Universal antireflection coatings for substrates for the visible spectral region

It is possible to design normal-incidence antireflection coatings that reduce the reflectance of any substrate with a refractive index that lies in the range of 1.48 to 1.75. The performance of such coatings depends on the width of the spectral region over which the reflectance is to be suppressed, on the coating materials used for their construction, and on the overall optical thickness of the layer system. For example, the calculated average spectral reflectance of a set of six different substrates with refractive indices 1.48, 1.55, 1.60, 1.65, 1.70, and 1.75, when coated with a 0.56-μm-thick, eight-layer antireflection coating designed for the 0.40-0.80-μm spectral region, was 0.34%. This is higher than the average reflectance that is attainable with a conventional antireflection coating of similar optical thicknesses designed for a particular refractive index. However, it is an acceptable value for most applications. With the universal type of antireflection coating described, it is thus possible to coat a number of different refractive-index substrates in one deposition run, and this can result in considerable cost and time savings.     

Comparison of antireflection surfaces based on two-dimensional binary gratings and thin-film coatings

A comparison of antireflection surfaces based on the two-dimensional binary gratings and thin-film coatings is presented. First, a two-dimensional hybrid binary grating is proposed and analyzed by use of a vector-based implementation of the rigorous coupled-wave analysis method. The optimum parameters of the structure are determined and the effects that changing them have on spectral characteristics of the structure are studied. Then this structure is compared with multilayer thin-film antireflection filters. These filters are designed by genetic algorithm and needle methods, which are powerful methods for multilayer filter design. The comparison results show that the sensitivity of the grating to changes in the incident wavelength is high. However, a reflectance of the order of 10(-3)% at the design wavelength can be achieved. The sensitivity of designed antireflection thin-film filters to wavelength changes is lower, however, and the minimum achievable reflectance is higher.     

Optical interference coatings design contest 2004

A manufacturable, broadband, broad-angle antireflection (AR) coating for the visible (13 designs submitted) and a minimum-shift immersed short-pass filter (12 designs submitted) were the subjects of the design contest held in conjunction with the 2004 Optical Interference Coatings topical meeting of the Optical Society of America. Under the specified constraints, the broadband, broad-angle AR coating could be made more than 65 nm wide. The statistical stability of manufacturing simulations is discussed. The short-pass filter could operate up to a +/- 5.5 degree angular range. The submitted designs are described and evaluated.     

Antireflection coating design for plastic optics

The coating of plastics for optical applications is intended to improve the mechanical durability of soft polymers and to serve an antireflection function. Usually a classic four-layer antireflection system is added on top of a single-layer hard coating. With needle optimization, an alternative coating design has been developed. The design is characterized by thin high-refractive-index layers that are almost evenly distributed over the whole stack. Plasma ion-assisted deposition was used to deposit coatings upon poly(methyl methacrylate), polycarbonate, and cyclo-olefin copolymer. Uniform antireflection and high scratch resistance have been achieved.     

Expanded viewpoint for broadband antireflection coating designs

Examining spectral regions outside of the band where an antireflection coating is specified can aid in finding optimal design solutions. The reflectance versus wavenumber plots at low frequencies indicate the overall thickness of the design. These plots also point to whether the design will provide the minimum possible average reflectance in the specified band. It has been discovered that these patterns are nearly replicated by the plot of a quarter-wave stack at peak frequency. It is also found that optimal solutions exist only at quantized intervals.     

Interference coatings based on synthesized silicon nitride

Silicon nitrides are synthesized by ion-assisted deposition with only one coating material and a nitrogen-ion-beam source. All the SiN(x) films are amorphous and mechanically strong. A wide range of refractive indices from 3.43 to 1.72 at a wavelength of 1550 nm is obtained. Near-IR antireflection coating and a bandpass filter based on the multilayers of SiN(x) and Si are demonstrated.     

