Silicon Microring Resonator Driven by High-Mobility Conductive Oxide Capacitor

Silicon photonics has rapidly become one of the most promising photonic integration platforms. Especially, microring resonator (MRR) plays a pivotal role in silicon photonics and has been widely used for electro-optic (E-O) modulators and wavelength filters due to its small footprint, low energy consumption, and high quality factor (Q-factor). Recently, indium-tin-oxide (ITO) has emerged as a new material that can be integrated with silicon MRRs using a metal-oxide-semiconductor (MOS) structure, which can offer significantly enhanced E-O effect and better energy efficiency. However, the performance is limited by the relatively low electron mobility, which induces relatively high optical loss and degrades Q-factor. This thesis focuses on the demonstration of high Q-factor MRR driven by high mobility transparent conductive oxide (TCO) material. In the first part, a passive MRR is optimized by fabrication and theoretical design, which achieves a high Q-factor of 20,000. Next, a MRR with a titanium-doped indium oxide gate has been demonstrated to obtain a tunability of 42 pm/V with a high Q-factor above 3,600. Besides, a new method has been developed to characterize the optical frequency free carrier mobility in the accumulation layer of the MOS structure. At the end of the thesis, different MRRs driven by high mobility TCO materials are compared. The simulation results indicate that an ultra-high tunability of 906 pm/V and a high Q-factor above 6,700 can be potentially achieved with slotted waveguide MRR

Integrated Inp Photonic Switches

Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been demonstrated. The diffusion process circumvents the need for isolation trenches, and hence optical losses can be significantly reduced. An efficient optical beam steering device based on InGaAsP multiple quantum wells is also demonstrated. The degree of lateral current spreading is easily regulated by controlling the zinc depth, allowing optimization of the injected currents. Beam steering over a 21 microns lateral distance with electrical current values as low as 12.5 mA are demonstrated. Using this principle, a reconfigurable 1x3 switch has been implemented with crosstalk levels better than -17 dB over a 50 nm wavelength range. At these low electrical current levels, uncooled and d.c. bias operation is made feasible. The use of multimode interference (MMI) structures as active devices have also been investigated. These devices operate by selective refractive index perturbation on very specific areas within the MMI structure, and this is again realized using zinc diffusion. Several variants such as a compact MMI modulator that is as short as 350 µm, a robust 2x2 photonic switch and a tunable MMI coupler have been demonstrated

Integral Optics: Lecture Notes

An introduction is given to the principles of integrated optics and optical guided-wave devices. The characteristics of dielectric waveguides are summarized and methods for their fabrication are described. An illustration is given of recent work on devices including directional couplers, filters, modulators, light deflectors, and lasers. The textbook reflects the latest achievements in the field of integrated optics, which have had a significant impact on the development of communication technology and methods for transmitting and processing information

Tamm plasmon polariton in planar structures: A brief overview and applications

Tamm plasmon provides a new avenue in plasmonics of interface states in planar multilayer structures due to its strong light matter interaction. This article reviews the research and development in Tamm plasmon polariton excited at the interface of a metal and a distributed Bragg reflector. Tamm plasmon offers an easy planar solution compared to patterned surface plasmon devices with huge field enhancement at the interface and does not require of any phase matching method for its excitation. The ease of depositing multilayer thin film stacks, direct optical excitation, and high-Q modes make Tamm plasmons an attractive field of research with potential practical applications. The basic properties of the Tamm plasmon modes including its dispersion, effect of different plasmon active metals, coupling with other resonant modes and their polarization splitting, and tunability of Tamm plasmon coupled hybrid modes under externally applied stimuli have been discussed. The application of Tamm plasmon modes in lasers, hot electron photodetectors, perfect absorbers, thermal emitters, light emitting devices, and sensors have also been discussed in detail. This review covers all the major advancements in this field over the last fifteen years with special emphasis on the application part

