The objective lens is a single element glass lens with one aspheric replicated surface and one flat surface. The manufacture of the aspheric surface by means of replication is suitable for high quality mass-production.
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.
Impurity doping of bismuth germanium oxide (BGO) has been found to yield large impovements in the photorefractive sensitivity (S1). A 17 fold increase over BGO has been obtained with fully titanium substituted BGO. This improvement is manifested as a simultaneous enhancement of the saturation diffraction efficiency and reduction of the characteristic time constant of the material. We suggest that the former arises from an increase in the effective electrooptic coefficient though the mechanism giving rise to the reduced time constant is as yet unknown.
We present experimental evidence that reflection at the crystal back face due to the large refractive indices of LiNbO3 and LiTaO3 is responsible for strong holographic scattering effects. By these means four-wave interaction phenomena occur. The light is isotropically scattered (equal polarization of incident and scattered wave) in a cone emerging in forward and backward direction from the sample with a cone angle equal to the angle of reflection. We explain the geometry of the patterns produced by the incident reflected and scattered beams and investigate the angular and time dependence of the scattered light.
The investigation of the photorefractive properties in various sillenite crystals (Bil2Si020 - Bil2Ge020) is presented. While in some crystals we find a photorefractive effect governed by electron migration as commonly admitted, we, for the first time, demonstrate that holes play the most important role in the grating recording process in some EGO samples. Thus controlling the charge carrier responsible for the photorefractive effect might lead to an optimisation of the material properties for device design.
The holographic recording properties, in particular response time, of the photorefractive materials GaAs and BSO are experimentally analysed and compared. The results from two Fourier based optical image processing systems are presented.
In this paper we discuss enhancement techniques for use with BSO and Ga As. These techniques include application of electric fields both a.c. and d.c. We consider the effects of crystal orientation and of beam polarisation and present results for two wave mixing in BSO and Ga As. For Ga As results we propose absorption gratings to fully explain our results. We show that the 43m structure of Ga As makes,it ideally suited for a four-wave mixing configuration with positive feedback.
Coherent optical image correlators have been the subject of much research since the early work, performed by Vander Lugt in 1964 . The use of conventional holographic techniques in such systems have proven to be inflexible in that the filter function cannot be updated at a speed comparable to that of the processing speed.
A photorefractive BSO crystal used as a light amplifier within an optical fibre ring cavity forms an optical oscillator whose transverse modes are the modes of the optical fibre. Several intracavity filtering techniques can thence be considered in order to select any particular transverse mode among the others, thus achieving an active generator of pure and isolated optical fibre modes.
In this report we present the up-to-date knowledge acquired in the design and manufacturing of inexpensive, high efficiency, holographic optical elements (HOE) such as focusing lenses, beam-splitters, lens arrays and integrated holographic optics for specific technical applications. One such application is the development and manufacturing of an integrated Laser-Doppler optics which contains several HOE. The holograms are generated in dichromated gelatin layers and exhibit very high diffraction efficiencies (98%). The resulting Laser--Doppler measuring volume is characterized by excellent optical quality and high S/N ratio.
We describe the possibility to use a single holographic optical element (HOE) for coupling between multimode optical fibers at a wavelength close to 1.3 μm. Dichromated gelatin is used as photosensitive medium for recording at 514 nm. Due to the large change of wavelength between recording and reconstruction of the FOE, the geometries of the experimental set up must be carefully choosen. First experimental results are presented, giving coupling losses of the device which is also designed to act as a wavelength division demultiplexer (for 4 different wavelengths centered on 1.3 μm, two consecutive wavelengths being separated by 30 nm).
This paper examines holographic mirrors used in Holographic Night Vision Goggles (HNVG). The characteristics of the DOEs such as diffraction efficiency, spectral bandwidth and homogeneity have been investigated experimentally. These performances have been tested in a geometry which simulates as close as possible the operating conditions of the HNVG. The advantages of this approach are discussed in comparision with the commonly used technique of characterization.
An analytical method for the design of holographic optical elements (HOE) for focussing laser scanners with minimum aberrations and optimum scan line definition is reported. It can be shown analytically, using second order (paraxial) approximation, that a circular motion of the HOE cannot generate a straight line in space without astigmatism of the focal spot. Accepting a slightly curved scan line, the astigmatism can be compensated. Experimental results for HOE with a wavelength shift between recording and reconstruction are demonstrated. The required aspherical wavefronts for the recording are realized with the help of computer generated holograms (CGH).
We consider optimization of phase functions of computer generated holograms used in conjunction with ordinary optical elements to reduce the aberrations of monocromatic optical systems. We develop matrix methods that are useful in first-order design of holographic optical systems, and in analysis and optimization of these systems for narrow laser beams, for which geometrical optics is not applicable. We also report experiences on optimization of phase functions by geometrical ray tracing with the aid of damped least squares algorithm. Design examples contain various telescope systems, in which the holographic secondary elements correct aberrations induced by the glass primary.
The paper deals with the synthesis of band-limited functions that are generated by properly low-pass filtering a sequence of equally-spaced width-modulated unit-height pulses; simply choosing the pulse widths proportional to the corresponding sample values of the band-limited function to be generated, would result in an error. The exact relationship between the pulse widths and the corresponding sample values of the band-limited function to be synthesized, is derived. Error reduction can be achieved by using this relationship to calculate the pulse widths from the required sample values; in principle, a band-limited function can thus be realised to any degree of accuracy. It is shown which amount of error reduction can be obtained, when only a limited number of terms of the exact relationship is taken into account. The application to computer-generated half-tone transparencies is described.
