Molding free-space light with guided wave–driven metasurfaces

Abstract

Metasurfaces with unparalleled controllability of light have shown great potential to revolutionize conventional optics. However, they mainly require external light excitation, which makes it difficult to fully integrate them on-chip. On the other hand, integrated photonics enables packing optical components densely on a chip, but it has limited free-space light controllability. Here, by dressing metasurfaces onto waveguides, we molded guided waves into any desired free-space modes to achieve complex free-space functions, such as out-of-plane beam deflection and focusing. This metasurface also breaks the degeneracy of clockwise- and counterclockwise-propagating whispering gallery modes in an active microring resonator, leading to on-chip direct orbital angular momentum lasing. Our study shows a viable route toward complete control of light across integrated photonics and free-space platforms and paves a way for creating multifunctional photonic integrated devices with agile access to free space, which enables a plethora of applications in communications, remote sensing, displays, etc.

Optical meta-waveguides for integrated photonics and beyond

“…• By saddling subwavelength architectures on top of dielectric waveguides, exquisite control over the electromagnetic fields is attainable to facilitate versatile couplers [36][37][38][39][40][41][42][43][44] , compact polarization-or wavelength-routers [48][49][50] , on-chip structured light generators 35,[45][46][47][77][78][79][80][81] , integrated mode convertors 51,[82][83][84][85][86][87][88][89] , sensors [90][91][92][93] and nonlinear devices 52,94,95 (discussed in Section "Dielectric waveguide-integrated meta-structures").…”

“…Another general case is applying meta-structures on waveguide surfaces to act as Mie resonators or Rayleigh scatterers [21][22][23] to perform designer index perturbations [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]136 . The structures can be metal or dielectric materials on top of as-fabricated waveguides after deposition and lift-off 35,37,[48][49][50][51][52] . Alternatively, these subwavelength features (either fully 38,39,47,[54][55][56][63][64][65][66][67][68] or partially etched 45,78,[84][85][86][87][88][89] ) ...…”

“…Brief physical fundamentals with explicit design methods and representative applications for meta-waveguides are comprehensively summarized. We highlight how incorporating the concepts of meta-optics with waveguide technologies can propel photonic integrated circuits into new heights, by providing versatile efficient coupling interfaces [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] , novel on-chip optical signal processing paradigms 12, and diverse platforms for sensing, imaging and artificial intelligence [57][58][59][60][74][75][76] . We further comment on current challenges in device design and practical hurdles from ripening into viable technology.…”

Free-Space Applications of Silicon Photonics: A Review

“…Shaping the free-space emission from a silicon photonic chip to create a focused beam has been achieved with different approaches [ 18 , 73 , 74 , 75 , 76 , 77 ]. Beam focusing allows optical excitation or sensing exclusively of a small volume in the space, which is critical for quantum computation with ion qubits [ 18 ], optical tweezers [ 78 ], optogenetics [ 17 ], FPA-based beam steerers [ 44 ], and microscopy.…”

Monolithic‐Integrated Multiplexed Devices Based on Metasurface‐Driven Guided Waves

“…Ni et al developed a hybrid architecture where metasurfaces are directly driven by guided wave to realize deflection and focusing. [27] This work solves the problem that the phase modulation of 2 cannot be realized on the waveguide. In contrast, Li et al constructed multiplexed holograms under surface plasmon polariton illuminations with different propagation directions, [28] which greatly increase the capacity of information transmission.…”