfaces (CASI) at City College. She is married and has two children, Nicolas, 12, and Marcela, 10, and lives in Teaneck, NJ. |
17th of April
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Optical Signal Processing by Parametric Devices
Dr. Colin McKinstrie,
Parametric devices based on four-wave mixing in fibers provide many functions that are required by optical communication systems. When operated in the linear regime, parametric devices provide amplification, frequency conversion and phase conjugation, all with high gain levels and broad bandwidths. They can also be used to buffer, monitor and switch optical signals. When operated in the nonlinear regime, parametric devices regenerate signals. They also produce entangled and squeezed states of light. In this talk recent research on parametric devices will be reviewed, and the implications of this research for classical and quantal communication systems will be discussed |
20th March 2009 - Court Senate Suite |
Organic electronics: interfaces, heterojunctions and semiconductor device engineering Professor Sir Richard Friend FRS Cavendish Laboratory, University of Cambridge FETs, LEDs and photovoltaic diodes are routinely fabricated with molecular semiconductors and polymers, and are now developed as viable technologies for large-area flexible electronics. However, they also allow the study of the basic electronic excitations of this broad class of materials. I will illustrate the control of electronic structure that can be obtained at interfaces, including excitons confined to semiconductor heterojunctions for LED and photovoltaic operation, and electrons and holes confined to semiconductor-dielectric interfaces in FETs. |
3rd of March |
Nonlinear Fiber Optics and Supercontinuum Generation: New Fibers, New Opportunities Prof. John M. Dudley Laboratoire d’Optique P.M. Research in nonlinear fiber optics is currently undergoing dramatic expansion, motivated by advances and developments in new classes of optical fiber and the ready availability of a wide range of optical pump sources. This lecture will survey selected recent work in this field that has investigated novel nonlinear propagation effects in both photonic crystal and highly nonlinear optical fibers, and will focus particular attention on the physics and applications of supercontinuum generation. The lecture will provide both a tutorial review of the basic supercontinuum generation broadening mechanisms as well as a discussion of recent developments and applications. |
9th of February at 11:30 |
Prof. Thomas Nann Chair in Nanoscale Science, Associate Director of the Energy Materials Laboratory |
30th January 2009 |
Organic micro and nano-photonic structures Prof. David Lidzey Department of Physics and Astronomy University of Sheffield By placing a luminescent dipole within an optical microcavity, a range of fascinating fundamental phenomena can be explored, which in many cases have direct relevance to advanced opto-electronic devices. I review our work on creating micro- and nano-photonic structures that contain fluorescent organic materials. The use of organic light-emitting materials has a number of potential advantages, including excitonic emission at room temperature, tailored chemical-specificity, enhanced oscillator strength and low lasing-thresholds. One structure of particular interest is the micro-pillar micro-cavity. To create such structures, we placed a film of a fluorescent dye between two high reflectivity mirrors, which are etched vertically to create a pillar having a lateral dimension of several microns. I show that the lateral confinement imposed by the low-dimensionality of the pillar can, in many cases lead to enhanced spontaneous-emission rates.
I then turn to the application of organic materials in nanocavity structures. Such structures are formed by creating a physical defect in a two-dimensional photonic crystal and can in principle be characterized by large Purcell-factors (enhanced spontaneous emission rates).Conventionally, optical nanocavities are created using materials such as GaAs or Si and operate at infra-red wavelengths. Such materials are not however optimized for use with visible-emitting organic materials, and thus we have explored the use of nanocavities based on silicon nitride. This material combines both relatively high refractive index and excellent transparency at visible wavelengths. Our goal is to create high Q-factor nanocavities in which a thin-film of an active organic material is immobilized on to the nanocavity surface. I present the results of both modelling and recent experimental measurements on such organic-semiconductor containing nanocavities, and discuss the applications of our structures as nano-sensor devices and single-photon light-sources. |
5th December 2008 |
Ultra-short pulse generation in quantum-dot
semiconductor laser diodes Dr. Mark Thompson Departments of Physics and Electrical Engineering University of Bristol Recent developments in quantum-dot mode-locked lasers are pushing the boundaries of short pulse generation from semiconductor laser diode sources. Novel materials and device structures are allowing sub 400fs pulse generation from these highly compact and efficient pulse sources. This talk will review some of the recent developments in this field of research, demonstrating pulse generation over a wide range of repetition rates, with high peak powers and low noise performances.
Mark Thompson holds a M.Phys degree in Physics from the University of Sheffield and a PhD degree in Optics from the University of Cambridge. He has previously worked for Corning Cables Ltd. (Helsby, UK), Bookham Technology Ltd. (Abingdon, UK), and the University of Cambridge. He has been a Lecturer at the Physics and Electrical Engineering Departments of the University of Bristol since September 2008. His research interests are in the field of photonic devices, particularly short pulse semiconductor laser diodes, quantum-dot devices and integrated quantum optic circuits. He has co-authored over 60 journal and conference publications.