It has been shown that synthetic phase-only filter formed by using different plane wave carriers may provide very high optical efficiency and can produce very sharp correlation peaks in the case of multiobjects correlation recognition. Binarizing the synthetic phase-only filter (SPOF) would make filter making much more easy. But binary synthetic phase-only filter (BSPOF) would produce undesirable noise which mainly consists of convolution-like peaks in the output plane. These noise peaks may sometime rise very high especially when objects are symmetrical. In this paper a random phase mask placed close to the BSPOF in the Fourier plane is used in the correlation system. It can spread the energy of the noise peaks in the output plane. So that, there is no any obvious noise peaks presented, however, at the same time, the sharp correlation-like peaks of SPOF are remained very well. The computer simulation results are given. The comparison of the correlation outputs of BSPOF with that of SPOF is discussed. And 3-D plots of correlation output are presented.
Focal lines of arbitrary position and orientation even parallel to the optical axis may be used in a variety of situations, such as display of 3-D images, contouring of inclined surfaces and holographic optical elements. A synthetic generation using a computer is promising because of the flexibility. Then, the wave propagation has to be simulated. We present a calculation by use of the stationary phase method and show the analogy to the solution of the wave equation. A cube composed of line segments is recorded in a hologram and reconstructed optically. For each line segment, a second line foci occurs in the Fourier plane of the hologram which causes irritation when the image is visually observed. Superposition of a slight random phase variation removes the ambiguity and allows secure accomodation. Intensity variations along the line segment can be introduced by superposition of several distributions which reconstruct the same line segment. A further generalization may be achieved to reconstruct nonstraight focal lines in 3-D.
Multiplexing techniques can be applied in 3D imaging to record the shape of 3D objects on 2D pictures taken from different directions. These pictures may be obtained from still cameras, TV-cameras or medical imaging systems such as computer-tomographs. A simulation of 3D objects by 2D perspective views generated by means of computer graphic methods is possible too. From these data true 3D images can be procreated by hologram synthesizing techniques. In this paper multiplexing techniques for recording of 3D objects and for synthesizing of holograms are discussed. Proposals are given for recording of 3D scenes by large diameter telescope-type imaging systems applying multiple lens cameras. Suggestions are made for an optoelectronic synthesis of still and animated holograms based on photo emulsions and optoelectronic holograms respectively. Two synthesizing methods are described: an optical synthesis utilizing 2D perspective views and a synthesis based on calculating and writing of the interference pattern onto the hologram. The 2D pictures and interference pattern are procreated by optoelectronic light valves. The hologram plate consists of photoemulsions for still holograms. For animated holograms very-high-resolution optoelectronic spatial light modulators are considered. Possible types of light modulators and light valves which can be used for the real-time holographic imaging system are discussed. It is shown that animated holographic 3D images can be obtained, if the optoelectronic light modulators are available.
A system based on multiplex holography has been developed for the display and storage of three-dimensional information. Volume ('stack') multiplex holograms have been produced for viewing on a novel white light display device based on dispersion compensation. The image processing and holographic techniques developed to optimise these results are described. The demonstration of potential applications of the displays for data from medical imaging, analytical techniques such as electron microscopy and scientific data analysis is detailed.
A two-step holographic process is presented where first step is recording of contiguous object slices at correspondingly ordered plate stripes. The second holographic recording is made out of the real pseudoscopic reconstruction after the first hologram. Illumination of the final hologram with a conjugate white light beam produces a rainbow presentation where colors encode the object depth contouring.
Techniques for production of holographic stereograms are described with special attention given to stereograms with computer-generated graphics. Photographic techniques and equipment for recording computer graphic imHLges are discussed. Applications in various fields are reviewed.
We propose an holographic method for the compression or shaping of optical pulses broadened by group velocity dispersion. The hologram is made in a photorefractive material by the interference of the broadened pulse and the corresponding Fourier transform limited pulse. In read-out the compressed pulse is reconstructed by diffraction.
Different computational techniques were used to simulate thermal characteristics of nodal points on substrate chips. Multiple distributed thermal disturbances were investigated through thermal resistance calculations among the substrate surface. The simulated results for multiple heat sources are similar to those experimented.
Holographic optical elements (HOEs)are more and more commonly used in all kind of optical design. When used in interferometry, holographic optics not only make it possible to avoid the use of expensive optical precision components, but allow under certain conditions a "holographic null correction" for all optical aberrations. In OIP, a holographic interferometer was built with the aim of studying transparent media. Convection phenomena in transparent fluida can be observed in real time; when using a complementary pair of lenses, deviations of a copy lens from a master one can be visualized. The interferometer can have a rather large visualization area (almost 100mm x 100mm), and has the possibility to zoom in onto the object. The image may be visualized by means of a CCD-camera. The interferometer operates entirely with HOE-technology, no conventional lens or beamsplitter is used, with exception for the microscope objective to produce a diverging laser beam. Four HOEs in dichromated gelatine are used to realize interferograms in a Mach-Zehnder configuration. The first acts as a holographic beamsplitter to produce a reference and an object beam; the second and the third are diffraction elements which convert the diverging object beam into a collimated one and back into a converging beam. On the last HOE a rest pattern has been recorded. The interference of an "active" object beam with the holographic "reconstructed" one produces the real-time interferogram corrected for optical aberrations of the system. The interferometer operates with an Ar-laser (λ=514nm) at this moment but will be modified to operate with a small built-in HeNe-laser.