High speed transmission systems (> 10 Gb/s) for cost-sensitive applications such as metropolitan network have attracted extensive interest due to the explosive data traffic growth in such applications. Optical orthogonal frequency division multiplexing (OFDM) based on direct modulation and direct detection for single-mode fiber (SMF) and multi-mode fiber (MMF) without optical amplification and chromatic dispersion (CD) compensation was proposed. Recent research has also shown that optical OFDM can be used with electronic dispersion compensation using direct detection in SMF. However, laser frequency chirp has been identified as a key limiting factor of capacity-versus-reach performance.In this paper, we present a novel concept of low cost optical OFDM with direct modulation of distributed feedback (DFB) lasers and coherent detection at 51.4 Gb/s and 64 QAM. A comprehensive theoretical model of the proposed system is developed. The proposed optical OFDM system concept and performance is based upon using electronic precompensation of laser frequency response, and electronic post compensation of DFB laser frequency chirp and CD. A numerical simulation of the transmission performance of the aforementioned system is conducted using different fiber lengths (40 km, 60 km, 120 km) and chirp parameters, which shows its attractiveness for access and metro applications.
In recent years, there has been an explosive growth of data traffic in datacenter interconnections. A significant amount of the installations within data centers are graded-index multimode fibers (GI-MMFs). These fibers enable the use of mode-division multiplexing to increase the fiber's capacity. The heart of such a multiplexing scheme is a spatial multiplexer. In this paper, we propose a simple tilted Gaussian beam multiplexer for GI-MMF using low-cost commercially available lenses. We derive an analytical expression for the power coupling coefficients using a tilted Gaussian beam launch into a GI-MMF. We use the analytical expression to perform an optimization algorithm for tilted Gaussian beams as a spatial multiplexer with GI-MMF. The optimization was performed for 3 Â 3, 4 Â 4, and 5 Â 5 multiple-input-multiple-output (MIMO) systems. Typical power coupling matrices exhibit maximum crosstalk of À12.5 dB with strong coupling efficiency that is greater than À0.6 dB.
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