2D Optical Phased Arrays for Laser Beam Steering Based on 3D Polymer
Photonic Integrated Circuits
Abstract
We propose a novel concept for the implementation of 2-dimensional (2D)
optical phased arrays (OPAs) with end-fire waveguides as antenna
elements (AEs), and we present its theoretical model and experimental
proof. The concept is based on the use of 3-dimensional (3D) photonic
integrated circuits (PICs) with multiple waveguiding layers on the
PolyBoard platform. In their simplest form, the 3D PICs comprise AEs at
different layers, vertical and lateral couplers for the distribution of
light among the AEs, and phase shifters for the execution of the 2D beam
scanning process. Using the field equivalence principle, we model the
radiated field from the single-mode waveguide of the platform at 1550
nm, and we find that the expected beam width is 12.7o.
We also investigate the perturbation that is induced into propagating
fields inside parallel waveguides in proximity, and we conclude that
waveguide spacings down to 6 µm can be safely used for development of
uniform OPAs in the PolyBoard platform. For OPAs with 6 µm pitch and 4
AEs, we find that the maximum steering angle is 14.0o
and the expected angular clearance, wherein the main radiation lobe is
higher than any grating lobe by at least 3, 6 and 10 dB is
10.8o, 7.6o and
2.8o, respectively. Based on our simulations, we
design and fabricate single- and 2-layer PICs with 1×4 and 2×4 OPAs. The
lateral pitch of the OPAs ranges from 10 down to 6 µm, while the
vertical pitch is 7.2 µm. We experimentally characterize these OPAs and
validate the potential of the 2-layer PICs for 2D beam scanning on the
azimuthal and elevation plane. The beam profiles and the main scanning
parameters such as the maximum steering angle and the relative intensity
between the main and the grating lobes are found in excellent agreement
with our simulations.