New deep learning techniques may hold the key to solving intractable photonics problems.

Abstract:At visible and infrared frequencies, metals show tantalizing promise for strong subwavelength resonances, but material loss typically dampens the response. We derive fundamental limits to the optical response of absorptive systems, bounding the largest enhancements possible given intrinsic material losses. Through basic conservation-of-energy principles, we derive geometry-independent limits to per-volume absorption and scattering rates, and to local-density-of-states enhancements that represent the power radiated or expended by a dipole near a material body. We provide examples of structures that approach our absorption and scattering limits at any frequency; by contrast, we find that common "antenna" structures fall far short of our radiative LDOS bounds, suggesting the possibility for significant further improvement. Underlying the limits is a simple metric, |χ| 2 / Im χ for a material with susceptibility χ, that enables broad technological evaluation of lossy materials across optical frequencies. 4. H. A. Atwater and A. Polman, "Plasmonics for improved photovoltaic devices," Nat. Mater. 9, 205-213 (2010). 5. G. V. Naik, J. Kim, and A. Boltasseva, "Oxides and nitrides as alternative plasmonic materials in the optical range [Invited]," Opt. Mater. Express 1, 1090-1099 (2011). 6. P. Tassin, T. Koschny, M. Kafesaki, and C. M. Soukoulis, "A comparison of graphene, superconductors and metals as conductors for metamaterials and plasmonics," Nat. Photonics 6, 259-264 (2012). 7. M. D. Arnold and M. G. Blaber, "Optical performance and metallic absorption in nanoplasmonic systems," Opt.Express 17, 3835-3847 (2009). 8. J. B. Khurgin and G. Sun, "In search of the elusive lossless metal," Appl. Phys. Lett. 96, 181102 (2010). 9. A. Raman, W. Shin, and S. Fan, "Upper bound on the modal material loss rate in plasmonic and metamaterial systems," Phys. Rev. Lett. 110, 183901 (2013). 10. J. B. Khurgin, "How to deal with the loss in plasmonics and metamaterials," Nat. Nanotechnol. 10, 2-6 (2015). 11. L. Novotny and B. Hecht, Principles of Nano-Optics (Cambridge University, 2012), 2nd ed. Electrons, and Plasmons, vol. 5 (W. A. Benjamin, 1964). 35. V. J. Keast, "Ab initio calculations of plasmons and interband transitions in the low-loss electron energy-loss spectrum," J. Electron Spectros. Relat. Phenomena 143, 97-104 (2005). 36. D. R. Lytle, P. S. Carney, J. C. Schotland, and E. Wolf, "Generalized optical theorem for reflection, transmission, and extinction of power for electromagnetic fields," Phys. Rev. E 71, 056610 (2005). 37. R. G. Newton, "Optical theorem and beyond," Am. J. Phys. 44, 639-642 (1976). Johnson, "Fundamental limits to extinction by metallic nanoparticles," Phys. Rev. Lett. 112, 123903 (2014).46. R. Fuchs, "Theory of the optical properties of ionic crystal cubes," Phys. Rev. B 11, 1732Rev. B 11, -1740Rev. B 11, (1975 14, 2783-2788 (2014). 142. U. Fano, "Effects of configuration interaction on intensities and phase shifts," Phys. Rev. 124, 1866Rev. 124, -1878Rev. 124, (1961. 143. K. Petermann, ...

The ability to display graphics and texts on a transparent screen can enable many useful applications. Here we create a transparent display by projecting monochromatic images onto a transparent medium embedded with nanoparticles that selectively scatter light at the projected wavelength. We describe the optimal design of such nanoparticles, and experimentally demonstrate this concept with a blue-color transparent display made of silver nanoparticles in a polymer matrix. This approach has attractive features including simplicity, wide viewing angle, scalability to large sizes and low cost.

Nanostructures with multiple resonances can exhibit a suppressed or even completely eliminated scattering of light, called a scattering dark state. We describe this phenomenon with a general treatment of light scattering from a multi-resonant nanostructure that is spherical or non-spherical but subwavelength in size. With multiple resonances in the same channel (i.e. same angular momentum and polarization), coherent interference always leads to scattering dark states in the low-absorption limit, regardless of the system details. The coupling between resonances is inevitable and can be interpreted as arising from far-field or near-field. This is a realization of coupled- and interference effects. 5-9 A particularly interesting phenomenon is the suppressed scattering in nanostructures with multiple plasmonic resonances, [10][11][12][13][14][15][16][17][18][19][20][21][22][23] plasmonic and excitonic resonances, [24][25][26][27][28][29][30] or dielectric resonances, 31,32 referred to collectively as a "scattering dark state." A wealth of models has been employed to describe this suppressed scattering, ranging from perturbative models, 12 generalization of the Fano formula, 13-15 and electrostatic approximation, 22,23 to coupled-mechanical-oscillator models. 17-21 These models reveal valuable insights and facilitate the design of specific structures with desired line shapes. However, the general criteria for observing such scattering dark states remain unclear. Non-scattering states have been known in atomic physics since the early works of Fano 33 and have been discovered in a variety of nanoscale systems in recent years [5][6][7][8]34,35 . However, Fano resonances generally concern the interference between a narrow discrete resonance and a broad resonance or continuum. Meanwhile, many occurrences of the scattering dark state involve the interference between multiple narrow discrete resonances, and it seems necessary to treat the multiple resonances at equal footing. Thus, we seek a formalism analogous to the phenomenon of coupled-resonator-induced transparency 5 that has been established in certain other systems such as coupled mechanical oscillators 36,37 , coupled cavities 38,39 , coupled microring resonators [40][41][42][43][44] , and planar metamaterials [45][46][47][48] .Here, we derive the general equations governing the resonant light scattering from a spherical or a non-spherical but subwavelength obstacle, accounting for multiple resonances with low loss. Due to the spherical symmetry (or the small size) of the obstacle, different channels of the multipole fields are decoupled. We find that within each channel, n resonances always lead to n − 1 scattering dark states in the low-absorption limit. This universal result is independent of the radiative decay rates of the resonances, method of coupling (can be 3 near-field or far-field), nature of the resonances (can be plasmon, exciton, whispering-gallery, etc.), number of resonances, which of the multipole, TE or TM polarization, and other system det...

No abstract