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Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency, especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning in the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles and propose a new figure-of-merit (FOM) tailored for reconfigurable meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 μm wavelength. The reconfigurable metalens features a record large switching contrast ratio of 29.5 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents a key experimental demonstration of a non-mechanical tunable metalens with diffraction-limited performance., Here, the authors report an active all-dielectric metasurface platform based on phase change materials, combining phase tuning in the full 2π range, and demonstrate aberration-free and multi-depth imaging with a non-mechanical tunable metalens.

Wide field-of-view (FOV) optical functionality is crucial for implementation of advanced imaging and image projection devices. Conventionally, wide FOV operation is attained with complicated assembly of multiple optical elements known as "fisheye lenses". Here we present a novel metalens design capable of performing diffraction-limited focusing and imaging over an unprecedented near 180° angular FOV. The lens is monolithically integrated on a one-piece flat substrate and involves only a single layer of metasurface that corrects third-order Seidel aberrations including coma, astigmatism, and field curvature. The metalens further features a planar focal surface, which enables considerably simplified system architectures for applications in imaging and projection. We fabricated the metalens using Huygens meta-atoms operating at 5.2 μm wavelength and experimentally demonstrated aberration-free focusing and imaging over the entire FOV. The design concept is generic and can be readily adapted to different meta-atom geometries and wavelength ranges to meet diverse application demands.

Optical metasurfaces, planar subwavelength nanoantenna arrays with the singular ability to sculpt wavefront in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel functionalities. A particularly intriguing research direction within this field is active metasurfaces, whose optical response can be dynamically tuned postfabrication, thus allowing a plurality of applications unattainable with traditional bulk optics. Designing reconfigurable optics based on active metasurfaces is, however, presented with a unique challenge, since the optical quality of the devices must be optimized at multiple optical states. In this article, we provide a critical review on the active meta-optics design principles and algorithms that are applied across structural hierarchies ranging from single meta-atoms to full meta-optical devices. The discussed approaches are illustrated by specific examples of reconfigurable metasurfaces based on optical phase-change materials.

On-chip scalable integration represents a major challenge for practical quantum devices. One particular challenge is to implement on-chip optical readout of spins in diamond. This readout requires ...

We demonstrated metasurface-based stereoscopic 3-D depth imaging featuring a record wide field-of-view of 170°.

Hyperbolic metamaterials (HMMs) have attracted significant attention due to the profound manipulation of the photonic density of states, resulting in the efficient optoelectronic devices with the enhanced light-matter interaction. HMMs are conventionally built on rigid large-size substrates with poor conformability and the absence of flexibility. Here, we demonstrate a grating collageable HMM (GCHMM), which is composed of eight alternating layers of Au and poly(methyl methacrylate) (PMMA) and PMMA grating nanostructure containing quantum dots (QDs). The QDs serve as a scattering gain medium performing a random laser action, and the grating nanostructure enhances the extraction of light from QDs. The GCHMM enhances laser action by 13 times, reduces lasing threshold by 46%, and increases differential quantum efficiency by 1.8 times as compared to a planar collageable HMM. In addition, the GCHMM can be retransferred multiple times to other substrates as well as provide sufficient protection in water and still retain an excellent performance. It also shows stable functionality even when transferred to a dental floss. The GCHMM, therefore, promises to become a versatile platform for foldable, adaptable, free-standing, and water-resistant optoelectronic device applications.

We report integration of chalcogenide phase change materials (GSST and Sb2Se3) with doped silicon-on-insulator heater arrays fabricated in a 90-nm silicon foundry. Reversible electrothermal switching of transmissive metasurfaces and integrated photonic devices are demonstrated.

Metasurfaces have become a promising means for manipulating optical wavefronts in flat and high-performance optical devices. Conventional metasurface device design relies on trial-and-error methods...

Optical phase change materials (PCMs) are a unique class of materials which exhibit extraordinarily large optical property change (e.g. refractive index change > 1) when undergoing a solid-state phase transition, and they have witnessed increasing adoption in active integrated photonics and metasurface devices in recent years. Here we report integration of chalcogenide phase change materials in the Lincoln Laboratory 8-inch Si foundry process and the demonstration of electrothermally switched phase-change photonic devices building on a wafer-scale silicon-on-insulator heater platform.

