There is an ongoing critical discussion about whether long-term durability of polymer optics can be guaranteed after passing accelerated tests, as the degradation mechanisms are very complex. Thick scratch resistant antireflective coatings AR-hard and antireflective nanostructured coatings AR-plas had been developed several years ago. The polymer substrates are exposed to plasma emissions and ion bombardment both during coating and structuring. On the other hand, cycloolefin-based polymers may undergo structural changes induced by plasma. For the present study, it was possible to re-examine coated samples a long time after their production. Various AR coatings and different cyclic olefin polymers were re-evaluated in terms of their optical properties and coating adhesion.
Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings can be flexibly adapted to different wavelengths. To generate an effective (> 99 %) light absorption of an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer’s material. On this basis, different black absorber coatings were developed and deposited on optical components for actual applications. A wideband black absorber for 400 -1000 nm wavelength on a space spectrometer slit, a bi-directional black coating for a single wavelength in the VIS, which can be wet-chemically etched for micro-patterning, and a black aperture for NIR and SWIR light on the exit face of a dispersion prism are presented.
Transparent and conductive oxides offer metal-like conductivity and high transmission in the visible spectrum. However, they suffer from reflection losses at the film interface due to their high refractive index. A method for producing an ITO nanostructure through plasma etching in a conventional deposition plant equipped with an APS plasma source is presented, resulting in conductive nanostructures with an effective refractive index as low as 1.3. This nanostructure was combined with an AR coating achieving minimal reflectance while maintaining a conductive surface that enables the removal of surface charges as it is needed in AR coatings for quantum computing applications.
This paper presents a novel approach to enhance the performance of Quantum dot (QD) based light-emitting diodes (LEDs) by incorporating Bragg resonator substrates. By depositing QD-LED layer stacks on tailored Bragg resonator substrates, the emission spectrum of red-emitting QD-LEDs is narrowed to less than 20 nm, and the emission pattern becomes more directional. Additionally, the modulation characteristics of QD-LEDs on Bragg-substrates are investigated. These findings demonstrate the potential to improve the usability of QD-LEDs in displays, lighting, and sensing applications.
The monitoring of anthropogenic CO2 by satellites (part of Copernicus, the European Union’s Earth Observation and Monitoring program) requires a special dispersive spectrometer. As a highly efficient light dispersing element, a Prism-Grating Prism (PG-P) optical element will operate in the program, mentioned above. Anti-reflection (AR) coatings and light blocking apertures are requested to suppress optical losses, to reduce stray light and to shape the beam. Beside the AR-coatings, deposition of “black” aperture as a coating directly on the PG-P element, allows to abstain a mechanical aperture. Thereby, reduced number of elements in the optical setup and therefore reduced payload of the satellite can be achieved. For this purpose, an antireflective coating inside a clear aperture combined with a light blocking and absorbing aperture-coating outside the clear aperture was realized. The developments shown in this contribution were performed for the application wavelength of 1590 - 1675 nm.
We present the design, manufacturing and characterization results of a customized high-resolution echelle grating. The grating was manufactured at Fraunhofer IOF and delivered to the NIRPS (Near Infrared Planet Searcher Instrument) consortium. The technology workflow for the manufacturing of the echelle grating is relying on wet-chemical etching, applied to crystalline silicon substrates, which enables the creation of highly determined micro-facets and surfaces over macroscopic dimensions. The echelle’s grating period and plateau size within one period are established based on electron-beam lithography. A binary pattern in a hard mask material is performed by dry-reactive ion etching while transferring the pattern in the silicon substrate is achieved by wet-chemical etching with potassium hydroxide. The grating is designed to operate at a blaze angle of 76° in a wavelength band of 0.9μm – 1.8μm. A gold coating is applied to increase the diffraction efficiency to about 70%; verified at wavelengths of 1030nm and 1640nm, respectively. The overall grating size is 78mm x 284mm providing a WFE of less than 70nm (RMS) measured throughout the full aperture. In this article we present the manufacturing workflow and structural inspection results of the manufactured echelle grating, having a critical eye on the impact of sub-surface defects of the initial silicon crystal. Moreover, we present optical performance test results covering diffraction efficiency, PSF, WFE and spectral ghosts. It is concluded that the imaging properties of the manufactured grating are as good as those of a plane gold mirror reference. Additional presentation content can be accessed on the supplemental content page. Additional presentation content can be accessed on the supplemental content page.