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21st November 2008 |
Nanoreplication and its application to photonic devices Dr. Duncan Allsopp |
17th October 2008 |
Nanotube Based Polymer Optoelectronics Dr. Andrea Ferrari Department of Engineering University of Cambridge Carbon nanotubes (CNTs) exhibit strong saturable absorption, i.e. they become transparent under sufficiently intense light. This has great potential for applications in photonics. By tuning the nanotube diameter it is easy to tune the saturable absorption in a broad optical range of interest for telecommunications, medicine and military applications. CNTs also have sub-picosecond relaxation times and are thus ideal for ultrafast photonics. The performance of CNTs based saturable absorbers strongly depends on the CNTs concentration, size of CNT bundles, and transparency of the matrix where CNTs are dispersed. CNT saturable absorbers can be produced by cheap wet chemistry and can be easily integrated into polymer photonic systems. The performance of CNTs based saturable absorbers strongly depends on concentration, the size of CNT bundles, and transparency of the matrix.
Here, we review the fabrication and characterization of saturable absorber based on CNT - polymer optical composites [1,2,3]. We use strong ultrasonication to obtain CNT solutions. Such solutions with different nanotube bundle sizes are then studied by photoluminescence excitation spectroscopy [4]. We find that exciton energy transfer between semiconducting CNTs is an efficient carrier relaxation channel in the bundles [4]. This fingerprints and quantifies the presence of small bundles and allows us to optimise the solutions used for composites preparation. The saturable absorption properties of such composites are studied with a femtosecond laser. We demonstrate picosecond pulse generation in a nanotube mode-locked waveguide laser [5], as well as 600 fs generation in an erbium doped fiber laser [1]. We also report a novel SWNT- polycarbonate polymer composite, with an absorption maximum at 1550 nm and a bandwidth of about 300 nm [6]. The composite shows strong saturable absorption with saturation intensity of 7 MW/cm2. We also demonstrate the first SWNT-mode-locked widely tunable fibre ring laser [7]. This is achieved through the control of amplification at the specific transitions of the Er3+ gain medium by placing a band-pass filter in a laser cavity [7]. Besides the wide tuning range, this laser also features a high optical signal-to-noise ratio and an excellent jitter performance. 1. A. G. Rozhin et al. Phys. Stat. Sol. (b) 243, 3551 (2006) |
| 1st September 2008 |
|
Coupling in Lasers and Applications to Self-Mixing Interferometry and Chaotic Cryptography
Professor Silvano Donati Department of Electronics, University of Pavia
Abstract: In this presentation, we start with a brief theoretical introduction to mutual and self coupling phenomena in laser oscillators, and then describe in detail two applications. The first is self-mixing interferometry for measurements of displacement, distance, vibration, and angle, and physical parameters like coupling factors, line width, alpha-factor. In this case, the laser undergoes self-injection at a weak level, leading to an amplitude and frequency modulation driven by an external optical path. The second application is optical chaos, which is generated by the laser source at strong levels of injection. We describe mutual and self-injection generation of chaos, and the first step of development to cryptography, that is synchronisation. Then, we will review several schemes of coding and decoding of information, i.e. chaotic masking and CSK (chaos shift keying) and how they can by implemented, along with theoretical and experimental results carried out recently. Silvano Donati has been a full Professor at the University of Pavia since 1980. He has authored two books (Photodetectors, Prentice Hall 1999, and Electrooptical Instrumentation, Prentice Hall 2004), about 250 papers in journal and conference proceedings, and has been the Guest Editor of a dozen Special Issues (JSTQE, JoO-A, Opt. Engineer, JQE etc.). His seminal papers on self-mixing interferometry and optical chaotic cryptography have totalled more than 500 citations. He is a Fellow of IEEE and of OSA. He founded and has been the Chair of the LEOS Italian Chapter. He has been a LEOS VP Region 8 member and BoG member of LEOS. He is presently the Chair of the IEEE Italy Section. |
| 16th May 2008 |
Photophysics of quantum dots in live cells *
Dr. Huw Summers Quantum dots have been rapidly adopted by the biomedical community as they provide a unique set of fluorescence properties. The photophysics of these nanocrystals is highly dependent on their local environment making them: unstable within biological systems or ideal biosensors depending upon your point of view. I will report on the use of QDs for live cell tracking, imaging and analysis highlighting the interplay between the biology and the dot photophysics. |
| Wide-field CARS-Microscopy: chemically sensitive microscopic imaging within nanoseconds
Professor Monika Ritsch-Marte Division for Biomedical Physics, Coherent anti-Stokes Raman Scattering (CARS) microscopy is a newly emerging microscopy technique that allows chemical imaging with high spatial and spectral resolution. Recently we have developed a non-scanning version of CARS-microscopy, using nanosecond laser pulses and a special excitation geometry that is designed to satisfy the phase matching condition over the whole field of view. This allows fast image acquisition, even “snapshots” with a single shot of laser pulses are possible. The performance and the potential of wide-field CARS-microscopy are demonstrated by various examples: The spatial resolution is sufficient for chemically selective imaging of (sub-)micron intracellular vesicles, containing e.g. lipids or lung surfactant. Moreover, the good spectral resolution of 5 wavenumbers and the low non-resonant background allow one to visually differentiate the small differences in the lipid composition inside living adipocyte cells that result from a diet on saturated versus unsaturated fatty acids.
