Volume 10, Issue 9

Nano-opto-electro-mechanical systems (NOEMS), considered as new platforms to study electronic and mechanical freedoms in the field of nanophotonics, have gained rapid progress in recent years. NOEMS offer exciting opportunities to manipulate information carriers using optical, electrical, and mechanical degrees of freedom, where the flow of light, dynamics of electrons, and mechanical vibration modes can be explored in both classical and quantum domains. By exploiting NOEMS concepts and technologies, high speed and low-power consumption switches, high-efficiency microwave-optical conversion devices, and multiple quantum information processing functions can be implemented through on-chip integration. This review will introduce the principles of NOEMS, summarize the recent developments, and important achievements, and give a prospect for the further applications and developments in this field.

Nanophotonic devices, composed of metals, dielectrics, or semiconductors, enable precise and high-spatial-resolution manipulation of electromagnetic waves by leveraging diverse light–matter interaction mechanisms at subwavelength length scales. Their compact size, light weight, versatile functionality and unprecedented performance are rapidly revolutionizing how optical devices and systems are constructed across the infrared, visible, and ultraviolet spectra. Here, we review recent advances and future opportunities of nanophotonic elements operating in the ultraviolet spectral region, which include plasmonic devices, optical metamaterials, and optical metasurfaces. We discuss their working principles, material platforms, fabrication, and characterization techniques, followed by representative device applications across various interdisciplinary areas such as imaging, sensing and spectroscopy. We conclude this review by elaborating on future opportunities and challenges for ultraviolet nanophotonic devices.

The demonstration of the first ruby laser in 1960 led to a revolution in science and technology. The lasers have significantly influenced the development of new approaches to spectroscopy, giving previously undreamed insights into physics, chemistry, and other scientific areas. The search for new materials for light amplification is one of the fundamental subjects of modern photonics and nanotechnology. In this review, we summarize the most appealing progress in developing liquid crystalline (LC) micro and nano-lasers during the last decade, together with their applications and description of perspectives for the future. We will describe the physical background necessary to understand the operation principles of LC lasers, including a description of radiative transition phenomena and LC matter. The article will be divided into separate sections concerning different approaches of LC lasers realization, including; band edge, DFB, DBR, VECSEL, and random cavities utilization. We will also discuss how the LC phases can influence the design of laser devices. Finally, the potential applications, perspectives, and conclusions will be discussed at the end of the article.

Integrated photonics based on silicon has drawn a lot of interests, since it is able to provide compact solution for functional devices, and its fabrication process is compatible with the mature complementary metal-oxide-semiconductor (CMOS) fabrication technology. In the meanwhile, silicon material itself has a few limitations, including an indirect bandgap of 1.1 eV, transparency wavelength of >1.1 μm, and insignificant second-order nonlinear optical property. Aluminum nitride (AlN), as a CMOS-compatible material, can overcome these limitations. It has a wide bandgap of 6.2 eV, a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect. Furthermore, it also exhibits piezoelectric and pyroelectric effects, which enable it to be utilized for optomechanical devices and pyroelectric photodetectors, respectively. In this review, the recent research works on integrated AlN photonics in the past decade have been summarized. The related material properties of AlN have been covered. After that, the demonstrated functional devices, including linear optical devices, optomechanical devices, emitters, photodetectors, metasurfaces, and nonlinear optical devices, are presented. Last but not the least, the summary and future outlook for the AlN-based integrated photonics are provided.