The study of the interaction of fibronectin and phosphorylcholine molecules with surfaces is of high relevance to understand the biological performance of bioactive coatings. To accomplish this task, one-dimensional photonic crystals supporting Bloch surface waves were interrogated in label-free and enhanced fluorescence operation modes. In particular, the enhanced fluorescence mode offers the possibility to confirm the presence of proteins with a sharp improvement of the resolution. Bioactive coatings based on fibronectin/ phosphorylcholine have thus the potential to not only enhance the body acceptance of implanted devices, but also extend the lifetime of such devices.
Human epidermal growth factor receptor 2 (HER2) over-expression occurs in 15–20% of breast cancers and it is generally associated with a dismal prognosis. In this work, we report on the use of one-dimensional photonic crystal biochips to detect clinically relevant concentrations of HER2 in human plasma samples. To this aim, we optimized an optical read-out system, combining both label-free and fluorescence detection, which makes use of biochips tailored with specific proteins for specific biological recognition. Our biochips were used to discriminate HER2 positive/negative human plasma samples providing a solid and reliable tool for clinical diagnostics.
We report on the development of a biosensing platform that combines label-free and fluorescence based detection on disposable Bloch surface wave biochips. This system is applied to the detection of the HER2-neu/ErbB2 clinical biomarker related to breast cancer development. We first describe the design and fabrication of the BSW biochips as well as the principle of operation of the optical reading instrument. Then, the approaches for surface functionalization and immobilization of proteins for specific detection on the biochips are discussed. Finally, experimental results on a sandwich immunoassay for ErbB2 detection in cell lysates are presented.
To effectively improve color neutrality of antireflection (AR) coatings, a layer with a very low refractive index (n < 1,3) must be used as the top layer. However, solid materials with such a low refractive index (n) does not exist. The deposition of low molecule weight organic materials as compact films, and a subsequent plasma etching procedure on these films, offered the possibility to produce a nanostructured layer with a very low refractive index as top layer for an antireflection coating. Strongly curved aspheric lenses were coated with such a super-broadband AR design (ARplas2) and the antireflection performance was measured at different locations on the lens. An average reflection < 0,25 % over the full visible wavelength range was measured even in the outermost region of the curvature.
A biosensor platform based on Bloch Surface Waves and operating in angular interrogation mode is applied to the detection of a clinical biomarker (HER2-neu/ERBB2) related to breast cancer initiation/progression. Preparing regions for specific recognition of different proteins as well as a reference on the biochip enables to correct the signal for nonspecific effects. Additionally, label-free analysis and surface wave enhanced fluorescence detection can be applied and compared directly on the platform. Cell lysates with high and low expression levels of ERBB2 are analyzed. Comparing the signals of such ERBB2 positive and negative samples estimates the limit of detection at 1.7 ng/mL. This is well below the threshold of 15 ng/mL set by the FDA for clinically useful ERBB2 detection in human serum, demonstrating that 1DPC-based biochips are attractive candidates for breast cancer detection/monitoring.
High-reflective coatings are indispensable in order to manufacture mirrors with highest possible reflectivity. The maximum reflectivity can be achieved by all-dielectric coatings; however, the spectral bandwidth of these mirrors is limited. For astronomical applications metal based coatings (Al, Au, Ag) are commonly applied, as they allow high reflectivity and at the same time a broad spectral bandwidth.
The increasing demand for early detection of diseases drives the efforts to develop more and more sensitive techniques to detect biomarkers in extremely low concentrations. Electromagnetic modes at the surface of one dimensional photonic crystals, usually called Bloch surface waves, were demonstrated to enhance the resolution and constitute an attractive alternative to surface plasmon polariton optical biosensors. We report on the development of Bloch surface wave biochips operating in both label-free and fluorescence modes and demonstrate their use in ovalbumin recognition assays.
