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Abstract The ability to confine and guide wave makes topological physics a promising platform for large local field enhancement and strong scattering immunity, which enables efficient nonlinear processes. In this research, we employ a mirror-stacking approach to achieve resonance through two distinct frequency localized states (LSs) in one-dimensional topological circuits, introducing a novel method for validating topological states to facilitate harmonic enhancement. Experimental results reveal that the harmonic wave power increases significantly, by two orders of magnitude, when both the fundamental and harmonic waves are in LSs, in contrast to cases where only one wave is localized. The conversion efficiency is 15.7 times that when the fundamental wave is in a localized state and the harmonic is in a transmission mode. This method, leveraging double-resonance in topological LSs, not only advances harmonic generation in topolectrical circuits but also opens up possibilities for innovative applications in the broader field of photonic technology.

Object identification and three-dimensional reconstruction techniques are always attractive research interests in machine vision, virtual reality, augmented reality, and biomedical engineering. Optical computing metasurface, as a two-dimensional artificial design component, has displayed the supernormal character of controlling phase, amplitude, polarization, and frequency distributions of the light beam, capable of performing mathematical operations on the input light field. Here, we propose and demonstrate an all-optical object identification technique based on optical computing metasurface, and apply it to 3D reconstruction. Unlike traditional mechanisms, this scheme reduces memory consumption in the processing of the contour surface extraction. The identification and reconstruction of experimental results from high-contrast and low-contrast objects agree well with the real objects. The exploration of the all-optical object identification and 3D reconstruction techniques provides potential applications of high efficiencies, low consumption, and compact systems.

Flat optical elements have attracted enormous attentions and act as promising candidates for the next generation of optical components. As one of the most outstanding representatives, liquid crystal (LC) has been widely applied in flat panel display industries and inspires the wavefront modulation with the development of LC alignment techniques. However, most LC elements perform only one type of optical manipulation and are difficult to realize the multifunctionality and light integration. Here, flat multifunctional liquid crystal elements (FMLCEs), merely composed of anisotropic LC molecules with space-variant orientations, are presented for multichannel information manipulation by means of polarization, space and wavelength multiplexing. Specifically, benefiting from the unique light response with the change of the incident polarization, observation plane, and working wavelength, a series of FMLCEs are demonstrated to achieve distinct near- and far-field display functions. The proposed strategy takes full advantage of basic optical parameters as the decrypted keys to improve the information capacity and security, and we expect it to find potential applications in information encryption, optical anti-counterfeiting, virtual/augmented reality, etc.

The large radius of potassium ions inevitably destabilizes the crystal structure of the cathode material in potassium-ion batteries, leading to capacity degradation. Here, authors demonstrate that phase-engineered amorphous vanadium oxide alleviates large volume variation and improves electrochemical behaviour.

The photonic spin Hall effect (SHE) refers to the transverse spin separation of photons with opposite spin angular momentum, after the beam passes through an optical interface or inhomogeneous medium, manifested as the spin-dependent splitting. It can be considered as an analogue of the SHE in electronic systems: the light’s right-circularly polarized and left-circularly polarized components play the role of the spin-up and spin-down electrons, and the refractive index gradient replaces the electronic potential gradient. Remarkably, the photonic SHE originates from the spin-orbit interaction of the photons and is mainly attributed to two different geometric phases, i.e., the spin-redirection Rytov-Vlasimirskii-Berry in momentum space and the Pancharatnam-Berry phase in Stokes parameter space. The unique properties of the photonic SHE and its powerful ability to manipulate the photon spin, gradually, make it a useful tool in precision metrology, analog optical computing and quantum imaging, etc. In this review, we provide a brief framework to describe the fundamentals and advances of photonic SHE, and give an overview on the emergent applications of this phenomenon in different scenes.