The quest for efficient programmable photonic circuits requires active optical components with low insertion loss, small form factor, and low electrical power consumption [1] . The most common low-loss phase shifter – the key building block – employs electrically driven heaters to exploit thermo-optic effects. However, these devices require a constant power supply, suffer from thermal crosstalk, and their sizes are typically >100 µm. Here, we demonstrate a novel alternative that meets all the aforementioned requirements. We use silicon-on-insulator (SOI) waveguides with patterned n ++ - n - n ++ doped-silicon microheaters to electrothermally switch, with a single pulse, a cell of Sb 2 Se 3 between its two optically distinct, nonvolatile states: amorphous and crystalline. Sb 2 Se 3 is a phase change material (PCM) that offers a ∆n ≈ 0.77 upon switching between states with vanishingly small losses at 1550nm [2] . This unique set of properties allows for phase-only modulation [3] , which sets a precedent in a growing PCM photonics field familiar with PCMs for amplitude modulation at the telecom band [4] .

We report the observation of enhanced third-harmonic generation in a mid-infrared metasurface based on the phase change material Ge 2 Sb 2 Se 4 Te 1 .

We demonstrate a large-area fabrication process for optical metasurfaces utilizing reusable SiN on Si nanostencils. To improve the yield of the nanostencil fabrication, we partially etch the front-side SiN layer to transfer the metasurface pattern from the resist to the nanostencil membrane, preserving the integrity of the membrane during the subsequent potassium hydroxide etch. To enhance the reliability and resolution of metasurface fabrication using the nanostencil, we spin coat a sacrificial layer of resist to precisely determine the gap between the nanostencil and the metasurface substrate for the subsequent liftoff. 1.5 mm diameter PbTe meta-lenses on C a F 2 fabricated using nanostencils show diffraction-limited focusing and focusing efficiencies of 42% for a 2 mm focal length lens and 53% for a 4 mm focal length lens. The nanostencils can also be cleaned using chemical cleaning methods for reuse.

Energy-efficient programmable photonic integrated circuits (PICs) are the cornerstone of on-chip classical and quantum optical technologies. Optical phase shifters constitute the fundamental building blocks which enable these programmable PICs. Thus far, carrier modulation and thermo-optical effect are the chosen phenomena for ultrafast and low-loss phase shifters, respectively; however, the state and information they carry are lost once the power is turned off-they are volatile. The volatility not only compromises energy efficiency due to their demand for constant power supply, but also precludes them from emerging applications such as in-memory computing. To circumvent this limitation, we introduce a novel phase shifting mechanism that exploits the nonvolatile refractive index modulation upon structural phase transition of Sb$_{2}$Se$_{3}$, a bi-stable transparent phase change material. A zero-static power and electrically-driven phase shifter was realized on a foundry-processed silicon-on-insulator platform, featuring record phase modulation up to 0.09 $\pi$/$\mu$m and a low insertion loss of 0.3 dB/$\pi$, which can be further improved upon streamlined design. We also pioneered a one-step partial amorphization scheme to enhance the speed and energy efficiency of PCM devices. A diverse cohort of programmable photonic devices were demonstrated based on the ultra-compact PCM phase shifter., Comment: 15 pages with 6 figures and 1 table

Nitrogen-vacancy centers in diamond have been long used for spin-based optical sensing and also considered viable candidates for implementing quantum information protocols using their spin degree of freedom. Their nanoscale size and the possibility of optical spin readout make them particularly attractive for the use in integrated nanophotonic and quantum optical devices. We will discuss how the optical Purcell effect in plasmonic systems affects the NV spin readout signal and present the demonstration of this readout through optical plasmons in an integrated nanophotonic interface. We will show that spin relaxometry is a powerful tool that allows to probe the magnonic density of states and its electrical tuning with sub-um spatial resolution. Furthermore, we will discuss how spin signal readout sensitivity can be enhanced with the use of plasmonic nanostructures deterministically assembled on the nanoscale.

We report on the nonlinear optical properties of the phase change material Ge2Sb2Se4Te1 (GSST). A 30-fold enhancement of third-harmonic generation is also demonstrated using a GSST metasurface operating in the mid-wave infrared region.

We report an electrically reconfigurable metasurface platform based on optical phase change materials. Multi-cycle reversible switching is realized using conductive micro-heaters. Large-contrast spectral tuning and beam-steering are demonstrated.

We demonstrate a nonvolatile, small-form-factor (20 m) phase-shifter based on low-loss phase-change materials (Ge2Sb2Se4Te1 and Sb2Se3) on SOI waveguides. We achieve continuous optical phase modulation and an MZI switch with 30 dB extinction ratio.