In this paper an overview is given of the PCVD process as applied for the large scale production of optical fibres for telecommunication. The specific merits and potentials of the process, such as the profile independent high deposition rate and excellent controllability are discribed. The current state of the art of the process, as it is used in the Eindhoven production unit, is a deposition rate of 1 g/min., a preform size equivalent to 28 km of fibre and a drawing speed of 4 m/s. Fibre characteristics are well within the requirements imposed by the telecommunication market. The PCVD process has also proven to be suited for the production of dispersion flattened singlemode fibres and high NA graded index fibres for short distance applications. For both fibre types the high refractive index differences obtained with fluorine doping are exploited. Depending upon the market demands all fibre types can be manufactured at the same productivity. Some trends are given towards further increase of productivity and reduction of fibre costs.

Gas lasers have shown to be capable of delivering tens of terrawatt aspeak power or tens of kilowatt as average power. The efficiencies of most high power gas lasers are relatively high compared with other types of lasers. For instance molecular lasers, oscillating on low lying vibrational levels, and excimer lasers may have intrinsic efficiencies above 10%.The wavelengths of these gas lasers cover the range from the far infrared to the ultra-violet region, say from 12000 to 193 nm. The most important properties are the scalability, optical homogeneity of the excited medium, and the relatively low price per watt of output power. The disadvantages may be the large size of the systems and the relatively narrow line width with limited tunability compared with solid state systems producing the same peak power.

An optical system with mirror, refractive or diffractive surfaces is characterized by a sequence of surfaces in space, - at a diffractive surface plus a characterization of the grating lines on the surface -. The mathematical model for the sequence of surfaces is a sequence of coordinate systems, with a surface being defined in each coordinate system.

Design a modern optical system requires the integration of expertise in widely different fields such as, lens design, thermal and mechanical analysis, sensors, etc. Each one of these introduces a large number of loosely constrained parameters which have to be properly chosen for the optimization of system design. In practice, an exhaustive search of all the possible alternatives is an operational impossibility and various 'short-cuts' to narrow the search are used. Commonly, experts in different fields are called upon to pool their resources to 'truncate-the-search-tree' and arrive at an optimum design. This traditional method of designing optical systems requires a significant commitment of resources and represents major bottleneck in implementing advanced optical systems. We have studied this problem in the context of AI with the hope of expediting this design process. It should, in principle, be possible to put both the optical heuristics (an expert's knowledge and experience) and the deep knowledge (fundamentals of optical system design, NASTRAN, CODE V, etc.) in a knowledge base from which rapid inferences can be drawn. To fully exploit a knowledge base one needs to create a suitable environment. A possible architecture for such an environment for optical system design is discussed here.

Interferences between the different propagation modes in an optical fiber called the modal noise, is already a well-known problem. Intensity fluctuations severely affect the perforMance in optical communication systems ; on the other hand, they can be used for sensors design. Pigtailed sources are often used in order to characterize optical fibers as well as in some optical devices. These fluctuations are caused by the instability of the source and by the presence of the pigtail. More particularly, we studied the fluctuations of the available energy and its repartition on the end-face of a graded index pigtail for different types of sources (coherent or incoherent), for various light wavelengths and constraints. We used a near field method and the convolution of the end pigtail image by an area of the same size. When the fiber has random vibrations in incoherent light, experimental values can be compared to the calculated values for the coupled energy and signal to noise ratio (S/B). In incoherent light, when fiber is motionless and in coherent light, an experimental study has been carried out for several wavelengths with the same set-up. In this paper, we give the results concerning the signal to noise ratio S/B according to the strain. We also estimate the speckle mean diameter with experimental values for several wavelengths. We characterized the modal noise influence in measurements for particular optical applications. The results of our experiments show the limits of the use of such sources in optical devices.