The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma. In such a wiggler, the laser-accelerated electrons emit THz radiations with a period closely related to the plasma thickness. The theoretical model and numerical simulations predict that a THz pulse with a laser–THz energy conversion of over 2.0%, an ultra-strong field exceeding 80 GV/m, a divergence angle of approximately 20° and a center frequency tunable from 4.4 to 1.5 THz can be generated from a laser of 430 mJ. Furthermore, we demonstrate that this method can work across a wide range of laser and plasma parameters, offering potential for future applications with extremely powerful THz pulses.

Summary: Computing metasurfaces have shown the extraordinary ability to precisely perform optical analog operations to the input light wave, and therefore exhibit greater potentials toward sensing applications. Here, we propose a unique application of computing metasurface for chiral edge sensing by incorporating a weak-value amplification technique. The computing metasurface performs the spatial differentiation operations of phase objects and extracts the edge-enhanced images, because the phase gradient generally occurs at the edge. The chirality-induced polarization rotation acts as the preselection state and the spatial differentiation operations in the metasurface provide weak coupling. The amplified pointer shift related to the tiny polarization rotation will eventually lead to an asymmetric edge-enhanced image. Owing to the high sensitivity of the weak-value amplification, we experimentally demonstrate a high-contrast recognition of chirality by edge detection, which may have potential applications in real-time measurement and separation of chiral enantiomers.

Abstract General plasmonic systems to realize plasmonically induced transparency (PIT) effect only exist one single PIT mainly because they only allow one single coupling pathway. In this study, we propose a distinct graphene resonator-based system, which is composed of graphene nanoribbons (GNRs) coupled with dielectric grating-loaded graphene layer resonators, to achieve two switchable PIT effects. By designing crossed directions of the resonators, the proposed system exists two different PIT effects characterized by different resonant positions and linewidths. These two PIT effects result from two separate and polarization-selective coupling pathways, allowing us to switch the PIT from one to the other by simply changing the polarization direction. Parametric studies are carried to demonstrate the coupling effects whereas the two-particle model is applied to explain the physical mechanism, finding excellent agreements between the numerical and theoretical results. Our proposal can be used to design switchable PIT-based plasmonic devices, such as tunable dual-band sensors and perfect absorbers.

Abstract MXenes, a new class of 2D transition metal carbides, nitrides, and carbonitrides, have attracted much attention due to their outstanding properties. Here, we report the broadband spatial self‐phase modulation of Ti2CT x MXene nanosheets dispersed in deionized water in the visible to near‐infrared regime, highlighting the broadband nonlinear optical (NLO) response of Ti2CT x MXene. Using ultrafast pulsed laser excitation, the nonlinear refractive index n2 and the third‐order nonlinear susceptibility χmonolayer3 of Ti2CT x MXene were measured to be ∼10−13 m2/W and ∼ 10−10 esu, respectively. Leveraging the large optical nonlinearity of Ti2CT x MXene, an all‐optical modulator in the visible regime was fabricated based on the spatial cross‐phase modulation effect. This work suggests that 2D MXenes are ideal broadband NLO materials with excellent prospects in NLO applications.

With unprecedented growth in data information over the past few decades, it is critically important to seek a faster and more efficient method to simplify data processing. In recent years, optical analog computing provides an available way due to its large capacity, energy saving, and high efficiency. Metasurfaces, as 2-dimensional artificial nanostructures, have shown an extraordinary ability for controlling light and paving a pathway toward all-optical analog computing. In this brief review, we discuss the latest development in metasurface-based optical analog computing. Theoretical fundamentals and experimental demonstrations of optical analog computing for resolving a variety of mathematical problems have been reviewed, including differential operation, convolution operation, and Fourier transformation. Finally, a brief introduction of emerging applications in microscopy imaging, quantum imaging, and holographic imaging is presented.

