46 FMCW tech FMCW technology combined with OPA is seen as promising for the all-solidstate Lidar. FMCW takes advantage of the laser source coherence, granting a high immunity to ambient light of the 3D imaging system. Inertia-less beam steering based on silicon-integrated OPA is an essential component for the solid-state Lidar. High-performance, integrated OPA should have a wide field of view and a small beam divergence. A silicon integrated OPA combined with an optical-frequency microcomb has been developed experimentally for a parallel Lidar system with four beams, each with a separate phase, to increase the FoV. The beam divergence and multi-beam quality are challenging to implement, but they are essential for producing parallel beams, with each carrying distinct wavelength information. An ultra-long, optical grating antenna with a low coupling constant and a low phase error is usually required for a small divergence. A millimetre-scale antenna can be implemented with small etching corrugations of silicon waveguide or assisted with the multi-layer material, such as silicon nitride. However, it demands high lithography precision, etching precision or heterogeneous material growth, which is complex to make and has a high cost. In the detection terminal, the coherent method is usually superior to the other implementations in the circumstance of low visibility or high background light. One system has been developed with a measured beam divergence of around 0.037° with the long optical grating antenna, which is consistent with the comb tooth spacing (101.3GHz). The signals from the multiple comb tooth, carrying distinct wavelength information, are output and steered by the integrated OPA. The all-solid-state parallel Lidar has been demonstrated with the FMCW method for 3D ranging. External modulation is used to obtain the parallelfrequency, modulated, multi-wavelength laser source with only one pump laser. Other designs improve the optics of FMCW flash Lidar by integrating critical components into a single device, opening up opportunities for compact and efficient systems for autonomous driving. This integrated version of the illumination optics of an FMCW flash Lidar is a first step towards a fully integrated Lidar sensor that cuts costs and boosts performance. Heterodyne detection consists of separating and then recombining a timevarying frequency laser beam. The split beam illuminating the scene undergoes a delay compared with the reference beam, resulting in a beating signal formation on the detector after recombination. Pairing FMCW with a flash illumination (simultaneous illumination of the whole scene) instead of a scanning technique offers potential benefits such as a higher frame rate due to parallel detection and the absence of moving parts. Full integration of this system would reduce fabrication costs, and increase scalability and compactness. An integrated design for the emission optics on a photonic chip is responsible for both functions of beam separation and scene illumination. An apodized grating coupler with few periods provides a large horizontal and vertical illumination April/May 2025 | Uncrewed Systems Technology Conceptual illustration of the FMCW system, based on an integrated microcomb combined with OPA, where the comb is pumped by the laser (Image courtesy of Zhejiang University) A full Lidar on a chip (Image courtesy of Lidwave)
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