Optical: systems and elements – Optical amplifier – Particular active medium
Patent
1994-08-19
1996-12-03
Hellner, Mark
Optical: systems and elements
Optical amplifier
Particular active medium
549348, 549352, 549353, 436 79, 436 74, H01S 300, C07D32100
Patent
active
055813984
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an optical amplifier doped with lanthanide ions. Such an optical amplifier is known from EP-A2-0 437 935, which describes an optical amplifier composed of an erbium.sup.3+ doped fibre. The erbium ions are excited with the aid of a laser, giving a fibre containing a large number of excited Er.sup.3+ ions. When optical beams (photons) having the same wavelength as the emission wavelength of the excited Er.sup.3+ ions traverse the fibre, they effect the transition of the ions from the excited state to a lower energy level with transmission of light. As has been mentioned, this light will have the same wavelength and phase as the photons traversing the fibre. Such a process is called stimulated emission. In this way the light beams are amplified, with the optical fibre acting as amplifier.
The optical amplifier as specified in EP-A2-0 437 935 is a glass fibre. For several years efforts have been made in the industry to replace optical glass fibres with optical polymeric material. Optical polymeric fibres have several advantages over optical glass fibres. They can be made by less complicated spinning processes and can easily be cut to the required size and attached to receiving and transmitting devices. Also, they are lighter and more flexible than glass fibres. An attendant advantage is that the shape of optical polymeric material need not be restricted to fibres. The polymeric material can also be shaped into so-called flat waveguides. In the remainder of the description the term optical waveguides refers to both fibres and flat waveguides.
So far, it has not proved possible to replace lanthanide doped optical amplifiers with optical amplifiers of polymeric material. This is because polymeric waveguides cannot be doped with lanthanides just like that, without introducing co-doping with water. For, trivalent lanthanide ions are highly hygroscopic. In consequence, when lanthanide ions are doped, water of crystallisation which is present on 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 have the above-indicated amplification, or have it in insufficient degree. Furthermore, light is absorbed to such an extent by OH-groups that polymeric optical waveguides in which OH-impurities are present will display optical attenuation. Doping of Er.sup.3+ ions in glass fibres ordinarily is carried out using Er.sub.2 O.sub.3. While this erbium oxide is not hygroscopic, it cannot be used in polymeric waveguides since it fails to dissolve in polymeric material. When glass fibres contain water or OH-containing impurities, these can easily be removed by greatly heating the fibres and drying them out, as it were. However, this is an unfortunate solution to the problem where polymeric waveguides are concerned, as they will usually decompose under such treatment.
The present invention has for its object to obviate these drawbacks and provide a functional lanthanide doped optical amplifier in which a polymeric waveguide is used as optical material. The invention hence consists in that the polymeric waveguide comprises the lanthanide ions in the form of a complex.
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 like the polymeric wavegu
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Mohlmann Gustaaf R.
van Veggel Franciscus C. J. M.
Akzo Nobel nv
Fennelly Richard P.
Hellner Mark
Morris Louis A.
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