Tip- and laser-based 3D nanofabrication in extended macroscopic working areas. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 4 (2021), 3, S. 132-148
The field of optical lithography is subject to intense research and has gained enormous improvement. However, the effort necessary for creating structures at the size of 20 nm and below is considerable using conventional technologies. This effort and the resulting financial requirements can only be tackled by few global companies and thus a paradigm change for the semiconductor industry is conceivable: custom design and solutions for specific applications will dominate future development (Fritze in: Panning EM, Liddle JA (eds) Novel patterning technologies. International society for optics and photonics. SPIE, Bellingham, 2021. https://doi.org/10.1117/12.2593229). For this reason, new aspects arise for future lithography, which is why enormous effort has been directed to the development of alternative fabrication technologies. Yet, the technologies emerging from this process, which are promising for coping with the current resolution and accuracy challenges, are only demonstrated as a proof-of-concept on a lab scale of several square micrometers. Such scale is not adequate for the requirements of modern lithography; therefore, there is the need for new and alternative cross-scale solutions to further advance the possibilities of unconventional nanotechnologies. Similar challenges arise because of the technical progress in various other fields, realizing new and unique functionalities based on nanoscale effects, e.g., in nanophotonics, quantum computing, energy harvesting, and life sciences. Experimental platforms for basic research in the field of scale-spanning nanomeasuring and nanofabrication are necessary for these tasks, which are available at the Technische Universität Ilmenau in the form of nanopositioning and nanomeasuring (NPM) machines. With this equipment, the limits of technical structurability are explored for high-performance tip-based and laser-based processes for enabling real 3D nanofabrication with the highest precision in an adequate working range of several thousand cubic millimeters.
https://doi.org/10.1007/s41871-021-00110-w
Lau effect using LED array for lithography. - In: Nanomanufacturing and metrology, ISSN 2520-8128, Bd. 4 (2021), 3, S. 165-174
Illumination with LEDs is of increasing interest in imaging and lithography. In particular, compared to lasers, LEDs are temporally and spatially incoherent, so that speckle effects can be avoided by the application of LEDs. Besides, LED arrays are qualified due to their high optical output power. However, LED arrays have not been widely used for investigating optical effects, e.g., the Lau effect. In this paper, we propose the application of an LED array for realizing the Lau effect by taking into account the influence of the coherence properties of illumination on the Lau effect. Using spatially incoherent illumination with the LED array or a single LED, triangular distributed Lau fringes can be obtained. We apply the obtained Lau fringes in the optical lithography to produce analog structures. Compared to a single LED, the Lau fringes using the LED array have significantly higher intensities. Hence, the exposure time in the lithography process is largely reduced.
https://doi.org/10.1007/s41871-021-00108-4
Highly anisotropic fluorine-based plasma etching of ultralow expansion glass. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 23 (2021), 6, 2001336, insges. 10 S.
Deep etching of glass and glass ceramics is far more challenging than silicon etching. For thermally insensitive microelectromechanical and microoptical systems, zero-expansion materials such as Zerodur or ultralow expansion (ULE) glass are intriguing. In contrast to Zerodur that exhibits a complex glass network composition, ULE glass consists of only two components, namely, TiO2 and SiO2. This fact is highly beneficial for plasma etching. Herein, a deep fluorine-based etching process for ULE 7972 glass is shown for the first time that yields an etch rate of up to 425 nm min^-1 while still achieving vertical sidewall angles of 87˚. The process offers a selectivity of almost 20 with respect to a nickel hard mask and is overall comparable with fused silica. The chemical surface composition is additionally investigated to elucidate the etching process and the impact of the tool configuration in comparison with previously published etching results achieved in Zerodur. Therefore, deep and narrow trenches can be etched in ULE glass with high anisotropy, which supports a prospective implementation of ULE glass microstructures, for instance, in metrology and miniaturized precision applications.
https://doi.org/10.1002/adem.202001336
Rotationally tunable multi-focal diffractive moiré lenses. - In: Applied optics, ISSN 2155-3165, Bd. 60 (2021), 17, S. 5145-5152
In this work, we show how the combination of cascaded multi-value phase diffractive optical elements can form a multi-focal moiré zone plate with tunable optical power in each diffraction order. The rotationally tunable moiré zone plate is capable of generating an array of equal intensity focal spots with a precisely adjustable axial distance along the propagation direction. Numerical simulations as well as experimental results verify that multiple focal spots are generated, and the distance between the generated uniform foci can be adjusted by a mutual rotation of one multi-value phase diffractive element with respect to the other.
