Two-dimensional multi-beam steering for parallel free-space optical communication based on a silicon nitride optical phase array

We propose and demonstrate a broadband two-dimensional multi-beam optical phased array (MOPA) with four beams based on a Butler matrix on a silicon nitride (Si3N4) platform. A beamforming network utilizing cascaded Butler matrix splitting arrays has been proposed to scale up the MOPA for the first time, to the best of our knowledge, significantly reducing the number of waveguide crossings. A 32-channel MOPA with four beams has been designed and fabricated with a uniform antenna pitch of 3.5 μm. Experimental results indicate that the field of view is 25.6° × 8.1°, with a beam divergence of 0.655° × 0.085°. Simultaneous multi-beam 2D high-power operation and independently scanning along the wavelength steering axis have been demonstrated. Furthermore, parallel and high-speed free-space optical communication based on the fabricated MOPA has been performed. Data transmission of 40 Gbps non-return-to-zero on–off keying has been achieved, revealing the potential of low system complexity and power-efficient multi-access data transmission.