Storage-Recovery Phenomenon in Magnonic Crystal

The phenomenon of coherent wave trapping and restoration is demonstrated experimentally in a magnonic crystal. Unlike the conventional scheme used in photonics, the trapping occurs not due to the deceleration of the incident wave when it enters the periodic structure but due to excitation of the quasinormal modes of the artificial crystal. This excitation occurs at the group velocity minima of the decelerated wave in narrow frequency regions near the edges of the band gaps of the crystal. The restoration of the traveling wave is implemented by means of phase-sensitive parametric amplification of the stored mode.

Figure 1

(a) Sketch of the experimental setup. The MC is fabricated in the form of YIG spin-wave waveguide with 10 grooves on its surface. The rf pump magnetic field is parallel to the bias field $H$. (b) Measured transmission characteristics (the ratio of the output signal intensity to the input) of the plane YIG film and MC for the magnetic field $H=1800\mathrm{Oe}$. Several band gaps are seen.

Figure 2

(a) The normalized time profiles of the restored signal measured at field $H=1860\mathrm{Oe}$ for different pumping powers: $P_{p1}=50\mathrm{mW}$, $P_{p2}=90\mathrm{mW}$, $P_{p3}=320\mathrm{mW}$. (b) Measured and calculated dependencies of the restored signal power and recovery time as a function of the pumping power.

Figure 3

Dependence of the restored signal power on the input signal phase. The signal and pump generators were locked in.

Figure 4

(a) Transmission of the spin-wave signal as a function of bias magnetic field (open circles for experiment, line for theory). (b) Dependence of the group velocity $v_{\mathrm{gr}}$ on the field $H$. The slight decrease in $v_{\mathrm{gr}}$ at the edges of the band gap is visible. (c) Measured restored signal power $P_R$ as a function of field $H$. One sees that the restored signal is visible only at the edges of the band gaps.

Figure 5

Lifetime ${\tau }_n$ (a) and frequency ${\omega }_n$ (b) of the quasinormal MC modes in the first pass-band calculated for $n=1-4$ as functions of the MC band gap half-width ${\Omega }_a$. Frequencies in (b) are measured from the center of the band gap ${\omega }_a$. MC traveling time $T_{\mathrm{gr}}=L/v_{\mathrm{gr}}$, where $L$ is the length of MC, is used as a normalization factor. The group velocity minimum frequency near the band gap edge is shown by a dashed line. The dotted line in (a) indicates the experimental conditions for the first band gap.