The use of optical fibres to guide light into spectroscopic instruments that utilize photo diode array detectors has been growing rapidly. However, as applications grow to include process control and remote monitoring, the need for a very compact, portable instrument has led to the need for a single component to accomodate both focussing and dispersive functions. In this paper we describe how optical fibres should be interfaced to an aberration corrected holographic diffraction grating system that disperses the spectra of reference and sample material onto a twin (or single) array series of photo diodes to permit dual beam spectroscopy.

The concept of using a parametric representation of wavelength rather than actual wavelength in a polynomial relating wavelength to refractive index is applied to a wide range of IR materials. Excellent agreement between calculated and published measurements of index is found. With such data it is possible to design lenses which are well-corrected with wavelength and temperature.

At more than 10 million US dollars, the HST primary mirror was a very costly optical surface. In contrast to conventional glass and ceramic mirror substrate, the Space-Forschungsgruppe have made ground based research in subject of carbon fibre composite technologies since eight years. ln the last two years matrix materials from Ciba-Geigy promise to take place instead of large optical areas with a very high rade of mass and a long term of production.

A space-borne Very High Resolution Radiometer (VHRR) telescope optics has been analysed for probable errors i.e., tilt, decentration and axial separaton, caused by fabrication and mounting. The degradation due to these errors in the system performance, characterised by the MTF (Modulation Transfer Function), has also been discussed. This paper briefly describes the design, indicating the performance of system and the tolerances associated with the design if the theoretical performance level is to be achieved; practical realisability of accuracies is also discussed. The MTF fall has been tabulated for different configuration of errors.

A null lens is described to test the hyperboloid primary mirror of Very High Resolution Radiometer (VHRR) telescope. It can be used to test a variety of optical systems or components. Conics and higher order aspheric mirrors can be tested with the same null lens if it can zoom the amount of spherical aberration introduced. It is a triplet lens with all spherical surfaces. The output F/No. and image position remains fixed during the zoom. The performance of this device has been analysed for hyperboloid mirror of diameter of 208 mm which works at F/2.0. The performance has been characterised by RMS wave front deformations. Test set up has been analysed for centered and decentered tolerances, irregularity in surfaces, single surface decenter and displacements and a group decentering tolerances. Final tolerance parameters for null lens have been tabulated.

The facet tracking principle for scanning polygons is described. A comparison using the optical invariant as a figure of merit shows that facet tracking systems are about four times as efficient as conventional scanning systems. The influence of different parameters such as polygon diameter and number of facets is discussed. It is possible to predict the final system performance by just considering the design parameters of the polygon. Finally, a new infrared scanner recently introduced on the market,the Thermovision 870, is described. Different design considerations are accounted for. The scanner is of the facet tracking type. It has built-in temperature references and uses a TE-cooled single element SPRITE detector as sensor. The optical system is essentially a mirror design with three aspheres. All mirrors are diamond turned and a special design goal has been to achieve close opto-mechanical integration.

A new, easy - to - operate schlieren system was designed and built at the Technical University, Budapest. The apparatus is mainly applicable for heat transfer investigations where high sensitivity is required and, in times, when large objects are studied on site. The mobile schlieren system consists of two mechanically independent units, an adjustable spherical mirror and the transmitter - receiver unit, which can be brought optically aligned by a laser aiming device.

We desribe a self-aligning scheme for a Point Diffraction Interferometer (PDI) to be utilized in connection with strongly aberrated wavefronts, like those customarily encountered in the analysis of stressed fluids. In spite of the fact that the focal plane intensity di-stribution is speckle type, a peak chaser maintains a bright speckle on top of the PDI pinhole, so that enough power is available in the reference beam and fringe visibility remains quite acceptable. We will show typical results obtained for thermal stresses in air and liquid mixtures.