For high quality optical coatings the knowledge of the losses of the deposited materials is essential. A precise measurement of low Im(n+iκ)≤ 10-6 at an intended operation wavelength and with low intensity can be achieved in waveguide configurations, whereby leaky waveguide configurations allow one to analyze losses of high- and low-index media of H-L-stacks as well due to resonances in the angle-dependent reflection curve. Numerical investigations reveal that different leaky wave schemes, e.g. Bragg-, Bloch- and Antiresonant-Reflecting waveguides, comply differently with practical requests. Loss figure evaluation requires peculiar attention due to measurement accuracy and ambiguities, thus suitable constraints for layer data and a proper merit-function construction have to be used.
A basic requirement for many optical applications is the reduction of Fresnel-reflections. Besides of interference coatings, nanostructures with sub-wavelength size as known from the eye of the night-flying moth can provide antireflective (AR) properties. The basic principle is to mix a material with air on a sub-wavelength scale to decrease the effective refractive index. To realize AR nanostructures on polymers, the self-organized formation of stochastically arranged antireflective structures using a low-pressure plasma etching process was studied. An advanced procedure involves the use of additional deposition of a thin oxide layer prior etching. A broad range of different structure morphologies exhibiting antireflective properties can be generated on almost all types of polymeric materials. For applications on glass, organic films are used as a transfer medium. Organic layers as thin film materials were evaluated to identify compounds suitable for forming nanostructures by plasma etching. The vapor deposition and etching of organic layers on glass offers a new possibility to achieve antireflective properties in a broad spectral range and for a wide range of light incidence.
Antireflective (AR) coatings for lenses with extreme curvature must be designed for use in the visible and the near-infrared ranges to ensure sufficient AR performance in the visible range on the inclined surfaces of such lenses. In this work, multiple inorganic and nanostructured organic layers are considered for use in AR coatings with alternating high-index and low-index layers and in arrangements with effective indices that decrease from the substrate side to the surrounding medium. An AR coating effective in the spectral range from 400 nm to 1400 nm was realized by combining a multilayer interference system with a plasma-etched organic layer. Step-down index systems or gradient layers with sufficient thickness are especially promising for lenses.
This study focuses on the atomic layer deposition (ALD) of high quality SiO2 thin films for optical application. One of the challenges for the application of dielectric ALD layers in optical coatings is the realization of low absorption and scattering losses. Furthermore the layers have to be prepared with a precise controlled thickness and repeatable optical properties. SiO2 films were deposited using tris[dimethylamino]silane (3DMAS) and oxygen plasma on Si(100)substrates, quartz and BK7 glass substrates at temperatures between 100 °C and 300 °C. Film growth rate and refractive indices of SiO2 thin films were studied as function of deposition temperature. A linear growth behavior of SiO2 ALD films is confirmed, allowing a scalability of film thickness just by counting ALD cycles. The grown films are resistant to abrasion and possess good adhesion to glass substrates. The optical losses of the films are negligible in the investigated spectral range from 250 nm to 1100 nm. An antireflective (AR) coating was prepared by atomic layer deposition using SiO2 as low refractive index material and HfO2 as high refractive index material.
Bloch surface waves (BSW) propagating at the boundary of truncated photonic crystals (1D-PC) have emerged as an attractive approach for label-free sensing in plasmon-like sensor configurations. Due to the very low losses in such dielectric thin film stacks, BSW feature very low angular resonance widths compared to the surface plasmon resonance (SPR) case. Besides label-free operation, the large field enhancement and the absence of quenching allow utilizing BSW coupled fluorescence detection to additionally sense the presence of fluorescent labels. This approach can be adapted to the case of angularly resolved resonance detection, thus giving rise to a combined label-free / labelled biosensor platform. It features a parallel analysis of multiple spots arranged as a one-dimensional array inside a microfluidic channel of a disposable chip. Application of such a combined biosensing approach to the detection of the Angiopoietin-2 cancer biomarker in buffer solutions is reported.
Optical sensors exploiting Bloch surface waves at the truncation edge of one dimensional photonic crystals are used here as a valid alternative to surface plasmon resonance operating in the Kretschmann-Raether configuration, and commonly adopted for label-free optical biosensing. In order to reduce the Bloch surface waves resonance width and increase the resolution it is desirable to work with one dimensional photonic crystals with as small losses as possible. However this makes that the resonances observed in a single polarization reflection scheme are shallow and difficult to track in a sensing experiment. Here we report on the practical implementation of an angularly resolved ellipsometric optical sensing scheme based on Bloch surface waves sustained by tantalia/silica multilayers. The angular resolution is obtained by a focused illumination at fixed wavelength and detecting the angular reflectance spectrum by means of a CMOS array detector. The experimental results, obtained by using one tantalia/silica multilayer with a defined structure, show that the limit of detection can be pushed below 2.1x10-7RIU/Hz1/2.