Design, production, and reverse engineering of two-octave antireflection coatings

We deal with design and production of optimal two-component antireflection (AR) coatings for an ultra broadband spectral range from 450 nm to 1800 nm. We demonstrate the whole design-production chain including design selection, choosing monitoring technique, coating production, and reverse engineering of the deposited coatings. At each step of this chain we provide thorough analysis on the basis of theoretical results and adequate computational manufacturing experiments. In order to produce the designed AR coatings we use magnetron sputtering deposition technique and accurate time monitoring.     

Infrared filters and dichroics for the advanced along-track scanning radiometer

The design and manufacture of the band-defining filters and their associated dichroic beam splitter for the 11- and the 12-μm infrared channels of the advanced along-track scanning radiometer are described. The filter requirements that have led to the choice of coating designs, coating materials, disposition of coatings, and effects of polarization are discussed. Overall spectral throughputs of the filter and dichroic interaction for the two channels are also presented.     

Multilayer antireflection coatings for the visible and near-infrared regions

With a high-refractive-index mixed-oxide dielectric material of ZrTiO(4) and ZrO(2) [Substance H2 (Sub2) from E. Merck, Darmstadt, Germany], in combination with magnesium flouride (MgF(2)), design optimization and experimental production of low-loss antireflection (AR) coatings are carried out. Design-optimization studies that make use of these materials as constituents of a seven-layer coating system demonstrate that when the useful bandwidth of an AR coating is extended to cover a wider spectral range, the designs are in general found to have increased integrated reflection loss, higher ripple, and increased spectral instability. The experimental studies on Sub2 material show that the films have excellent optical performance over a wider process window, the advantage of which is demonstrated in the production of different AR coatings on a variety of glasses with refractive indices that range from 1.45 to 1.784 and different mechanical, thermal, and chemical properties. The manufacturing process of AR coatings shows a consistency better than 99% with respect to optical properties and durability.     

Global sensitivity analysis of bandpass and antireflection coating manufacturing by numerical space filling designs

We present the effectiveness of global sensitivity analyses of optical coatings manufacturing to assess the robustness of filters by computer experiments. The most critical interactions of layers are determined for a 29 quarter-wave layer bandpass filter and for an antireflection coating with eight non-quarter-wave layers. Two monitoring techniques with the associated production performances are considered, and their influence on the interactions classification is discussed. Global sensitivity analyses by numerical space filling designs give clues to improve filter manufacturing against error effects and to assess the potential robustness of the coatings.     

Influence of grating parameters on the linewidths of external-cavity diode lasers

We investigate experimentally the influence of the grating reflectivity, grating resolution, and diode facet antireflection (AR) coating on the intrinsic linewidth of an external-cavity diode laser built with a diffraction grating in a Littrow configuration. Grating lasers at 399, 780, and 852 nm are determined to have typical linewidths between 250 and 600 kHz from measurements of their frequency noise power spectral densities. The linewidths are little affected by the presence of an AR coating on the diode facet but narrow as the grating reflectivity and grating resolution are increased, with the resolution exerting a greater effect. We also use frequency noise measurements to characterize a laser mount with improved mechanical stability.     

Guided-mode resonance filter with an antireflective surface consisting of a buffer layer with refractive index equal to that of the grating

A type of guided-mode resonance filter (GMRF) with an antireflective surface consisting of a buffer layer with refractive index equal to that of the grating is proposed, and the approximate design approach is presented. The relation between the filter linewidth and the coupling loss is used to analyze the filter properties by using different derivation methods. It is shown that the dispersion equation of the slab waveguide may provide a reliable approximation in estimating the resonance locations of the GMRF with an antireflective surface. The buffer layer functions as an intermediate layer between the grating and waveguide layers. This reduces the coupling and out-coupling of a mode of the waveguide, which results in significant reduction of the coupling loss and the filter linewidth with the antireflection condition nearly preserved. By changing the thickness of the buffer layer, different linewidths can be obtained with spectral symmetry and sideband suppression almost kept the same. The slight shift of resonance wavelengths due to the variety of the buffer layer thickness and the etching effects can be adjusted to the design value by changing the grating period. Accurate etch depth control to avoid underetching is necessary. The electric field distributions under resonance conditions shows that the buffer layer increases the mode confinement, thus narrowing the filter linewidth.     

