Glass for optical waveguides or the like

Details Glass for optical waveguides or the like Glass for optical waveguides or the like

2000-07-11

2002-12-03

Ngo, Hung N. (Department: 2874)

Optical waveguides

Having particular optical characteristic modifying chemical...

Reexamination Certificate

active

06490399

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to glass for optical waveguides or the like.
RELATED TECHNOLOGY
Optical waveguides are being increasingly used as transmission lines in telecommunications networks. In addition, optical waveguides are finding increasing use in medicine, sensor technology and for the transmission of high optical powers for the machining of materials. For telecommunications, use appears to be made predominantly of single-mode fibers made of silica glass with a core that is approximately 10 &mgr;m in diameter and a cladding with a lower refractive index and a diameter of 125 &mgr;m. Some optical waveguides are made of silica glass and are characterized by high transmission capacity and low attenuation. At the minimum attenuation given a wavelength of 1.57 &mgr;m, values of approx. 0.20 dB/km are obtained. In 1986, the reference by G. Tanaka et al., “Characteristics of Pure Silica Core Single Mode Optical Fiber”, Sumitomo Electric Technical Review 26(1987)43, refers to an optimum value of 0.15 dB/km.
The reference Patent Abstracts of Japan: JP-A-60090845, purportedly describes a gas rinsing with helium and deuterium during the vitrification of porous SiO
2
(silica glass) and GeO
2
-doped silica glass is described. The helium reduces the structure defects in the silica glass during this process and thereupon completely passes off. Deuterium is a hydrogen isotope and expels hydrogen atoms from the material, so that OD-groups instead of OH-groups form in the preform. OH-groups, which can be deemed as impurity in concentrations of less than 0.0001% in silica glass, cause absorption bands in the infrared wavelength range. When hydrogen is replaced by deuterium, the absorption bands shift to longer wavelengths. In this manner, ranges which are important, for example, for optical telecommunications and have additional losses due to the OH absorption, are then free from additional absorption. This technology is costly and has not gained acceptance in practice, because meanwhile, the fiber manufacturers reduce the OH concentration in the silica glass to the extent that the OH absorption virtually plays no role any longer.
In addition, in the reference Database, Chemical Abstracts: Accession No. 81:44002, a silica glass doped with
29
Si is apparently described generally.
The attenuation &agr; of single-mode fibers above a wavelength of 1 &mgr;m is composed of three components. These are the scattering &agr;
s
, the OH absorption &agr;
OH
and the infrared absorption &agr;
IR
. The OH absorption is due to the inclusion of a small concentration of OH ions in the silica glass. It is very highly dependent on the wavelength and manifests itself in the spectral attenuation curve by an absorption band at approximately 1.4 &mgr;m. In the wavelength range of importance for optical telecommunications between 1.5 and 1.7 &mgr;m, the attenuation is virtually determined only by the scattering losses and the infrared absorption. The scattering losses are due essentially to Rayleigh scattering and decrease with increasing wavelength &lgr; with 1/&lgr;
4
. The infrared absorption starts at around 1.5 &mgr;m and rises steeply with increasing wavelength. The minimum attenuation is at 1.57 &mgr;m, because this is where the decrease of the scattering losses and the increase of the infrared absorption are of identical magnitude.
FIG. 1
shows the described situation with reference to the spectral attenuation curve of a single-mode fiber for the wavelength range between 1.1 and 1.7 &mgr;m. The OH absorption band at 1.4 &mgr;m is clearly evident. At its minimum at 1.57 &mgr;m, this fiber has an attenuation of 0.17 dB/km. The characteristic curve of the scattering losses without OH and infrared absorption is shown by the broken line. OH absorption plays virtually no role for the wavelengths above 1.5 &mgr;m. Starting from around 1.6 &mgr;m, there is then a steep rise in infrared absorption. The reference by M. E. Lines et al., “Calcium Aluminate Glasses As Potential Ultralow-Loss Optical Materials At 1.5-1.9 &mgr;m”, Journal of Non-Crystalline Solids 107(1989)251, purportedly describes that infrared absorption is calculated according to the formula &agr;
IR
=A·e
−a/1
. In this context, A=6·10′ dB/km and a=48 &mgr;m is given for silica glass. An infrared absorption of 0.02 dB/km and 0.33 dB/km is calculated therefrom for 1.55 &mgr;m and 1.7 &mgr;m, respectively. The infrared absorption in glasses is caused by the tails of extremely strong vibration bands (phonons) in the long-wave infrared range, as purportedly described by the reference by S. Kobayashi et al., “Characteristics of Optical Fibers in Infrared Wavelength Region”, Review of Electrical Communications Laboratories 26,3-4(1978)453. The dominant absorption band of pure silica glass is at 9.1 &mgr;m and has, at its maximum, an attenuation of 10
10
dB/km. The spectral position and width of the absorption band are determined by the masses of the atoms involved, i.e., in the case of silica glass, by the masses of silicon and oxygen. The basic physical principles of this are purportedly presented in detail in the reference by T. Ruf et. al.: “Von Federn und Massen: Physik isotopenreiner Halbleiter” (“Of Springs and Masses the Physics of Isotropically Pure Semiconductors”), Physikalische Blätter 52,11(1996)1115. For pure and doped silica glass, which to date has been employed for the manufacture of optical waveguides, use is made of natural isotope mixtures of the elements involved, i.e., silicon and oxygen in the case of pure silica glass. Germanium and fluorine are mainly used as dopants.
SUMMARY OF THE INVENTION
An object of the present invention is to provide glass with reduced infrared absorption, the glass being especially suitable for optical waveguides with significantly reduced, minimal attenuation coefficients and for effective manufacture.
The present invention provides an optical waveguide comprising a glass material including pure or doped silica glass, the pure or doped silica glass including atoms of at least one element, respective atoms of a first element of the at least one element having a mass number distribution more heavily weighted toward higher mass numbers than a natural mass number distribution of isotopes of the first element.
Owing to the fact that glass is made up of atoms with mass numbers higher than the mass numbers of the natural isotope distribution, the increased mass numbers (atomic masses) result in a shift of the absorption bands toward longer wavelengths and in a reduction of the line width. These two effects mean that the start of infrared absorption is shifted toward longer wavelengths, with the result that there is a considerably broader spectrum of application for optical waveguides or the like made from such glasses. The costs of the optical waveguides account for only a small portion of the total costs, especially in the case of elaborately manufactured submarine, or undersea, cables. Owing to the reduced attenuation of the optical waveguides according to the invention, it is thus possible to economize on or entirely dispense with repeaters/amplifiers, the result being that, in many cases, despite increased fiber costs, there are, overall, considerable cost savings with improved transmission quality in the construction of submarine cable links or for trunk cables over land.


REFERENCES:
patent: 3779628 (1973-12-01), Kapron et al.
patent: 4188089 (1980-02-01), Gliemeroth et al.
patent: 4988163 (1991-01-01), Cohen et al.
patent: 5491767 (1996-02-01), Mcpherson et al.
patent: 0 068 388 (1983-01-01), None
patent: 60 51625 (1985-03-01), None
Mütze, ABC Der Optik, Verlag Werner Dausien, Hanau, I.Aufl., 1961, S. 412.*
Kobayashi et al, “Characteristics of Optical Fibers in Infrared Wavelength Region”, Review of Electrical Communications Laboratories 26,3-4(1978)453.*

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