Wideband Guided-Light Beam Deflection and RF Spectral Analysis Using Magnetostatic Forward Volume Waves*

Abstract

Magnetooptic (MO) interactions between guided-optical waves and magnetostatic waves (MSW) in Yttrium Iron Garnet-Gadolinium Gallium Garnet (YIG-GGG) waveguides has become a subject of increasing interest in recent years. Similar to the guided-wave acoustooptic (AO) interaction in which the surface acoustic wave (SAW) induces a moving optical grating [1], the guided-wave MO interaction results from the moving optical grating induced by the MSW. Specifically, in noncollinear coplanar geometry, as shown in Fig.1, a portion of an incident guided-light wave is Bragg diffracted and mode-converted (TE- to TM-mode and vice versa). We have recently obtained a very large bandwidth and high diffraction efficiency in such interaction geometry with magnetostatic forward volume waves (MSFVW) [2]. For example, a -3dB bandwidth of 1.03GHz centered at 6.0GHz was obtained at the optical wavelength of 1.317μm using a single microstripline transducer together with a fixed homogeneous DC magnetic field of 3500 Oe. As in the AO Bragg diffraction in which the resulting modulator is called the AO Bragg cell, the resulting MO modulator may be called the MO Bragg cell. In a continuing effort we have used the wideband MO Bragg cell to perform, for the first time, wideband light beam deflection and RF spectral analysis, and have obtained large numbers of deflected light spots and frequency channels. In this paper detailed results of both the experiments and related analysis are presented. It should be noted that a number of studies on bulk-wave MO interactions involving an unguided light wave and spin and/or magnetoelastic waves were reported [3-7] in the late 60's and early 70's. To the best of our knowledge, however, neither work on light beam deflection nor on RF spectral analysis using such bulk-wave MO interactions has been reported.