wideband guided wave magneto-optic (mo) modulation by magnetostatic surface waves (mssw) in yttrium iron garnet (yig)-gadolinium gallium garnet (ggg) has been demonstrated in a noncollinear coplanar interaction geometry. excitation of the mssw and efficient mo interaction at 1.152 and 1.302 mu m optical wavelengths were accomplished over a wide frequency range of 3 to 7 ghz by linear electronic tuning of the dc magnetic field from 500 to 1700 gauss. the mode conversion efficiency for 1.302 mu m optical wavelength was measured to be 8.13 percent at 1.00 watt rf drive power. theoretical analysis and experimental results both show that the mode conversion in this noncollinear configuration is caused by a combination of faraday and cotton-mouton effects induced by the dc magnetic field and the mssw. such interaction configuration should result in a number of integrated optic devices for wideband communication and signal processing applications at electronically tunable microwave carrier frequencies