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All-linear time reversal by a dynamic artificial crystal.

Chumak AV, Tiberkevich VS, Karenowska AD, Serga AA, Gregg JF, Slavin AN, Hillebrands B - Nat Commun (2010)

Bottom Line: The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance.Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing.As a result, a linear coupling between wave components with wave vectors k≈π/a and k'=k-2π/a≈-π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet.

View Article: PubMed Central - PubMed

Affiliation: Fachbereich Physik and Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Kaiserslautern 67663, Germany. chumak@physik.uni-kl.de

ABSTRACT
The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance. Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing. In this paper, we report the experimental realization of all-linear time reversal. The time-reversal mechanism we propose is based on the dynamic control of an artificial crystal structure, and is demonstrated in a spin-wave system using a dynamic magnonic crystal. The crystal is switched from an homogeneous state to one in which its properties vary with spatial period a, while a propagating wave packet is inside. As a result, a linear coupling between wave components with wave vectors k≈π/a and k'=k-2π/a≈-π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet. The reversal mechanism is entirely general and so applicable to artificial crystal systems of any physical nature.

No MeSH data available.


Related in: MedlinePlus

Schematic diagram illustrating frequency inversion by the dynamic magnonic crystal.The diagonal lines (green and red) represent the spin-wave dispersion curve. Incident signal waves have positive wave vectors (green section) and those reflected by the DMC have negative wave vectors (red section). These two groups of waves are counter propagating. Black dots mark the reference frequency fa lying in the centre of the bandgap and corresponding to the Bragg wave vectors ±ka=±π/a. The green open circle and square illustrate two spectral components of an incident signal waveform. The spatially periodic magnetic modulation of the waveguide's magnetic bias field brought about by the application of the current pulse to the DMC meander structure couples these components to corresponding components of a reflected waveform (red open circle and square). The difference between the wave vectors of the signal and reflected waves is fixed by the lattice constant a of the DMC so that the k-spectrum of the reflected waveform is uniformly shifted to the left by Δk=2π/a=2ka (lower panel). This uniform shift in k-space results in spectral inversion in the frequency domain (right panel). The reference frequency fa (black dots) is not shifted and provides the axis of inversion.
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f2: Schematic diagram illustrating frequency inversion by the dynamic magnonic crystal.The diagonal lines (green and red) represent the spin-wave dispersion curve. Incident signal waves have positive wave vectors (green section) and those reflected by the DMC have negative wave vectors (red section). These two groups of waves are counter propagating. Black dots mark the reference frequency fa lying in the centre of the bandgap and corresponding to the Bragg wave vectors ±ka=±π/a. The green open circle and square illustrate two spectral components of an incident signal waveform. The spatially periodic magnetic modulation of the waveguide's magnetic bias field brought about by the application of the current pulse to the DMC meander structure couples these components to corresponding components of a reflected waveform (red open circle and square). The difference between the wave vectors of the signal and reflected waves is fixed by the lattice constant a of the DMC so that the k-spectrum of the reflected waveform is uniformly shifted to the left by Δk=2π/a=2ka (lower panel). This uniform shift in k-space results in spectral inversion in the frequency domain (right panel). The reference frequency fa (black dots) is not shifted and provides the axis of inversion.

Mentions: The reflected frequency fR=f(kR) can be determined using a linear Taylor expansion of the dispersion relationship f(k) about kS≈ka. The incident signal frequency is given by fS=f(kS)≈fa+v(kS−ka)/(2π), where fa=f(ka) is the centre frequency of the DMC bandgap and v=2πdf (ka)/dka is the spin-wave group velocity. Using equation (1) and the inversion symmetry of the dispersion curve, the frequency of the reflected wave can be written as fR≈fa−v(kS−ka)/(2π). Thus, the frequencies of the counter-propagating incident and reflected waves are connected by the simple relation 2 that is, they are inverted with respect to the centre of the bandgap fa. This process of dynamic reflection and linear frequency inversion is illustrated schematically in Figure 2.


All-linear time reversal by a dynamic artificial crystal.

