High efficiency magnetooptic Bragg cell modulators using nonuniform bias magnetic field

Magnetostatic wave (MSW)-based guided-wave magnetooptic (MO) Bragg cell modulators in YIG-GGG waveguide have demonstrated a number of unique advantages in comparison to their acoustooptic (AO) counterparts. However, the MO Bragg diffraction efficiency that has been reported heretofore was relatively low. In this paper we report a new technique for large enhancement of the diffraction efficiency using a nonuniform bias magnetic field. Since the velocity of propagation of the MSW is a sensitive function of the bias magnetic field, a nonuniform magnetic field will modify the wavefront of the MSW and, thus, create a lensing effect upon the MSW which in turn reduces its angular beam spread, and results in a higher diffraction efficiency. For example, the experimental data obtained for the cases with uniform and nonuniform bias magnetic fields at the carrier center frequency range of 2.3-3.5 GHz have demonstrated a diffraction efficiency enhancement by two to six times. Also, the measured frequency responses indicate that the nonuniform bias magnetic field has had only a minor effect on the bandwidth of the MO Bragg cell modulator