The 50 most-cited articles in Optics Letters, 2024

In this Letter, two novel, to the best of our knowledge, quartz tuning forks (QTFs) with trapezoidal-head and round-head were designed and adopted for quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing. Based on finite element analysis, a theoretical simulation model was established to optimize the design of QTF. For performance comparison, a reported T-head QTF and a commercial QTF were also investigated. The designed QTFs have decreased resonant frequency ( f 0 ) and increased gap between the two prongs of QTF. The experimentally determined f 0 of the T-head QTF, trapezoidal-head QTF, and round-head QTF were 8690.69 Hz, 9471.67 Hz, and 9499.28 Hz, respectively. The corresponding quality ( Q ) factors were measured as 11,142, 11,411, and 11,874. Compared to the commercial QTF, the resonance frequencies of these QTFs have reduced by 73.45%, 71.07%, and 70.99% while maintaining a comparable Q factor to the commercially mature QTF. Methane (CH 4 ) was chosen as the analyte to verify the QTFs’ performance. Compared with the commercial QTF, the signal-to-noise ratio (SNR) of the…

In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS 3 nanosheets. We prepared two-layer HfS 3 nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS 3 -based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS 3 material. Furthermore, we utilized the two-layer HfS 3 materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS 3 material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS 3 materials and highlights their potential for advanced optoelectronic devices.

High-dimensional quantum systems expand quantum channel capacity and information storage space. By implementing high-dimensional quantum logic gates, the speed of quantum computing can be practically enhanced. We propose a deterministic 4 × 4-dimensional controlled-not (CNOT) gate for a hybrid system without ancillary qudits required, where the spatial and polarization states of a single photon serve as a control qudit of four dimensions, whereas two electron-spin states in nitrogen-vacancy (NV) centers act as a four-dimensional target qudit. As the control qudits are easily operated employing simple optical elements and the target qudits are available for storage, the CNOT gate works in a deterministic way, and it can be flexibly extended to n × n-dimensional (n > 4) quantum gates for other hybrid systems or different photonic degrees of freedoms. The efficiency and fidelity of the CNOT gate are analyzed aligning with current technological capabilities, finding that they have satisfactory performances.

In this Letter, a quasi-distributed quartz enhanced photoacoustic spectroscopy (QEPAS) gas sensing system based on hollow waveguide micropores (HWGMP) was reported for the first time, to the best of our knowledge. Three micropores were developed on the HWG to achieve distributed detection units. Three self-designed quartz tuning forks (QTFs) with low resonant frequency of 8.7 kHz were selected as the acoustic wave transducer to improve the detection performance. Compared with micro-nano fiber evanescent wave (FEW) QEPAS, the HWGMP-QEPAS sensor has advantages such as strong anti-interference ability, low loss, and low cost. Acetylene (C 2 H 2 ) was selected as the target gas to verify the characteristics of the reported sensor. The experimental results showed that the three QTFs almost had the same sensing ability and possessed an excellent linear concentration response to C 2 H 2 . The minimum detection limits (MDLs) for the three QTFs were determined as 68.90, 68.31, and 66.62 ppm, respectively. Allan deviation analysis indicated that the system had good long-term stability, and…

Topological interface states (TISs), known for their distinctive capabilities in manipulating electromagnetic waves, have attracted significant interest. However, in conventional all-dielectric one-dimensional photonic crystal (1DPC) heterostructures, TISs strongly depend on incident angle, which limits their practical applications. Here, we realize an angle-independent TIS in 1DPC heterostructures containing hyperbolic metamaterials (HMMs) for transverse magnetic polarized waves. We begin with the design of two kinds of angle-independent photonic bandgaps (PBGs) in two 1DPCs with symmetric unit cells based on the phase-variation compensation effect. From the Zak phases of the upper and lower bands, the topological properties of PBGs in two 1DPCs are different. By harnessing different topological properties, we can realize an angle-independent TIS in the heterostructure composed of these two 1DPCs. Moreover, we further discover that the angle-independent property of the TIS is robust against the layer thickness variation due to topological protection, making the experimental…

