Secure distribution of high-speed digital encryption/decryption keys over a classical fiber channel is strongly pursued for realizing perfect secrecy communication systems. However, it is still challenging to achieve a secret key rate in the order of tens of gigabits per second to be comparable with the bit rate of commercial fiber-optic systems. In this paper, we propose and experimentally demonstrate a novel solution for high-speed secure key distribution based on temporal steganography and private chaotic phase scrambling in the classical physical layer. The encryption key is temporally concealed into the background noise in the time domain and randomly phase scrambled bit-by-bit by a private chaotic signal, which provides two layers of enhanced security to guarantee the privacy of key distribution while providing a high secret key rate. We experimentally achieved a record classical secret key rate of 10 Gb/s with a bit error rate lower than the hard-decision forward error correction (HD-FEC) over a 40 km standard single mode fiber. The proposed solution holds great promise for achieving high-speed key distribution in the classical fiber channel by combining steganographic transmission and chaotic scrambling.

Ultraviolet (UV) imaging enables a diverse array of applications, such as material composition analysis, biological fluorescence imaging, and detecting defects in semiconductor manufacturing. However, scientific-grade UV cameras with high quantum efficiency are expensive and include complex thermoelectric cooling systems. Here, we demonstrate a UV computational ghost imaging (UV-CGI) method to provide a cost-effective UV imaging and detection strategy. By applying spatial–temporal illumination patterns and using a 325 nm laser source, a single-pixel detector is enough to reconstruct the images of objects. We use UV-CGI to distinguish four UV-sensitive sunscreen areas with different densities on a sample. Furthermore, we demonstrate dark-field UV-CGI in both transmission and reflection schemes. By only collecting the scattered light from objects, we can detect the edges of pure phase objects and small scratches on a compact disc. Our results showcase a feasible low-cost solution for nondestructive UV imaging and detection. By combining it with other imaging techniques, such as hyperspectral imaging or time-resolved imaging, a compact and versatile UV computational imaging platform may be realized for future applications.

Light-sheet fluorescence microscopy (LSFM) has played an important role in bio-imaging due to its advantages of high photon efficiency, fast speed, and long-term imaging capabilities. The perpendicular layout between LSFM excitation and detection often limits the 3D resolutions as well as their isotropy. Here, we report on a reflective type light-sheet microscope with a mini-prism used as an optical path reflector. The conventional high NA objectives can be used both in excitation and detection with this design. Isotropic resolutions in 3D down to 300 nm could be achieved without deconvolution. The proposed method also enables easy transform of a conventional fluorescence microscope to high performance light-sheet microscopy.

The pyramid wavefront sensor (PWFS) can provide the sensitivity needed for demanding adaptive optics applications, such as imaging exoplanets using the future extremely large telescopes of over 30 m of diameter (D). However, its exquisite sensitivity has a limited linear range of operation, or dynamic range, although it can be extended through the use of beam modulation—despite sacrificing sensitivity and requiring additional optical hardware. Inspired by artificial intelligence techniques, this work proposes to train an optical layer—comprising a passive diffractive element placed at a conjugated Fourier plane of the pyramid prism—to boost the linear response of the pyramid sensor without the need for cumbersome modulation. We develop an end-2-end simulation to train the diffractive element, which acts as an optical preconditioner to the traditional least-square modal phase estimation process. Simulation results with a large range of turbulence conditions show a noticeable improvement in the aberration estimation performance equivalent to over 3λ/D of modulation when using the optically preconditioned deep PWFS (DPWFS). Experimental results validate the advantages of using the designed optical layer, where the DPWFS can pair the performance of a traditional PWFS with 2λ/D of modulation. Designing and adding an optical preconditioner to the PWFS is just the tip of the iceberg, since the proposed deep optics methodology can be used for the design of a completely new generation of wavefront sensors that can better fit the demands of sophisticated adaptive optics applications such as ground-to-space and underwater optical communications and imaging through scattering media.

The optical frequency comb serves as a powerful tool for distance measurement by integrating numerous stable optical modes into interferometric measurements, enabling unprecedented absolute measurement precision. Nonetheless, due to the periodicity of its pulse train, the comb suffers from measurement dead zones and ambiguities, thereby impeding its practical applications. Here, we present a linear group delay spectral interferometer for achieving precise full-range distance measurements. By employing a carefully designed linear group delay (LGD) device for phase modulation of the comb modes, interference can occur and be easily measured at any position. Our approach effectively eliminates the dead zones and ambiguities in comb-based ranging, without the need for cumbersome auxiliary scanning reference devices or reliance on complex high-repetition-rate combs or high-resolution spectrometers. We conducted length metrology experiments using a mode-locked comb referenced to a rubidium clock, achieving a large nonambiguity range up to 0.3 m, covering the entire measurement period. The maximum deviation compared to a laser interferometer was less than 1.5 μm, and the minimum Allan deviation during long-term measurements reached 5.47 nm at a 500 s averaging time. The approach ensures high accuracy while maintaining a simple structure, without relying on complex external devices, thereby propelling the practical implementation of comb-based length metrology.

