In a study published in the Journal of the Optical Society of America B, a research team led by SHAO Shuai from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) proposed a multi-beam steering technique with low grating lobes using unequally spaced phased array. 

Optical phased array (OPA) uses lasers operating in the optical waveband as the information carrier, and is not subject to traditional radio interference. The OPA can be integrated on a chip with small size, light weight, good flexibility and low power consumption. These advantages make the OPA extremely attractive in the fields of free space optical communication, light detection and ranging, image projection, lidar and optical storage.

However, limited by current fabrication levels, current OPA elements can achieve a minimum spacing much greater than half the wavelength of the light. Small spacing between adjacent elements can cause crosstalk in the emitted beam. Large grating lobes not only reduce the main beam energy concentration, but also affect the beam scanning range. Consequently, Suppression of grating lobes is an urgent problem to be solved at this stage.

Some techniques have been shown to suppress grating lobes, such as particle swarm optimization (PSO) and genetic algorithm (GA). These techniques were used to optimize the arrangement of the phased array elements. The optimized array spacing was no longer uniform and the grating lobes were significantly reduced. There techniques were proposed in the case of single beam steering and were equally applicable to multi-beam steering.

To investigate the performance of the proposed method, the far-field pattern of the optimized unequally spaced SA was simulated when the dual-beam directions were at ±10? and ±20?. The results showed that the grating lobes were suppressed and the peak sidelobe levels (PSLL) as low as 0.2163 and 0.225 were achieved.