M.P. Oude Wolbers

Optical properties of erbium-doped organic polydentate cage complexes

The optical properties of different erbium (Er)-doped polydentate hemispherand organic cage complexes are studied, for use in polymer-based planar optical amplifiers. Room temperature photoluminescence at 1.54 um is observed, due to an intra-4 f transition in Er31. The Er is directly excited into one of the 4 f manifolds (at 488 nm), or indirectly (at 287 nm) via the aromatic part of the cage. The luminescence spectrum is 70 nm wide (full width at half maximum), the highest known for any Er-doped material, enabling high gain bandwidth for optical amplification. The absorption cross section at 1.54 um is 1.1x10 -20 cm2, higher than in most other Er-doped materials, which allows the attainment of high gain. Measurements were performed on complexes in KBr tablets, in which the complex is present in the form of small crystallites, or dissolved in the organic solvents dimethylformamide and butanol-OD. In KBr the luminescence lifetime at 1.54 um is <0.5 us, possibly due to concentration quenching effects. In butanol-OD solution, the lifetime is 0.8 us, still well below the radiative lifetime of 4 ms estimated from the measured absorption cross sections. Experiments on the selective deuteration of the near-neighbor C–H bonds around the Er3+-ion indicate that these are not the major quenching sites of the Er31 luminescence. Temperature dependent luminescence measurements indicate that temperature quenching is very small. It is therefore concluded that an alternative luminescence quenching mechanism takes place, presumably due to the presence of O–H groups on the Er-doped complex (originating either from the synthesis or from the solution). Finally a calculation is made of the gain performance of a planar polymer waveguide amplifier based on these Er complexes, resulting in a threshold pump power of 1.4 mW and a typical gain of 1.7 dB /cm.

Near-IR Luminescent Rare Earth Ion–Sensitizer Complexes

Rare earth ions, with relatively long luminescence lifetimes, have significant advantages for application in fields as varied as diagnostics and optical amplification. In diagnostics the long luminescence lifetimes allow for extremely sensitive time-gated detection, where the difference in temporal behavior of scatter and background fluorescence and the long-lived rare earth luminescence is utilized. In optical amplification the long excited-state lifetime makes it easier to obtain population inversion, a requirement for effective stimulated emission. Unfortunately the absorption cross section of rare earth ion transitions is extremely low. However, via sensitized excitation by means of a suitable organic molecule, efficient excitation is obtained. It is shown that excitation in the visible part of the spectrum can be used to excite rare earth ions which luminesce in the near-IR, such as ytterbium, neodymium, and erbium, via a fluorescein-derivative as sensitizer. The advantages of this approach are manifold. Low-cost light sources are available for the visible part of the spectrum, and interferences from the matrix (scatter, absorption) are minimal. Detection in the near-IR is almost interference-free. For optical amplification the wavelength regions around 1300 and 1550 nm, which can be covered with the neodymium and erbium complexes, respectively, are the most important for applications in optical telecommunication.

Characterization of IP flows eligible for lambda-connections in optical networks

The advance on data transmission in optical networks has allowed data forwarding decisions to be taken at multiple levels in the protocol stack (e.g., at network and optical levels). With such capability, big IP flows can be moved from the network level and switched completely at the optical level over lambda-connections, where they get better quality of service (QoS). Meanwhile, the regular IP routing level is offloaded and can serve smaller flows better. With the continuous growing of traffic on the Internet, the selection of big IP flows can become difficult to be done by using current management approaches (conventional management and generalized multiprotocol label switching (GMPLS) signaling). The University of Twente (UT) is researching the use of self-management as an alternative to overcome this issue. In order to properly identify IP flows eligible to be moved to the optical level, the characteristics of these flows must be known, though. In this context, this paper analyses some of the characteristics of IP flows eligible to the optical level by observing their size, duration, throughput, and recurrence. In this analysis, we observe those characteristics while using various definitions for an IP flow as well as using different time intervals. The main contribution of this paper is to show the behavior of IP flows eligible for lambda-connections. Not in the least, we also show how this knowledge can be used in our self-management of optical networks approach.