Experimental demonstration of a silicon nanophotonic antenna for far-field broadened optical phased arrays

Optical antennas play a pivotal role in interfacing integrated photonic circuits with free-space systems.Designing antennas for optical phased arrays ideally requires achieving compact antenna apertures,wide radiation angles,and high radiation efficiency all at once,which presents a significant challenge.Here,we experimentally demonstrate a novel ultra-compact silicon grating antenna,utilizing subwavelength grating nanostructures arranged in a transversally interleaved topology to control the antenna radiation pattern.Through near-field phase engineering,we increase the antenna’s far-field beam width beyond the Fraunhofer limit for a given aperture size.The antenna incorporates a single-etch grating and a Bragg reflector implemented on a 300-nm-thick silicon-oninsulator(SOI)platform.Experimental characterizations demonstrate a beam width of 44°×52°with−3.22 dB diffraction efficiency,for an aperture size of 3.4μm×1.78μm.Furthermore,to the best of our knowledge,a novel topology of a 2D antenna array is demonstrated for the first time,leveraging evanescently coupled architecture to yield a very compact antenna array.We validated the functionality of our antenna design through its integration into this new 2D array topology.Specifically,we demonstrate a small proof-of-concept two-dimensional optical phased array with 2×4 elements and a wide beam steering range of 19.3º×39.7º.A path towards scalability and larger-scale integration is also demonstrated on the antenna array of 8×20 elements with a transverse beam steering of 31.4º.

Fully integrated and broadband Si-rich silicon nitride wavelength converter based on Bragg scattering intermodal four-wave mixing

Intermodal four-wave mixing(FWM)processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide.This allows,in principle,to place signals in different spectral regions and satisfy the phase matching condition over considerably larger bandwidths compared to intramodal processes.However,the demonstrations reported so far have shown a limited bandwidth and suffered from the lack of on-chip components designed for broadband manipulation of different modes.We demonstrate here a silicon-rich silicon nitride wavelength converter based on Bragg scattering intermodal FWM,which integrates mode conversion,multiplexing and de-multiplexing functionalities on-chip.The system enables wavelength conversion between pump waves and a signal located in different telecommunication bands(separated by 60 nm)with a 3 dB bandwidth exceeding 70 nm,which represents,to our knowledge,the widest bandwidth ever achieved in an intermodal FWM-based system.

Ultra-broadband nanophotonic phase shifter based on subwavelength metamaterial waveguides

Optical phase shifters are extensively used in integrated optics not only for telecom and datacom applications but also for sensors and quantum computing.While various active solutions have been demonstrated,progress in passive phase shifters is still lacking.Here we present a new type of ultra-broadband 90°phase shifter,which exploits the anisotropy and dispersion engineering in subwavelength metamaterial waveguides.Our Floquet–Bloch calculations predict a phase-shift error below 1.7°over an unprecedented operation range from 1.35 to 1.75μm,i.e.,400 nm bandwidth covering the E,S,C,L,and U telecommunication bands.The flat spectral response of our phase shifter is maintained even in the presence of fabrication errors up to 20 nm,showing greater robustness than conventional structures.Our device was experimentally demonstrated using standard220 nm thick SOI wafers,showing a fourfold reduction in the phase variation compared to conventional phase shifters within the 145 nm wavelength range of our measurement setup.The proposed subwavelength engineered phase shifter paves the way for novel photonic integrated circuits with an ultra-broadband performance.

Next-generation siliconphotonics:introduction

In the past decade,silicon photonics has been making tremendous progress in terms of device functionality and performances as well as circuit integration for many practical applications ranging from communication,sensing,and information processing.This special issue,including four review articles and nine research articles,aims to provide a comprehensive overview of this exciting field.They offer a collective summary of recent progresses,in-depth discussions of the state-of-the-art,and insights into forthcoming developments that are well poised to drive silicon photonics technology into its next generation.

Polarization-independent multimode interference coupler with anisotropy-engineered bricked metamaterial

Many applications, including optical multiplexing, switching, and detection, call for low-cost and broadband photonic devices with polarization-independent operation. While the silicon-on-insulator platform is well positioned to fulfill most of these requirements, its strong birefringence hinders the development of polarizationagnostic devices. Here we leverage the recently proposed bricked metamaterial topology to design, for the first time, to our knowledge, a polarization-independent 2 × 2 multimode interference coupler using standard 220 nm silicon thickness. Our device can be fabricated with a single etch step and is optimized for the O-band,covering a wavelength range of 160 nm with excess loss, polarization-dependent loss, and imbalance below 1 dB and phase errors of less than 5°, as demonstrated with full three-dimensional finite-difference time-domain simulations.