Bloch surface waves (BSW) propagating at the surface of truncated, one-dimensional crystals are valid candidates to improve sensors based on surface plasmon polaritons, usually referred to as surface plasmon resonance (SPR). The low losses introduced by the dielectric BSW stacks enable to achieve resonance widths much below the ones of SPR, thus proposing improved sensing results. A simplified, bi-linear model of the resonance intensity distribution is applied to estimate the effect of the resonance properties onto the measurement noise. This yields a limit of detection (LoD) that is used to optimize a BSW supporting thin film stack and to quantitatively compare SPR and BSW sensors. The results indicate that an order of magnitude reduction of the LoD is within reach when sufficient sampling of narrow BSW resonances is achieved.
A small molecule is a low molecular weight organic compound which is by definition not a polymer. Therefore, physical
vapor deposition by evaporation as common for inorganic oxides is often possible. Organic layers can be useful as
components of interference stacks for different functions. A number of organic compounds have interesting UV
absorption characteristics and can be used to protect UV-sensitive polymers such as polycarbonate. In addition, organic
layers can be applied to generate nanostructured thin films with a very low effective refractive index, as shown recently
for polymers. A structured organic single layer can be applied as an antireflective (AR) coating for a glass lens. The
applicability of several small molecule compounds will be discussed in this paper.
Within this paper, we present a novel approach for an optical system for a near infrared (IR) line camera, which exists of
only one monolithical optical element with 3 optical free form surfaces. The optical design was performed with respect
to the following requirements given by the application: wavelength range 0.9 μm to 1.7 μm, field angle 75° x 2°,
horizontal angular resolution 0.5°. Within the design process one of the three optical surfaces is formed biconic, two are
realized as cylindrical surface. The calculated component was realized by means of diamond UP manufacturing. Two of
the optical surfaces were metallized to work as mirrors for the above mentioned spectral range. The realized element has
a size of less than 8 cm3; it was finally characterized.
A new technology based on plasma etching has been developed to produce antireflective surface structures. By choosing thin initial layers and variable plasma conditions, a broad range of nanostructures can be obtained on various polymers. A broadband antireflective effect can be achieved that is less sensitive to the incident angle of light compared to multilayer interference coatings. Thin layers of silica help in mechanical protection, especially if the structured surface is nearly enclosed by the protection layer. In addition, surfaces that show both antireflective properties and an antifogging effect have been prepared. Combinations of SiO2 and fluorine-containing layers were found to be useful in obtaining
super-hydrophobic behavior. This advanced plasma etching is not limited to a special plasma source and the suitability of different plasma sources is discussed.
Antireflection (AR) properties are required for optical surfaces to avoid disturbing reflections as well as to improve the transmission of optical systems. The common method to reduce the reflection on optics is vacuum deposition of interference coatings. However, special efforts are required for each type of plastic to develop polymer-capable vacuum coating processes due to the manifold chemical and physical properties of optical polymers. An alternative procedure for the antireflection of polymers is the generation of surface structures that decrease the index of refraction in a surface region. In this paper, the suitability of the miscellaneous thermoplastic polymers for plasma-ion assisted deposition processes is evaluated. This comprises the study of damage effects caused by the contact with plasma and high-energy radiation as well as the development of special coating designs and of suitable process conditions. Coating properties achieved are discussed for PMMA and poly-cycloolefines. The same ion source arrangement as used for coating has been applied for etching an antireflective sub-wavelength surface structure into PMMA. In summary, the paper shows the practical application fields for both technologies.
The performance of the high temperature resistant polymers Pleximid, APEC and Ultrason as substrate materials in plasma-assisted physical vapor deposition processes was studied and compared with well-known thermoplastics for optical applications. Different effects of UV irradiation and plasma exposure on the polymers' optical features, surface energy and adhesion properties for oxide layers, typically used for interference multilayer coatings, are shown.
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