Abstract
We introduce a new type of states for light in multimode waveguides featuring strongly enhanced or reduced spectral correlations. Based on the experimentally measured multi-spectral transmission matrix of a multimode fiber, we generate a set of states that outperform the established "principal modes" in terms of the spectral stability of their output spatial field profiles. Inverting this concept also allows us to create states with a minimal spectral correlation width, whose output profiles are considerably more sensitive to a frequency change than typical input wavefronts. The resulting "super-" and "anti-principal" modes are made orthogonal to each other even in the presence of mode-dependent loss. By decomposing them in the principal mode basis, we show that the super-principal modes are formed via interference of principal modes with closeby delay times, whereas the anti-principal modes are a superposition of principal modes with the most different delay times available in the fiber. Such novel states are expected to have broad applications in fiber communication, imaging, and spectroscopy.
Highlights
Based on the experimentally measured multispectral transmission matrix of a multimode fiber, we generate a set of states that outperform the established “principal modes” in terms of the spectral stability of their output spatial field profiles
By decomposing them in the principal-mode basis, we show that the super-principalmodes are formed via interference of principal modes with close delay times, whereas the anti-principalmodes are a superposition of principal modes with the most-different delay times available in the fiber
In the regime of strong mode coupling where all of the results shown above were obtained, we find that both principal modes” (PMs) and super-PMs consist of most linearly polarized (LP) modes, and the higher-order LP modes have smaller contributions due to higher loss
Summary
Multimode optical fibers (MMFs) are complex and versatile systems that have wide-range applications from optical transmission [1,2,3,4,5,6,7,8,9,10,11], imaging [12,13,14,15,16,17,18,19,20,21,22,23], and manipulation [24,25] to high-power lasers [26,27] and amplifiers [28,29]. They have a finite spectral width, limiting the bandwidth of input signals that can maintain the temporal pulse shape and spatial coherence after being transmitted This limitation is severe for MMFs with strong mode mixing, as well as for disordered media, where the bandwidth of PMs is narrow. If it was possible to create a state in the MMF with much reduced spectral correlation, one could greatly suppress the spatial coherence at the MMF output by launching broadband light into such a state We introduce such novel states of light that have the aforementioned unique characteristics, and we generate them experimentally by addressing the spatial degrees of freedom of a MMF with wave-front shaping techniques. Our analysis illustrates that the PMs provide a powerful basis for synthesizing new types of states with unique spatial, temporal, and spectral characteristics
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