Low-operation-voltage electro-optical modulator based on Fe:KNbO_3 crystal

摘要

Results of low- and high-frequency modulation of laser beam, propagating both in the direction of optical axis and along three crystallographic axes in Fe-doped KNbO_3 crystal, are presented. It was found, that the high-frequency electro-optical constants of Fe:KNbO_3 are: r_(33) = (53±3) pm/V, r_(13) = (21 ± 3)pm/V, and r_(51) = (88 ± 11)pm/V. The difference between high- and low-frequency values is about 20% and this is in good accordance with known data for nominally pure crystal. We found also, that there was no twinning effect in this crystal under the electrical fields up to 2.5 kV/cm. The half-wave voltage was only 800 V at the wavelength of 633 nm in a longitudinal configuration of modulator. We measure also that bandpass of light modulation in Fe:KNbO_3 is equal to at least 6 MHz. In our experiments we also determined the speed of acoustic waves, created in the crystal by inverse piezoelectric effect, when fast HV electrical pulse is applied to it, these values are V_1=(5600 ± 100) m/s and v_2=(6400 ± 100) m/s along 0z and 0x axes correspondingly.