Metasurface Based Mid-infrared Devices

The development of compact, efficient, and powerful mid-infrared devices is mainly restrained by the limited choice of materials due to the high loss of conventional optical materials in the mid-infrared range. The aim of this work was to find alternative novel materials which would enable the realization of devices with smaller size while maintaining its functionality. Metasurface and graphene have emerged as promising materials which can help us to manipulate the infrared light within nano-meter scale thickness. In this thesis, three different mid-infrared devices, thermal emitter, wave trapping sensor and phase modulator were designed based on either metasurface or both metasurface and graphene. Devices were all fabricated with modern semiconductor fabrication processes and their performances were also fully investigated, both experimentally and through simulations. A metasurface was first designed as a frequency selective layer on a graphene thermal emitter to tailor the graybody emission spectrum from a graphene filament into two discrete narrow bands for applications such as gas sensing or molecule detection. The emission and reflectance spectra of the devices were characterised using (FTIR) Fourier transform infrared spectroscopy and showed good agreement with simulations based on the Finite-difference time-domain (FDTD). method. The use of a metasurface to enhance the interaction between molecular vibrations and the evanescent waves, in a total attenuated reflectance system, was also explored. A complementary ring-resonator structure was patterned onto both silicon and SiO2/Si substrates, and the spectral properties of both devices were characterised using an FTIR-ATR system. Experiments were undertaken using 5µL mixtures containing trace amounts of butyl acetate diluted with oleic acid. Without the use of a metasurface, the minimum concentration of butyl acetate that could be clearly detected was 10%, whereas the use of the metasurface on the SiO2/Si substrate allowed the detection of 1% butyl acetate. Finally, graphene was integrated into a metasurface structure to achieve tunability of the design. The third device investigated was a phase modulator which shows the capability to change the amplitude and phase of the reflected wave by electrostatically gating the graphene from -90V to 90V. A dynamic beam steering lens model which is made up of a unit cell consisting of four phase modulator with different phase shift was also proposed to control the angle for the reflected wave from specular to 30°.Engineering and Physical Sciences Research Council (EPSRC

LASER Tech Briefs, February 1995

Topics included in this issue of LASER Tech Briefs are: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Mechanics, Fabrication, and Mathematics and Information Sciences, an

Dynamically Tunable Plasmonic Structural Color

Functional surfaces which can control light across the electromagnetic spectrum are highly desirable. With the aid of advanced modeling and fabrication techniques, researchers have demonstrated surfaces with near arbitrary tailoring of reflected/transmitted amplitude, phase and polarization - the applications for which are diverse as light itself. These systems often comprise of structured metals and dielectrics that, when combined, manifest resonances dependent on structural dimensions. This attribute provides a convenient and direct path to arbitrarily engineer the surface\u27s optical characteristics across many electromagnetic regimes. But while many of these plasmonic systems struggle to compete with the efficiency of pre-existing technologies, the ability to tune plamsonic structures post-fabrication is a distinct advantage which may lead to novel devices. In this work, I will summarize fundamental and applied aspects of tunable plasmonic systems as applied to the visible and infrared regimes. I will demonstrate how liquid crystal may be used to dynamically and reversibly tune the plasmonic resonances of metallic surfaces on a millisecond time scale. For the visible, this results in dynamic color-changing surfaces capable of covering the entire RGB color space and which is compatible with active addressing schemes. I will then show the application of these concepts to infrared absorbers through the use of liquid crystal and phase change materials. The later of these devices can find use in infrared data/image encoding, thermal management and camouflage. Together, these works explore the limits of tunable plasmonic systems and the novel devices they might lead to

