Operation of electrooptic modulators is based on the principle of induced birefringence. Pockels cell is such device which can produce controllable birefringence by applying voltage to the cell. The cell contains uniaxial crystal, which becomes biaxial when electric field is applied. If new axes induced by the applied electric field are at 45° to the plane of polarization of the incident beam, the incident beam is split into two equal orthogonally polarized components. They propagate in a crystal with different velocities because of induced different refraction indexes. Induced birefringence Δn is proportional to the applied electric field and on the crystal length l it gives controlled phase retardation Γ between these components, which is used for the incident beam modulation.
There are only two basic designs of Pockels cells:
1. Pockels cell with longitudinal electrooptic effect, employing a crystal in which electric field is applied along the direction of the optical beam.
2. Pockels cell with transverse electrooptic effect, utilizing a crystal in which electric field is perpendicular to the direction of the optical beam.
Solaris Optics produces KDDP Pockels cells and Lithiumniobate Pockels cells.