On-chip Si3N4 Grating coupler for magneto-optical trap in cold atom systems

Cold atoms play an important role in fundamental physics, precision timekeeping, quantum sensing and quantum computing. The fabrication of cold atoms requires the use of magneto-optical trap (MOT), but current magneto-optical traps require a variety of complex and voluminous optical infrastructures that hamper their practical application. The development of integrated photonic circuits offers the opportunity to achieve integrated MOTs. Here, we take advantage of the ultra-low loss of the silicon nitride platform to design a grating coupler for coupling a beam from a waveguide to free space on a silicon nitride platform. Its wavelength is 780 nm, the coupling angle is 30°, and the spot beam waist radius is 2 mm at a height of 5 mm on the chip.