Extreme nonlinear optics in highly excited semiconductors

In dieser Arbeit werden extreme nichtlineare optische Phänomene in hoch angeregten ZnO Halbleiterproben untersucht. ZnO hat eine Bandlücke von 3,2 eV im nahen ultravioletten Spektralbereich und die optische Anregung erfolgt mit starken Lichtfeldern im nahen bis fernen nfrarot. Folglich ist die Energie der Photonen sehr viel kleiner als die Bandlücke des Materials. Bei den optischen Phönomenen, die untersucht wurden, ist die Reaktion des Materials durcheine nichtlineare Abhängigkeit des Ausgangs- von der Eingangssignalstärke gekennzeichnet. Insbesondere wurde die kohärente Umwandlung von Laserlicht in hohe Ordnungen der ursprünglichen Lichtfrequenz, auch bekannt als Erzeugung hoher Harmonischer (HHG), und optisch gepumptes Lasing untersucht. HHG in Festkörpern resultiert aus einer Kombination von Laserfeld getriebenen nichtlinearen Intraband-Strömen und Interband-Polarisationsfeldern, und Lasing ist das Ergebnis der Verstärkung von Licht durch stimulierte Emission. HHG von Laserpulsen im mittleren IR wurde in stark optisch angeregten kristallinem ZnO untersucht. Die gemessene HHG Emission zeigt ein Sättigungsverhalten und eine starke spektrale Blauverschiebung der harmonischen Ordnungen als Funktion der freien Ladungsträger. Darüber hinaus führen interatomare Kräfte aufgrund einer starken Modifikation der elektro-nischen Struktur zu einer Verschiebung der Gitterionen. Ein Pump-Probe-Experiment wurde durchgeführt, um die transiente Modulation des HHG-Prozesses als Funktion des Schwingungs-zustands der Gitterionen zu bestimmen. Die gemessenen Modulationsfrequenzen stimmen mit den charakteristischen optischen Phononenfrequenzen von ZnO überein. Folglich zeigte das Experiment die Wechselwirkung der Elektronen mit den Gitterionen auf einer Zeitskala kürzer als die halbe Schwingungsperiode des Laserfeldes. Laserpulse im mittleren IR-Spektralbereich mit wenigen Zyklen und kontrollierbarer absolutenphase (carrier envelope phase, CEP) wurden zur Erzeugung hoher Harmonischer in kristallinem ZnO benutzt, um eine einfache Methode zur Vermessung des relativen CEP des Laserpulses zudemonstrieren. Hierfür wurde die Interferenz spektral überlappender harmonischer Ordnungenausgewertet. Lasing setzt ein, wenn die Vestärkung aufgrund der stimulierten Emission die Verluste über-steigt. Um Verstärkung zu ermöglichen, muss die angeregte Ladungsträgerdichte einen Schwell-wert übersteigen (Inversion). Laseremission aufgrund optischer Anregung mit ultravioleten Licht in polykristallinen ZnO Dünnfilmen und ZnO-Nanodrähten (NW) wurde bereits demonstriert. In dieser Arbeit werden jedoch starke Lichtfelder im Spektralbereich vom nahen IR (0,8μm, 1,5 eV) bis zum fernen IR (10μm, 0,13 eV) benutzt, um optisch gepumptes Lasingin polykristallinen ZnO-Dünnfilmen und ZnO-NWs zu erreichen. Dabei ist das Verhältnis der Materialbandlücke zur Photonenenergie im Bereich zwischen 3 und 26.Die Laser- und spontanen Photolumineszenz (PL)-Emission von ZnO-Dünnfilmen wurde ge-messen, um die Auswirkung einer Materialdotierung und den Effekt der Pumplaserpolarisati-on (Elliptizität) auf die Laserschwelle bzw. die Lichtabsorption zu untersuchen. In Alumini-um dotierten ZnO-Dünnschichtproben ist die Pumpschwellenintensität im Vergleich zu einer intrinsischen Probe reduziert und Licht im nahen IR bei 0,8 μm wird effizienter über einen Drei-Photonen-Absorptionsprozess in ZnO absorbiert, wenn der Pumplaser linear anstelle von zirkular polarisiert ist. Die Messung der PL-Emission von Dünnschichtproben als Funktion der Pumplaserpolarisation stellt eine einfache Methode zur zerstörungsfreien Bestimmung des Absorptionskoeffizienten von zirkular polarisiertem Licht dar. Die Schwellwerte der Pumplaserintensität und des Verstärkungskoeffizienten um Lasing in ZnO-NW, angeordnet in vertikal ausgerichteten Arrays, zu erreichen, wurden experimentell verglichen. Die Ergebnisse ergaben, dass die Emissionseigenschaften von NW Arrays, durch die Einzeldrahtparameter definiert sind. Aufgrund der starken elektrischen Felder und der Licht-Materie-Wechselwirkung fern der Absorptionsresonanz erfolgt die Absorption von