Buffer layers for the design of broadband optical filters

The use of buffer layers is a promising technique in the attempts developed for the design of optical multilayer coatings when two widely separated spectral regions are under consideration. Here we show that the buffer layer, associated with matching layers as in the application mentioned above, can also be exploited in a successive step process to broaden the spectral bandwidth of beam splitters or antireflection coatings.     

膜厚对导电氧化锌宽带抗反射涂层的太赫兹传输影响

利用直流磁控溅射方法,在石英基底上制备了可用于太赫兹电磁波频率范围内的宽带抗反射涂层的掺铝氧化锌导电薄膜。在太赫兹时域光谱频率0.1~1.0THz范围内研究不同厚度的氧化锌薄膜的介电响应,得到了与频率相关的电导率、吸收和薄膜折射率,着重研究了膜厚对太赫兹波传输特性的调制作用。实验结果很好地符合了经典的Drude模型,表明可以通过控制氧化锌薄膜的厚度来改变太赫兹波的传输特性,并且导电氧化锌薄膜能够作为太赫兹频段范围的宽带抗反射涂层应用于衬底和光学器件上。     

Development of optical coatings for 157-nm lithography. II. Reflectance,absorption, and scatter measurement

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendor's coating design by that vendor's coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.     

钼酸铅晶体表面红外增透膜的研究

本文讨论了用于钼酸铅晶体表面的宽带红外增透膜的设计以及其在真空环境中的制备。膜系设计中 ,运用反射率图解法以获得满意的光学性能 ;与传统的热蒸发镀膜工艺相比 ,在真空沉积过程中采用了离子辅助沉积技术 ,从而大大提高了膜层的光学特性及膜层品质。试验表明所镀膜层性能优异 ,在光纤通信领域具有广阔的应用前景     

Dichroic rugate filters

We reduce the sidelobes that are present in the bandpass zones of rugate filters, using antireflection coatings to design dichroic rugate filters. Our designs are based on the formalism of equivalent systems that allow us to consider a rugate filter a simple equivalent layer with equivalent optical admittance and equivalent phase thickness functions. Rugate filters with apodization were considered.     

Fourier transform technique with frequency filtering for optical thin-film design

A Fourier analysis of existing and potentially complex refractive index profiles is often useful in the resolution of thin-film design problems. Applications of a frequency-filtering technique, which consists of the suppression of undesired spatial frequencies from the refractive index profiles, are described. A new, extremely simple antireflection coating synthesis method based on this concept is proposed.     

Antireflection coatings for UV radiation obtained by molecular-beam deposition

We have developed fluoride antireflection (AR) coatings on MgF(2) substrates for a wavelength of 248 nm by molecular-beam deposition. Transmission and laser-induced damage threshold of the samples were measured and atomic force microscope (AFM) investigations were carried out. We compare a 14-layer design for AR coatings with sublayer thicknesses of 12 nm with a conventional two-layer design with quarter-wavelength thicknesses. The laser-induced damage threshold of the 14-layer coating is slightly higher than that of the two-layer coating. The AFM surface images show that the 14-layer coating has a smoother surface than the two-layer coating.     

Estimation of the average residual reflectance of broadband antireflection coatings

We deal with optimal two-material antireflection (AR) coatings for the visible and adjacent spectral regions. It has been shown before that, for a given set of input parameters (refractive indices of the substrate, ambient medium and high- and low-index coating materials, and for a given spectral width of the AR coating), such designs consist of one or more clusters of layers of approximately constant optical thickness and number of layers. We show that, through the analysis of many different optimal coatings, it is possible to derive two parameters for a simple empirical expression that relates the residual average reflectance in the AR region to the number of clusters. These parameters are given for all possible combinations of relative spectral bandwidth equal to 2, 3, and 4; low-index to ambient-medium index ratio equal to 1.38 and 1.45; and high-to-low index ratio equal to 1.4, 1.5, and 1.7. The agreement between the numerically and the empirically calculated values of residual average reflectance is excellent. From the information presented the optical thin-film designer can quickly calculate the required number of layers and the overall optical thickness of an AR coating having the desired achievable residual average reflectance.