Silicon Photonics Wavelength-Independent C-Band Tunable Optical Filter With Feasible Thermal Tuning Requirements

A filter design based on Vernier microrings and wideband directional couplers is proposed for ASE noise suppression in next generation DCI applications. We demonstrate a 40 nm FSR-free filter with > 20.5 dB average ER and 3dB-BW of 75 GHz, achieving wavelength-independent performance and full tunability with a maximum tuning temperature of 75 K.Comment: This work has been partially funded by the German Ministry of Education and Research under the grant agreement 13N14937 (PEARLS

Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources

Integrierte siliziumphotonische Faserkoppelgitter

Um dem stetig steigenden Bedarf an Bandbreite gerecht zu werden, werden zunehmend nicht mehr ausreichend performante elektronische Kommunikationskanäle durch optische Übertragungsstrecken ersetzt. Viel Forschungsarbeit konzentriert sich in den letzten Jahren die ansonsten für weite Übertragungsstrecken eingesetzten optischen Kanäle auch für kurze Distanzen einzusetzen, wie zum Beispiel die Chip zu Chip oder On-Chip Kommunikation. Die Integration von photonischen Komponenten ermöglicht den Entwurf von äußerst schnellen Transceivern, die für die immer komplexeren Modulationsformate notwendig sind. Silicon-on-Insulator hat sich hierbei als exzellente Plattform herausgestellt, da dieses Materialsystem die notwendigen optischen Eigenschaften aufweist und zusätzlich die Co-Integration von photonischen und elektronischen Bauelementen zulässt, die sich so gegenseitig in ihrer Funktionalität ergänzen können. Durch den sehr hohen Brechungsindex von Silizium in Infrarotbereich des elektromagnetischen Spektrums lassen sich hier sehr kompakte und verlustarme Wellenleiter herstellen, die einen Durchmesser von nur wenigen hundert Nanometern aufweisen. Diese ansonsten hilfreiche Eigenschaft stellt allerdings auch eine große Schwierigkeit dar, da das Koppeln von Siliziumphotonischen Wellenleitern an externe Komponenten mit Hilfe optischer Fasern von mehreren Mikrometern Durchmesser unter Umständen sehr verlustreich ist. In dieser Arbeit wird daher das Problem der Faser-Chip-Kopplung analysiert und Lösungen basierend auf siliziumphotonischen Faser-Gitterkopplern vorgestellt. Angefangen mit einem sehr einfachen Koppelgitter, das für den Wellenlängenbereich um λ=1310nm konzipiert ist und eine gemessene Koppeleffizienz von -3.8dB aufweist, werden weiter verfeinerte Gitterkoppler für die Betriebswellenlänge von λ=1550nm vorgestellt. Mit einer lokal auf dem Gitterkoppler gewachsenen epitaktischen Siliziumschicht werden 1.7dB Verlust erzielt, der weiter verringert werden kann, wenn - wie durch Simulationen gezeigt - ein zweiter Ätzschritt dem ansonsten uniformen Gitter hinzugefügt wird. Im Anschluss wird die Frage diskutiert, wie ein optimales Koppelgitter unter Einhaltung bestimmter technologischer Einschränkungen auszusehen hat, wenn man bedenkt, dass bereits eine leichte Nichtuniformität gute Verbesserungen der Koppeleffizienz zur Folge hat. Zwei metaheuristische Suchalgorithmen wurden eingesetzt und solche Koppelgitter zu erzeugen, die schlussendlich eine theoretische Koppeleffizienz von -0.7dB aufwiesen. Zusätzlich zu den bisherigen Untersuchungen wurden polarisationsteilende, zweidimensionale Gitter untersucht, die eine gemessene Koppeleffizienz von -5.8dB zeigten, wobei eine geometrische Transformation, die man an diesen Gittern vornehmen kann, dieses Wert noch einmal steigern kann. Die letzte Untersuchung befasst sich mit einem Gitter, das zur Kopplung von höheren Fasermoden konzipiert ist. Durch eine Beleuchtung des Koppelgitters von gegenüberliegenden Enden aus und durch die Ausnutzung der ersten höheren Mode des integrierten Wellenleiters können die Fasermoden LP01, LP11,a, LP11,b und LP21,a in zwei orthogonalen Polarisationen erzeugt werden.To satisfy the ever increasing demand in bandwidth in modern communication systems, optical transmission is replacing the increasingly insufficient electronic communication devices. Although primarily employed for large distances, much research has been focused recently on the application of optical communication on much smaller ranges, such as chip to chip or even on-chip transmission. Integrating photonic components enables the conception of high speed transceivers, that are necessary for the multi-level transmission systems, which will provide the necessary bandwidth in years to come. The Silicon-on-Insulator platform is the prime candidate for this as it provides excellent properties for silicon photonic components and also enables the co-integration of optical functionality alongside with electronic devices, thus complementing the shortcomings of either technology. Due to the high refractive index in the near-infrared region of the electromagnetic spectrum, silicon provides for very compact waveguides of only a few hundred nanometers in size. However, this otherwise beneficial property states a problem when trying to connect a compact silicon waveguide with the external world: Coupling light between an optical fiber of several microns in size and a much smaller integrated waveguide is potentially a very lossy endeavor. This thesis addresses the problem of fiber-chip-coupling by means of silicon photonic grating couplers and describes solutions to varying problems and technological constraints. Starting with a very basic grating coupler designed for the vacuum wavelength λ=1310nm and offering a measured coupling efficiency of -3.8dB more complex and better performing gratings for the wavelength region around λ=1550nm are presented. With a locally grown epitaxial silicon layer on top of the grating coupler 1.7dB coupling loss were achieved, which was shown by simulations could be further improved by making use of a second grating etch step to the otherwise uniform grating. Following this line of thought, the question was raised, how an optimal grating should be composed, given that non-uniformity may enhance the coupling efficiency. Two metaheuristic search algorithms were employed to generate such gratings, which resulted in a theoretical coupling efficiency of -0.7dB. Furthermore, polarization splitting grating couplers were investigated showing a coupling efficiency of -5.8dB and it was shown, that using a geometrical transformation on the grating coupler this could be further improved. The last grating demonstrated, is designed for the coupling of higher order fiber modes. By illuminating the grating from opposing ends and by utilizing the first higher order mode of the integrated waveguide the fiber modes LP01, LP11,a, LP11,b and LP21,a in two orthogonal polarizations could be excited