Licht über Interbandanregung aufgrund von Multiphotonenabsorption und Tunneln sowie Elektron-Elektron-Wechselwirkung (Stoßionisation)als Folge der Intraband-Elektronenbeschleunigung. Die Rolle der Interband- und Intraband-Absorptionsprozesse wurde durch Vergleichen der experimentellen Ergebnisse mit Berechnungen mittels eines Ratengleichenmodelles identifiziert.This thesis studies extreme nonlinear optical phenomena in highly excited ZnO semiconductor samples. ZnO with a band gap of 3.2 eV, in the near-ultraviolet spectral range, is irradiated with far-o resonance strong light fields in the near to the far-infrared. The response of the matter is characterized by a nonlinear dependence of the output on the input signal strength. Specifically, the coherent conversion of laser light into high orders of the original frequency, also known as high harmonic generation (HHG) and optically pumped lasing were investigated. HHG in solids results from a combination of laser field driven nonlinear intraband currents and interband polarization fields and lasing is the result of light amplification by stimulated emission. HHG from mid-IR laser pulses was investigated in crystalline bulk ZnO far out of its equilibrium state. As a result the saturation of the harmonic radiation and a strong spectral blueshift of the harmonic orders were measured as a function of the free carrier density. Furthermore, interatomic forces due to strong modification of the electronic structure lead to lattice ion displacement. Performing a pump-probe experiment, the transient modulation of the HHG process reveals the vibration state of the material. The modulation frequency overlaps with the characteristic optical phonon frequencies of ZnO. Consequently, the experiment revealed an interaction of the ionic- and electronic structure on a timescale below the oscillation period of the laser field. Using few-cycle and CEP controllable mid-IR laser pulses to generate high harmonics in crystalline ZnO, a simple method to measure the relative CEP of the laser pulse was demonstrated using the interference of spectrally overlapping harmonic orders. Lasing sets in when the material gain, due to stimulated emission, overcomes the material losses. For that, the excited electron density has to overcome a threshold value (inversion). Optical pump lasing was demonstrated upon UV pumping in polycrystalline ZnO thin films and ZnO nanowires (NW). However here, strong light fields in spectral range from the near-IR (0.8 m, 1.5 eV) to the far-IR (10 m, 0.13 eV) optically pump lasing in polycrystalline ZnO thin films and ZnO NWs. Thus, the ratios of the material band gap to the photon energy covered the range from 3 to 26. Studying the lasing and the spontaneous photoluminescence (PL) emission from ZnO thin films, the eect of Aluminium doping and the eect of the pump laser ellipticity on the lasing thresh-III old and light absorption, respectively, was determined. Aluminium doped ZnO thin film sample reduce the pump threshold intensity compared to an intrinsic sample and near-IR light at 0.8 m is more ecient absorbed via a three photon absorption process in ZnO when the laser is polarized linearly instead of circularly. Measuring the PL emission from thin film samples as a function of the pump laser polarization, depicts a simple method to determine the absorption coecient for circular polarized light in a non-destructive manner. Comparing the pump laser threshold intensity with the threshold gain value, which were determined by the averaged parameters of the ZnONWforming a vertically aligned array revealed that the emission properties of the NW array is defined by the single wire parameters. Due to the strong applied electric fields and the light-matter interaction far-o the resonance, the absorption of light via interband excitation occurs due to the multiphoton absorption and tunneling as well as electron-electron interaction (impact ionization) upon intraband free carrier absorption. The contribution of the interband and intraband absorption processes were identified by comparing the experimental results with calculations from a rate equation laser model