The field of metasurface research has rapidly developed in the past decade. Electron-beam lithography (EBL) is an excellent tool used for rapid prototyping of metasurfaces. However, Gaussian-beam EBL generally struggles with low throughput. In conjunction with the recent rise of interest in metasurfaces made of low-index dielectric materials, we propose in this study the use of a relatively unexplored chemically amplified resist, SU-8 with EBL, as a method for rapid prototyping of low-index metasurfaces. We demonstrate the use of SU-8 grating on silicon for cost-efficient fabrication of an all-dielectric multilevel security print for anti-counterfeiting purposes, which encrypt different optical information with different light illumination conditions, namely, bright-field reflection, dark-field reflection, and cross-polarized reflection. The large-scale print (1 mm2) could be exposed in a relatively short time (∼11 min) due to the ultrahigh sensitivity of the resist, while the feature size of ∼200 nm was maintained, demonstrating that SU-8 EBL resist serves as a good candidate for rapid prototyping of metasurface designs. Our results could find applications in the general area of increasing EBL patterning speed for a variety of other devices and structures.
Multi-dimensional optical imaging systems that simultaneously gather intensity, depth, polarimetric, and spectral information have numerous applications in medical sciences, robotics, and surveillance. Nevertheless, most current approaches require mechanical moving parts or multiple modulation processes and thus suffer from long acquisition time, high system complexity, or low sampling resolution. Here, a methodology to build snapshot multi-dimensional lensless imaging is proposed by combining planar-optics and computational technology, benefiting from sufficient flexibilities in optical engineering and robust information reconstructions. Specifically, a liquid crystal diffuser based on geometric phase modulation is designed to simultaneously encode the spatial, spectral, and polarization information of an object into a snapshot detected speckle pattern. At the same time, a post-processing algorithm acts as a special decoder to recover the hidden information in the speckle with the independent and unique point spread function related to the position, wavelength, and chirality. With the merits of snapshot acquisition, multi-dimensional perception ability, simple optical configuration, and compact device size, our approach can find broad potential applications in object recognition and classification.
Metasurfaces are subwavelength structured thin films consisting of arrays of units that allow the control of polarization, phase, and amplitude of light over a subwavelength thickness. Recent developments in topological photonics have greatly broadened the horizon in designing metasurfaces for novel functional applications. In this review, we summarize recent progress in the research field of topological metasurfaces, first from the perspectives of passive and active in the classical regime, and then in the quantum regime. More specifically, we begin by examining the passive topological phenomena in two-dimensional photonic systems, including both time-reversal broken systems and time-reversal preserved systems. Subsequently, we discuss the cutting-edge studies of active topological metasurfaces, including nonlinear topological metasurfaces and reconfigurable topological metasurfaces. After overviewing topological metasurfaces in the classical regime, we show how they could provide a new platform for quantum information and quantum many-body physics. Finally, we conclude and describe some challenges and future directions of this fast-evolving field.
Photonic technology combined with artificial intelligence plays a key role in the development of the latest smart system trends, integrating cutting-edge technology with machine learning models. This paper proposes a transmission-reflection analysis based system using dielectric nanoparticle-doped fiber combined with artificial intelligence to address one of the major problems in the distributed sensing approach: reducing the cost while maintaining high spatial resolution to close the gap between distributed sensors and the general public. Machine learning-based models are designed to classify the perturbed positions when the same force is used and force regression when different forces are applied on each position. The results show an accuracy of 99.43% in the position classification of multiple disturbances and an rms error of 1.53 N in the force regression, which represents 5% of the force range. In addition, a smart environment using the current system is proposed, which presented 100% accuracy in identifying the positions of different persons in the environment. This smart environment enables remote home care of patients with high reliability, intelligent decision-making, and a predictive capability.
Quantitative phase imaging (QPI) by differential phase contrast (DPC) with partially coherent illumination provides speckle-free imaging and lateral resolution beyond the coherent diffraction limit, demonstrating great potential in biomedical imaging applications. Generally, DPC employs weak object approximation to linearize the phase-to-intensity image formation, simplifying the solution to the phase retrieval as a two-dimensional deconvolution with the corresponding phase transfer function. Despite its widespread adoption, weak object approximation still lacks a precise and clear definition, suggesting that the accuracy of the QPI results, especially for samples with large phase values, is yet to be verified. In this paper, we analyze the weak object approximation condition quantitatively and explicitly give its strict definition that is applicable to arbitrary samples and illumination apertures. Furthermore, an iterative deconvolution QPI technique based on pseudo-weak object approximation is proposed to overcome the difficulty of applying DPC to large-phase samples without additional data acquisition. Experiments with standard microlens arrays and MCF-7 cells demonstrated that the proposed method can effectively extend DPC beyond weak object approximation to high-precision three-dimensional morphological characterization of large-phase technical and biological samples.
