Controlling 1550-nm light through a multimode fiber using a Hadamard encoding algorithm

To meet the demand for higher capacity fiber-optic communication, multimode fibers have gradually attracted attention, but they introduce spatial distortions. To overcome this limitation, wavefront shaping technology promises to control scattered light after it is transmitted through multimode fibers. In this work, we introduce a Hadamard encoding algorithm (HEA) to control 1550-nm light that has passed through a multimode fiber. A series of Hadamard bases is iteratively added to the current optimum phase map, and the coefficient of each order is determined through a simple four-step phase-shifting mechanism. Using a laser source at 1550-nm wavelength, we experimentally achieved an optical focus through a 2-meter-long multimode fiber. With 1024 orders, the experimental enhancement reached 690, which is 86% of the theoretical value. As far as we know, this is the best result ever reported in focusing 1550-nm light through a multimode fiber. Moreover, we note that the HEA can also be used to reduce the intensity of the targeted light, suggesting broad applications in glare suppression. These results demonstrate superior performance in controlling targeted light transport through a multimode fiber at a telecommunication wavelength. We anticipate that this work will open new possibilities in a variety of applications in fiber optics.