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Resonant plasmonic and metamaterial structures allow for control of fundamental optical processes such as absorption, emission and refraction at the nanoscale. Considerable recent research has focused on energy absorption processes, and plasmonic nanostructures have been shown to enhance the performance of photovoltaic and thermophotovoltaic cells. Although reducing metallic losses is a widely sought goal in nanophotonics, the design of nanostructured 'black' super absorbers from materials comprising only lossless dielectric materials and highly reflective noble metals represents a new research direction. Here we demonstrate an ultrathin (260 nm) plasmonic super absorber consisting of a metal–insulator–metal stack with a nanostructured top silver film composed of crossed trapezoidal arrays. Our super absorber yields broadband and polarization-independent resonant light absorption over the entire visible spectrum (400–700 nm) with an average measured absorption of 0.71 and simulated absorption of 0.85. Proposed nanostructured absorbers open a path to realize ultrathin black metamaterials based on resonant absorption. Plasmonic nanostructures and metamaterials can augment the performance of photovoltaic and thermophotovoltaic cells by enhancing their absorption properties. Aydin et al . demonstrate a broadband, ultrathin plasmonic super absorber using crossed trapezoids as part of a metal–insulator–metal stack.

Optical frequency comb is an enabling technology for a multitude of applications from metrology to ranging and communications. The tremendous progress in sources of optical frequency combs has mostly been centered around the near-infrared spectral region, while many applications demand sources in the visible and mid-infrared, which have so far been challenging to achieve, especially in nanophotonics. Here, we report widely tunable frequency comb generation using optical parametric oscillators in lithium niobate nanophotonics. We demonstrate sub-picosecond frequency combs tunable beyond an octave extending from 1.5 up to 3.3 μm with femtojoule-level thresholds on a single chip. We utilize the up-conversion of the infrared combs to generate visible frequency combs reaching 620 nm on the same chip. The ultra-broadband tunability and visible-to-mid-infrared spectral coverage of our source highlight a practical and universal path for the realization of efficient frequency comb sources in nanophotonics, overcoming their spectral sparsity. Here the authors provide the experimental demonstration of a widely tunable integrated frequency comb source unlocking the spectrum from the visible to the mid-infrared in a thin-film lithium niobate platform.

The use of silicon nanostructures in solar cells offers a number of benefits, such as the fact they can be used on flexible substrates. A silicon wire-array structure, containing reflecting nanoparticles for enhanced absorption, is now shown to achieve 96% peak absorption efficiency, capturing 85% of light with only 1% of the silicon used in comparable commercial cells. Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 . To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit 18 for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

The introduction of nonlinear nanophotonic devices to the field of optical frequency comb metrology has enabled new opportunities for low-power and chip-integrated clocks, high-precision frequency synthesis and broad-bandwidth spectroscopy. However, most of these advances remain constrained to the near-infrared region of the spectrum, which has restricted the integration of frequency combs with numerous quantum and atomic systems in the ultraviolet and visible ranges. Here we overcome this shortcoming with the introduction of multisegment nanophotonic thin-film lithium niobate waveguides that combine engineered dispersion and chirped quasi-phase matching for efficient supercontinuum generation via the combination of χ (2) and χ (3) nonlinearities. With only 90 pJ of pulse energy at 1,550 nm, we achieve gap-free frequency comb coverage spanning 330–2,400 nm. The conversion efficiency from the near-infrared pump to the ultraviolet–visible region of 350–550 nm is 17%, and our modelling of optimized poling structures predicts an even higher efficiency. Harmonic generation via the χ (2) nonlinearity in the same waveguide directly yields the carrier-envelope offset frequency and a means to verify the comb coherence at wavelengths as short as 350 nm. Our results provide an integrated photonics approach to create visible and ultraviolet frequency combs that will impact precision spectroscopy, quantum information processing and optical clock applications in this important spectral window. By combining engineered dispersion and chirped quasi-phase matching in multisegment nanophotonic thin-film lithium niobate waveguides, the generation of gap-free frequency comb spanning from 330 to 2,400 nm can be realized with only 90 pJ of pulse energy at 1,550 nm.

Improvements in temporal resolution of single-photon detectors enable increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging, and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the most efficient time-resolving single-photon-counting detectors available in the near-infrared, but understanding of the fundamental limits of timing resolution in these devices has been limited due to a lack of investigations into the timescales involved in the detection process. We introduce an experimental technique to probe the detection latency in SNSPDs and show that the key to achieving low timing jitter is the use of materials with low latency. By using a specialized niobium nitride SNSPD we demonstrate that the system temporal resolution can be as good as 2.6 ± 0.2 ps for visible wavelengths and 4.3 ± 0.2 ps at 1,550 nm.Knowledge about detection latency provides a guideline to reduce the timing jitter of niobium nitride superconducting nanowire single-photon detectors. A timing jitter of 2.6 ps at visible wavelength and 4.3 ps at 1,550 nm is achieved.

Metamaterial designs are typically limited to a narrow operating bandwidth that is predetermined by the fabricated dimensions. Various approaches have previously been used to introduce post-fabrication tunability and thus enable active metamaterials. In this work, we exploit the mechanical deformability of a highly compliant polymeric substrate to achieve dynamic, tunable resonant frequency shifts greater than a resonant linewidth. We investigate the effect of metamaterial shape on the plastic deformation limit of resonators. We find that, for designs in which the local strain is evenly distributed, the response is elastic under larger global tensile strains. The plastic and elastic limits of resonator deformation are explored and the results indicate that, once deformed, the resonators operate within a new envelope of elastic response. We also demonstrate the use of coupled resonator systems to add an additional degree of freedom to the frequency tunability and show that compliant substrates can be used as a tool to test coupling strength. Finally, we illustrate how compliant metamaterials could be used as infrared sensors, and show enhancement of an infrared vibration absorption feature by a factor of 225.

Nature Materials 9, 239–244 (2010); published online: 14 February 2010; corrected after print: 19 February 2010. In the version of this Letter originally published, the first sentence in the Acknowledgements should have been: “This work was supported by BP and in part by the Department of Energy EFRC program under grant DE-SC0001293, and made use of facilities supported by the Center for Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center at Caltech.