Electro-optically Controlled Switching and Deflection in Domain-Engineered LiNbO3

We report a beam deflection technique that exploits electric-field controlled deflection and total internal reflection at the interface between two anti-parallel domains realized in a single crystal lithium niobate wafer. The LiNbO3 z-cut sample was 500-μm-thick and was photolithographically patterned and poled by means of an applied electric field, in order to realize two adjacent regions of opposite domain orientation. The boundary between these domains should be very regular and free from residual stress, but in practice, a small residual index difference exists at the interface. An electric filed Ez applied across the interface region, produces equal in magnitude, but opposite in sign, refractive index variations between the adjacent anti-parallel domains. For sufficiently large index variation, and for grazing incidence geometry, that is when the incidence angle is between 87° and 89°, we obtain a high efficient beam deflection. Furthermore, if the incidence angle approaches the limit angle, which is about 89°, the Total Internal Reflection (TIR) occurs, producing an abrupt beam switch from transmission to reflection, characterized with a theoretical 100% switching contrast. However, the residual interface stress generates significant Fresnel reflection from this interface at high grazing angles, limiting the switching contrast ratio achievable at 20 dB. We present data obtained for wavelengths of 632.8 nm and 4.5 μm; at the latter wavelength we demonstrated the possibility to perform amplitude modulation faster than mechanical chopping, in a spectral region where no Pockels cells are available