Mechanical robustness of MMF datacom interconnections using center-launching technique

Summary form only given. The analysis of the impact of mechanical perturbations on the system performance is an important issue to assure robustness in board-to-board and data server interconnections, as required by ETSI recommendations [1]. This robustness has to be guaranteed also in case of optical solutions [2], normally based on multi-mode fiber (MMF) communications, demonstrating easy handling and flexibility. In this paper we consider the case of single-mode fiber (SMF)-like propagation in MMF achieved by considering the so-called mode-field matched center-launching technique [3,4], in order to show a complete transmission transparency in the interconnection, when the board output and the board input are directly connected to the link without opto-electronic conversion at the transmitter and electro-optic conversion at the receiver. By exploiting center-launching technique in a MMF affected by mechanical vibrations, the data transmission could be deteriorated by the eventual excitation of the higher order modes in the MMF [5] in these board-to-board system. By means of suitable experimental investigation we demonstrate the robustness of center-launching technique in MMF, confirming SMF-like propagation and excluding multimode propagation, even in presence of mechanical stress. The transparent interconnection is experimented as shown in the inset of Fig. 1 left, where the SMF pigtail output of a single-mode VCSEL at 1335 nm, suitable for high-speed applications [6-8], modulated at 1 Gb/s, is fusion-spliced directly to a 2-m OM2 standard graded-index legacy MMF in order to match just the fundamental mode. The MMF is affected by mechanical vibrations up to about 1 kHz, induced by a shaker. Different backplane configurations are reproduced, detecting the MMF output directly by a free-space photodiode or coupling it into a final SMF operating as a spatial filter. No BER penalties are obtained for vibrations with frequency up to about 1 kHz, as reported in Fig.1.