Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – Process of manufacturing optical fibers – waveguides – or...
Reexamination Certificate
1996-12-23
2001-04-24
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
Process of manufacturing optical fibers, waveguides, or...
C065S424000, C065S430000
Reexamination Certificate
active
06220059
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical component for the transmission of high-energy ultraviolet radiation, which has a transmission region of synthetically manufactured quartz glass, in which hydrogen and/or deuterium is contained in a concentration of at least 5×10
19
molecules per cubic centimeter, and which is encased at least partially in a first blocking layer imperious to hydrogen or one which impedes the diffusion of hydrogen.
Such a component is disclosed in DE-C 1 40 34 059. The optical component described therein is in the form of a fiber with a core of synthetic quartz glass and a jacket enveloping the core which has a lower index of refraction than the core. The core glass of the generic component is charged with hydrogen in a concentration of at least 1×10
19
molecules per cm
3
and has a hydroxyl ion concentration of 600 ppm. To prevent hydrogen loss by diffusion the fiber is encased in a diffusion blocking layer of graphite with a thickness of 0.2 &mgr;m. A tight graphite coating can effectively prevent hydrogen loss, so that the mechanical and optical properties of the fiber remain preserved over a long period of time; the application of such a coating is, however, relatively expensive.
SUMMARY OF THE INVENTION
The present invention, therefore, is addressed to the problem of producing a component for the transmission of high-energy UV light in which the mechanical and optical properties remain preserved over a long period of time in practical use, and which at the same time will be easy to manufacture at low cost.
The invention furthermore relates to a method of producing an optical component for the transmission of high-energy UV light by preparing an optical fiber of synthetic quartz glass or of doped synthetic quartz glass, which is provided with a transmission region for the transmission of high-energy UV light, and charging the transmission region with hydrogen and/or with deuterium.
Such a method is disclosed in JP A 6-56457. In the method described therein, an optical fiber is treated in an atmosphere containing hydrogen at a temperature ranging between 1000° C. and 2000° C. It has been found, however, that with this method high hydrogen or deuterium concentrations of at least 5×10
19
molecules/cm
3
cannot be reached.
The invention is thus addressed to the problem of devising a method by which high hydrogen or deuterium concentrations can be achieved in the transmission region of the optical component.
The invention furthermore relates to a special manner of using an optical component for the transmission of high-energy UV light, wherein the component has a transmission region of synthetically made quartz glass in which hydrogen and/or deuterium are contained in a concentration of at least 5×10
19
molecules/cm
3
.
It is known, from European patent application EP-Al 0 401 845 to use optical components, such as lenses, prisms, filters or windows for the transmission of high-energy ultraviolet radiation in the wavelength range below 360 nm. The optical components proposed for the purpose consist of high-purity, synthetic quartz glass with a hydrogen concentration in the range from 1×10
16
molecules/cm
3
to 1×10
20
molecules/cm
3
.
The optical power and energy densities that can be transmitted by means of optical components are limited by material-specific destruction thresholds above which the optical properties of the transmission media are changed irreversibly. It has been found that hydrogen is able to prevent or heal such radiation damage in quartz glass. The energy densities of the UV light transmitted according to EP-Al 0 401 845 are, for example, around 0.1 J/cm
2
per pulse (in the case of radiation of a wavelength of 193 nm) or about 0.4 J/cm
2
per pulse (in the case of radiation of a wavelength of 248 nm). The quartz glass was found to have maximum stability under radiation at a hydrogen charge of approximately 1×10
18
to 1×10
19
molecules/cm
3
, depending on the wavelength of the radiation. At higher hydrogen concentrations the stability under radiation was observed to be poorer.
The present invention is therefore also addressed to the problem of devising a method of application optimized for the transmission of high-energy UV light.
With regard to the optical component, the problem described above is solved by the invention by the fact that the blocking layer consists of quartz glass.
A blocking layer of quartz glass is especially easy to produce and is optically transparent throughout the UV wavelength range down to wavelengths of approximately 180 nm. The blocking layer can be made of a quartz glass with a lower refractive index than the quartz glass of the transmission region, and therefore it can contribute to carrying light in the transmission region. By means of the blocking layer the hydrogen concentration in the transmission region can be kept at a high level.
The transmission region is to be understood to mean that region of the component in which the UV light produces the highest defect rates due to its transmission. This is, for example, the light-carrying core in a fiber; in the case of a lens it is especially the entry and exit surfaces for the radiation.
With regard to stability of the component under radiation, hydrogen and deuterium are equally effective. If in connection with the charging of quartz glass the term “hydrogen” is used it is to be understood here and hereinafter to mean hydrogen and/or deuterium unless otherwise expressly stated.
The charge of hydrogen or deuterium is determined by spectroscopy. For the hydrogen charge a basic vibration used is 2.42 &mgr;m, and for the deuterium charge the basic vibration used is 3.58 &mgr;m. To arrive at quantitative figures, a calibration specimen with a known hydrogen or deuterium charge is measured at these wavelengths and the result is used for comparison with the corresponding measurement made in the unknown hydrogen or deuterium concentration.
The component can be encased completely or partially with the blocking layer. In some applications it is important that the functional surfaces be provided with the blocking layer. The term, “functional surfaces,” is to be understood to mean those surfaces of the transmission region in which the UV light enters the component or exits from the component or which contribute to the guidance of the UV light, such as for example the mantle glass enveloping the core of a fiber optic. The optical components are, for example, fibers, lenses, prisms, windows, masking plates or filters.
A component has proven to be especially appropriate in which the thickness of the first blocking layer is between 5% and 50%, preferably 20%, of the total outside dimension of the transmission region and the blocking layer. This prevents the loss of hydrogen from the transmission region by diffusion. The thicker the first blocking layer is made, the more effective is the prevention of such hydrogen loss from the transmission region. There is no definite maximum layer thickness; it is determined primarily by economic considerations.
For example, in the case of a component in the form of a fiber optic, the thickness of the first blocking layer will be the thickness of the mantle glass enveloping the fiber core, while the term, “total outside dimension of the carrier core and blocking layer” in that case, means the outside diameter of the mantle glass. The core of the optical fiber is in that case the transmission region. As the thickness of the blocking layer increases the diffusion of hydrogen out of the fiber is increasingly impeded, but this positive effect in the case of blocking layer thicknesses above the stated maximum limit is counteracted by the relative increase of the cross-sectional area of the fiber at the expense of the core area carrying the UV light.
Advantageously, a blocking layer enveloping the first blocking layer is provided, containing aluminum, chromium, nickel, lead, silver, gold, graphite, a carbide, nitride or oxynitride, especially silicon oxynitride. By
Grzesik Ulrich
Hillrichs Georg
Klein Karl-Friedrich
Yamagata Shigeru
Heraeus Quarzglas GmbH
Hoffmann John
Tiajoloff Andrew L.
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