Surface acoustic wave (SAW) resonators based on lithium tantalate (LT, LiTaO3) wafers are crucial elements of mobile communication filters. The use of intrinsic LT wafers typically brings about low fabrication accuracy of SAW resonators due to strong UV reflection in the lithography process. This hinders their resonance frequency control seriously in industrial manufacture. LT doping and chemical reduction could be applied to decrease the UV reflection of LT wafers for high lithographic precision. However, conventional methods fail to provide a fast and nondestructive approach to identify the UV performance of standard single-side polished LT wafers for high-precision frequency control. Here, we propose a convenient on-line sensing scheme based on the colorimetry of reduced Fe-doped LT wafers and build up an automatic testing system for industrial applications. The levels of Fe doping and chemical reduction are evaluated by the lightness and color difference of LT-based wafers. The correlation between the wafer visible colorimetry and UV reflection is established to refine the lithography process and specifically manipulate the frequency performance of SAW resonators. Our study provides a powerful tool for the fabrication control of SAW resonators and will inspire more applications on sophisticated devices of mobile communication.

Plasmonic sensing technology has attracted considerable attention for high sensitivity due to the ability to effectively localize and manipulate light. In this study, we demonstrate a refractive index (RI) sensing scheme based on open-loop twisted meta-molecule arrays using the versatile nano-kirigami principle. RI sensing has the features of a small footprint, flexible control, and simple preparation. By engineering the morphology of meta-molecules or the RI of the ambient medium, the chiral surface lattice resonances can be significantly enhanced, and the wavelength, intensity, and sign of circular dichroism (CD) can be flexibly tailored. Utilizing the relation between the wavelength of the CD peak and the RI of the superstrate, the RI sensor achieves a sensitivity of 1133 nm/RIU. Additionally, we analyze these chiroptical responses by performing electromagnetic multipolar decomposition and electric field distributions. Our study may serve as an ideal platform for applications of RI measurement and provide new insights into the manipulation of chiral light–matter interactions.

Nanoparticles made of different materials usually support optical resonances in the visible to near infrared spectral range, such as the localized surface plasmons observed in metallic nanoparticles and the Mie resonances observed in dielectric ones. Such optical resonances, which are important for practical applications, depend strongly on the morphologies of nanoparticles. Laser irradiation is a simple but effective way to modify such optical resonances through the change in the morphology of a nanoparticle. Although laser-induced shaping of metallic nanoparticles has been successfully demonstrated, it remains a big challenge for dielectric nanoparticles due to their larger Young’s modulus and smaller thermal conductivities. Here, we proposed and demonstrated a strategy for realizing controllable shaping of high-index dielectric nanoparticles by exploiting the giant optical force induced by femtosecond laser pulses. It was found that both Si and Ge nanoparticles can be lit up by resonantly exciting the optical resonances with femtosecond laser pulses, leading to the luminescence burst when the laser power exceeds a threshold. In addition, the morphologies of Si and Ge nanoparticles can be modified by utilizing the giant absorption force exerted on them and the reduced Young’s modulus at high temperatures. The shape transformation from sphere to ellipsoid can be realized by laser irradiation, leading to the blueshifts of the optical resonances. It was found that Si and Ge nanoparticles were generally elongated along the direction parallel to the polarization of the laser light. Controllable shaping of Si and Ge can be achieved by deliberately adjusting the excitation wavelength and the laser power. Our findings are helpful for understanding the giant absorption force of femtosecond laser light and are useful for designing nanoscale photonic devices based on shaped high-index nanoparticles.

Optical clock networks have distinct advantages for the dissemination of time/frequency, geodesy, and fundamental research. To realize such a network, the telecom band and optical atomic clocks have to be coherently bridged. Since the telecom band and optical atomic clocks reside in a distinct spectral region, second-harmonic generation is usually introduced to bridge the large frequency gap. In this paper, we introduce a new method to coherently link a 1550 nm continuous wave laser with a Ti:sapphire mode-locked laser-based optical frequency comb. By coupling the 1550 nm continuous wave laser light and the Ti:sapphire comb light together into a photonic crystal fiber, nonlinear interaction takes place, and new comblike frequency components related to the 1550 nm laser frequency are generated in the visible region. Consequently, we can detect beat notes between two combs in the visible region with a signal-to-noise ratio of more than 40 dB in a resolution bandwidth of 300 kHz. With this signal, we realize an optical frequency divider for converting the frequency of optical clocks in the visible region to the telecom band at 1.55 μm. An out-of-loop measurement shows that the additional noise and uncertainty induced in optical frequency conversion are 5×10-18 at 1 s averaging time and 2.2×10-19, respectively, which are limited by the uncompensated light path fluctuation but fulfill precision measurement using state-of-the-art optical clocks.

