We demonstrate both theoretically and experimentally how to achieve wave states that are optimal for transferring momentum, torque, etc. on a target of arbitrary shape embedded in an arbitrary environment.
We demonstrate both theoretically and experimentally how to generate wave states that are optimal for transferring momentum, torque, etc. on a target of arbitrary shape embedded in an arbitrary environment.
The central goal in optical wave control is to manipulate light fields so that they fulfil a certain function, such as for imaging, detection and efficient transmission across complex photonic media. To reach this goal, different techniques have been considered, either for shaping an incoming wavefront or for shaping the medium itself. This talk covers two novel insights for both of these two contrasting approaches and their application to disordered media.
In the first part of this talk I will speak about how to control wave scattering by delicately designing the refractive index of a scattering medium. In particular, I will show how to completely eliminate the highly fluctuating intensity profile inside a disordered material by adding a tailored gain and loss profile to it. The resulting constant-intensity waves in such non-Hermitian scattering landscapes are free of any backscattering and feature perfect transmission even through highly disordered media [1].
In the second part of this talk, I will present a novel approach for shaping a wave incident on a disordered medium to achieve a focus deep inside of it. This approach is based on a prior measurement of the system's transmission matrix and its derivative with respect to a shift of the target one aims to focus on. I will explain the connection of this novel approach to the concept of "principal modes" and present an experimental realization in the microwave regime [2].
[1] Konstantinos G Makris, Andre Brandstötter, Philipp Ambichl, Ziad H Musslimani, and Stefan Rotter. Wave propagation through disordered media without backscattering and intensity variations. Light: Science & Applications 6, e17035 (2017); doi: 10.1038/lsa.2017.35
[2] Philipp Ambichl, Andre Brandstötter, Julian Böhm, Matthias Kühmayer, Ulrich Kuhl, and Stefan Rotter. Focusing inside disordered media with the generalized Wigner-Smith operator. Phys. Rev. Lett. accepted article; arXiv:1703.07250
Optical pulses propagating through a multimode fiber with random mode mixing experience temporal broadening and distortion. Principal modes have been proposed to overcome modal dispersion. They are the eigenstates of the time delay operator and the associated eigenvalues are the delay times. Principal modes retain the spatial profiles of output fields to the first order of frequency variation. In the weak mode coupling regime, principal modes are superpositions of fiber eigenmodes with similar propagation constants. In the strong mode coupling regime, a principal mode is composed of all fiber modes with very different propagation constant, yet it has a well-defined delay time due to multipath interference, which can be controlled by adjusting the spatial profile of incident field.
The spectral bandwidth of principal modes determines the temporal width of optical pulses that can be transmitted through the multimode fiber without distortion. In the weak mode coupling regime, principal modes with short and long delay times have broader bandwidths, while in the strong mode coupling regime, the principal modes with intermediate delay times have the broadest bandwidths. The opposite behaviors reveal two distinct mechanisms that are responsible for the principal mode bandwidth in the weak and strong mode coupling regimes. We further investigate how the mode-dependent loss modifies the principal modes. Our study provides physical understanding of spatiotemporal dynamics in a multimode fiber with varying degree of mode mixing, which is important for controlling pulse propagation through a multimode fiber.
We investigate the shot noise in phase-coherent transport through quantum cavities by a two dimensional ab-initio
simulation of the scattering problem. In particular, we study the influence of quantum scattering mechanisms
on the transport statistics by tuning the strength of a disorder potential and the openings of the dot. For small
cavity openings we find the shot noise for disordered samples to be of almost equal magnitude as for clean samples
where transport is ballistic. We explain this finding by diffractive scattering at the cavity openings which act
as strong noise sources. For ballistic cavities we demonstrate the emergence of "noiseless scattering states",
irrespective of sharp-edged entrance and exit lead mouths. Our numerical results for the onset thresholds of
these "classical" states are in very good agreement with analytical estimates.
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