Large-scale nanophotonic phased array

Abstract

Electromagnetic phased arrays at radio frequencies are well known and have enabled applications ranging from communications to radar, broadcasting and astronomy. The ability to generate arbitrary radiation patterns with large-scale phased arrays has long been pursued. Although it is extremely expensive and cumbersome to deploy large-scale radiofrequency phased arrays, optical phased arrays have a unique advantage in that the much shorter optical wavelength holds promise for large-scale integration. However, the short optical wavelength also imposes stringent requirements on fabrication. As a consequence, although optical phased arrays have been studied with various platforms and recently with chip-scale nanophotonics, all of the demonstrations so far are restricted to one-dimensional or small-scale two-dimensional arrays. Here we report the demonstration of a large-scale two-dimensional nanophotonic phased array (NPA), in which 64 × 64 (4,096) optical nanoantennas are densely integrated on a silicon chip within a footprint of 576 μm × 576 μm with all of the nanoantennas precisely balanced in power and aligned in phase to generate a designed, sophisticated radiation pattern in the far field. We also show that active phase tunability can be realized in the proposed NPA by demonstrating dynamic beam steering and shaping with an 8 × 8 array. This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide-semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips. In turn, this enables arbitrary radiation pattern generation using NPAs and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large-scale deployment in applications such as communication, laser detection and ranging, three-dimensional holography and biomedical sciences, to name just a few.

High-density waveguide superlattices with low crosstalk

“…For example, a phased array ideally requires emitters with l/2 pitches to achieve maximal beam steering range. Halfwavelength pitches are routinely used in microwave-phased arrays, but have been a challenge for optical-phased arrays (OPAs) 20,40,41 . The current waveguide superlattice can be used in certain silicon-based OPA configurations 18,19 to deliver phasemodulated signals to an array of output waveguide-facets (or waveguide-gratings) radiating signals at l/2 pitches, which results in l/2-pitch optical-phased arrays.…”

“…Note that in many applications such as wavelength (de)multiplexers 20,40,41 , spectrometers and optical-phased arrays 25,26 , the number of waveguides in the input/output arrays can be fairly large. The superlattice approach can reduce crosstalk for a large number of waveguides whereas the prior approach applies only to two waveguides.…”

“…Assume all waveguides have equal input power, the overall crosstalk summed from contributions of all other waveguides will be o À 20.2 dB for the worst waveguide channel. Note that optical-phased arrays often use equal power among channels 20,40,41 . In many WDM systems, the optical power values in channels are often balanced/equalized 49 .…”

“…Waveguide arrays are among the cornerstones of such systems. For example, waveguide arrays are widely used in emerging applications such as optical-phased arrays [18][19][20][21] , space-division multiplexing 22 and chip-scale optical interconnects 23,24 , and conventional applications such as wavelength-division multiplexers 25,26 . On the other hand, a waveguide array or a waveguide lattice can also be viewed 27 as fully analogous to a periodic chain of atoms, which lends itself to a broad spectrum of fascinating scientific possibilities ranging from Anderson localization of light 28,29 to parity-time symmetric effects 30 .…”

High-Speed, Phase-Dominant Spatial Light Modulation with Silicon-Based Active Resonant Antennas

“…The demonstrated design can be easily integrated in a scalable fashion using conventional CMOS technology (e.g. silicon photonics 34,35 ), allowing large-scale phase-dominant SLMs to be implemented on inexpensive and compact photonic chips. As such, the presented spatial light modulation device will enable cost-effective beam steering solutions for LiDAR and scanning microscopy.…”