In the last decades, research and development of microfluidics have made extraordinary progress, since they have revolutionized the biological and chemical fields as a backbone of lab-on-a-chip systems. Further advancement pushes to miniaturize the architectures to nanoscale in terms of both the sizes and the fluid dynamics for some specific applications including investigation of biological sub-cellular aspects and chemical analysis with much improved detection limits. In particular, nano-scale channels offer new opportunities for tests at single cell or even molecular levels. Thus, nanofluidics, which is a microfluidic system involving channels with nanometer dimensions typically smaller than several hundred nm, has been proposed as an ideal platform for investigating fundamental molecular events at the cell-extracellular milieu interface, biological sensing, and more recently for studying cancer cell migration in a space much narrower than the cell size. In addition, nanofluidics can be used for sample manipulation in analytical chemistry, such as sample injections, separation, purifications or for quantitative and qualitative determinations. Among the nanofabrication technologies, ultrafast laser manufacturing is a promising tool for fabrication of nanofluidics due to its flexibility, versatility, high fabrication resolution and three dimensional (3D) fabrication capability. In this paper, we review the technological advancements of nanofluidic systems, with emphasis on fabrication methods, in particular ultrafast laser manufacturing. We present the challenges for issues concerning channel sizes and fluid dynamics, and introduce the applications in physics, biology, chemistry and engineering with future prospects.

The optoelectronic properties of semiconductor nanoparticles make them valuable candidates for the long-term monitoring of transmembrane electric fields in excitable cells. In this work, we show that the electric field sensitivity of the fluorescence intensity of type-I and quasi-type-II quantum dots and quantum rods is enhanced under two-photon excitation compared to single-photon excitation. Based on the superior electric field sensitivity of the two-photon excited fluorescence, we demonstrate the ability of quantum dots and rods to track fast switching E-fields. These findings indicate the potential of semiconductor nanoparticles as cellular voltage probes in multiphoton imaging.

Multi-level exciton-polariton systems offer an attractive platform for studies of non-linear optical phenomena. However, studies of such consequential non-linear phenomena as polariton condensation and lasing in planar microcavities have so far been limited to two-level systems, where the condensation takes place in the lowest attainable state. Here, we report non-equilibrium Bose–Einstein condensation of exciton-polaritons and low threshold, dual-wavelength polariton lasing in vertically coupled, double planar microcavities. Moreover, we find that the presence of the non-resonantly driven condensate triggers interbranch exciton-polariton transfer in the form of energy-degenerate parametric scattering. Such an effect has so far been observed only under excitation that is strictly resonant in terms of the energy and incidence angle. We describe theoretically our time-integrated and time-resolved photoluminescence investigations by an open-dissipative Gross–Pitaevskii equation-based model. Our platform’s inherent tunability is promising for construction of planar lattices, enabling three-dimensional polariton hopping and realization of photonic devices, such as all-optical polariton-based logic gates.

Exceptional points (EPs) are the singularities of a non-Hermitian system where the eigenenergies and eigenstates simultaneously coalesce, a topological property that gives rise to a plethora of exotic phenomena. Probing the EPs and associated effects requires the system to go through the EPs. However, the ultrahigh sensitivity of an isolated EP to the external disturbances makes accessing the EPs difficult. To overcome this limit, many approaches have been presented to form the exceptional line/ring and surface. Here, we demonstrate that a quantum exceptional chamber, which is a three-dimensional collection of the EPs, can be constructed in the coupled plasmon-quantum dot (QD) systems by the nondipole effect of the QD. For an asymmetric QD adjacent to a plasmonic nanoparticle, it is found that the contributions of multipole transitions to the coupling strength can be larger than that of dipole transition. The orientation-dependent quantum interference between the dipole and multipole transitions can lead to controllable switch between the weak and strong coupling, and provides an extra degree of freedom to form a high-dimension EP space. Our approach provides a robust platform for accessing the quantum EPs and related applications.

Cephalopods camouflage abilities arise from highly specialized chromatic elements in their skin, chromatophores, iridophores, and leucophores, that enable them to display complex and rapidly changing color patterns. Despite the extensive study of these chromatic elements in squid and cuttlefish, full characterization of their individual optical response is still elusive in the Octopus species. We present here detailed multispectral analysis and mapping of the Octopus bimaculoides skin that allows to precisely identify the spatial distribution of the animal’s pigmented and structural elements. The mutual interaction of chromatophores and iridophores is also characterized both in terms of spectral response and spatial localization. The spectral information obtained through this analysis helps to understand the complexity and behavior of these natural tissues while continuing to serve as an inspiration for the fabrication of advanced, chromatically adaptable materials.

