Switchable phase/intensity sensor made with ring-shaped and hexagonal ferroelectric domains

We present a device, similar to a Shack-Hartmann sensor, that can detect both the intensity distribution and wavefront of an incident wave. Its operation is based on the use of an array of electrically controllable Fresnel zone plates made in a ferroelectric crystal, lithium niobate. This sensor, which requires only one camera, can be quickly switched between intensity- and phase-detecting modes. Two kinds of arrays are shown: Fresnel zone plates with a few ring-shaped ferroelectric domains and plates made with nested hexagonal domains. Both arrays are suitable for use in a Shack-Hartmann wavefront sensor. However, since in lithium niobate domains naturally tend to form hexagons, it is easier to make hexagonal, rather than ring-shaped, domains and, consequently, smaller zone plates can be produced. This allows an increase in the number of zone plates and a reduction in their focal length, which improves the fidelity of the reconstructed wavefront.