Optische und Elektronische Materialien E-12 (H)

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I³-Projekt - Adaptive optical material based on water condensation in nanoporous structures
It is expected to demonstrate an adaptive optical material based on water condensation in nanoporous materials. Water-infused nanoporous silica or alumina represent particularly environmentally friendly platform for sustainable development of materials. Such adaptive materials can be used as functional coating for self-regulating surfaces and smart windows where depending on the illumination and temperature the sun radiation can be transmitted, absorbed, or reflected. It can also be used to have an adaptive structural color sensitive to temperature, humidity or even the wavelength of incident radiation. These smart surfaces and windows have large palette of potential applications in the area of effective solar energy utilization overcoming effects of climate change. Self-adjustment is an important property of natural materials. Development of artificial materials with similar capability based on environmentally friendly materials is an important further step in material science. In this I3 project we propose to show one example of such a material with an optical functionality.
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AI for photonics
Neural networks are applied to investigate structure-property relations of structured optical materials. Such properties as effective medium parameters, photonic band diagrams and band gaps are considered. Methods are developed to address the direct and inverse problems, which are prediction of properties from structure and proposal of structure for required properties, correspondingly. Also, an optimization problem is solve, where topology is changed to maximize required properties.
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SFB 986: Subproject C09 - Hole emission from tunable metallic meta-materials
Metallic metamaterials, such as nanoporous gold, have numerous advantages over other nanoscale materials with respect to the adaptability of the relation between structure and photonic properties. By variation of the surface-to-volume ratio and by implementation of a functional nano layer, the TP will investigate the photonic generation and the transfer of electron deficits (holes) via an electrochemical oxidation reaction at the interface to a liquid phase. We aim at novel insights on the applicability of the metamaterial "nanoporous gold" as photoanode material.
847
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Quasi-disordered structures with 2D and 3D complete photonic bandgaps with arbitrarily small refractive-index contrast
In this project we investigate 2D and 3D quasi-disordered structures which can be considered as a new kind of distributed photonic quasicrystals. We envisage these to have a complete photonic bandgap even for arbitrarily small refractive-index contrasts. While the structures appear completely disordered and lack any discernible symmetry, they actually possess a long-range order along with a high degree of symmetry giving them unique properties. The dielectric distribution of this material is mathematically obtained by a superposition of sinusoidal gratings with random orientation and random phase. If the number of gratings used for the generation of the structure is optimized, the individual bandgaps of the gratings can overlap to form a complete and isotropic photonic bandgap. Additionally, the formation of the isotropic bandgap leads to low group velocities at its edges for all directions. Therefore, a strong enhancement of the emission of a source immersed in the structured medium can be observed at these frequencies.The main objective of this project is to show that even for very low refractive-index contrasts a complete photonic bandgap can be found with the structuration scheme we propose. We want to show a conclusive theory how to obtain the optimal structure parameters (refractive-index contrast, number of gratings, size) for the maximal opening of the bandgap. This theory is to be proven by simulations of 2D and 3D structures. In a systematic numerical study simulations should also reveal the sensitivity of the refractive-index contrast minimally required for a complete photonic bandgap on various kinds of defects, thus indicate practical limitations stronger than the theoretical ones. Based on our approach, we envisage realizing a complete 3D bandgap for a refractive-index contrast as low as 1.55:1 (polymer/air) or 1.43:1 (glass/air). The quasi-disordered structures will be manufactured in 2D and 3D and characterised for their transmission and reflection properties. Our approach can be used to control spontaneous and stimulated emission in 2D and 3D structures with a low refractive-index contrast. Our novel distributed quasicrystals can therefore widen the range of materials available for the realization of photonic bandgaps and thus can pave the way for new applications. The results will also be interesting beyond the photonic community, as the proposed approach extends the theory of quasicrystals and localisation phenomena in electronic, mechanical and other wave systems.
