H. J. Frankena

Fluid jet polishing of optical surfaces

We present a new finishing process that is capable of locally shaping and polishing optical surfaces of complex shapes. A fluid jet system is used to guide a premixed slurry at pressures less than 6 bars to the optical surface. We used a slurry comprising water and 10% #800 SiC abrasives (21.8 mum) to reduce the surface roughness of a BK7 sample from 350 to 25 nm rms and to vary the shape of a polished sample BK7, maintaining its surface roughness of 1.6 nm rms, thereby proving both the shaping and polishing possibilities of the presented method.

First InP-based reconfigurable integrated add-drop multiplexer

A four-channel reconfigurable integrated add-drop multiplexer on InP-substrate is reported. The device consists of a 5/spl times/5 PHASAR demultiplexer integrated with Mach-Zehnder interferometer electrooptical switches. Total device size is 3/spl times/6 mm/sup 2/. All routing configurations of four wavelengths have been demonstrated. Crosstalk values are better than -20 dB. On-chip loss for the dropped or added signals and for the signals coupled from the input to the output port are lower than 7 and 11 dB, respectively.

Polarization-independent dilated InP-based space switch with low crosstalk

A polarization-independent dilated switch with a low crosstalk level has been realized. In this switch, the crosstalk signal is attenuated by using controllable electrooptical attenuators which do not disturb the input signal. A reverse bias of 20 V on the attenuators reduces the crosstalk value of the dilated switch from -32 dB to -40 dB. The excess loss of the total switch is about 9 dB.

Equivalent layers: another way to look at them

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.

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

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.

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

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.

Investigation of acceleration of a vectorial beam propagation method

Acceleration of a vectorial finite difference beam propagation method is investigated. Several steps, including use of a modified Crank-Nicholson scheme, a decreased initial error, a reduced iteration parameter and a transparent boundary condition, are discussed. The resulting program has a speed fast enough for calculations of intricate structures on a conventional workstation.

Determination of the Optimum Starting Surface for the Generation of Aspherical Surfaces of Revolution

We present a method to obtain the optimum surface shape for use as a starting point for the machining of aspherical surfaces of revolution. Applying this method, the volume that remains to be machined away can be set below an acceptable value. Subsequently, it is shown how this method can be applied for conic surfaces.

Thickness matching in planar multilayer waveguides

A theoretical method is described from which the thickness of an arbitrary layer in a dielectric multilayer stack is determined if all other thicknesses and all refractive indices are given, such that a prescribed effective index for a given mode of the stack is obtained. The same theory can determine the optimal cover thickness of such a stack for prism coupling. Experimental verification shows effective indices that are in agreement with the designed values.

Linear Correction Of The Influence Of Thickness Errors During The Evaporation Process

During the production of dielectric thin film stacks for optical use, small thickness errors are unavoidable. These can be detrimental for the reflectance curve R as a function of the wavelength λ. If the thickness error for a certain layer is known, however, its influence on the reflectance can be reduced by correcting the thicknesses of the following layers. Starting from the matrix of derivatives ∂Rj/∂tk, where Rj is the reflectance of the j-th extremum and tk the thickness of the k-th layer, a method is developed which calculates these corrections during the production process of the stack. Examples will be given, using a quartz crystal monitoring system by which an error is easy detectable. Using this method, the deviations in the reflectance curve can be reduced by a factor of about five. This resulting reduction is strongly dependent on the error in the last layer of the stack for which no compensation is possible.