Currently existing dense wavelength division multiplexing (DWDM) networks start to migrate from numerous point-to-point links towards meshed, transparent, optical networks with dynamically routed light paths. This increases the need for appropriate network monitoring and supervision methods. Optical performance monitoring (OPM) has to be cost-effective. Thus additional spendings for OPM have to be significantly smaller than the savings in OPEX due to increased reliability and ease of operation, administration, and maintenance (OAM). We elaborate on different advanced monitoring concepts. First, we discuss general failure scenarios in meshed networks. Then we describe software based failure root cause analysis and its implementation. We conclude that by implementing appropriate software algorithms in the network hardware effort can be significantly reduced. Finally, we assess different advanced OPM methods which may show up as useful to enable OPM in future optical networks.
Presently, formerly independent autonomous optical links are growing increasingly into meshed networks making measures for performance monitoring and automated error analysis a necessity. At the same time adaptive electronic equalizers are becoming integrated by default into optical receivers in order to mitigate distortions which are ubiquitous on every fiber link. In this paper we investigate the possibility of using these already available components for identifying and quantifying optical distortions and thus, performing network monitoring without additional expensive optical equipment.
Optical data transmission has undergone a tremendous evolution. Starting with unrepeated point-to-point transmission in the 80s the inventions of wavelength division multiplexing (WDM) and erbium doped fiber amplifiers (EDFAs) have let to an explosion of system capacity as well as of system reach. After the steep downturn of recent years network operators have now regained the strength to upgrade their networks and to implement new services. This paper will review current and upcoming technologies in the long haul (LH) and ultra long haul (ULH) data transmission. It will further discuss the future evolution of transparent optical networks towards dynamically routed meshed optical networks with respect to operator’s technical operational and economical requirements. Upgradeability turns out as a key issue as it on the one hand side facilitates low front investments for network providers and on the other hand side enables organic and flexible network growth.
Multicore fiber (MCF) can absorb pump radiation at small length giving opportunity to construct compact fiber laser. Phase-locking of generation in different microcores improves the output radiation beam quality. We have developed simple analytical description of multiple imaging of periodical field distribution propagating in space -- fractional Talbot effect, and have shown that this effect allows phase-locking MCF ever in the case of large variation of microcore parameters. The reason is all of the microcores to be equally coupled each with other: the global (parallel) coupling. Partial phase-locking has been demonstrated in experiment with fiber laser, consisting from 18-cores MCF and ¼-th Talbot length annular waveguide.
Multiple images formation after propagation of periodical wave field over a fraction of Talbot distance (Zr) was received explicitly. The phase-locking of multi core fiber laser radiation was achieved experimentally by usage sector mirror placed at a distance of Zr/8.
Multicore fiber-lasers are designed to build high-power short length fiber-lasers. In our case the active single- mode cores (micro cores) are placed on a ring inside a big pump core. The micro cores are placed together very closely so that evanescent coupling between adjacent micro cores should be provided. To understand the coupling behavior in a multicore fiber in order to phase-lock all the micro cores we measured experimentally the coupling constant between the micro cores. Simultaneously we calculated the evolution of an injected field in a multicore fiber. In the experiment and in the simulations 38 micro cores with a diameter of approximately 6.9 micrometers are placed on a ring with a diameter of 115 micrometers . The distance between adjacent cores is about 2.6 micrometers . The measured coupling constant of 2cexp equals 0.82 mm-1 is in good agreement with the value 2cth equals 0.83 mm-1. Furthermore the phase evolution in each micro core was evaluated.
Multimode interference is fairly known from the 1D case of slab waveguides. We present for the first time to our knowledge the reconstruction of the 2D radial symmetric structure of a multicore fiber laser in a multimode fiber. In the concept of multicore fiber, rare earth-doped single mode waveguides (micro cores) are placed on a ring inside a big pump core. The situation of injecting radiation from N incoherent emitting sources into a multimode waveguide is described analytically. Experimental and numerical results for various multimode diameters and fiber lengths dealing with the reconstruction of the injected near-field pattern and the corresponding far-field patterns are presented. We propose that the reconstructed field could be re-injected into the multicore fiber-laser in order to introduce parallel coupling of all emitters. Additionally, using the multimode fiber as a passive element, without re-injection, the on-axis intensity of the multicore laser radiation is significantly increased by a single pass through a multimode fiber with a certain length. This effect takes place without any loss of energy.
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