A photonic implementation of a wavelength meter typically applies an interferometer to measure the frequency-dependent phase shift provided by an optical delay line. This work shows that the information to be retrieved is encoded by a vector restricted to a circular cone within a 3D Cartesian object space. The measured data belong to the image of the object space under a linear orthogonal map. Component impairments result in broken orthogonal symmetry, but the mapping remains linear. The circular cone is retained as the object space, which suggests that the conventional conic section fitting for the wavelength meter application is a premature reduction of the object space from R3 to R2. The inverse map, constructed by a learning algorithm, compensates impairments such as source intensity fluctuation and errors in delay time, coupler transmission, and photoreceiver sensitivity while being robust to noise. The simple algorithm does not require initial estimates for all parameters except for a broad bracket of the delay; further, weak nonlinearity introduced by uncertain delay can be corrected by a robust golden search algorithm. The phase-retrieval process is invariant to source power and its fluctuation. Simulations demonstrate that, to the extent that the ten parameters of the interferometer model capture all significant impairments, a precision limited only by the level of random noise is attainable. Applied to measured data collected from a fabricated Si3N4 wavelength meter, greater than an order of magnitude improvement in precision compared with the conventional method is achieved.
High-energy pulsed lasers in the green spectral region are of tremendous interest for applications in space laser ranging, underwater detection, precise processing, and scientific research. Semiconductor pulsed lasers currently are difficult to access to the so-called “green gap,” and high-energy green pulsed lasers still heavily rely on the nonlinear frequency conversion of near-IR lasers, precluding compact and low-cost green laser systems. Here, we address this challenge by demonstrating, for the first time to the best of our knowledge, millijoule-level green pulses generated directly from a fiber laser. The green pulsed fiber laser consists of a 450 nm pump laser diode, a Ho3+-doped ZBLAN fiber, and a cavity-dumping module based on a visible wavelength acousto-optic modulator. Stable pulse operation in the cavity-dumping regime at 543 nm is observed with a tunable repetition rate in a large range of 100 Hz–3 MHz and a pulse duration of 72–116 ns. The maximum pulse energy of 3.17 mJ at 100 Hz is successfully achieved, which is three orders of magnitude higher than those of the rare-earth-doped fiber green lasers previously reported. This work provides a model for compact, high-efficiency, and high-energy visible fiber pulsed lasers.
Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation. Reconfigurable chirality through the 3D morphological transformation of chiral materials is significant for greater freedom in tailoring light but remains a challenge. Inspired by the unique 3D morphological memory capability of shape memory alloys (SMAs), we demonstrate and discuss a chiral resonator in the microwave regime that can realize reconfigurable chirality through 3D morphological transformation. The introduction of heating film realizes voltage control of SMA’s morphology for utilizing the temperature sensitivity of SMA better, enabling arbitrary control of circular dichroism (CD) flip and CD intensity. The qualitative and quantitative analysis of the surface current distribution of chiral enantiomers reveals that the chirality of meta-atoms originates from the surge of electric dipole px and electric quadrupole Q. It is worth mentioning that the proposed strategy to achieve reconfigurable chirality using 3D morphological transformations can be directly extended to other higher frequencies, such as visible, infrared, and terahertz bands. Significantly, our paradigm to study the relationship between complex 3D morphology and chirality holds potential for application in biosensing, spin detection, and spin-selective devices.
Perfect optical vortices (POVs), characterized as a ring radius independent of topological charge (TC), possess extensive application in particle manipulation and optical communication. At present, the complex and bulky optical device for generating POVs has been miniaturized by leveraging the metasurface, and either spin-dependent or spin-independent POV conversions have been further accomplished. Nevertheless, it is still challenging to generate superposed POVs for incidences with orthogonal circular polarization. Here, a spin-multiplexed all-dielectric metasurface method for generating superposed POVs in the terahertz frequency range is proposed and demonstrated. By using the multiple meta-atom comprised structure as the basic unit, the complex amplitude of two superposed POVs is modulated, decoupled, and subsequently encoded to left- and right-handed circular polarization incidences. Furthermore, two kinds of metasurfaces are fabricated and characterized to validate this controlling method. It is demonstrated that the measured intensity and phase distributions match well with the calculation of the Rayleigh–Sommerfeld diffraction integral, and the radius of superposed POVs is independent of TCs. This work provides promising opportunities for developing ultracompact terahertz functional devices applied to complex structured light generation and terahertz communication, and exploring sophisticated spin angular momentum and orbital angular momentum interactions like the photonic spin-Hall effect.
