Electron beam pattern generators are nowadays used extensively for the production of masks and for direct writing on wafers. For obvious reasons electron beam pattern generators are optimized for integrated circuit fabrication. However there is also considerable potential for the use of electron beam lithography in other areas. In this paper recent trends in the development of electron beam pattern generators are described and the problems encountered in the application of electron beam machines in other areas e.g. integrated optics are discussed.
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.
A review of published work in the field of chalcogenide glass optical fibers for mid-infrared is presented. Fabrication processes, optical and mechanical properties are discussed. Present fibers are appropriate for short distance applications. CO power transmission can be considered.
This paper outlines intrinsic absorption and scattering mechanisms in chalcogenide glass fibres and how these combine to determine the waveband over which useful transmission can be achieved. Examples are presented to show how intrinsic losses can be minimised by optimising the glass composition. Extrinsic sources of loss, which include impurities and fibre imperfections, together with some of the techniques used to minimise them, are then described. Particular attention is paid to the loss mechanisms that predominate at important mid-infrared operating wavelengths, and the current best results that have been achieved with various types of chalcogenide fibre are presented.
The optical characteristics of several different chalcogenide bulk glasses and single core fibers were investigated. The spectral transmittance of bulk glasses was measured between 0.8 and 15 μm. A decrease in transmittance of the bulk material at elevated temperatures were shown to occur beyond 8 μm. At 100°C and a wavelength of 10.6 μm the effect was measured to be between 3.5 and 10 dB/m depending on material. Coated fibers were drawn from the bulk material and the fiber attenuation between 9.2 and 11 μm was between 6 and 30 dB/m depending on the material, coating, wavelength and fiber diameter.
The strength characteristics of several different chalcogenide fibers, drawn from commercially available materials were investigated. Both core and core/clad fibers were used in the study. Two measuring techniques were employed (bending and tensile) to measure the strength of these fibers. Tensile testing indicated the core glasses to have a strength between 10-20 kpsi (68-135 MPa). Bend test showed these strengths to be between 20-70 kpsi (135-474 MPa). Cladded fibers displayed an additional tensile strength of 4 kpsi (27 MPa) and additional bending strength of 15-30 kpsi (102-234 MPa).
Chalcogenide-halide /C-H/ glasses for infrared optical fibers were studied, using compositions from the Ge-Se-I, As-Se-I and As-S-I systems, which exhibited good forming ability and thermal stability. By substituting I for Se, As-I or Ge-I bonds appeared, the concentration of As-Se or Ge-Se bonds decreased and intrinsic multiphonon absorption at 10 um was also diminished. The prepared glasses were characterized by lower Tg values; for fiber formation, a new method utilizing pumping glass melts into capillaries has been developed.
Considerable interest has been shown recently in the potential of flexible hollow core waveguides for the transmission of CO2 laser radiation. The theoretical background relevant to the principles of operation will be outlined, together with the possible advantages of such waveguides. Comparisons will be made between transmission characteristics predicted by the theoretical treatments currently available, and those observed experimentally. The materials properties involved in determining the performance of hollow core waveguides will be described and the potential for improving transmission characteristics through choice of waveguide material will be discussed.
Hollow planar optical waveguides have been realized for single mode propagation of IR radiation beams at 10.6 μm. Attenuation of about 0.15 dB/m has been obtained for the first order TE0 mode in metallic waveguides and about 0.3 dB/m for both TE0 and TM1 modes in dielectric coated metallic waveguides (composite structures). Using a flexible structure, TE and TM losses better than 1 dB/m are obtained for curvature radii of about 30 cm.
The problem of transmission of CO2 laser radiation through hollow fibers and waveguides was studied theoretically and confirmed experimentally. The transmission of the laser radiation through metal and metal-dielectric tubes was measured and compared with the theoretical data based on a ray model solution. This makes possible the investigation of the transmission of the CO2 radiation through waveguides when the internal wall is covered with a metal or a metal-dielectric film. It was shown theoretically and proved experimentally that the transmission of the CO2 radiation is possible even through bent waveguides.
Crystalline fibers are considered as the most promising fibers for the region 5÷20 μm. The relation of optical and mechanical characteristics of fibers with parameters of the initial crystals and their extrusion is shown. The mechanisms of optical losses including those induced by ∝ - or UV-radiation are discussed together with the optical damage of fibers, induced by continuous or pulsed radiation of CO2-laser.
