The advent of metasurfaces in recent years has ushered in a revolutionary means to manipulate the behavior of light on the nanoscale. The design of such structures, to date, has relied on the expertise of an optical scientist to guide a progression of electromagnetic simulations that iteratively solve Maxwell's equations until a locally optimized solution can be attained. In this work, we identify a solution to circumvent this conventional design procedure by means of a deep learning architecture. When fed an input set of customer-defined optical spectra, the constructed generative network generates candidate patterns that match the on-demand spectra with high fidelity. This approach reveals an opportunity to expedite the discovery and design of metasurfaces for tailored optical responses in a systematic, inverse-design manner.

We demonstrate enormously strong chiral effects from a photonic metamaterial consisting of an array of dual-layer twisted-arcs with a total thickness of ∼ λ/6. Experimental results reveal a circular dichroism of ∼ 0.35 in the absolute value and a maximum polarization rotation of ∼ 305°/λ in a near-infrared wavelength region. A transmission of greater than 50% is achieved at the frequency where the polarization rotation peaks. Retrieved parameters from measured quantities further indicate an actual optical activity of 76° per λ and a difference of 0.42 in the indices of refraction for the two circularly polarized waves of opposite handedness.

Highly reproducible organometallic-halide-perovskite-based devices are fabricated by a manufacturing process, which is demonstrated. Various shapes that are hard to synthesize directly are fabricated, and many unique properties are achieved.The fabrication procedure is utilized to create a photodetector and the detection sensitivity is significantly improved. The results will bring revolutionary advancement to the future of lead-halide-perovskite-based optoelectronic devices.

A chiral metamaterial produces both distinguishable linear and non-linear resonant features when probed with left and right circularly polarized light. The material demonstrates a linear transmission contrast of 0.5 between left and right circular polarizations and a 20× contrast between second-harmonic responses from the two incident polarizations. Non-linear and linear response images probed with circularly polarized light show strongly defined contrast.

Conventional metallic mirrors flip the spin of a circularly polarized wave upon normal incidence by inverting the direction of the propagation vector. Altering or maintaining the spin state of light waves carrying data is a critical need to be met at the brink of photonic information processing. In this work, we report a chiral metamaterial mirror that strongly absorbs a circularly polarized wave of one spin state and reflects that of the opposite spin in a manner conserving the circular polarization. A circular dichroic response in reflection as large as ∼0.5 is experimentally observed in a near-infrared wavelength band. By imaging a fabricated pattern composed of the enantiomeric unit cells, we directly visualize the two key features of our engineered meta-mirrors, namely the chiral-selective absorption and the polarization preservation upon reflection. Beyond the linear regime, the chiral resonances enhance light-matter interaction under circularly polarized excitation, greatly boosting the ability of the metamaterial to perform chiral-selective signal generation and optical imaging in the nonlinear regime. Chiral meta-mirrors, exhibiting giant chiroptical responses and spin-selective near-field enhancement, hold great promise for applications in polarization sensitive electro-optical information processing and biosensing.

Layered black phosphorus has triggered enormous interest since its recent emergence. Compared to most other two-dimensional materials, black phosphorus features a moderate band gap and pronounced in-plane anisotropy, which stems from the unique atomicpuckering crystal structure. The future potential of black phosphorus in optoelectronics demands a deeper understanding of its unique anisotropic behavior. In particular, the phase information of light when interacting with the material is imperative for many applications in the optical regime.In this work we have comprehensively studied a wide range of optical anisotropic properties of black phosphorus, including the Raman scattering, extinction spectra, and phase retardance by utilizing conventional spectral measurements and a uniquely developed interferometric spectroscopy and imaging technique. The phase retardance of light passed through black phosphorus is exploited in conjunction with polarization interferometric techniques to demonstrate an optical contrast an order of magnitude higher than a purely polarization-based measurement could offer.The past decade has witnessed the explosive development of two-dimensional (2D) materials, whose ever-expanding family now represents one of the most exciting frontiers in physics and materials science. The intriguing physical properties of 2D materials, primarily derived from their out of plane quantum confinement and the strong in-plane bonding, have enabled diverse applications in electronics, mechanics, as well as optics and photonics. 1-7 Among this new class of material, graphene has laid the foundation for the 2D frontier of nanoscale optical applications in integrated nano-photonics, 8, 9 ultrafast light detection, 10, 11 and plasmonics. 12, 13 Now, this field is quickly being populated with other materials such as transition metal dichalcogenide (TMDC) which exhibit exotic properties of their own. For instance, TMDC has demonstrated optical helicity controlled valley polarization which opens pathways for valleytronics. 14-17 Recently, layered black phosphorus (BP) has been reintroduced to the family from its dormancy a century ago. [18][19][20][21] As a new member of the 2D material class, BP bridges the semi-metallic graphene and semiconducting TMDC with a moderate band gap. [22][23][24][25][26] Compared to most other 2D materials, whose electronic and photonic properties are isotropic in-plane, the most distinguishable property of BP is its in-plane anisotropy stemming from the unique atomic-puckering crystal structure. Previous studies have revealed a range of intriguing anisotropic behaviors of BP in terms of its optical spectrum, Raman scattering, light absorption, photo-detection, and electrical conductivity. 27-34 While these properties reported in the literature have formed a valuable basis, many applications in the optical domain demand more information regarding the wave characteristics of the interacting light with the BP medium, specifically its phase. Moreover, the manipulation of the phase retardan...

Metamaterials have not only enabled unprecedented flexibility in producing unconventional optical properties that are not found in nature, they have also provided exciting potential to create customized nonlinear media with high-order properties correlated to linear behaviour. Two particularly compelling directions are active metamaterials, whose optical properties can be purposely tailored by external stimuli in a reversible manner, and nonlinear metamaterials, which enable intensity-dependent frequency conversion of light waves. Here, by exploring the interaction of these two directions, we leverage the electrical and optical functions simultaneously supported in nanostructured metals and demonstrate electrically controlled nonlinear optical processes from a metamaterial. Both second harmonic generation and optical rectification, enhanced by the resonance behaviour in the metamaterial absorber, are modulated externally with applied voltage signals. Our results reveal an opportunity to exploit optical metamaterials as self-contained, dynamic electro-optic systems with intrinsically embedded electrical functions and optical nonlinearities.

Metamaterials have enabled the realization of unconventional electromagnetic properties not found in nature, which provokes us to rethink the established rules of optics in both the linear and nonlinear regimes. One of the most intriguing phenomena in nonlinear metamaterials is 'backward phase-matching', which describes counter-propagating fundamental and harmonic waves in a negative-index medium. Predicted nearly a decade ago, this process is still awaiting a definitive experimental confirmation at optical frequencies. Here, we report optical measurements showing backward phase-matching by exploiting two distinct modes in a nonlinear plasmonic waveguide, where the real parts of the mode refractive indices are 3.4 and -3.4 for the fundamental and the harmonic waves respectively. The observed peak conversion efficiency at the excitation wavelength of ∼780 nm indicates the fulfilment of the phase-matching condition of k(2ω) = 2k(ω) and n(2ω) = -n(ω), where the coherent harmonic wave emerges along a direction opposite to that of the incoming fundamental light.