Lanthanide ions are widely used as the active luminescent material in optical amplifiers and lasers. The major advantages of the lanthanide ions are the long luminescence lifetime and the high quantum efficiency that can be achieved at the major telecommunication wavelengths of 1300 and 1530 nm. The ions are extremely stable under laser action because the optical transitions involve electronic transitions within the ion itself. No chemical bonds are involved so degradation does not occur. The long luminescence lifetime of the lanthanide ions makes laser action relatively easy to achieve with cheap pump sources.
The luminescence of the ions is widely utilized when integrated into inorganic materials, like crystals or glasses. These materials are often fabricated at high temperatures using high-cost materials. For optical glass fiber technology the high costs of integration of the optical components can even exceed the fabrication costs of the components itself. This has disadvantages especially in short range telecommunication where the optical signals have to be processed in a number of optical components.
To be efficient, optical amplifiers and lasers require complex optical signals that cover a broad wavelength range. In order to achieve this, a large number of optical components are needed. For example, the Er3+-doped fiber amplifier (EDFA) is the most used amplifier, because the optical transition of the Er3+ ion at 1530 nm coincides with the minimum loss window of optical glass fibers. However, there is a low-loss window. To cover the low-loss window, other lanthanide ions also attract a lot of attention, like Pr3+ and Nd3+ for amplification around 1300 nm and Tm3+ for amplification around 1450 nm. Such complexity of optical componentry causes glass fibre technology to be expensive.
The prior art has shown that planar waveguide structures have significant advantages in this technology. They could for instance profit from current lithography and thus be potentially low cost. In addition, planar structure are potentially easy to integrate with other optical components. A disadvantage in the (polymer-based) integrated wavelength structure is that they have relatively high optical losses. This disadvantage could in principle be overcome by integration of an optical amplifiers to compensate for the optical losses occurring during the manipulation of the data signals.
Polymers are materials that attract a lot of attention for the use in planar waveguides, because of the low cost processing and flexibility these polymers offer in the processing. The prior art L. H. Slooff, A. van Blaaderen, A. Polman, G. A. Hebbink, S. I. Klink, F. C. J. M. van Veggel, D. N. Reinhoudt; Rare-earth Doped Polymers for Planar Optical Amplifiers J. Appl. Phys. 2002, 91, 3955-3980 incorporated herein by reference) has shown the utility of lanthanide doped organic polymers. Polymers have the advantage that they can be processed at low temperatures.
A further advantage of polymers is that using standard techniques it is relatively easy to make different structures. This makes it possible to integrate a wide variety of optical components like splitters, couplers, multiplexers, and amplifiers. Hence polymers can lower the cost of optical systems. The prior art has shown that organic polymers have a clear potential as low-cost devices, but (intrinsic and extrinsic) optical losses are still relatively high.
Most recently, doped semiconductor nanoparticles have been developed. For example, U.S. Patent Publication No. 20030030067 discloses some Mn.sup.2+ doped semiconductor nanoparticles. In the application the doped semiconductor nanoparticles are contemplated for us in upconversion luminescence (“UCL”) materials and methods of making and using same. In the application, any dopant capable of increasing the fluorescence intensity or quantum efficiency of the bulk material or nanoparticle is contemplated for use. With respect to semiconductor nanoparticles, such as ZnS, a dopant capable of increasing fluorescence intensity or quantum efficiency due to the increase of the oscillator strength and the efficient energy transfer from the host to the dopant upon photoexcitation is contemplated. Typically, the dopant will have a high d-d transition rate—e.g. Mn.sup.2+ has a d-d transition of .sup.4T.sub.1.fwdarw.sup.6A.sub.1. Any dopant having a high d-d transition rate and that is also capable of increasing the luminescence intensity or quantum efficiency of the UCL material is contemplated for use. Hence, the dopants could be broadly classified as rare earth ions—e.g. Tb.sup.3+, Ce.sup.3+ or Eu.sup.3+. The success of these doping procedures has been under discussion. In most of the papers direct prove of the energy transfer of the semi-conductor host to the lanthanide ion is not proven, because an excitation spectrum of the lanthanide ion is missing. O. E. Raola, G. F. Strouse Nano Lett. 2002, 2, 1443., incorporated herein by reference, reported the doping of Eu3+ ions in CdSe nanoparticles, starting with Eu2+, but no luminescence studies were performed to see if energy transfer from the nanoparticle host to the lanthanide ion takes place. Difficulties in doping most likely arise from the large difference in size between the host cation and the lanthanide ion, the charge mismatch between the cations, and the low affinity of lanthanide ions towards sulfur and selenium.
Problems arise when lanthanide ions are used as the active material in polymer-based optical amplifiers. The luminescence of lanthanide ions, especially the ions emitting at the wavelengths that are of interest for telecommunication, is quenched significantly due to the presence of the organic bonds of the polymer. To increase the luminescence of the lanthanide ions the ion has to be shielded from the polymer environment and one way to do this is by the synthesis of organic complexes, in which an organic ligand is coordinated to the lanthanide ion. Reducing the amount of organic bonds in close proximity to the lanthanide ion has improved the luminescence a little bit, but still quenching is a major constraint to the approach.
It is an object of the present invention to overcome the deficiencies of the prior art.