HIGH-EFFICIENCY GUIDED-WAVE MAGNETOOPTIC BRAGG CELL MODULATOR USING NONUNIFORM BIAS MAGNETIC-FIELD

A technique for large enhancement of the diffraction efficiency of a g uided-wave magnetooptic (MO) Bragg cell modulator using a nonuniform b ias magnetic field in bismuth-doped yttrium iron garnet-gadolinium gal lium garnet waveguide is reported. Since the velocity of propagation o f the magnetostatic forward volume wave (MSFVW) varies with the bias m agnetic field, a bias magnetic field of proper spatial distribution wi ll modify its wave front and, thus, create a lensing effect upon the M SFVW. This lensing effect in turn reduces the angular beam spread of t he MSFVW, and results in a higher MO Bragg diffraction efficiency. The experimental data obtained for the cases with uniform and nonuniform bias magnetic fields at the carrier center frequency range of 2.0-3.5 GHz have demonstrated a diffraction efficiency enhancement by two to s ix times. A diffraction efficiency as high as 70% has also been accomp lished. Furthermore, the measured frequency responses indicate that th e nonuniform bias magnetic field has had only a mild effect on the ban dwidth of the MO Bragg cell modulator. (C) 1997 American Institute of Physics. [S0003-6951(97)04351-9].