We propose an all-optical fiber-based device able to accomplish both polarization control and OSNR enhancement of an amplitude modulated optical signal, affected by unpolarized additive white Gaussian noise, at the same time. The proposed noise cleaning device is made of a nonlinear lossless polarizer (NLP), that performs polarization control, followed by an ideal polarizing filter that removes the orthogonally polarized half of additive noise. The NLP transforms every input signal polarization into a unique, well defined output polarization (without any loss of signal energy) and its task is to impose a signal polarization aligned with the transparent eigenstate of the polarizing filter. In order to effectively control the polarization of the modulated signal, we show that two different NLP configurations (with counter- or co-propagating pump laser) are needed, as a function of the signal polarization coherence time. The NLP is designed so that polarization attraction is effective only on the "noiseless" (i.e., information-bearing) component of the signal and not on noise, that remains unpolarized at the NLP output. Hence, the proposed device is able to discriminate signal power (that is preserved) from in-band noise power (that is partly suppressed). Since signal repolarization is detrimental if applied to polarization-multiplexed formats, the noise cleaner application is limited here to "legacy" links, with 10 Gb/s OOK modulation, still representing the most common format in deployed networks. By employing the appropriate NLP configurations, we obtain an OSNR gain close to 3dB. Furthermore, we show how the achievable OSNR gain can be estimated theoretically.
Numerical simulations of semiconductor optical amplifiers (SOA) often are time consuming. Making simplifying assumptions, we obtain a fast model based on the reservoir, representing the total number of useful carriers. In this paper, we explain how this model is developed and how the gain is parameterized. We demonstrate that the scattering losses, dropped in the derivation of the reservoir model, can be re-introduced by applying a simple transformation to the gain coefficient. In this way, the accuracy of the model is greatly increased, but its level of complexity remains low.
Among the various possible production techniques of silica- on-silicon integrated optical devices, sol-gel is the one which combines low cost with a great flexibility and the ease of doping the silica matrix with nonlinear and active compounds. In the frame of an European project, we have investigated the application of the sol-gel technique to the realization of an erbium-doped optical amplifier, operating in the third telecommunication window. Here, in particular, we refer to the development of an optimum fabrication strategy for the guiding structure. A strip-loaded configuration was chosen. Design optimization was carried out by means of a MATLAB software code, mainly based on the Effective Index Method. For what concerns the technical side, two different routes were followed: that of the Low Index Load and that of the High Index Load. Pros and cons of both structures were carefully evaluated through numerical simulations as well as experimental analysis, in order to choose the best performing one. Results of the design procedure and the characterization of the fabricated waveguides are described here.
Silica-on-silicon waveguides have been fabricated doping core layer with phosphorus and germanium. Plasma Enhanced Chemical Vapor Deposition has been used to grow all layers starting from liquid metalorganic compounds. Co-doping assures chemical (Ge) and geometrical (P) homogeneity with optical fibers and allows to propagation losses of 1 dB/cm (not reflowed samples). Low cost, high realization rate and process compatibility with other microelectronic components make this technology very attractive for industrial production.
A new integrated optical device is demonstrated for the polarisation independent spectrum analysis of in fiber optical radiation. The device exploits the heterodyne detection of the optical signals from the output of an acousto-optical tunable filter fabricated on XY LiNbO3. The device is used to analyse and multiplex the optical signals from Fiber Bragg Grating sensors.
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