There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Artificial Neural Networks have dramatically improved performance for many machine learning tasks. We demonstrate a new architecture for a fully optical neural network that enables a computational speed enhancement of at least two orders of magnitude and three orders of magnitude in power efficiency over state-of-the-art electronics.

Deep learning with coherent nanophotonic circuits

Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.

/pdf/alternative-plasmonic-materials-beyond-gold-and-silver-1p8fd7ol50.pdf

Alternative Plasmonic Materials: Beyond Gold and Silver

Invisibility devices have captured the human imagination for many years. Recent theories have proposed schemes for cloaking devices using transformation optics and conformal mapping. Metamaterials, with spatially tailored properties, have provided the necessary medium by enabling precise control over the flow of electromagnetic waves. Using metamaterials, the first microwave cloaking has been achieved but the realization of cloaking at optical frequencies, a key step towards achieving actual invisibility, has remained elusive. Here, we report the first experimental demonstration of optical cloaking. The optical 'carpet' cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. The cloak consists only of isotropic dielectric materials, which enables broadband and low-loss invisibility at a wavelength range of 1,400-1,800 nm.

An optical cloak made of dielectrics

Nonlinear photonic chips can generate and process signals all-optically with far superior performance to that possible electronically — particularly with respect to speed. Although silicon-on-insulator has been the leading platform for nonlinear optics, its high two-photon absorption at telecommunication wavelengths poses a fundamental limitation. We review recent progress in non-silicon CMOS-compatible platforms for nonlinear optics, with a focus on Si3N4 and Hydex®. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement. We highlight their potential future impact as well as the challenges to achieving practical solutions for many key applications. This article reviews recent progress in the use of silicon nitride and Hydex as non-silicon-based CMOS-compatible platforms for nonlinear optics. New capabilities such as on-chip optical frequency comb generation, ultrafast optical pulse generation and measurement using these materials, and their potential future impact and challenges are covered.

New CMOS-compatible platforms based on silicon nitride and hydex for nonlinear optics

Scientists have realized a graphene electro-optic modulator operating with a 30 GHz bandwidth and with a state-of-the-art modulation efficiency of 1.5 dB V−1, paving the way for fast digital communications.

Graphene electro-optic modulator with 30 GHz bandwidth

The ability to render objects invisible using a cloak (such that they are not detectable by an external observer) has long been a tantalizing goal1,2,3,4,5,6. Here, we demonstrate a cloak operating in the near infrared at a wavelength of 1,550 nm. The cloak conceals a deformation on a flat reflecting surface, under which an object can be hidden. The device has an area of 225 µm2 and hides a region of 1.6 µm2. It is composed of nanometre-size silicon structures with spatially varying densities across the cloak. The density variation is defined using transformation optics to define the effective index distribution of the cloak. A triangular array of silicon nanostructures is experimentally demonstrated to function as an optical cloaking device, operating in the near-infrared at a wavelength of 1550 nm. This approach could, in principle, be extended to larger areas using fabrication techniques such as nanoimprinting.

Silicon nanostructure cloak operating at optical frequencies

On-chip optical resonators have the promise of revolutionizing numerous fields, including metrology and sensing; however, their optical losses have always lagged behind those of their larger discrete resonator counterparts based on crystalline materials and silica microtoroids. Silicon nitride (Si3N4) ring resonators open up capabilities for frequency comb generation, optical clocks, and high-precision sensing on an integrated platform. However, simultaneously achieving a high quality factor (Q) and high confinement in Si3N4 (critical for nonlinear processes, for example) remains a challenge. Here we show that addressing surface roughness enables overcoming the loss limitations and achieving high-confinement on-chip ring resonators with Q of 37 million for a ring of 2.5 μm width and 67 million for a ring of 10 μm width. We show a clear systematic path for achieving these high Qs, and these techniques can also be used to reduce losses in other material platforms independent of geometry. Furthermore, we demonstrate optical parametric oscillation using the 2.5 μm wide ring with sub-milliwatt pump powers and extract the loss limited by the material absorption in our films to be 0.13±0.05  dB/m, which corresponds to an absorption-limited Q of at least 170 million by comparing two resonators with different degrees of confinement. Our work provides a chip-scale platform for applications such as ultralow-power frequency comb generation, laser stabilization, and sideband-resolved optomechanics.

Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold

Optical frequency combs in the mid-infrared are required for molecular gas detection applications but their realization in compact microresonator-based platforms is challenging. Here, Griffith et al. demonstrate on-chip broadband comb generation on a silicon microresonator spanning from 2.1 to 3.5 μm.

/pdf/silicon-chip-mid-infrared-frequency-comb-generation-4q9wtazhlj.pdf

Silicon-chip mid-infrared frequency comb generation

Dual-comb spectroscopy is a powerful technique for real-time, broadband optical sampling of molecular spectra, which requires no moving components. Recent developments with microresonator-based platforms have enabled frequency combs at the chip scale. However, the need to precisely match the resonance wavelengths of distinct high quality-factor microcavities has hindered the development of on-chip dual combs. We report the simultaneous generation of two microresonator combs on the same chip from a single laser, drastically reducing experimental complexity. We demonstrate broadband optical spectra spanning 51 THz and low-noise operation of both combs by deterministically tuning into soliton mode-locked states using integrated microheaters, resulting in narrow ( 1 GHz).

/pdf/on-chip-dual-comb-source-for-spectroscopy-4x19w2lgyl.pdf

Jaime Cardenas

Papers

Graphene electro-optic modulator with 30 GHz bandwidth

Silicon nanostructure cloak operating at optical frequencies

Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold

Silicon-chip mid-infrared frequency comb generation

On-chip dual-comb source for spectroscopy