Optical properties of black silicon structures ALD-coated with Al 2 O 3

Atomic layer deposited (ALD) Al 2 O 3 coatings were applied on black silicon (b-Si) structures. The coated nanostructures were investigated regarding their reflective and transmissive behaviour. For a systematic study of the influence of the Al 2 O 3 coating, ALD coatings with a varying layer thickness were deposited on three b-Si structures with different morphologies. With a scanning electron microscope the morphological evolution of the coating process on the structures was examined. The optical characteristics of the different structures were investigated by spectral transmission and reflection measurements. The usability of the structures for highly efficient absorbers and antireflection (AR) functionalities in the different spectral regions is discussed

Iridium wire grid polarizer fabricated using atomic layer deposition

In this work, an effective multistep process toward fabrication of an iridium wire grid polarizer for UV applications involving a frequency doubling process based on ultrafast electron beam lithography and atomic layer deposition is presented. The choice of iridium as grating material is based on its good optical properties and a superior oxidation resistance. Furthermore, atomic layer deposition of iridium allows a precise adjustment of the structural parameters of the grating much better than other deposition techniques like sputtering for example. At the target wavelength of 250 nm, a transmission of about 45% and an extinction ratio of 87 are achieved

Transmission Gratings relying on Huygens Metasurfaces for short-wave to long-wave infrared applications

In many spectroscopic applications, diffraction gratings are the pivotal optical component which is used to decompose white light into its spectrum. However, design and manufacturing of diffraction gratings for the infrared spectral domain operating in transmission bares its own challenges, i.e. a very limited choice of transparent materials. Here we present our effort on exploiting Huygens-metasurface structures for design and manufacturing of diffraction gratings intended for operation in the short-wave (around 2µm) up to the long-wave infrared region (>10µm). Silicon nano-pillars are the material system of choice since they exhibit the best compromise between optical performance and manufacturing feasibility. We present specific designs as well as measurement results of a demonstrator sample

Silicon wire grid polarizer for ultraviolet applications

We present a silicon wire grid polarizer operating down to a wavelength of 300 nm. Besides metallic grating materials, semiconductors also offer appropriate material properties to realize wire grid polarizers in the ultraviolet (UV) spectral range. The presented polarizer with a period of 140 nm was realized by means of electron beam lithography and dry etching using amorphous silicon as the grating material. At a wavelength of 365 nm, a transmission of 42% and an extinction ratio of 90 (19.5 dB) are measured. The spectral bandwidth of these polarizers in the UV-spectral range is about 100 nm

High contrast gratings for high-precision metrology

Experiments in the field of high-precision optical metrology are crucially limited by thermal noise of the optical components such as mirrors or beam splitters. Amorphous coatings stacks are found to be a main source for these thermal fluctuations. In this contribution we present approaches to realize coating free optical components based on resonant high contrast gratings (HCGs) made of crystalline silicon. It is shown that beside classical cavity mirrors the concept of HCGs can also be used for reflective cavity couplers. We compare the advantages and challenges of these HCG reflectors with distributed Bragg reflectors made of crystalline coatings for applications in optical metrology

Self-organized, effective medium Black Silicon for infrared antireflection

Statistical Black Silicon antireflection structures for the mid-infrared spectral region, fabricated by Inductively Coupled Plasma Reactive Ion Etching, are investigated. Upon variation of etch duration scaling of the structure morphologies is observed and related to the optical losses in specular transmittance. By means of statistical morphology analysis, an effective medium criterion for the examined structures is derived that can be used as a design rule for maximizing sample transmittance at a given wavelength. To obtain Black Silicon antireflection structures with elevated bandwidth, an additional deep-etch step is proposed and demonstrated

Diffractive optical elements based on subwavelength high-contrast gratings

We report on novel concepts for reflective diffractive elements based on high-contrast gratings. To demonstrate the possibilities for such devices reflective cavity couplers with three output ports are investigated. A diffracting period is superposed to a highly reflective subwavelength grating in order to realize diffractive elements. This superposition can be realized with a periodic depth, fill factor or period modulation of the reflector. Further, to limit the total transmission of the device it is necessary to enhance its angular tolerance. We discuss different approaches in order to realize this increased reflectivity in broad range of the angular spectrum. The contribution focuses on the material combination silicon-silica, but the presented concepts also hold for other material combinations with large index contrast and even for monolithic silicon structures