A variety of modern super-resolution microscopy methods provide researchers with previously inconceivable biological sample imaging opportunities at a molecular resolution. All of these techniques excel at imaging samples that are close to the coverslip, however imaging at large depths remains a challenge due to aberrations caused by the sample, diminishing the resolution of the microscope. Originating in astro-imaging, the adaptive optics (AO) approach for wavefront shaping using a deformable mirror is gaining momentum in modern microscopy as a convenient approach for wavefront control. AO has the ability not only to correct aberrations but also enables engineering of the PSF shape, allowing localization of the emitter axial position over several microns. In this study, we demonstrate remote focusing as another AO benefit for super-resolution microscopy. We show the ability to record volumetric data (45 × 45 × 10 µm), while keeping the sample axially stabilized using a standard widefield setup with an adaptive optics addon. We processed the data with single-molecule localization routines and/or computed spatiotemporal correlations, demonstrating subdiffraction resolution.

Topological interface states are formed when two photonic crystals with overlapping band gaps are brought into contact. In this work, we show a planar binary structure with such an interface state in the visible spectral region. Furthermore, we incorporate a thin layer of an active organic material into the structure, providing gain under optical excitation. We observe a transition from fluorescence to lasing under sufficiently strong pump energy density. These results are the first realization of a planar topological laser, based on a topological interface state instead of a cavity like most of other laser devices. We show that the topological nature of the resonance leads to a so-called “topological protection”, i.e. stability against layer thickness variations as long as inversion symmetry is preserved: even for large changes in thickness of layers next to the interface, the resonant state remains relatively stable, enabling design flexibility superior to conventional planar microcavity devices.

Plasmonic core–molecule–shell (CMS) nanojunctions provide a versatile platform for studying electron transport through conductive molecules under light excitation. In general, the impact of electron transport on the near-field response of CMS nanojunctions is more prominent than on the far-field property. In this work, we use two-photon luminescence (TPL) spectroscopy to probe the effect of electron transport on the plasmonic properties of gold CMS nanojunctions. Theoretical calculations show that the TPL response of such nanojunctions is closely related to the near-field enhancement inside the metal regions, and can be strongly affected by the electron transport through the embedded molecules. TPL excitation spectroscopy results for three CMS nanojunctions (0.7, 0.9 and 1.5 nm junction widths) reveal no perceivable contribution from their low-energy plasmon modes. This observation can be well explained by a quantum-corrected model, assuming significant conductance for the molecular layers and thus efficient charge transport through the junctions. Furthermore, we explore the charge transport mechanism by investigating the junction width dependent TPL intensity under a given excitation wavelength. Our study contributes to the field of molecular electronic plasmonics through opening up a new avenue for studying quantum charge transport in molecular junctions by non-linear optical spectroscopy.

Analog optical computing has been an innovation and research interest in last several years, thanks to the ultra-high speed (potential for real-time processing), ultra-low power consumption and capability of parallel processing. Although great efforts have been made recently, no on-chip optical spatial-domain integrator has been experimentally demonstrated, to the best of our knowledge. Based on Fourier optics and metasurface, we design and fabricate an on-chip optical integrator using silicon-on-insulator (SOI) platform. The proposed integrator is able to integrate the electric field in spatial domain. As a proof-of-concept demonstration, a representative optical signal is well integrated to the desired distribution. Compared with theoretical expectation, the similarity coefficients of the simulated and experimental results are 83 and 78%, respectively. The proposed scheme has potential of performing more complex and ultra-high-speed computing for artificial intelligence.