We propose a scheme to achieve nonreciprocal magnon blockade via the Barnett effect in a magnon-based hybrid system. Due to the rotating yttrium iron garnet (YIG) sphere, the Barnett shift induced by the Barnett effect can be tuned from positive to negative via controlling magnetic field direction, leading to nonreciprocity. We show that a nonreciprocal unconventional magnon blockade (UMB) can emerge only from one magnetic field direction but not from the other side. Particularly, by further tuning system parameters, we simultaneously observe a nonreciprocal conventional magnon blockade (CMB) and a nonreciprocal UMB. This result achieves a switch between efficiency (UMB) and purity (CMB) of a single-magnon blockade. Interestingly, stronger UMB can be reached under stronger qubit-magnon coupling, even the strong coupling regime. Moreover, the nonreciprocity of the magnon blockade is sensitive to temperature. This work opens up a way for achieving quantum nonreciprocal magnetic devices and chiral magnon communications.

We have demonstrated, for the first time to our knowledge, a single-carrier 220-Gbit/s wireless link over 214-m distance within hard-decision forward error correction (HD-FEC) limit using a 300-GHz-band photonics-based system incorporated with on-line digital signal processing (DSP). The approach to obtaining these results was to optimize the transmission system by using a low-noised two-tone laser system to the transmitter and receiver and to apply the unique Fresnel region of the antenna to achieve longer distances. These research results are expected to serve as a low-cost and basic communication system technology for promising backhaul wireless communications in the sixth-generation era.

Molybdenum disulfide (MoS 2 ), as a representative transition metal disulfide material, has contributed significantly to the development of plasmonic technology toward the near-infrared (NIR). In this Letter, the physical mechanism of MoS 2 excitation of surface plasmon resonance (SPR) in the NIR is investigated, and it is shown that the MoS 2 film can induce the resonance dip to move toward the NIR and demonstrate a sensitivity higher than that in the visible band. A dual-channel SPR sensor capable of operating in the visible and NIR bands for refractive index (RI) detection was also prepared using the cascade method. The simulated and experimental results of the sensor show consistency. The experimental results show that the maximum sensitivity of the NIR detection channel is 14600 nm/RIU in the RI range of 1.333–1.420, which is 37% higher than the sensitivity of the visible channel. However, the visible channel has the advantage of a narrow FWHM. Therefore, the proposed cascaded dual-channel RI sensor combines high sensitivity and narrow FWHM. This dual-channel construction…

An ultrahigh-speed phase demodulation system was designed for the Fabry-Perot (F-P) interferometric sensor based on fiber array parallel spectral detection. A high-power amplified spontaneous emission (ASE) source served as the broadband detection light. The spectrum generated by the dispersion of the F-P interference light through an arrayed waveguide grating (AWG) was incident into the fiber array and was detected in parallel by 48 photodiodes. The 48-channel signals were acquired synchronously and processed in real time to achieve a phase demodulation for the F-P cavity at 200 kHz. As a result, a low-resolution spectral detection and demodulation system was constructed with high speed. The length demodulation range of the F-P cavity was 60-700 µm, and the demodulation resolution was as high as 0.22 nm. The designed high-sensitivity demodulator is expected to be used for ultrasonic and high-frequency vibration detection.

In the realm of ultrafast laser technology, the exploration of two-dimensional materials as saturable absorbers (SA) has garnered significant research interest. Our research investigates the characteristics of SnTe thin films, a topological crystalline insulator material, as a potential saturable absorber for ultrafast lasers. Using the molecular beam epitaxy (MBE) technique, we analyze the films' morphology and composition through atomic force microscopy (AFM) and successfully deposit SnTe epilayers on Au(111)/mica substrates. Through the utilization of SnTe-SA, an erbium-doped fiber laser is fabricated, demonstrating a pulse output with a width of 276 fs and a center wavelength of 1560 nm, highlighting the potential of SnTe films in manufacturing ultrafast optical devices. Additionally, tightly bound solitons with a soliton interval of 1.01 ps are observed, contributing to the exploration of soliton nonlinear dynamics.

Nonreciprocal devices are essential and crucial in optics for source protection and signal separation. A hybrid grating system consisting of a silicon grating, a graphene layer, and a silicon waveguide layer is employed to create a high-Q quasi-BIC (bound state in the continuum). Then, the high-Q properties of the quasi-BIC are harnessed to enhance the third-order nonlinear effect of silicon, thereby improving the nonreciprocal characteristics of the device. The nonreciprocal transmittance ratio of the device can be tunable by adjusting the graphene Fermi energy level, achieving tunability ranging from 0.0865 to 30.57 dB. It also enables the best performance of the device over a wider range of frequency bands. This study provides a new, to the best of our knowledge, method for designing tunable nonreciprocal devices with a wide range of potential applications.

