Fig. 1. Implementations of a silicon photonic OPA combined with grating emitters. The inset shows the far-field image^[46].

Fig. 2. Schematic diagram of the traditional single-polarized unidirectional lidar and the dual-polarized bidirectional integrated solid-state lidar.

Fig. 3. A general picture of the specific effects that the dual-polarized bidirectional lidar can selectively achieve. AR, angular resolution; FOV, field of view. TE/TM outputs are shown with solid/dashed lines, and different wavelengths are shown in different colors. The arrow on top of the wavelength indicates the propagating direction of the signal.

Fig. 4. Schematic diagram of polarization-multiplexed OPA^[58].

Fig. 5. (a) Calculated far field of 1600-nm TE-polarized mode; (b) calculated far field of 1500-nm TM-polarized mode; (c) beam-steering range of the 340-nm grating emitter in two polarization modes^[58].

Fig. 6. (a) Expanding the longitudinal scanning range of OPA by polarization multiplexing. α represents the phase difference between adjacent channels. (b) Schematic diagram of the improved optical antenna. θ represents the longitudinal steering angle, while ψ represents the lateral steering angle. (c) Longitudinal steering range θ of TE₀ and TM₀ modes by adjusting the work wavelength while maintaining a phase difference of 0°^[59].

Fig. 7. (a) Diagram of the proposed polarized multiplexing OPA; (b) vertical beam-steering range of Grt2 was computed by adjusting Wgrt2 from 0.36 to 0.46 µm. The red area represents Grt1 with the specified parameters^[61].

Fig. 8. Schematics of a beam-steering device based on the enhanced angular dispersion of gratings on slow-light waveguides. (a) LSPCW that enhances the top emission intensity using a shallow grating; (b) LSPCW array with prism lens for 2D beam steering, which preserves collimation conditions across a broad range of θ, and (c) the beam can be steered in the ϕ direction by choosing a certain LSPCW from its array, which follows the same principle as described in Ref. [16]. (d) Continuous beam steering in the ±θ^′ direction, containing θ^′ = 0°, is achieved by transforming θ into θ^′ using the prism lens and altering the direction of light incidence on the LSPCW^[62].

Fig. 9. (a) Theoretical structure of a wide-angle OPA, wherein no additional layers are included. (b) Schematic and (c) cross section of a wide FOV waveguide GC antenna^[63].

Fig. 10. Optimized WGA’s normalized far-field pattern^[63].

Fig. 11. (a) Configuration of a GC based on counterpropagating TE-polarized beams to double the beam-steering angle; (b) GC and system configuration utilizing counterpropagating TE-polarized beams^[64].

Fig. 12. Transmittance and output angles of four beams. Arrows mark four wavelengths’ locations^[64].

Fig. 13. Configuration of the device consisting of two GCs with orthogonal polarization modes^[65].

Fig. 14. Output angle of the two diffracted beams for 3D simulation, computed theoretically and through numerical simulation^[65].

Fig. 15. (a) Device configuration of two GCs. (b) System diagram of LiDAR transmitter system to increase the beam-steering angle^[66].

Fig. 16. (a) Theoretical and numerical 3D results of TE and TM beams’ output angles; (b) linear regression of eight beams’ output angles^[66].

Fig. 17. Schematic diagram of the proposed dual-polarized bidirectional OPA and the total longitudinal scanning range of the proposed OPA^[67].

Fig. 18. System configuration using dual-polarized bidirectional beams. The TE/TM outputs are represented by solid and dotted lines. The signal’s direction of propagation is shown by the arrow above the wavelength. Various wavelengths are shown in different colors^[68].

Fig. 19. (a) Numerical simulation results of the output angles for 16 beams; (b) linear regression analysis on the output angles of eight beams located on the right side of the vertical line, which is perpendicular to the SOI waveguide plane^[68].

Table 1. Comparison of the Lidar’s Parameters