Nonlinear photonic crystals, in which the quadratic nonlinear coefficient is spatially modulated, are widely used to enable efficient three wave mixing interactions. Many periodic and quasi-periodic structures have been used in recent years for phase matching collinear and non-collinear interactions. Most of these structures offer discrete phase matching solutions and can be used to generate optical radiation at a single and specific direction. In this work we present a new type of structures that offers continuous non-collinear phase matching possibilities, allowing continuous wavelength and temperature controlled all-optical deflection.
We designed and manufactured the proposed structures in a Stoichiometric Lithium Tantalate crystal. The inverted domains consist of a set of arcs arranged in the propagation direction. This arrangement results in a periodic pattern in the propagation direction and a chirped pattern in the transverse direction. A second harmonic generation experiment was performed on the crystal structures to examine the phase matching properties. Varying the pump wavelength from 1545 nm to 1536 nm at 150 0C resulted in continuous angular deflection of the second harmonic wave up to ~2.5°. Continuous deflection was also obtained by varying the crystal temperature at a fixed pump wavelength. These structures can be used for various all-optical deflection applications, e.g. optical-controlled light deflector using two cascaded nonlinear processes: an up-conversion process of signal and control beams, where the output angle is controlled by the frequency of the controlling beam, followed by a down conversion process, creating a beam at the signal frequency in the desired angle.