Results on the growing of single-crystal sapphire and heavy metal halide fibers from the melt by Stepanov's method (capillar technique) are reported. In order to minimise the optical losses due to surface imperfections single-crystal halide graded-index fibers with the total diameter between 0.2 and 1.2 mm and length up to 7-8 m were grown. The pre-sence of a crystalline cladding allowed to lower the surface scattering losses of graded-index fibers down for 5-10 times in comparison with unclad fibers.
The results on the designing of the first diode laser spectrometers for the middle IR region using crystalline fibers from KRS-5 or KRS-13 are presented. The advantages of the fiber diode laser spectrometers and gas monitors provide the simplification of their constructions and the substantial widening of their applications without the deterioration of spectral resolution 0.005 cm-1.
The characteristics of glasses and fibres based on zirconium fluoride are reviewed. The fundamental limits to attenuation due to intrinsic processes in these materials are surveyed, leading to a predicted minimum loss approaching 0.01 dB/km at the likely operating wavelength of 2.55 μm. Current limitations due to extrinsic scattering and absorption are analysed, showing that most of the excess loss comes from wavelength-independent scattering due to small bubbles, crystallites and other small particles. These extrinsic mechanisms limit the attenuation to around 1dB/km in the best current fibres. Design criteria for single mode fibres are also reviewed, taking into account dispersion and mode field effects to optimise microbending and splicing characteristics.
A new family of fluoride glasses mainly based on InF3 and BaF2 has been optimized in order to increase the resistance against devitrification. These rrulticomponent glasses showing an exceptional transmission from 0.2 μ to 8 μm are potential candidates for the 3-5 μm region either in bulk or fibers. A second new group of I.R. glasses has been discovered in the Te-CI and Te-Br binary systems. These glasses exhibit a large transparency domain lying from 2-13 μm for the Te3Cl2 glass and 2-18 μm for the Te3Br2 glass. This original class of vitreous material shows a good resistance against devitrification, reasonable stability in normal atmosphere and glass temperatures in the 80-90°C range.
Commercial starting materials are presently not pure enough to attain the near-intrinsic attenuation necessary for the use of heavy metal fluoride glass (HMFG) in telecommunication quality optical fibers. The purity requirement provided in the work of Ohishi et al. , and the comprehensive work of France et al.  in which the oxidation state was con-trolled, suggest that cationic impurities must be limited for each element to the levels shown in Table 1. It can be argued that slightly less stringent purities than those shown in Table 1 are adequate, but the purity levels available from one repu-table commercial supplier are far greater than those required for a number of critical elements.
Heavy metal fluoride fibers have attracted considerable attention recently as lightguides for infrared optical devices. Besides the optical loss mechanical performance of the fiber is of major interest. At present fiber strength suffers from surface crystallization prior to or during fiber drawing. We developed an etching method for the preparation of preforms with clean surface. Drawing these preforms under optimized conditions in a dry atmosphere results in fibers with improved strength. So far, mean value of 400 N/mm2 tensile strength have been achieved. Maximum values of 800 N/mm2 measured on etched fibers indicate an even higher strength potential for the material itself.
Applications of infrared transmitting fibers in the field of gas sensing devices are reviewed with particular emphasis to fluorozirconate materials. Promising performance parameters of IR-fiber-optical detection schemes are discussed in comparison to conventional techniques. Fibre requirements regarding geometrical data, spectral attenuation, mechanical as well as environmental durability for future applications are summarized. Currently available fluorozirconate fibers have been experimentally characterized. Methane and carbon dioxid have been remotely measured using IR-fibers coupled to a Fourier spectrometer.
We estimate the performances of future long haul and high bit rate systems based on fluoride glass fibre technology, taking into account non linear effects. It is shown that capacity links of 1000 (Gbit/s)2.km at 2.5 μm can be realized, either with direct or coherent detection, if total attenuation of cabled fibre can be lowered down to 0.03 to 0.05 dB/km. Guidelines for the design of the fibre are given.
The very high bandwidth distance product of monomode silica fibres has given them an almost total monopoly of trunk telecommunications installations over the last 3 years. As this market saturates, attention is being concentrated on lower echelons of the telecoms hierarchy and on other local communications needs often bunched together under the title Local Area Networks. While these newer targets will also appreciate high bandwidth the existing media, e.g., copper twisted pair or coaxial cable are in many situations adequate and would presently be cheaper. To challenge in this area it is therefore necessary to lower costs and to offer alternative advantages than pure bandwidth.
Low attenuation PMMA-core optical fibers, first demonstrated by NTT's laboratory, have become industrial products. The spectral attenuation, transmission characteristics coupled with visible LEDs, high speed signal transmission up to 150 Mbps using an 800 nm LD, and influence of moisture are presented. Advances in applications are reviewed.