Mid-infrared (mid-IR) fiber laser sources at 3.5 μm have wide applications in spectroscopy, environmental monitoring, medicine, and defense countermeasures. In this work, we experimentally investigate a dual-end double wavelength pumped (i.e. both fiber ends pumped by 976 nm and 1973 nm, respectively) Er3+: ZBLAN fiber laser at 3.5 μm in detail. In the experiment, we carefully evaluate the lasing characteristics in terms of output power and scalability in contrast to the single-end pumping regime. The dual-end pumped Er3+: ZBLAN fiber laser yields a maximum output power of 1.72 W at the launched 1973 nm pump power of 8.39 W limited only by the available output power of the 1973 nm laser pump. The operation wavelength is experimentally found to be in a range from 3440 nm to 3620 nm depending on the pump power level. Lasing characteristics for Er3+: ZBLAN fibers with different lengths and doping concentrations and other cavity parameters are also investigated in this pumping regime to optimize the lasing performance.

Optical technology may provide important architectures for future computing, such as analog optical computing and image processing. Compared with traditional electric operation, optical operation has shown some unique advantages including faster operating speeds and lower power consumption. Here, we propose an optical full differentiator based on the spin–orbit interaction of light at a simple optical interface. The optical differential operation is independent of the wavelength due to the purely geometric nature of the phenomenon. As an important application of the fully differential operation, the wavelength-independent image processing of edge detection is demonstrated. By adjusting the polarization of the incident beam, the one-dimension edge imaging at any desirable direction can be obtained. The wavelength-independent image processing of edge detection provides possible applications in autonomous driving, target recognition, microscopic imaging, and augmented reality.

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. However, the precise and real-time detection of the reaction rate remains challenging due to its fast and dynamical process. In this paper, the photonic spin Hall effect is proposed to realize the ultrasensitive and real-time detection of the reaction rate of sucrose hydrolysis. By incorporating with quantum weak measurement, the photonic spin-Hall shift acts as the measurement pointer, and the optical rotation in the process of sucrose hydrolysis acts as the postselection state. The high measurement resolution with 1.25 × 10−4 degree is achieved due to the weak-value amplification in quantum weak measurement which outperforms the standard polarimeter. In our scheme, the amplified measurement pointer is real-time monitoring the chemical reaction process. It does not involve any mechanical adjustment of optical elements once the experimental setup is established and thereby realizes a real-time detection of the dynamic chemical reaction.

We demonstrated the dissipative soliton generation from a passively mode-locked ytterbium-doped fiber laser operating at 1041 nm by using evanescent field interaction with gold nanorods (GNR) saturable absorber (SA) experimentally. The GNRs, which have broadband longitudinal surface plasmon resonance absorption from ~800 to ~1500 nm, are synthesized by a seed-mediated growth method, and then composited with a D-shaped fiber to form the GNRs SA. The GNRs SA shows a modulation depth of 9.7% and low saturation intensity of 0.302 MW/cm2 . With the proposed GNRs SA, a dissipative soliton fiber laser was achieved with pulse duration 162.3 ps, repetition rate of 6.649 MHz at 1041 nm for a pump power of 220 mW. In addition, the signal-to-noise ratio can reach ~77 dB. The experimental result may make inroads for the nonlinear optical applications of the plasmonic nanomaterials.

Liquid crystal (LC) circular polarization gratings (PGs), also known as Pancharatnam–Berry (PB) phase deflectors, are diffractive waveplates with linearly changed optical anisotropy axes. Due to the high diffraction efficiency, polarization selectivity character, and simple fabrication process, photoalignment LC PGs have been widely studied and developed especially in polarization management and beam split. In this review paper, we analyze the physical principles, show the exposure methods and fabrication process, and present relevant promising applications in photonics and imaging optics.

Abstract We report the spatial self-phase modulation (SSPM) effect for solution dispersions of black phosphorus (BP). The experimental results suggest that this concentration-dependent coherent light diffraction is due to the ultrafast and large third-order optical nonlinearity of BP. The third-order nonlinear susceptibility of BP has been simply obtained about 10−19 m2/V2 by analyzing the experimental results. The fast relaxation time during dynamic relaxation is obtained as 0.13 ps. Our experimental results imply novel potential application of BP in ultrafast nonlinear phase modulation devices based on their nonlinear optical response.

