Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
1999-08-01
2002-01-08
Ben, Loha (Department: 2873)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S141000, C359S342000, C436S074000, C549S348000, C549S352000, C534S015000
Reexamination Certificate
active
06337944
ABSTRACT:
FIELD OF INVENTION
The invention relates to an optical waveguide doped with a lanthanide ion-sensitizer complex. Optical waveguides doped with lanthanide ions are known from EP-A2-0,437,935, which discloses an optical waveguide composed of an Er
3+
doped fiber. The erbium ions are excited with the aid of a laser, giving a fiber containing a large number of Er
3+
ions excited to such an extent that population inversion occurs, i.e. that more Er
3+
ions are in the excited state than in the ground state. When optical beams (photons) having the same wavelength as the emission wavelength of the excited Er
3+
ions traverse the fiber, they effect the transition of the ions from the excited state to a lower energy level with transmission of light. This light has the same wavelength and phase as the photons traversing the fiber. Such a process is called stimulated emission. In this way the optical fiber acts as waveguide of the light beams.
DESCRIPTION RELATIVE TO THE PRIOR ART
The optical waveguide, as specified in EP-A2-0,437,935, is a glass fiber. For several years efforts have been made to replace optical glass fibers with optical polymeric fibers. Optical polymeric fibers have several advantages over optical glass fibers. They can be made by less complicated spinning processes, easily cut to the required size, and attached to receiving and transmitting devices. Also, they are lighter and more flexible than glass fibers. A further advantage is that the shape of the optical polymeric material is not restricted to fibers. The polymeric material can also be shaped into so-called planar waveguides. In the remainder of this description the term “optical waveguide” refers to both fibers and planar waveguides.
So far, it has not proved possible to replace lanthanide-doped optical waveguides with optical waveguides of polymeric material. This is because polymeric waveguides cannot be doped with lanthanide metals. In particular, lanthanide ions used for amplification in the telecommunication transmission windows in the near-IR are very sensitive to radiationless deactivation, which counteracts their sensitivity as optical waveguides. The deactivation is brought about by high-energy vibrations near the lanthanide ion. Most effective are O—H, N—H, and C—H vibrational modes. The risk of co-doping with water is a major problem of organic lanthanide complexes, because trivalent lanthanide ions are extremely hygroscopic. In consequence, when lanthanide ions are doped, crystallization water which is present in the lanthanide salt is also introduced into the waveguide. Alternatively, lanthanide ions already present in the waveguide may interact with water or other OH-containing impurities. Water and other OH-containing impurities quench the excited state of the trivalent lanthanide ions. So, unless further steps are taken, a lanthanide-doped optical polymeric waveguide will not show the above-indicated amplification, or not show it in sufficient degree. Furthermore, light is absorbed by OH-groups to such an extent that polymeric optical waveguides, in which OH-impurities are present, will display optical attenuation. Doping of Er
3+
ions in glass fibers ordinarily is carried out using Er
2
O
3
. This compound, however, cannot be used in polymeric optical waveguides since it fails to dissolve in polymeric material. When glass fibers contain water or OH-containing impurities, these can easily be removed by heating the fibers and drying them out. However, this is an unfortunate solution to the problem where polymeric optical waveguides are concerned, as they will usually decompose under such treatment.
OBJECT OF THE INVENTION
The present invention has for its object to obviate these drawbacks and provide a functional lanthanide-doped optical waveguide in which a polymeric waveguide is used as optical material. Hence, the invention consists in that the polymeric waveguide comprises a lanthanide ion-sensitizer complex, wherein the sensitizer absorbs in the 400-1200 nm region, and preferably in the 600-1000 nm region.
The term “complex” in this connection refers to a compound in which the lanthanide ion is encapsulated by a host molecule. If a complex is provided in which trivalent lanthanide is fully encapsulated, the lanthanide ions are not, or at any rate less, in a position to interact with water or other OH-containing impurities. Moreover, it appears that any water present when such a complex is formed is stripped off the lanthanide. A further advantage of such a lanthanide complex is that it dissolves or mixes with the polymeric material far more readily than lanthanide salts or lanthanide oxides do. This is because the host molecule comprises organic material, just as the polymeric waveguides do. Hence, it is possible for the lanthanide to be incorporated into a polymeric optical fiber in a permanently anhydrous state in the form of a complex, thus maintaining the advantages of polymeric optical fibers over glass fibers. In this way a lanthanide-doped polymeric optical waveguide is provided which has all the above-mentioned advantages of polymeric optical waveguides to boot.
An organic ligand is used as a sensitizer. The organic ligand is excited in a strong absorption band to more efficiently populate the excited state of the rare-earth ion, after which the energy is transferred to an excited state of the rare-earth ion. A significant gain in excitation efficiency can be obtained via this route. The absorption coefficients of the (forbidden transitions of the) rare-earth ions are extremely low, typically 1-10 l mol
−1
cm
−1
, whereas organic ligands may have absorption coefficients which are 3-4 orders of magnitude higher, because allowed &pgr;—&pgr;* transitions are probed.
Preferred organic sensitizers are selected from fluorescein derivatives such as fluorexon, eosin, erythrosin, fluorescein, rose bengal, calcium green, and oregon green; triphenylmethane derivatives such as methylthymol blue, xylenol orange, brilliant blue, methyl green, and malachite green; porphyrin derivatives; rhodamine derivatives such as rhodamine 6G, tetrabromorhodamine, and lissamine; phenothiazine derivatives such as thionin and methylene blue; phenoxazine derivatives such as nile blue; coumarin derivatives; acridin derivatives such as acridin orange; (thio)indigo derivatives; carbocyanine derivatives; squaraine derivatives; buckminster fullerenes, and (na)phthalocyanine derivatives.
These compounds and derivatives are well-known to those skilled in the art. Coumarin derivatives, for instance, include 2- and 4-coumarins such as coumarin 120, 124, 445, 450, 490, 500, 503, and trifluoromethylcoumarin. Other sensitizers which absorb in the visible region can also be employed.
The state of the art of lanthanide complexes as active material in polymeric waveguides has been disclosed in EP 618,892. Important advantages of polymeric optical waveguides, as opposed to the conventionally applied inorganic optical waveguides, are the ease of handling the polymeric materials, which entails more flexibility and possibilities as to the devices which can be prepared (e.g., hybrids of switches and waveguides, direct coupling to laser source or detector), and reduction of manufacturing costs. Another advantage when an organic complex is used in a polymer host, is that higher doping of the waveguide can be realized than with inorganic ions in an inorganic host. This requires good compatibility of complex and host, which has been realized by the complexes described in EP 618,892, wherein a net neutral complex was obtained by application of a negatively charged ligand. A disadvantage of these organic complexes is that most organic ligands contain bonds which give highly energetic vibrational modes, which bonds usually are not present in inorganic hosts, or in the case of coordinated water molecules being present in the complex, can be removed by high-temperature treatment. Obviously, such treatment cannot be applied to organic complexes, which would decompose. It is therefore vital that the org
Ben Loha
Green Kevin E.
JDS Uniphase Photonics C.V.
Lacasse Randy W.
Lacasse and Associates
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