Optical Phased Arrays for High Speed, Non-Mechanical Beam Steering Applications

Abstract

Optical beam steering has many applications ranging from sensing and detecting to light and image projection. A hybrid annealed proton exchange waveguide with a vertically integrated arsenic trisulfide waveguide on a lithium niobate substrate was used to create a low-loss, high-speed optical phased array that allows for the non-mechanical steering of 1550 nm light on an integrated optic platform. The high electro-optic coefficient of the x-cut y-propagating LiNbO₃ (r₃₃ = 30.8 pm/V) is utilized by electrode structures fabricated on the LiNbO3 substrate to create low-power, low-loss beam steering with high-speed bandwidths, capable of 10 GHz and larger, as demonstrated by commercial LiNbO₃ modulators. The introduction of the higher refractive index As₂S₃ waveguide is critical because it leads to a highly confined optical mode. The design, simulation, and fabrication of this device are presented here.

For measurements and as a preliminary proof of concept, two different platforms have been employed in series to leverage EO tuning. An APE:LiNbO₃ optical phased array was fabricated and edge coupled to a silicon nitride 8x8 waveguide array that condenses the output pitch and utilizes the Triplex™ waveguide technology. To characterize and tune this device, a 3 lens imaging system was utilized to produce both near- and far- field intensity patterns of the output of the OPA on a static image plane. At the image plane, a high resolution infrared camera was used to observe the resulting intensity pattern. The control software for tuning the OPA can read the intensity incident at a specified position on the detector array, and has an electronically controlled pulse width modulation hardware interface to drive the electro-optic phase shifters. Beam steering was achieved using an iterative tuning algorithm to maximize the intensity at a specified location.