We prepared the gold nanorods (GNRs) via seed-mediated growth method, and fabricated the fiber-compatible saturable absorption device with it. We found that the nonlinear absorption behavior of the fiber-compatible GNRs saturable absorber can be tuned by introducing an external modulation laser. With the modulating power varying from 0 to 100 mW, the modulation depth of the saturable absorber could be tuned from 22.85% to 17.91%. Based on the all-optical modulation method with GNRs, the pulse width and repetition rate tunable Q-switched pulses can be delivered from an erbium-doped fiber laser.

An amendment to this paper has been published and can be accessed via the original article.

The mutual energy-exchange interactions in two orthogonally polarized components of vector dark soliton, which is automatically formed in a normal-dispersion fiber laser cavity in the presence of reverse saturable absorption, and dissipative cavity effects, had been theoretically and numerically investigated. Under specific cavity parameters, a vector dark soliton with periodic coherent energy exchange could be formed and well described by a semianalytic method. The multiple vector dark solitons with energy exchange were also demonstrated by combining gain bandwidth and a reverse saturable absorption effect.

Through employing a cost-effective solvothermal method, ultrathin topological insulator (TI) bismuth telluride (Bi2Te3) nanosheets with uniform hexagonal nanostructures had been synthesized. Thanks to the uniformity of few-layer TI dispersion, we are able to adopt the drop-casting approach in order to directly transfer few-layer TI and, therefore, form a self-assembled uniform volatile TI membrane that is suitably deposited onto the end facet of an optical fiber as an effective optical saturable absorber. Its saturable absorption parameters could be deliberately tailored by thinning its thickness by mechanical exfoliation. The incorporation of the as-fabricated saturable absorber inside the fiber laser cavity allows for the operation of either a microsecond or a femtosecond pulse because different saturable absorption parameters can decide whether the fiber laser operates in the mode-locking or Q-switching state. Our work provides a convenient way of fabricating a high-quality TI membrane-based saturable absorber with promising applications for laser operation.

In this paper, we put forward a novel method for the management of optical collapse through controlling anomalous nonlinear diffraction (NLD) originating from the vectoral effect in metamaterials with simultaneous cubic electric and magnetic nonlinearity, particularly focusing on the unusual behaviors different from those in ordinary positive-index materials. First, NLD in metamaterials can be positive or negative, which makes it possible for us to offer greatly enhanced design freedom to manipulate the behavior of optical collapse at will. Then, it is further demonstrated that the negative NLD can arrest the catastrophic self-focusing of optical wave; however, the positive NLD will lead to the acceleration of its occurrence, as opposed to the case in ordinary positive-index materials. Our analysis is performed by directly numerically solving the nonlinear Schrödinger equation, as well as by using the modulation theory, both showing consistent results. These findings show that NLD in metamaterials can provide a more powerful tool in controlling the collapse of optical wave when compared with the corresponding case in ordinary positive-index materials.

In this paper, we proposed a cavity containing colloidal ferrofluids to enhance the Goos-Hänchen (GH) shifts of reflected and transmitted light beams. By optimizing the parameters of the cavity, the resonance inside the cavity was strengthened, and we obtained huge GH shifts. Magnetocontrolled negative GH shifts have been also analyzed. We found that a suitable cavity with optimized structural parameters can enhance the effect of the GH shifts on ferrofluids, which have an extremely small volume parameter and a small shell thickness parameter. Numerical simulations confirm the theoretical analysis. This paper has considerable potential for applications such as magnetic field sensors and optical switches.

We experimentally demonstrate a stable passively mode-locked Raman fiber laser delivering high-energy pulses that can be switched between the regime of hundreds of nanoseconds and that of picoseconds by the nonlinear polarization rotation technique. Maximum average output power values of 304 and 53 mW are obtained, respectively, for the two typical mode-locking states with the pulse duration of 500 ns and 180 ps at the fundamental repetition rate of 275 kHz. The corresponding single pulse energy is as much as 1.1 μJ and 193 nJ, respectively. To the best of our knowledge, this is the highest pulse energy achieved from mode-locked Raman fiber lasers reported so far.

