Beam steering in LIDAR systems is essential for directing and scanning laser beams over a wide field of view (FOV). One promising method for achieving this is by using EO crystals, which allow fast and precise beam deflection without mechanical components. This method leverages the electro-optic effect, where the refractive index of a crystal changes in response to an applied electric field. As a result, the beam’s path can be altered by modifying the optical path difference (OPD) within the crystal.
Beam deflection in a first crystal followed by the beam traveling through a second crystal. A half-wave-plate (not shown) is between the two crystals.
For bulk beam steering, light passes through the EO crystal, which creates an OPD, thereby deflecting the beam. Unlike traditional mechanical systems, EO-based steering does not require resets, and the angular deflection is typically achieved within a single or double-crystal configuration. Each dimension can be controlled using separate crystals, with one crystal handling steering in the first dimension and the second crystal adjusting the second dimension. The challenge, however, is to manage “beam walk-off,” a phenomenon where the deflected beam gradually drifts inside the crystal due to refraction. This walk-off must be minimized to avoid hitting the side walls of the crystal, especially for large deflection angles.
In terms of optimization, the goal is to maximize the beam-steering angle while minimizing switching time and power loss. The interaction length of the EO crystals must be minimized to reduce beam blockage. Beam steering is controlled by adjusting the voltage applied across the crystal electrodes, with the steering angle being proportional to the applied voltage or its square. Precise voltage control is essential for achieving accurate beam deflection, and special care is needed to address hysteresis, where the crystal’s response to voltage might lag or deviate upon reversing the voltage polarity.
Additionally, certain types of EO crystals, such as Lithium Niobate (LiNbO₃), Potassium Tantalate Niobate (KTN), and Strontium Barium Niobate (SBN), are highly suited for LIDAR applications due to their large EO coefficients and high refractive index changes under reasonable voltages. These crystals offer fast switching times, robustness, and the ability to handle larger deflection angles without mechanical components.
By optimizing EO crystal beam steering configurations, it is possible to design compact, efficient, and fast-scanning LIDAR systems suitable for autonomous vehicles and various industrial applications.
