Highly efficient electro-optical modulator for unpolarized light

The principle of operation of the proposed electro-optical modulator is based on two physical phenomena: spatial separation of ordinary and extraordinary rays and rotation of the plane of polarization of light as a result of the electro-optical effect. The modulator consists of three optical elements in the form of parallelepipeds. The active element is made of lithium niobate (LiNbO₃) crystal. Light-transmitting coatings are deposited on the polished faces perpendicular to the Z axis. Metal electrodes are applied on both sides along the X-axis. When a half-wave voltage U_λ/2 is applied, the plane of polarization of light passing through the active element rotates by an angle of 90o. Light-splitting elements made of calcite are located in front of and behind the active element. Unpolarized laser radiation falls on the entrance edge of the calcite crystal, where it is split into ordinary and extraordinary rays that fall on the active element. In the absence of a half-wave voltage on the lithium niobate crystal, the direction of polarization of the ordinary and extraordinary rays at the output does not change. If a half-wave voltage is applied to a lithium niobate crystal, the polarization directions of these rays rotate by 90°. When they hit the calcite crystal, the ray that was an extraordinary ray in the first calcite element becomes ordinary in the second calcite element, and, accordingly, the ordinary ray becomes extraordinary. As a result, at the output of the third element of the modulator, the rays are separated by a certain distance. Such a modulator allows the use of unpolarized radiation without the usual 50% power loss, which corresponds to a twofold increase in radiation power. Based on specially developed software, the electro-optical effect was optimized to make the most efficient use of lithium niobate crystals as active elements of the created electro-optical modulator.