Dynamic infrared thermal camouflage technology has attracted extensive attention due to its ability to thermally conceal targets in various environmental backgrounds by tuning thermal emission. The use of phase change materials (PCMs) offers numerous advantages, including zero static power, rapid modulation rate, and large emissivity tuning range. However, existing PCM solutions still encounter several practical application challenges, such as temperature uniformity, amorphization achievement, and adaptability to different environments. In this paper, we present the design of an electrically controlled metal-insulator-metal thermal emitter based on a PCM metasurface, and numerically investigate its emissivity tunability, physical mechanisms, heat conduction, and thermal camouflage performance across different backgrounds. Furthermore, the influence of the quench rate on amorphization was studied to provide a guidance for evaluating and optimizing device structures. Simulation results reveal that the thermal emitter exhibits a wide spectral emissivity tuning range between 8 and 14 μm, considerable quench rates for achieving amorphization, and the ability to provide thermal camouflage across a wide background temperature range. Therefore, it is anticipated that this contribution will promote the development of PCM-based thermal emitters for practical dynamic infrared thermal camouflage technology with broad applications in both civilian and military domains.

Circular dichroism (CD) is extensively used in various material systems for applications including biological detection, enantioselective catalysis, and chiral separation. This paper introduces a chiral absorptive metasurface that exhibits a circular polarization-selective effect in dual bands—positive and negative CD peaks at short wavelengths and long wavelengths, respectively. Significantly, we uncover that this phenomenon extends beyond the far-field optical response, as it is also observed in the photothermal effect and the dynamics of thermally induced fluid motion. By carefully engineering the metasurface design, we achieve two distinct CD signals with high g factors (∼1) at the wavelengths of 877 nm and 1045 nm, respectively. The findings presented in this study advance our comprehension of CD and offer promising prospects for enhancing chiral light–matter interactions in the domains of nanophotonics and optofluidics.

Janus metasurface holography with asymmetric transmission characteristics provides new degrees of freedom for multiplexing technologies. However, earlier metasurfaces with asymmetrical transmission faced limitations in terms of tunability and multifunctionality. In this study, we propose a metasurface color holographic encryption scheme with dynamic switching and asymmetric transmission at visible frequencies using a low-loss nonvolatile optical phase-change material, Sb2S3. Using a modified holographic optimization strategy, we achieved high-fidelity asymmetric holographic imaging of a nanostructured metasurface. By controlling the incident direction and wavelength of visible light, as well as the level of crystallization of Sb2S3, this reconfigurable metasurface enables the precise manipulation of tunable color holographic image displays. In particular, in the semi-crystalline state of Sb2S3, the encoded information can be securely encrypted using a two-channel color-holographic image, whereas only a preset camouflaged image is displayed in the crystalline or amorphous state of Sb2S3. The proposed multiencrypted Janus metasurface provides a potential approach for dynamic holographic displays with ultrahigh capacity, holographic encryption, and information storage.

Scintillators are widely utilized in high-energy radiation detection in view of their high light yield and short fluorescence decay time. However, constrained by their current shortcomings, such as complex fabrication procedures, high temperature, and difficulty in the large scale, it is difficult to meet the increasing demand for cost-effective, flexible, and environment-friendly X-ray detection using traditional scintillators. Perovskite-related cesium copper halide scintillators have recently received multitudinous research due to their tunable emission wavelength, high photoluminescence quantum yield (PLQY), and excellent optical properties. Herein, we demonstrated a facile solution-synthesis route for indium-doped all-inorganic cesium copper iodide (Cs3Cu2I5) powders and a high scintillation yield flexible film utilizing indium-doped Cs3Cu2I5 powders. The large area flexible films achieved a PLQY as high as 90.2% by appropriately adjusting the indium doping concentration, much higher than the undoped one (73.9%). Moreover, benefiting from low self-absorption and high PLQY, the Cs3Cu2I5:In films exhibited ultralow detection limit of 56.2 nGy/s, high spatial resolution up to 11.3 lp/mm, and marvelous relative light output with strong stability, facilitating that Cs3Cu2I5:In films are excellent candidates for X-ray medical radiography. Our work provides an effective strategy for developing environment-friendly, low-cost, and efficient scintillator films, showing great potential in the application of high-performance X-ray imaging.