An optical frequency domain reflectometry (OFDR) shape sensor was demonstrated based on a femtosecond-laser-inscribed weak fiber Bragg grating (WFBG) array in a multicore fiber (MCF). A WFBG array consisting of 60 identical WFBGs was successfully inscribed in each core along a 60 cm long MCF using the femtosecond-laser point-by-point technology, where the length and space of each WFBG were 2 and 8 mm, respectively. The strain distribution of each core in two-dimensional (2D) and three-dimensional (3D) shape sensing was successfully demodulated using the traditional cross correlation algorithm, attributed to the accurate localization of each WFBG. The minimum reconstruction error per unit length of the 2D and 3D shape sensors has been improved to 1.08% and 1.07%, respectively, using the apparent curvature vector method based on the Bishop frame.

A novel approach-integrating a simulated annealing (SA) algorithm with deep learning (DL) acceleration-is presented for the rapid and accurate development of terahertz perfect absorbers through forward prediction and backward design. The forward neural network (FNN) effectively deduces the absorption spectrum based on metasurface geometry, resulting in an 80,000-fold increase in computational speed compared to a full-wave solver. Furthermore, the absorber's structure can be precisely and promptly derived from the desired response. The incorporation of the SA algorithm significantly enhances design efficiency. We successfully designed low-frequency, high-frequency, and broadband absorbers spanning the 4 to 16 THz range with an error margin below 0.02 and a remarkably short design time of only 10 min. Additionally, the proposed model in this Letter introduces a novel, to our knowledge, method for metasurface design at terahertz frequencies such as the design of metamaterials across optical, thermal, and mechanical domains.

Computer vision technology has been applied in various fields such as identification, surveillance, and robot vision. However, computer vision algorithms used for human-related tasks operate on human images, which raises data security and privacy concerns. In this Letter, we propose an image-free human keypoint detection technique using a few coded illuminations and a single-pixel detector. Our proposed method can complete the keypoint detection task at an ultralow sampling rate on a measured one-dimensional sequence without image reconstruction, thus protecting privacy from the data collection stage and preventing the acquisition of detailed visual information from the source. The network is designed to optimize both the illumination patterns and the human keypoint predictor with an encoder-decoder framework. For model training and validation, we used 2000 images from Leeds Sport Dataset and COCO Dataset. By incorporating EfficientNet backbone, the inference time is reduced from 4 s to 0.10 s. In the simulation, the proposed network achieves 91.7% average precision. Our…

Topological photonic crystals (PCs) provide an effective method for controlling how light propagates and concentrates through their topological states. However, it remains unclear whether topological states can be obtained by combining two different two-dimensional (2D) PCs with topological non-trivial states. In this Letter, two types of 2D Penrose-square (P-S) PCs are proposed. These PCs can generate topological edge states (TESs) and topological corner states (TCSs) within the low-frequency part of the bandgap. Moreover, by combining these two non-trivial PCs, a total of two groups of TESs and four groups of TCSs can be generated in both the high-frequency and low-frequency parts of the common bandgap. To the best of our knowledge, the two proposed P-S PCs offer a new platform for investigating topological photonics and related devices, providing novel approaches and perspectives for generating topological states in 2D PCs.

We produce families of two-dimensional gap solitons (GSs) maintained by moiré lattices (MLs) composed of linear and nonlinear sublattices, with the defocusing sign of the nonlinearity. Depending on the angle between the sublattices, the ML may be quasiperiodic or periodic, composed of mutually incommensurate or commensurate sublattices, respectively (in the latter case, the inter-lattice angle corresponds to Pythagorean triples). The GSs include fundamental, quadrupole, and octupole solitons, as well as quadrupoles and octupoles carrying unitary vorticity. Stability segments of the GS families are identified by means of the linearized equation for small perturbations, and confirmed by direct simulations of perturbed evolution.