https://doi.org/10.1364/AO.427422
Husimi functions for coupled optical resonators. - In: Journal of the Optical Society of America, ISSN 1520-8532, Bd. 38 (2021), 4, S. 573-578
Phase-space analysis has been widely used in the past for the study of optical resonant systems. While it is usually employed to analyze the far-field behavior of resonant systems, we focus here on its applicability to coupling problems. By looking at the phase-space description of both the resonant mode and the exciting source, it is possible to understand the coupling mechanisms as well as to gain insights and approximate the coupling behavior with reduced computational effort. In this work, we develop the framework for this idea and apply it to a system of an asymmetric dielectric resonator coupled to a waveguide.
https://doi.org/10.1364/JOSAA.422740
Design von Zoomobjektiven mit verstimmbaren Linsen am Beispiel eines Laser Zoomteleskopes. - In: Jahrbuch Optik und Feinmechanik, ISSN 0075-272X, Bd. 66 (2020), S. 17-39
Es wird eine Methodik zum Finden optimaler Startsysteme für Zoomoptiken mit mindestens einer verstimmbaren Linse auf der Basis des kollinearen Modells vorgestellt. Hierbei spielt die im Programm PARAX [1] enthaltene allgemeine kollineare Berechnungsstrategie eine Rolle. An einem konkreten Beispiel, einem Laserzoom-Teleskop, wid die Funktionsweise der allgemeinen Berechnungsstrategie nachvollziehbar gezeigt. Der große Vorteil dieser Methodik besteht darin, dass man nicht mehr für jeden Systemtyp einer Zoomoptik in Abhängigkeit von der Anzahl der optischen Baugruppen und der Lage der verstimmbaren Linsen bzw. der axial beweglichen Elemente einen extra Formelapparat benötigt.
Fabrication and characterization of deformed microdisk cavities in silicon dioxide with high Q-factor. - In: Applied optics, ISSN 2155-3165, Bd. 59 (2020), 26, S. 7893-7899
We demonstrate the excitation and characterization of whispering gallery modes in a deformed optical microcavity. To fabricate deformed microdisk microresonators we established a fabrication process relying on dry plasma etching tools for many degrees of freedom and a shape-accurate morphology. This approach allowed us to fabricate resonators of different sizes with a controlled sidewall angle and underetching in large quantities with reproducible properties such as a surface roughness RQ ≤ 2nm. The excitation and characterization of these modes were achieved by using a state-of-the-art tapered fiber coupling setup with a narrow linewidth tunable laser source. The conducted measurements in shortegg resonators showed at least two modes within a spectral range of about 237 pm. The highest Q-factors measured were in the range of 105. Wave optical eigenmode and frequency domain simulations were conducted that could partially reproduce the observed behavior and therefore allow us to compare the experimental results.
https://doi.org/10.1364/AO.398108
Composite spiral multi-value zone plates. - In: Applied optics, ISSN 2155-3165, Bd. 59 (2020), 15, S. 4618-4623
We present composite spiral multi-value phase zone plates that are achieved by sectioning a spiral multi-value phase zone plate into several radial regions. Each region is composed of specially structured Fresnel zones with optimized phase values and an embedded basic topological charge. In numerical studies, it is shown that the proposed element is capable of producing equal intensity arrays of petal-like modes as well as dark optical ring lattice structures along the optical axis in multiple focal planes of the diffractive element. Additionally, it is demonstrated that the generated petal-like modes can be rotated in a controllable manner by implementing an angular frequency shift between the two composited spiral multi-value phase zone plates. We also illustrate that the rotation angle is independent of the diffraction order. Experimental results are included to verify the theoretical outcomes, where the phase pattern of the composite spiral multi-value zone plate is encoded onto a spatial light modulator.
https://doi.org/10.1364/AO.392746
Evaluation of quadratic phase hologram calculation algorithms in the Fourier regime. - In: Applied optics, ISSN 2155-3165, Bd. 59 (2020), 6, S. 1501-1506
The display of phase-only holograms with a spatial light modulator (SLM) has many applications due to its potential for dynamic three-dimensional projection of arbitrary patterns. We describe an innovative modification of the quadratic phase method for hologram calculation that uses error diffusion for initialization of an iterative phase retrieval algorithm. We compare the performance of our algorithm to other variations of hologram calculation approaches that use the quadratic phase method in the Fourier regime. Parameter variation is conducted for finding the differences and limits of the methods. Experiments with an SLM show the validity of the simulations.
https://doi.org/10.1364/AO.381547
A study of imprint and etching behavior on fused silica of a new tailored resist mr-NIL213FC for soft UV-NIL. - In: Micro and nano engineering, ISSN 2590-0072, Bd. 6 (2020), 100047, S. 1-7
https://doi.org/10.1016/j.mne.2020.100047