Chumak AV, Tiberkevich VS, Karenowska AD, Serga AA, Gregg JF, Slavin AN, Hillebrands B - Nat Commun (2010)

Schematic diagram illustrating frequency inversion by the dynamic magnonic crystal.The diagonal lines (green and red) represent the spin-wave dispersion curve. Incident signal waves have positive wave vectors (green section) and those reflected by the DMC have negative wave vectors (red section). These two groups of waves are counter propagating. Black dots mark the reference frequency fa lying in the centre of the bandgap and corresponding to the Bragg wave vectors ±ka=±π/a. The green open circle and square illustrate two spectral components of an incident signal waveform. The spatially periodic magnetic modulation of the waveguide's magnetic bias field brought about by the application of the current pulse to the DMC meander structure couples these components to corresponding components of a reflected waveform (red open circle and square). The difference between the wave vectors of the signal and reflected waves is fixed by the lattice constant a of the DMC so that the k-spectrum of the reflected waveform is uniformly shifted to the left by Δk=2π/a=2ka (lower panel). This uniform shift in k-space results in spectral inversion in the frequency domain (right panel). The reference frequency fa (black dots) is not shifted and provides the axis of inversion.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105294&req=5

f2: Schematic diagram illustrating frequency inversion by the dynamic magnonic crystal.The diagonal lines (green and red) represent the spin-wave dispersion curve. Incident signal waves have positive wave vectors (green section) and those reflected by the DMC have negative wave vectors (red section). These two groups of waves are counter propagating. Black dots mark the reference frequency fa lying in the centre of the bandgap and corresponding to the Bragg wave vectors ±ka=±π/a. The green open circle and square illustrate two spectral components of an incident signal waveform. The spatially periodic magnetic modulation of the waveguide's magnetic bias field brought about by the application of the current pulse to the DMC meander structure couples these components to corresponding components of a reflected waveform (red open circle and square). The difference between the wave vectors of the signal and reflected waves is fixed by the lattice constant a of the DMC so that the k-spectrum of the reflected waveform is uniformly shifted to the left by Δk=2π/a=2ka (lower panel). This uniform shift in k-space results in spectral inversion in the frequency domain (right panel). The reference frequency fa (black dots) is not shifted and provides the axis of inversion.
Mentions: The reflected frequency fR=f(kR) can be determined using a linear Taylor expansion of the dispersion relationship f(k) about kS≈ka. The incident signal frequency is given by fS=f(kS)≈fa+v(kS−ka)/(2π), where fa=f(ka) is the centre frequency of the DMC bandgap and v=2πdf (ka)/dka is the spin-wave group velocity. Using equation (1) and the inversion symmetry of the dispersion curve, the frequency of the reflected wave can be written as fR≈fa−v(kS−ka)/(2π). Thus, the frequencies of the counter-propagating incident and reflected waves are connected by the simple relation 2 that is, they are inverted with respect to the centre of the bandgap fa. This process of dynamic reflection and linear frequency inversion is illustrated schematically in Figure 2.

Bottom Line: The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance.Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing.As a result, a linear coupling between wave components with wave vectors k≈π/a and k'=k-2π/a≈-π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet.

View Article: PubMed Central - PubMed

Affiliation: Fachbereich Physik and Forschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Kaiserslautern 67663, Germany. chumak@physik.uni-kl.de

ABSTRACT
The time reversal of pulsed signals or propagating wave packets has long been recognized to have profound scientific and technological significance. Until now, all experimentally verified time-reversal mechanisms have been reliant upon nonlinear phenomena such as four-wave mixing. In this paper, we report the experimental realization of all-linear time reversal. The time-reversal mechanism we propose is based on the dynamic control of an artificial crystal structure, and is demonstrated in a spin-wave system using a dynamic magnonic crystal. The crystal is switched from an homogeneous state to one in which its properties vary with spatial period a, while a propagating wave packet is inside. As a result, a linear coupling between wave components with wave vectors k≈π/a and k'=k-2π/a≈-π/a is produced, which leads to spectral inversion, and thus to the formation of a time-reversed wave packet. The reversal mechanism is entirely general and so applicable to artificial crystal systems of any physical nature.

No MeSH data available.


Related in: MedlinePlus