CARS image of a living lung cell containing small vesicles of unstained pulmonary surfactant Reference Heinrich C., A. Hofer, A. Ritsch, C. Ciardi, S. Bernet, M. Ritsch-Marte: Selective imaging of saturated and unsaturated lipids by wide-field CARS-microscopy, Opt. Express 16, 2597-2708 (2008) |
| 24th April 2008 |
The Photon Science Institute at Dr. Mark Dickinson Following the merger of the *Because the lecture theatre is unavailable, this seminar will be held at 4pm in the Institute's large meeting room on the 5th floor of the Wolfson Centre. Tea/coffee and biscuits will be available afterward as usual. |
| 14th January 2008 |
CMOS for Optoelectronics Dr. Robert Henderson
Integrated Micro and Nano Systems Research Institute
School of Engineering and Electronics
University of Edinburgh
Abstract
This talk will look at the various applications of CMOS process technology for optoelectronics ranging from CMOS image sensors, optical communications, display technologies to optical biosensors. Recent trends in custom CMOS processes, wafer level packaging and 3D integration driven by the explosive growth in mobile imaging will be discussed with respect to opportunities in other areas of optoelectronics. Finally, some promising research directions towards truly integrated, micro-scale optical-electrical-chemical sensors and systems will be presented. |
| 9th November 2007 (3:30) |
Silicon-based Photonics at McMaster University Prof. Paul Jessop Department of Engineering Physics, McMaster University, Hamilton, Ontario, Canada Abstract Silicon is unquestionably the material of choice for microelectronic device manufacture, and CMOS is the dominant processing technology. In contrast, there is no single dominant material for photonic devices and there is no corresponding industry standard for processing. Silicon is one of a great many materials that are used for photonic devices, and it has some well known shortcomings. However, interest in silicon photonics is now growing very rapidly as photonics technology matures, placing an emphasis on increased device functionality and reduction in manufacturing costs. The prospect of adopting the well established technology of CMOS integrated circuit fabrication for manufacturing optical components is extremely attractive in terms of costs, and it is a natural path toward monolithic integration of optical components with electronic control circuitry. I will discuss optical waveguide fabrication in silicon and report on recent work aimed at developing a number of the basic building blocks that will enable more complex silicon photonic integrated circuits. These include wavelength demultiplexers, polarization rotators and optical modulators. A monolithic photonic integrated circuit will also require a viable silicon light source as well as fast and efficient silicon detectors for long wavelengths (e.g. 1.55 µm) where silicon waveguides are transparent. Our group has successfully demonstrated that a solution to the detector problem lies in localized defect engineering to introduce mid-bandgap electronic levels. We have also looked at the light emission characteristics of silicon nanocrystals, however the ideal of an electrically pumped silicon laser remains an elusive goal. In collaboration with a group at Carleton University in Ottawa, we are fabricating a highly-integrated silicon photonic device that includes some of the devices we recently demonstrated in stand-alone format together with integrated electronic circuitry on the same chip. This device has a detector and attenuator located on a shared optical waveguide and linked via a trans-impedance amplifier, thus providing a feedback mechanism. The result is the self-levelling of waveguide coupled power. Other configurations of the same functionality provide monitored attenuation and black-box optical switching. |
| 14th September 2007 |
New technologies for image guided diagnostic and therapy Prof. Andreas Melzer Founding Director of the Institute for Medical Science & Technology, Universities Dundee and St. Andrews, Dundee, DD1 4HN
Abstract - click here requires |
| 20th of July 2007 |
Spectroscopic properties of rare-earth doped hosts and their applications Prof. Animesh Jha The Institute for Materials Research, Houldsworth Building, Clarendon Road, University of Leeds, Leeds LS2 9JT (UK) Abstract The lecture will explain the significance of rare-earth (RE) ion-glass host interaction for engineering waveguide devices, which can potentially bring together short fibres or planar waveguides with a single pump source and filters together for designing a fully integrated photonic device. In this talk we review and exemplify new results in the light of the ion-host interactions in Sm 3+-, Er 3+-, Tm 3+- and Ho 3+-doped tellurium and fluorosilicate oxide hosts for photoluminescence analysis at visible, near-IR, and mid-IR wavelengths. The emphasis in this talk is to exploit currently available fibre-pigtailed 980 nm and multimode high-wattage 800 nm pumps for both up and down conversion schemes. Optical amplifications in S-, C- and L bands are explained by using 980 nm pumping scheme. We also explain the spectroscopic features of visible (RGB) and mid-IR lasers beyond 1900 nm for spectroscopy of chemical and biological species. |
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