Facile metagrating holograms with broadband and extreme angle tolerance

The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths.The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application,in addition to high fabrication precision demands.Utilizing a different design principle,we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances(near-grazing incidence)in the visible–near-infrared regime.By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters,the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle.The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand,thereby opening new routes for flat optics with high performances and improved practicality.

Note on the Longest Paths in {K_(1,4),K_(1,4)+e}-free Graphs

A graph G is{K_(1,4),K_(1,4)+e}-free if G contains no induced subgraph isomorphic to K_(1,4) or KI,a+e In this paper,we show that G has a path which is either hamiltonian or of length at least 25(G)+2 if G is a connected{K_(1,4),K_(1,4)+e}-free graph on at least 7 vertices.

Multifunctional metasurface: from extraordinary optical transmission to extraordinary optical diffraction in a single structure: publisher's note

This publisher＇s note reports the revision of authors＇ name spelling in Photon. Res. 6, 443 （2018）.

Mid-infrared waveguiding in three-dimensional microstructured optical waveguides fabricated by femtosecond-laser writing and phosphoric acid etching

We fabricated a three-dimensional microstructured optical waveguide(MOW)in a single-crystal using femtosecond-laser writing and phosphoric acid etching techniques,and observed excellent midinfrared waveguiding performance with low loss of^0.5 d B∕cm.Tracks with a periodic arrangement were written inside the yttrium aluminum garnet(YAG)crystal via femtosecond laser inscription,and then etched by the phosphoric acid(H3 PO4)to form hollow structures.The evolution of the microstructure of tracks was investigated in detail.The function of the MOW was analyzed by different numerical methods,indicating the proposed MOW can effectively operate in quasi-single-mode pattern in the midinfrared wavelength range,which agrees well with our experiment results.

All-angle reflectionless negative refraction with ideal photonic Weyl metamaterials

Negative refraction,an unnatural optical phenomenon in which the incident and the refracted waves reside on the same side of the surface normal,has been demonstrated with the invention of negative index media based on artificially engineered photonic structures called metamaterials.It has received wide attention due to its potential applications in imaging,nonlinear optics,and electromagnetic cloaking.However,it is highly challenging to realize negative refraction operating at all angles and with the perfect transmission.In this work,leveraging the recent development in topological photonics,we propose to realize reflection less negative refraction for all incident angles with a topological metamaterial.The proposed metamaterial possesses two Weyl points of opposite topological charges.By interfacing the metamaterial with a perfect electric conductor(PEC)or a perfect magnetic conductor(PMC),the Fermi arc connecting the two Weyl points can take the form of a half-circle possessing a positive or a negative refractive index.Importantly,due to the topological protection,there is no reflection at the interface between the PEC and PMC covered areas,leading to the observation of all-angle negative refraction without reflection at the boundary.Our work provides a new platform for manipulating the propagation of surface waves,which may find applications in the construction of integrated photonic devices.

Five-channel frequency-division multiplexing using low-loss epsilon-near-zero metamaterial waveguide

The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.