Robust and Broadband Optical Coupling by Topological Waveguide Arrays

Abstract

Photonic topological states have been exploited to give rise to robust optical behaviors that are quite insensitive to local defects or perturbations, which provide a promising solution for robust photonic integrations. Specifically, for example, optical coupling between waveguides is a universal function in integrated photonics. However, the coupling performance usually suffers from high structure‐sensitivity and challenges current manufacturing for massive production. Here, the topological edge state in a finite Su–Schriffer–Heeger modeled optical waveguide array is explored and robust optical coupling (e.g., directional coupling and beam splitting) is demonstrated, which is quite insensitive to structural variations. It is experimentally proved that even a large discrepancy (21–26% structural deviation) in silicon waveguides gaps has little influence on optical coupling (>90% performance), while conventional counterparts totally break down. Moreover, thanks to such a topological design, the devices show much broader working bandwidth (≈10 times performance improvement) than the conventional ones, greatly favoring the photonic integrations. This work would inspire new families of optical devices with robust and broadband properties that can excite more interesting and useful exploration in both fields, and possibly open a new avenue toward topological devices with unique properties and functionalities.

Artificial gauge induced dispersionless coupling for broadband photonic waveguide integration

“…For example, the adiabatic optical couplers exhibit broadband property but have a large footprint (~150 μm) 14 . The same is true for the topological inspired designs (footprint ~80 μm) 24 . On the contrary, the inverse design methods usually have compact footprints, while the performances highly depend on the design optimization algorithm [15][16][17][18] .…”

“…Tremendous efforts have been made to control the evanescent wave coupling and realize the broadband property. e.g., the adiabatic structures [12][13][14] , inverse design methods [15][16][17][18] , metamaterials [19][20][21][22][23] , and topological designs 24,25 . However, the multiple desired qualities are difficult to reach at the same time, usually, one satisfied performance needs to sacrifice in other important aspects.…”

Non-Hermitian topological coupler for elastic waves

“…As classical analogies of the quantum topological insulators [7], the associated unidirectional propagating edge states have been extended into different classical wave regimes such as pho-tonics [8,9], airborne acoustics [10][11][12][13][14], water waves [15] and elastic waves [16][17][18][19][20][21]. Up to date, topology has found applications in waveguide coupling [22], robust Fano resonance [23], vortex lasing [24], and one-way propagation of signals for communications and spin-wave manipulation devices [25,26]. Therefore, topologically protected edge states with backscattering-immune and spin-momentum locking effects provide robustness of operating classical waves.…”

Tailoring Topological Edge States with Photonic Crystal Nanobeam Cavities

“…Another elegant and powerful subwavelength-scale nontrivial topology approach is the Su-Schrieffer-Heeger (SSH) model, which was originally introduced to describe fractionalized electric charges in polyacetylene and has recently attracted considerable attention in photonics. Photonic SSH structures have been extensively investigated and applied to a broad range of platforms from microwave to optical regime including photonic superlattices 38 , plasmonic waveguides 39 , zigzag arrays of dielectric resonator chain 40 , dielectric nanoparticles 41 , polariton micropillars 7 , micro-ring resonator arrays 42,43 , photonic crystal L3 nanocavity dimer array 44 , dielectric waveguides [45][46][47][48][49] . These platforms open avenues to on-chip photonic devices for robust topologically protected light manipulation.…”