The discrete diffraction phenomena was studied in optics both theoretically and experimentally by scanning tunneling optical microscopy in arrays of equally spaced identical waveguide elements [1,2]. Coupled Yttrium iron garnet (YIG) structures are of great interest nowadays due to extremely small spin-wave loss in this material and the possibility of spin-wave wave propagation control. Coupled YIG waveguides can be used as components in the tunable signal processing devices (nonlinear couplers, nonlinear switches) [3].
This report shows the results of investigation of the spatio-temporal dynamics of magnetization in the laterally coupled planar YIG waveguide array by Brillouin light scattering (BLS) spectroscopy [4]. The structure was fabricated from a sample of the YIG film thickness of 7.7 mm, grown on the basis of GaGd-garnet (GGG) thickness of 0.5 mm by laser cutting (Fig.1, a). The microstrip antenna with the width of 30 mm formed on the Al2O3 substrate was used for the MSSW excitation in the central waveguide (number n=0 in Fig.1, a). The structure was magnetized by an in-plane magnetic field of H0=1300 Oe parallel to the microstrip antennas. The discrete diffraction of surface spin wave in a lateral coupled YIG waveguide array was demonstrated experimentally with BLS technique in planar waveguide geometry, when a single input channel with number n=0 is excited. The different levels of input RF power, different pulse-modulated and continuous microwave signals of different frequencies were considered. The central waveguide (n=0) was excited by tapered part of planar YIG waveguide. Decomposition of eigenmodes reveals the width modes interference in the central waveguide. Due to the symmetry breaking of the taper structure the spatial distribution of the magnetization corresponds to the superposition of the lowest odd modes (m = 1,3) in the input waveguide and the odd (m = 1) and even (m = 2) modes in central waveguide with a number n=0.
Experimental studies of the frequency transmission coefficients, spatio-temporal dynamics of MSSW propagation and power transmission between waveguides in array were performed. The different levels of input RF power, different pulse-modulated and continuous microwave signals of different frequencies were considered. The spatial distributions of the square of high frequency magnetization |m(y,z)|2 are shown in Fig.1, b. The input signal frequency is f0=5.233 GHz, power is Pin = 5 dBm.
It was shown that the degree of system discreteness could be regulated by changing the external bias magnetic field angle. The dependence of coupling between the waveguide channels on the parameters of spin wave (wavenumber, frequency, power) makes the continuous regulation of spin wave path possible.
Nonlinear propagation, interactions between waves and generation of discrete solitons are interesting field for further studies.
REFERENCES
[1]. Lederer F., Stegeman G.I., Christodoulides D.N. et al., Phys. Rep. 463, 1 26 (2008).
[2]. Valle G.D., Longhi S., Lapo P., Appl. Phys. Lett. 90, 261118 (2007).
[3]. Serga A.A., Chumak A.V., and Hillebrands B., J. Phys. D: Appl.Phys. 43, 264002 (2010).
[4]. Demokritov S.O., Hillebrands B., and Slavin A.N., Phys. Rep. 348, 441–489 (2001).