Generation and applications of spectral-spatially correlated principal mode in multimode fibers

Light propagating through multimode fibers experiences multiple scattering, leading to complex speckle output patterns and significant dispersion. In this work, we propose a unique light state called the spectral-spatially correlated principal mode (S2 principal mode) in multimode fibers. This mode demonstrates an ability to simultaneously manipulate the spectral correlation and spatial distribution of the output field under strong mode coupling. Such simultaneous control over multiple dimensions of the output field is achieved through measuring the generalized Wigner-Smith operator of the multimode fiber transmission. Experimental results showcase a substantial improvement in the spectral stability of the output spatial field profiles for these states. As a result, the S2 principal modes offer precise localization of the output field within a designated region and mitigate distortions of the confined spots caused by modal dispersion. The advantages of S2 principal modes are further showcased through their application in encrypting optical information transmission via multimode optical fibers. We anticipate these modes will find extensive applications in fiber optic communications, imaging, and spectroscopy, while also serving as inspiration for the discovery of other intriguing optical states.