Dynamical control of perfect absorption plays an indispensable role in optical switch and modulators. However, it always suffers from the limited modulation range, small depth, and susceptible absorption efficiencies. Here, we propose a new strategy based on Friedrich–Wintgen bound states in the continuum (F–W BICs) to realize a tunable perfect absorber with large dynamic modulation range. For proof of concept, we demonstrate a pentaband ultrahigh absorption system consisting of graphene gratings and graphene sheets through elaborately tuning F–W BIC. The nature of the F–W BIC arises from the destructive interference between Fabry–Perot resonance and guided mode resonance modes in the coherent phase-matching condition. The radiation channels are avoided from crossing. The BIC can be dynamically modulated by engineering the Fermi level of graphene gratings, which breaks the traditional modulation methods with an incidence angle. Remarkably, the perfect absorber with this F–W BIC approach achieves the largest modulation range of up to 3.5 THz. We believe that this work provides a new way to dynamically engineer perfect absorption and stimulates the development of multiband ultracompact devices.
Valley Hall topological photonic crystals, inspired by topological insulators in condensed matter physics, have provided a promising solution to control the flow of light. Recently, the dynamic manipulation property of topological photonic crystals has been widely studied. Here, we propose a novel solution for programmable valley photonic crystals, called field programmable topological edge array (FPTEA), based on the field reorientation property of nematic liquid crystals and robust valley-protected edge modes. FPTEA is composed of an array of graphene-like lattices with C3 symmetry, in which the birefringence of liquid crystal is larger than 0.5105. Due to the dielectric anisotropy of liquid crystals being sensitive to external fields such as light, heat, electric, and magnetic fields, each lattice is tunable, and the topological propagation routes and even the lattice parameters can be dynamically changed while changing the distribution of external fields. We numerically demonstrate three methods of composing an FPTEA device to design arbitrary passive optical devices by electric driving, thermal inducing, or UV writing. These results show the great application potential of liquid crystals in topological photonic crystals, and enrich the design of programmable integrated topological devices with broad working bandwidth ranging from microwave to visible light.
Locking the sophisticated and expensive entanglement sources at the shared relay node is a promising choice for building a star-type quantum network with efficient use of quantum resources, where the involved parties only need to equip low-cost and simple homodyne detectors. Here, to our best knowledge, we demonstrate the first experimental continuous variable quantum key distribution with an entanglement source between the two users. We consider a practical partially characterized entangled source and establish the security analysis model of the protocol under realistic conditions. By applying a biased base technology, the higher key rate than that of the original protocol is achieved. The experimental results demonstrate that the distance between two users can reach up to 60 km over telecom single-mode fiber, implying the feasibility for high-rate and secure communication with a shared entangled source at metropolitan distances.
Compared to pure vortex waves, the superposition state of spherical waves and vortex waves has enough degrees of freedom to upgrade applications in particle manipulation, information encryption, and large-capacity communications. Here, we propose a new scheme to achieve superposition states and multichannel transmission of vortex and spherical waves. Two transmissive all-silicon metasurfaces that enable mutual interference between linearly polarized (LP) waves in the terahertz region are demonstrated. Type A can achieve interference between x and y polarized waves, while type B can achieve interference between x (or y) and x (or y) polarized waves. The multichannel transmission and superposition states of topological charges of +3, +2, and +4 are designed and demonstrated from theoretical, simulative, and experimental perspectives at 1.1 THz. In addition, the objective fact that the focused superposition state must be observed close to the focal plane is also revealed. The measured results are in good agreement with the theoretical and simulative results. This work provides an idea for the design of ultrathin terahertz devices and could be applied in the fields of information encryption and high-frequency communications.
Frequency detuning of mode-locked fiber lasers displays many remarkable nonlinear dynamical behaviors. Here we report for the first time the evolution of pulses from mode-locking through period pulsation to Q-switched mode-locking for three fundamental cases. Our experiments are performed in a hybrid actively and passively amplitude-modulated all-fiber polarization-maintaining mode-locked fiber laser, where the amplitude modulation frequency artificially deviates from the fundamental frequency of the cavity. We design and numerically simulate the laser with coupled Ginzburg–Landau equations. The experimentally observed dynamics of the mode detuning process is discussed with the assistance of the fitted model and numerical simulations, showing the generalizability of the optical mode detuning variation process. Our work provides fundamental insights for understanding perturbations in nonlinear optical resonant cavities and expands the ideas for studying chaotic path theory in hybrid mode-locked fiber lasers.
Measuring magnetic response from spin and current is of fundamental interest in condensed matter physics. Negatively charged nitrogen-vacancy (NV-) centers in diamond are emerging as a robust and versatile quantum sensor owing to their high sensitivity, nanometer-scale spatial resolution, and noninvasive operation with access to static and dynamic magnetic and electron transport properties. In this review, we discuss the rapidly growing interest in the implementation of NV- magnetometry to explore condensed matter physics, focusing on three topics: anti/ferromagnetic materials, superconductors, and metals/semimetals/semiconductors.
This publisher’s note corrects the authorship in Photon. Res.10, 2828 (2022)PRHEIZ2327-912510.1364/PRJ.469340.