GHz Bandwidth Magnetooptic Interaction in YIG-GGG Waveguide Using Magnetostatic Forward Volume Waves

Abstract

From the dispersion relations of the magnetostatic waves (MSW) in Yttrium Iron Garnet - Gadolinium Gallium Garnet (YIG-GGG) thin film[1], it is found that while the theoretical bandwidth of the magnetostatic surface waves (MSSW) decreases considerably as the carrier frequency is increased, the theoretical bandwidth of the magnetostatic forward volume waves (MSFVW) increases substantially with the carrier frequency. We have noted previously the decrease of magnetooptic (MO) bandwidth from 487 MHz to 250 MHz in noncollinear coplanar guided-wave interaction involving the MSSW[2] as the carrier frequency was increased from 3.0 GHz to 7.0 GHz. However, in view of the dispersion characteristics of the MSFVW as mentioned above, the MO bandwidth associated with noncollinear coplanar interaction involving the MSFVW can potentially be significantly larger than that involving the MSSW as the carrier frequency goes beyond 2.0 GHz. Since it is of great interest to accomplish wideband MO interaction at high carrier frequency, the MSFVW was also used in our earlier work. For example, a MO bandwidth of 550 MHz (defined at the two -3dB points) and a TM0 to TE0 mode-conversion efficiency of 0.5% were obtained in our earlier experiment with the MSFVW centered at 3.0 GHz using a homogeneous (uniform) DC magnetic, field of 2250 Oe[3]. Recently, a technique for enhancement of MO bandwidth that employs inhomogeneous DC magnetic field[4] was reported[5]. In that particular work, an increase of MO bandwidth from 30 to 350 MHz (defined between the null points or approximately 125 MHz based on the conventional definition of -3dB points) centered at the carrier frequency of 1.45 GHz was obtained at the optical wavelength of 1.15µm by switching from a homogeneous to an inhomogeneous DC magnetic field. Specifically, an inhomogeneous field that varied from 2150 to 2350 Oe across an 8.0 mm aperture of the MSFVW transducer was used. Due to the concomitant "channelization effect" with the resulting MSFVW the measured TM0 to TE0 mode-conversion efficiency was found to decrease from 1.0 to 0.03% by switching from the homogeneous to the inhomogeneous field.