The optical imaging properties of the Surface Photodeposition (SP) effect is described. The investigation shows that the process can be used as an imaging and recording method, realizable with various light sources such as lasers, high pressure discharge illuminators or conventional incandescent white light sources. Since the process is readily controllable by the dose of radiation delivered to the photosystem, accurate film thicknesses can be obtained. This facilitates the preparation of various optical devices such as coatings, filters, phase retardation plates, holograms, gratings and optical patterns of recorded data. The resolution and contrast were tested by projection and mask contact methods. In both methods the linewidth resolution obtained for the recorded images was about 1-2 (μm). This figure, however, was the basic resolution of the optical imaging system and the original mask. Theoretical arguments lead us to assume that the effect can provide even better resolution due to its special feature as a direct one step additive photographic process.

A universal algorithmic method for directly detectable incorrect words decoding is described and diseussed. The presented model of decoder allows for the minimization of transmission error extension in decoding process subject to the line code and statistics of input data. Selected line codes are examined to support necessary numerical examples for the presented theory.

The shape of an aspherical surface can optically be measured by focusing a small light spot on its surface. Scanning in a line across the surface and going through the apex of the surface, one can interferometrically detect its shape. This paper describes the performance and limitations of such a scanning-spot interferometer. Special attention is paid to the ability to measure very steep aspherical surfaces.

This paper will describe a first order analytical technique for evaluating the Strehl ratio of a system composed of various optical components which use multilayer optical thin films. The basic elements of the model are to provide budgeting criteria that will permit the maximum energy in the central lobe of a far field distribution. Budgeting components will consist of figure error on the component, thermal distortion for transient and steady-state, pressure ripple for cooled substrates, and energy loss due to scatter and absorption in the coatings and the substrate.

This paper will describe a first order analytical technique for evaluating the Strehl ratio of a system composed of various optical components which use rugate optical thin films. The basic elements of the model are to provide budgeting criteria that will permit the maximum energy in the central lobe of a far field distribution. Budgeting components will consist of figure error on the component, thermal distortion for transient and steady-state, pressure ripple for cooled substrates, and energy loss due to scatter and absorption in the coatings and the substrate.

For the development of optical coatings (as high power laser mirrors) of higher and higher performances, it is necessary to use more and more powerful characterization means for optical thin films. The highly sensitive and simple technique of Photothermal Deflection Spectroscopy (P.D.S.) gives the absorption losses down to ultra low level. We show that this method can be applied to transparent single layers. Techniques used for photothermal signal calibration are presented. Photothermal signal versus wavelength for absorbing layers (extinction coefficients from some 10-3) is compared with absorption spectra obtained by classical spectrophotometry. Experimental results are given which show the sensi-tivity of the method. Extinction coefficients that do not exceed some 10-7 can be measured. P.D.S. can also give absorption losses for multilayer coatings. Some results on narrow band filters are presented.

The use of Moire fringes for the measurement of mass transfer is reported. In this application, changes in surface profile on a naphthalene plate due to mass transfer take place. The profile changes are measured using Moire fringes and the results are compared with an existing measuring device which uses a height sensitive stylus. Fringe patterns are illustrated on both flat and cylindrical surfaces.

An optical speckle shearing technique has been used to produce high quality displacement contours originating from out-of-plane displacement in plates of PMMA. An analysis of stress shows good agreement between the experimental and theoretical values. An electronic speckle shearing technique is being developed to provide on-line, 'real time' stress analysis.

In order to obtain the views of UK industry on the use of available standards relating to optical quality surface inspection leading companies, involved in the manufacture and use of optical surfaces, were approached. From their replies to a questionnaire it became clear that improvements were required in most areas.

We investigate how aspherical optical surfaces engraved in photoresist coatings avail against static wavefront aberrations up to 3 μ. The spherical aberration of a singlet lens is corrected for. The image given by a cassegrainian telescope of 143 mm diameter with a peak to valley 0,62 µ wavefront error and 7" slopes is improved by a 16 mm diameter intrafocal phase equalizer corrector plate. We then discuss extrapolations of our laboratory experiments.