Generally, an optical vortex lattice (OVL) is generated via the superposition of two specific vortex beams. Thus far, OVL has been successfully employed to trap atoms via the dark cores. The topological charge (TC) on each optical vortex (OV) in the lattice is only ±1. Consequently, the orbital angular momentum (OAM) on the lattice is ignored. To expand the potential applications, it is necessary to rediscover and exploit OAM. Here we propose a novel high-order OVL (HO-OVL) that combines the phase multiplication and the arbitrary mode-controllable techniques. TC on each OV in the lattice is up to 51, which generates sufficient OAM to manipulate microparticles. Thereafter, the entire lattice can be modulated to desirable arbitrary modes. Finally, yeast cells are trapped and rotated by the proposed HO-OVL. To the best of our knowledge, this is the first realization of the complex motion of microparticles via OVL. Thus, this work successfully exploits OAM on OVL, thereby revealing potential applications in particle manipulation and optical tweezers.

Great progress in nanophotonics has been demonstrated in tailoring the impinging beams. The physics behind those intriguing effects is to a large extent governed by the parameter of the optical phase. While, simple nanostructures usually suffer from fundamental limitations on their efficiency in wave transformation, especially in the transmission system, associated with their inadequate phase accumulation, challenge their implementation in practical application. Here, we describe a transparent nanostructure built from a pair of partially overlapped gold and aluminum semi-nanoshells that show almost π phase accumulation through material-dependent plasmon resonances. Combined with an optical slab waveguide, the bimetallic metagratings exhibit prominent directional color routing properties in transmission light, which result from switchable Fano resonances between plasmon resonances of bimetallic nanostructures and ±1 order waveguide diffraction modes at two opposite oblique incidences due to sufficient phase shift provided by the asymmetric and bimetallic plasmon resonators. Both theoretical and experimental results show that the Fano-resonance-assisted color routing exhibits a relatively broadband tuning range (∼150 nm with an efficiency of up to 50%) and a color routing efficiency of up to 70% at the central wavelength of λ  = 600 nm.

Metal-oxides hold promise as superior plasmonic materials in the mid-infrared compared to metals, although their integration over established material technologies still remains challenging. We demonstrate localized surface plasmons in self-assembled, hemispherical CdZnO metal-oxide nanoparticles on GaAs, as a route to enhance the absorption in mid-infrared photodetectors. In this system, two localized surface plasmon modes are identified at 5.3 and 2.7 μm, which yield an enhancement of the light intensity in the underlying GaAs. In the case of the long-wavelength mode the enhancement is as large as 100 near the interface, and persists at depths down to 50 nm. We show numerically that both modes can be coupled to infrared intersubband transitions in GaAs-based multiple quantum wells, yielding an absorbed power gain as high as 5.5, and allowing light absorption at normal incidence. Experimentally, we demonstrate this coupling in a nanoparticle/multiple quantum well structure, where under p -polarization the intersubband absorption is enhanced by a factor of 2.5 and is still observed under s -polarization, forbidden by the usual absorption selection rules. Thus, the integration of CdZnO on GaAs can help improve the figures of merit of quantum well infrared photodetectors, concept that can be extended to other midinfrared detector technologies.

Personalized therapeutic vaccines against immune desert tumors are an increasingly important field in current cancer immunotherapy. However, limitations in neoantigen recognition, impotent immune cells, and a lack of intratumoral infiltrated lymphocytes pose challenges for the cancer vaccines. Resected tumors contain various of patient-specific tumor autoantigens (TA), and its derived photonanovaccines have unique competency to overcome abovementioned barriers. We constructed a novel personalized photonanovaccine (B@TA-R848) with surgically sourced TA modified on two-dimensional boron nanosheets (BNSs) via polydopamine coating and loaded with immune adjuvant R848. B@TA-R848 has good properties of drug delivery and release, photoacoustic imaging, photothermal effect, and biocompatibility. In a mouse triple-negative breast cancer model, B@TA-R848-based photonanovaccine induced effective systemic antitumor immune responses, altered the local tumor microenvironment, and increased the intratumoral infiltration of immune cells. The combined photo immunotherapy could significantly inhibit tumor growth, recurrence, and metastasis. This work develops a novel photonanovaccine for low immunogenicity and high metastatic potential tumors, which is of great significance for exploring the clinical development of personalized tumor vaccines against immune desert tumors.