In this paper, a patch-antenna-array enhanced quantum cascade detector with freely switchable operating modes among mid-wave, long-wave, and dual-color was proposed and discussed. The dual-color absorption occurs in a single active region through an optimized coupled miniband diagonal-transition subbands arrangement, and a successful separation of the operation regimes was realized by two nested antenna arrays with different patch sizes up to room temperature. At 77 K, the 5.7-μm channel achieved a peak responsivity of 34.6 mA/W and exhibited a detectivity of 2.0×1010 Jones, while the 10.0-μm channel achieved a peak responsivity of 87.5 mA/W, giving a detectivity of 5.0×1010 Jones. Under a polarization modulation of the incident light, the minimum cross talk of the mid-wave and the long-wave operating modes was 1:22.5 and 1:7.6, respectively. This demonstration opens a new prospect for multicolor infrared imaging chip integration technology.

Overcoming the diffraction limit is crucial for obtaining high-resolution images and observing fine microstructures. With this conventional difficulty still puzzling us and the prosperous development of wave dynamics of light interacting with gravitational fields in recent years, how spatial curvature affects the diffraction limit is an attractive and important question. Here we investigate the issue of the diffraction limit and optical resolution on two-dimensional curved space—surfaces of revolution (SORs) with constant or variable spatial curvature. We show that the diffraction limit decreases and the resolution is improved on SORs with positive Gaussian curvature, opening a new avenue to super-resolution. The diffraction limit is also influenced by the propagation direction, as well as the propagation distance in curved space with variable spatial curvature. These results provide a possible method to control the optical resolution in curved space or equivalent waveguides with varying refractive index distribution and may allow one to detect the presence of the nonuniform strong gravitational effect by probing locally the optical resolution.

Metasurfaces with spin-selective transmission play an increasingly critical role in realizing optical chiral responses, especially for strong intrinsic chirality, which is limited to complex three-dimensional geometry. In this paper, we propose a planar metasurface capable of generating maximal intrinsic chirality and achieving dual-band spin-selective transmission utilizing dual quasi-bound states in the continuum (quasi-BICs) caused by the structural symmetry breaking. Interestingly, the value of circular dichroism (CD) and the transmittance of two kinds of circular polarization states can be arbitrarily controlled by tuning the asymmetry parameter. Remarkable CD approaching unity with the maximum transmittance up to 0.95 is experimentally achieved in the dual band. Furthermore, assisted by chiral BICs, the application in polarization multiplexed near-field image display is also exhibited. Our work provides a new avenue to flexibly control intrinsic chirality in planar structure and offers an alternative strategy to develop chiral sensing, multiband spin-selective transmission, and high-performance circularly polarized wave detection. The basic principle and design method of our experiments in the microwave regime can be extended to other bands, such as the terahertz and infrared wavelengths.

On-chip polarization controllers are extremely important for various optical systems. In this paper, a compact and robust silicon-based on-chip polarization controller is proposed and demonstrated by integrating a special polarization converter and phase shifters. The special polarization converter consists of a 1×1 Mach–Zehnder interferometer with two polarization-dependent mode converters at the input/output ends. When light with an arbitrary state of polarization (SOP) is launched into the chip, the TE0 and TM0 modes are simultaneously excited. The polarization extinction ratio (PER) and the phase difference for the TE0/TM0 modes are tuned by controlling the first phase shifter, the polarization converter, and the second phase shifter. As a result, one can reconstruct the light SOP at the output port. The fabricated polarization controller, as compact as ∼150 μm×700 μm, exhibits an excess loss of less than 1 dB and a record PER range of >54 dB for arbitrary input light beams in the wavelength range of 1530–1620 nm.

The terahertz (THz) wave is at the intersection between photonics and electronics in the electromagnetic spectrum. Since the vibration mode of many biomedical molecules and the weak interaction mode inside the molecules fall in the THz regime, utilizing THz radiation as a signal source to operate substance information sensing has its unique advantages. Recently, the metamaterial sensor (metasensor) has greatly enhanced the interaction between signal and substances and spectral selectivity on the subwavelength scale. However, most past review articles have demonstrated the THz metasensor in terms of their structures, applications, or materials. Until recently, with the rapid development of metasensing technologies, the molecular information has paid much more attention to the platform of THz metasensors. In this review, we comprehensively introduce the THz metasensor for detecting not only the featureless refractive index but also the vibrational/chiral molecular information of analytes. The objectives of this review are to improve metasensing specificity either by chemical material-assisted analyte capture or by physical molecular information. Later, to boost THz absorption features in a certain frequency, the resonant responses of metasensors can be tuned to the molecular vibrational modes of target molecules, while frequency multiplexing techniques are reviewed to enhance broadband THz spectroscopic fingerprints. The chiral metasensors are also summarized to specific identification chiral molecules. Finally, the potential prospects of next generation THz metasensors are discussed. Compared to featureless refractive index metasensing, the specific metasensor platforms accelerated by material modification and molecular information will lead to greater impact in the advancement of trace detection of conformational dynamics of biomolecules in practical applications.