Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2002-06-17
2003-07-22
Bruce, David V. (Department: 2882)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S144000
Reexamination Certificate
active
06597850
ABSTRACT:
The present invention relates to an optical fiber including an intermetallic compound to absorb hydrogen. The present invention also relates to an optical fiber cable including such an intermetallic compound for absorbing hydrogen.
An optical fiber itself comprises a light-guiding portion made of optionally-doped silica, and it is covered as a general rule by a primary covering and optionally by a secondary covering, generally made of polymer, in order to protect it from its environment. Such a covered fiber is usually intended for inclusion in a data transmission cable. An optical fiber cable used for transmitting data is a cable comprising at least one optical fiber included in a housing, which housing may be made in part out of metal or of plastics material, said cable possibly also having reinforcing components to provide traction strength or other metal components such as armoring or coverings.
The problem of attenuation in optical signal transmission due to hydrogen being absorbed into the silica lattice of optical fibers is known. Thus, U.S. Pat. No. 4,718,747, for example, proposes a solution which consists in introducing an element or an alloy of elements or an intermetallic compound of elements from groups III, IV, V, and VIII of the periodic table in an optical fiber structure or an optical fiber cable. Said elements are preferably lanthanides for group III, titanium, zirconium, and hafnium for group IV, vanadium, niobium, and tantalum for group V, and palladium for group VIII, and in still more preferred manner, these elements are lanthanum, zirconium, hafnium, vanadium, niobium, tantalum, or palladium. Palladium is the element that is in most widespread use in practice.
Unfortunately, such a solution implies using metals which are very expensive, for example the best known of them is palladium (Pd). Furthermore, the compounds obtained from groups III, IV, and V are easily polluted by other gases (such as carbon dioxide CO
2
, carbon monoxide CO, or oxygen O
2
) and can thus turn out to react very poorly with hydrogen once they have been polluted. Consequently, they are difficult to use, particularly industrially, since precautions need to be taken to ensure that they are conserved under an inert atmosphere, . . . . Finally, compounds based on elements from column VIII of the periodic table generally present high plateau pressures and form unstable hydrides with hydrogen. A demand has therefore appeared for compounds that provide better performance in terms of hydrogen absorption.
The intermetallic compound for absorbing hydrogen in accordance with the invention seeks to mitigate the drawbacks of prior art solutions, and in particular to enable hydrogen to be absorbed within optical fibers by forming stable hydrides of low plateau pressure, and thus greater capacity to reduce the presence of hydrogen within optical fiber cables.
The invention thus provides an optical fiber comprising a light-guiding portion and a peripheral portion around its light-guiding portion, the peripheral portion being constituted by at least one protective covering, the optical fiber including, in a covering outside its light-guiding portion, at least one crystalline intermetallic compound made up of at least two metals, the compound having a plateau pressure during hydride formation that is less than equal to 5×10
−2
atmospheres (atm) (where 1 atm=1.013×10
5
pascals (Pa)) measured by a PCT (pressure composition temperature) method and of the form AB
x
M
y
, where:
A is constituted by at least one element from columns IIa, IIIb, or IVb of the periodic classification of the elements (CAS version);
B is constituted by at least one element from columns Vb, VIII, or IIIa of the periodic classification of the elements (CAS version);
M contains at least one element from columns VIb, VIIb, Ib, or IIb of the periodic classification of the elements (CAS version);
with:
0≦x≦10;
0≦y≦3 if A contains elements from column IIa only; and
0.2≦y≦3 if A contains at least one element from columns IIIb or IVb.
Said crystalline intermetallic compound present in a covering outside the light-guiding portion of the fiber can be incorporated in the optical fiber in various ways, for example by being incorporated in at least one covering of said fiber.
The invention also provides an optical fiber cable having at least one optical fiber, the cable including at least one crystalline intermetallic compound formed by at least two metals, having a plateau pressure during hydride formation that is less than or equal to 5×10
−2
atm measured at 30° C. by a PCT method, the compound being of the form AB
x
M
y
, where:
A is constituted by at least one element from columns IIa, IIIb, or IVb of the periodic classification of the elements (CAS version);
B is constituted by at least one element from columns Vb, VIII, or IIIa of the periodic classification of the elements (CAS version);
M contains at least one element from columns VIb, VIIb, Ib, or IIb of the periodic classification of the elements (CAS version);
with:
0≦x≦10;
0≦y≦3 if A contains elements from column IIa only; and
0.2≦y≦3 if A contains at least one element from columns IIIb or IVb.
In an embodiment of the invention, said crystalline intermetallic compound, whether present in an optical fiber or in an optical fiber cable is coated at least in part by a deposit of metal having the effect of protecting said intermetallic compound from pollution by a gas different from hydrogen such as oxygen O
2
, carbon monoxide CO, or carbon dioxide CO
2
, for example, and where said deposit nevertheless enables hydrogen to diffuse to the intermetallic compound. Such a metal deposit can be a deposit of nickel (Ni) or of copper (Cu).
Said crystalline intermetallic compound can be incorporated in the optical fiber cable in various ways, for example in a matrix, such as a DSM 3471-2-102 covering, in a polymer compound such as a Vestodur 3000 polybutylene terephthalate for the housing tube when said tube is made of polymer material, in a filler gel such as a Huber LA444 cable gel, or in any other manner available to the person skilled in the art.
Advantageously, such a crystalline intermetallic compound presents a plateau pressure which fixes the partial pressure of residual hydrogen in the cable at a very low level, less than or equal to 5×10
−2
atm so that attenuation is very low. One of the advantages of the crystalline intermetallic compound used in accordance with the invention in an optical fiber or in an optical fiber cable is that the equilibrium pressure plateau is preferably as flat as possible so as to maintain a performance level that is as constant as possible. Finally, another advantage of said crystalline intermetallic compound is that its absorption capacity is preferably as high as possible so as to maximize the lifetime of the optical fiber cable. This characteristic is generally expressed in terms of H/M, H/ABxMy, or as a percentage by weight.
Various examples of crystalline intermetallic compounds suitable for use in the invention in an optical fiber or an in optical fiber cable are given below.
A first example of a crystalline intermetallic compound usable in the invention is an alloy of the AB
5
type, optionally at least partially, i.e. partially or totally, substituted by M. In the family of AB
5
type alloys, the best known is LaNi
5
which has a plateau pressure of 1.7 atm at 250° C., which makes this compound unsuitable for the present invention. Substituting the Ni with Cr (column VIb) makes it possible to lower the plateau pressure to 0.04 atm for the compound LaNi
4
Cr when characterized at the same temperature; the resulting intermetallic compound thus comes within the invention. Substituting the Ni with Mn (column VIIb) makes it possible to lower the plateau pressure to 0.02 atm for the compound LaNi
4
Mn at 20° C.; the resulting crystalline intermetallic compound thus comes within the invention.
A second example of a crystalline intermetallic compound suitable for u
Andrieu Xavier
Decaumont Anne
Knosp Bernard
Alcatel
Bruce David V.
Song Hoon K.
Sughrue & Mion, PLLC
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