Taking silicon photonics modulators to a higher performance level : state-of-the-art and a review of new technologies

Optical links are moving to higher and higher transmission speeds while shrinking to shorter and shorter ranges where optical links are envisaged even at the chip scale. The scaling in data speed and span of the optical links demands modulators to be concurrently performant and cost-effective. Silicon photonics (SiPh), a photonic integrated circuit technology that leverages the fabrication sophistication of complementary metal-oxide-semiconductor technology, is well-positioned to deliver the performance, price, and manufacturing volume for the high-speed modulators of future optical communication links. SiPh has relied on the plasma dispersion effect, either in injection, depletion, or accumulation mode, to demonstrate efficient high-speed modulators. The high-speed plasma dispersion silicon modulators have been commercially deployed and have demonstrated excellent performance. Recent years have seen a paradigm shift where the integration of various electro-refractive and electro-absorptive materials has opened up additional routes toward performant SiPh modulators. These modulators are in the early years of their development. They promise to extend the performance beyond the limits set by the physical properties of silicon. The focus of our study is to provide a comprehensive review of contemporary (i.e., plasma dispersion modulators) and new modulator implementations that involve the integration of novel materials with SiPh

Bright Single-Photon Sources Based on Anti-Reflection Coated Deterministic Quantum Dot Microlenses

We report on enhancing the photon-extraction efficiency (PEE) of deterministic quantum dot (QD) microlenses via anti-reflection (AR) coating. The AR-coating deposited on top of the curved microlens surface is composed of a thin layer of Ta2O5, and is found to effectively reduce back-reflection of light at the semiconductor-vacuum interface. A statistical analysis of spectroscopic data reveals, that the AR-coating improves the light out-coupling of respective microlenses by a factor of 1.57 ± 0.71, in quantitative agreement with numerical calculations. Taking the enhancement factor into account, we predict improved out-coupling of light with a PEE of up to 50%. The quantum nature of emission from QDs integrated into AR-coated microlenses is demonstrated via photon auto-correlation measurements revealing strong suppression of two-photon emission events with g(2)(0) = 0.05 ± 0.02. As such, these bright non-classical light sources are highly attractive with respect to applications in the field of quantum cryptography