Optical Phased Arrays (OPAs) provide distinctive non-mechanical beam steering and control capabilities, and have exhibited great application potential in LiDAR, wireless optical communications and other fields. At the heart of an OPA is the ability to precisely control the phase of each channel in the array, thereby achieving beam forming and steering in free space without requiring any physically moving parts. This significantly enhances response speed and system reliability. In recent years, the rising of integrated optical phased array chips adds the benefits of small size, low cost, and higher speed.

However, current integrated OPA chips are often limited to using a single beam for steering, not exploiting the full potential of OPAs. For example, LiDAR used in autonomous driving often encounters the scenario of multiple independently moving objects (cars, pedestrians, etc.). If independent multiple beams can be generated to point at each object, each object's position will be detected and followed more promptly. However, existing issues of in integrated OPAs such as inherent random phase errors due to fabrication variation hinder the realization of independent multi-beam generation.

To overcome this limitation, the team led by Professor Wei Jiang from Nanjing University, in collaboration with Professor Jinshan Su from Yili Normal University, explored multi-beam generation and control using an integrated optical phased array. By introducing subarray partitioning into the phased array and developing a suitable phase control strategy, independently controlled multiple beams can be generated simultaneously, which are verified by simulation and experiment with dual-beams. The results are published entitled "Independent dual beams generated by array element division in integrated optical phased arrays" in Chinese Optics Letters, Vol. 22, No. 7, 2024.

Fig. 1 Generation of independent dual-beams by an OPA chip. (a) Schematic illustration of beams pointing at two independent objects; (b) Experimental results.

Starting from OPA's working principle, the research team delved into the theoretical basis of multi-beam generation, focusing on the generation of independently controlled dual-beams by dividing the optical phased array into two sub-arrays. Subsequently, a multi-step process was developed to generate and distribute sub-array phase parameters in presence of random phase errors, assisted by analysis of far-field beam patterns. This approach effectively overcomes the severe beam deformation and dissolution caused by random phase variation originating from imperfect fabrication processes of OPA chips. As such, it ensured the quality and stability of the output dual beams. With this combination of theoretical insight and technical advancement, the team demonstrated precise control of independent dual-beams in the far-field using an OPA chip. By combining the half-wavelength pitch waveguide superlattice structure that the team had previously proposed, the dependent secondary beams were eliminated from the OPA output, further ensuring the independence and purity of the dual-beams. As a result, the field-of-view (FoV) for the independent dual-beams generated by the OPA chip was expanded to 100°. Further experimentation revealed that by adjusting the number of elements in the sub-arrays, it was possible to regulate the relative intensity of the beams while keeping their directions unchanged.

The work validates the feasibility of achieving independent multi-beam capabilities over a wide field-of-view using integrated OPAs, which holds promise for empowering LiDAR applications in multi-object scenarios and provides new perspectives for beam control technologies in related fields. In the future, the team will further investigate the device physics of integrated OPAs built upon silicon photonics technology, and continuously explore new applications.