Increased received power and decreased modal noise by preferential excitation of low-order modes in multimode optical-fiber transmission systems

The dependence of the performance of a simple multi-mode optical-fiber transmission system on launch conditions is evaluated. Current methods of aligning lensed multimode fiber pigtails to injection lasers are shown to generate excessive levels of attenuation and modal noise. By altering these launch conditions, we are able to achieve an increase in the received power level of as much as 1.4 dB, and a decrease of the relative modal noise level of as much as 2.8 dB. Some of these improvements should be readily achievable in multimode optical-fiber systems.