The authors' experience with the application of the needle optimization technique to the design of optical coating is summarized. A physical interpretation of the technique is provided, and its main features are identified. Guidelines on the application of the needle optimization technique to various types of design problems are given.

Application of the needle optimization technique to the design of optical coatings.

The manufacture of complicated optical coatings consisting of many layers of different thicknesses can be a challenge, especially if the deposition technique does not produce dense layers. Deposition errors in a layer can affect not only the desired performance of a multilayer, but can also lead to a complete breakdown of the monitoring and control of subsequent layers. The best chance to achieve the desired optical performance of a multilayer involves deposition error compensation. In this process, the construction parameters of a completed layer are evaluated to determine if any deposition errors have occurred and then the remaining layers of the multilayer system are reoptimized to compensate for any errors made. This paper describes a versatile deposition error compensation program developed at the National Research Council of Canada for the simulation and real-time control of the manufacture of multilayers composed of dielectric or absorbing films. To model porous layers, an effective medium theory approach is used to relate the optical constants of the layer in vacuum and air to the microstructure of the layer. In the simulation mode, random errors are applied to the thickness and porosity of the layers and measurement errors are also included. The best monitoring strategy for the manufacture of a given multilayer is established on the basis of statistical information obtained from a number of these simulations. In this paper the results of calculations on the effectiveness of various monitoring strategies are presented for a sharp edge filter produced by three different physical vapor deposition methods. An extensive list of references to previous papers dealing with sources of errors during deposition is also provided.

Deposition error compensation for optical multilayer coatings. I. Theoretical description

We demonstrate the existence of electromagnetic surface modes and surface plasma waves in the interface of a one-dimensional photonic crystal and a metal. These modes can exist in the region in which bandgaps of the photonic crystal overlap and in the region below the plasma frequency of a metal in the frequency wave-vector space. An analytic dispersion relation to determine the existence of these electromagnetic surface modes is obtained, and it is shown that these modes can be excited and observed without prism or grating configurations even under normal incidence from vacuum.

Photonic surface-wave excitation: photonic crystal–metal interface

New developments in spectroellipsometry : the challenge of surfaces

Real-time optical diagnostics for epitaxial growth

A three-step design procedure is developed for dielectric stacks which are required to be nonpolarizing for a given wavelength λr and angle of incidence θ0,r, at which the reflectance Rr is prescribed. The method leads to solutions in which only three layer materials occur and can be applied for a wide range of values of θ0,r and Rr. The media can be chosen from the available coating materials. Furthermore, the procedure offers the possibility of optimizing with respect to the behavior of the reflectance in the neighborhood of λr and θ0,r. An example is elaborated, and its results are compared with an actually produced coating.

Nonpolarizing beam splitter design

The planning of an optical monitoring process for nonquarterwave stacks, using standard equipment for turning value monitoring, is a rather complicated procedure. It is shown that by using a computer program together with some simple rules the planning becomes a more straightforward task. Detailed examples are presented.

Optical monitoring of nonquarterwave stacks.

We describe the behavior of the equivalent refractive index (or Herpin index) and equivalent phase thickness in relation to the phase thicknesses of the layers in a dielectric stack. This relation is visualized by a diagram that provides insight into the existing solutions for given combinations of the Herpin index and the equivalent phase thickness. Furthermore, it can be used for the explanation of the occurrence of stop bands and of the dispersion of equivalent layer stacks.

Equivalent layers : another way to look at them

A new fabrication technique for the generation of optical aspherical surfaces of revolution is presented. This fabrication technique combines the characteristics of conventional loose abrasive machining with features of high-precision machining tools. A prototype of the machine tool based on this fabrication technique is currently being developed. We describe the characteristics of this method. Fabrication of aspherical ultraprecise surfaces using a tube is a line-contact method for the generation of both on- and off-axis, convex and concave, aspherical surfaces of revolution. It employs a self-correcting process and enables the use of loose-abrasive ductile grinding [Appl. Opt.30, 2761–2777 (1991)] and subsequent bowl-feed polishing [Appl. Opt.26, 696–703 (1987); Opt. Eng.31, 1086–1092 (1992); Appl. Opt.33, 89–95 (1994)] for the generation of aspherical surfaces.

Loose abrasive line-contact machining of aspherical optical surfaces of revolution

A new technique, fabrication of aspherical ultraprecise surfaces using a tube, is applied to the generation of conic surfaces of revolution, which also demonstrates that it is possible to generate different kinds of surfaces with the same tube. Surfaces are considered that are generated with the same tube with an elliptical edge but with different off-axis distances and different angles between the tube and the surface. Subsequently it is shown that the generated surface is always a radial section of a conic surface. In addition it is proven that the shape of the generated conic surface is independent of the off-axis distance. With each elliptical tube edge a range of different conic surfaces can be made depending on the angle between tube and surface. The more the tube edge resembles a circle, the larger will be the range of different surfaces. For each tube an angle between the tube and the surface exists at which it generates an on- or off-axis part of a semi-ellipsoid. Finally, an optimization technique is presented for the determination of the best combination of process-determining parameters for the generation of a certain conic surface.

C. J. van der Laan

Papers

Nonpolarizing beam splitter design

Optical monitoring of nonquarterwave stacks.

Equivalent layers : another way to look at them

Loose abrasive line-contact machining of aspherical optical surfaces of revolution

Generation of on-axis and off-axis conic surfaces of revolution by applying a tubular tool.