272
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I³-Lab - Hamburg Electronics Lab for Integrated Optoelectronical Systems
238
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Relativistic photonic band gap mirror on chip
In this proposal we first time draft the route towards experimental realisation of photonic crystal based relativistic mirrors which can be used to dramatically manipulate the frequency and bandwidth of optical signals. For that we propose to realise a system of coupled photonic crystal waveguides and operate it close to the point of degeneracy, also called Dirac point. This degeneracy can be lifted by free carriers generated via two photon absorption of the pump pulse. The lifted degeneracy will constitute a local photonic band gap, where the spatial boundary of this band gap will move with the group velocity of the pump pulse. The optical signal at a frequency within the local band gap will experience reflection with frequency shift and bandwidth change. The proposed system will allow an exploitation of the relativistic mirror in integrated optics technology. The main goals of this project are the realisation of coupled waveguides with small propagation loss close to the Dirac point, as well as efficient injection of the signal and pump pulses into the waveguide system. Afterwards the dynamic experiments of signal reflection from relativistic photonic band gap front are planned. It is expected that the signal duration can be compressed by 10-100 times after reflection without significant frequency shift. Experimental realisation of photonic band gap fronts will also make possible the investigation of other related effects, e.g. spontaneous generation of photons at the front.The project is submitted in the frame of the Joint Sino-German call for proposals organised by the German Research Foundation (DFG) and the National Natural Science Foundation of China (NSFC). It will be conducted in cooperation with Dr. Juntao Li and Dr. Xinlun Cai from Sun Yat-sen University (SYSU), Guangzhou, China. The project at SYSU will concentrate on the design optimization for lithography and ion etching processes and on fabrication of low loss coupled photonic crystal waveguides. The challenge is the adjustment of manufacturing processes for nanometer precision. The applicants at Hamburg University of Technology (TUHH) will design the structures and measure relativistic effects on chip.
4965
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Optical properties of nanoporous gold
Nanoporous gold with porosity much smaller as the light wavelength represent an optical metamaterial. It has distinct optical response which can be attributed to plasmonic resonances and conduction in network structure. We develop effective medium models for nanoporous gold taking into account structural and material properties. Large surface to volume ratio of nanoporous gold can be also used to change its optical properties via surface modifications. Additionally absorption in nanoporous gold can lead to excitation of hot electrons and hot holes that can be utilized for photoemission and chemical reactions at the surface.
1174
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Photocatalytic water splitting with nanoporous gold
Nanoporous gold represents a connected network of nanometer sized gold ligaments. Due to its high surface to volume ratio it is expected that solar radiation can be efficiently used for water splitting reaction at the surface. The nanoporous gold can be also functionlised with a metal oxide coating via atomic layer deposition to improve the photocatalytic activity. Depending on the applied bias the nanoporous gold electrode can be used as an electrode for hydrogen or oxygen production.
2521
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Infrared gas sensing with silicon photonics
Introduction Many gases are colorless and odorless and therefore are not perceived by the human sense organs. For toxic gases the monitoring in buildings is indispensable, as for example gas leakages can lead to tremendous health damages. But also the detection of nontoxic gases is of utmost importance for many applications as process control or breath analysis for clinical diagnosis. Many gases exhibit absorption lines in specific fingerprint regions in the mid-infrared wavelength range, for example, CO2 shows high absorption between 4.2 and 4.3 µm. Thus an optical signal at the gas specific wavelength range can interact with the gas and its intensity will be decreased. Optical sensors detect the change in intensity in the fingerprint regions and thus get information about the present gas concentration. In general, an optical sensor consists of three components: 1. a source that emits radiation in the gas specific wavelength range, 2. a gas cell that provides a large interaction length between the light signal and the gas, 3. a detector that is able to detect even small intensity changes. Goals The overall aim of this project is to develop an optical gas sensor on a silicon chip that offers small size and low power consumption. This would open up the way to low-cost mass-production and also allow the implementation of gas sensors into portable devices like mobile phones. In contrast to free-path optical sensing, our approach is based on integrated photonics where light will be guided inside the silicon chip. The evanescent field can interact with gases in the environment and can thus be used for optical sensing. Our current research is based on the following topics: - Integrated silicon based thermal emitter - 2D integrating cell - Integrated silicon based MIR detector
1413
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SFB 986: Subproject C02 - Multiscale photonic materials with adjustable radial Anisotropy
Project C2 investigates the optical scattering of ordered and disordered multiscale systems. The basic building block (motif) of the scattering system is extended to spheres and cylinders with adjustable radial anisotropy. This creates additional flexibility in adapting the spectral and scattering direction-determining behavior of ordered and disordered systems. The radial anisotropy is achieved by an additional structure on the sub-wavelength scale, namely by radially symmetric multilayer conformal nanometer thick coatings or by arrangements of liquid crystal molecules.
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