We demonstrated the dual-wavelength simultaneously Q-switched Nd: Lu2O3 laser with a topological insulator Bi2Se3 as the Q-switcher. The continuous-wave Nd:Lu2O3 crystal laser with the slope efficiency of 31% was achieved, and the first Nd:Lu2O3 pulsed laser operation was reported, as far as we know. By using the wavelength-insensitive saturable absorption of topological insulators, the dual wavelength of the Nd:Lu2O3 crystal laser can be Q-switched simultaneously without the frequency selection of the saturable absorber, since the emission cross-sections of Nd:Lu2O3 at the wavelengths of 1077 and 1081 nm are comparable. The results indicate that the topological insulator is wavelength-insensitive and should be suitable for the dual-wavelength simultaneously Q-switched laser as a passive Q-switcher. It can be proposed that this work would provide an efficient technology for the dual-wavelength simultaneously Q-switched laser, which has promising applications in many regimes.

We have theoretically investigated the group delay of the TE-polarized beam reflected from a Fabry-Perot cavity with the insertion of the graphene sheets in the near-infrared band. It is shown that even a single-layer graphene allows for notable variation of group delay. Group delay can be enlarged negatively and can be switched from positive to negative, or vice versa. Importantly, the group delay depends on the Fermi energy of the graphene sheets, and thus, it can be actively controlled through electrical or chemical modification of the charge carrier density of the graphene. Furthermore, the influences of the position of graphene in the Fabry-Perot cavity, the mirror transmittance, and the number of graphene layers on group delay are clarified.

The existence of Weyl nodes in the momentum space is a hallmark of a Weyl semimetal (WSM). A WSM can be confirmed by observing its Fermi arcs with separated Weyl nodes. In this paper, we study the spin–orbit interaction of light on the surface of a WSM thin film. Our results show that the spin-dependent splitting induced by the spin–orbit interaction is related to the separation of Weyl nodes. By proposing an amplification technique called weak measurements, the distance of the nodes can be precisely determined. This system may have an application in characterizing other parameters of WSM.

In this article, a ferroelectric liquid crystal (FLC) dammann grating (DG) is demonstrated based on the patterned photoalignment technology. By applying low electric field (10 V) on the FLC DG, the grating can switch between a diffractive state with 7 × 7 optical spots array and a non-diffractive state, depending on the polarity of electric field. The FLC DG shows very fast switching speed with switching on time and off time to be only 81 μs and 59 μs respectively. Comparing with other fast LC DGs such as the ones based on blue phase LC or dual-frequency LC, the switching speed of the proposed FLC DG is about one order faster, which provides great potential and perspective for the FLC DG to be applied in a broad range of optical applications such as optical communication and beam shaping.

An in-band pumped 1.645-μm Er:YAG ceramic laser passively Q-switched by a topological insulator: Bi2Te3 saturable absorber is reported. The average output power could reach up to 210 mW, corresponding to a pulsewidth, a pulse repetition rate, and a per-pulse energy of 6.3 μs, 40.7 kHz, and 5.3 μJ, respectively. This result indicates that the topological insulator: Bi2Te3 could be a promising saturable absorber such as graphene, with potential applications for solid-state lasers.

We have theoretically investigated the Goos-Hänchen (GH) shift of the TM-polarized beam reflected from a graphene-on-dielectric surface near the Brewster angle. It is shown that even a single-layer graphene allows for notable variation of the GH shift. The GH shift can be enlarged and switched from positive to negative or vice versa. Importantly, the GH shift depends on the Fermi energy, and thus, it can be electrically controlled through electrical or chemical modification of the charge carrier density of the graphene. Furthermore, the relationship between the GH shift and the electron-phonon relaxation time and the number of graphene layers is clarified.