A novel, to the best of our knowledge, optical fiber whispering-gallery mode (WGM) sensor for simultaneously measuring humidity and temperature is proposed and investigated. The proposed sensor is realized by a polyvinyl alcohol (PVA)-coated capillary tube coupling with an optical single-mode fiber (SMF), which is integrated with a fiber Bragg grating (FBG). The as-fabricated sensor can be used not only for relative humidity (RH) sensing but also for temperature detection. The achieved humidity and temperature sensitivities are -181.2 pm/%RH and 10.5 pm/°C, respectively. The easy fabrication and very high sensitivity of the proposed sensor are attractive features for high-precision and wide-range RH sensing applications.

Fringe projection profilometry based on MEMS micro-vibration mirrors is very promising due to its rapid projection, large depth of field, compact size, and low cost. Although high-frequency fringes can achieve accurate reconstruction, the projector must offer sufficient pixel resolution. In this paper, we proposed a high-resolution projection technique called the delay superposition method. During a single exposure time of the camera, the projector projects a group of low-resolution fringe patterns, which are delayed according to the movement characteristics of the vibration mirror. Then, the camera exposure superimposes these low-resolution images to form a high-resolution image. These two steps effectively subdivide the angle intervals, thereby achieving a pixel interpolation. Finally, experimental results show that the proposed method can significantly improve the projector's pixel resolution and reconstruction accuracy. The proposed method allows the MEMS projector's pixel resolution (along one direction) to far exceed that of common DLP projectors. It holds great application…

We present the highest, to the best of our knowledge, average power from a laser-driven single-cycle THz source demonstrated so far, using optical rectification in the tilted pulse front geometry in cryogenically cooled lithium niobate, pumped by a commercially available 500 W ultrafast thin-disk ytterbium (Yb) amplifier. We study repetition rate-dependent effects in our setup at 100 and 40 kHz at this high average power, revealing different optimal fluence conditions for efficient conversion. The demonstrated sources with multi-100 mW average power at these high repetition rates combine high THz pulse energies and high repetition rate and are thus ideally suited for nonlinear THz spectroscopy experiments with significantly reduced measurement times. The presented result is a first benchmark for high average power THz time-domain spectroscopy systems for nonlinear spectroscopy, driven by very high average power ultrafast Yb lasers.

In this Letter, we propose and investigate a retroreflective optical integrated sensing and communication (RO-ISAC) system using orthogonal frequency division multiplexing (OFDM) and corner cube reflector (CCR). To accurately model the reflected sensing channel of the RO-ISAC system, both a point source model and an area source model are proposed according to the two main types of light sources that are widely used. Detailed theoretical and experimental results are presented to verify the accuracy of the proposed channel models and evaluate the communication and sensing performance of the considered RO-ISAC system.

The study of salicylideneaniline (SA) and its derivatives is critical due to their special photophysical properties and environmental sensitivity. In this work, the density time-dependent functional theory (TDDFT) and complete-active-space self-consistent-field (CASSCF) methods were carried out to calculate the substituent effect on excited-state properties and dynamics of SA derivatives. We found the para-substitution triggers the excited-state intramolecular proton transfer (ESIPT) reaction, exhibiting the dual-fluorescent phenomena. However, the meta- and ortho-substitutions impel the non-radiative transition process along the minimum energy conical intersection (MECI), forming the twisted intramolecular charge transfer (TICT) state to prevent ESIPT. This investigation of substituent effects on the photochemical processes and photophysical properties will provide the benchmarks for the design of fluorescent materials.

A monolithic fiber laser emitting 1.7 W at 3920 nm is experimentally demonstrated in a Ho 3+ :InF 3 fiber. The cavity comprises a pair of highly reflective fiber Bragg gratings written in the active fiber with the femtosecond phase-mask scanning technique and is spliced to the pump diode with a robust silica-to-fluoride fiber splice. This work is an important step toward high-power all-fiber laser operating in the vicinity of 4 µm.

Longitudinal detection of hemodynamic changes based on wearable devices is imperative for monitoring human healthcare. Photoacoustic effect is extremely sensitive to variations in hemoglobin. Therefore, wearable photoacoustic devices are apt to monitor human healthcare via the observation of hemodynamics. However, the bulky system and difficulties in miniaturizing and optimizing the imaging interface restrict the development of wearable photoacoustic devices for human use. In this study, we developed a wearable photoacoustic watch with a fully integrated system in a backpack that has a size of 450 mm × 300 mm × 200 mm and an affordable weight of 7 kg for an adult to wear. The watch has a size of 43 mm × 30 mm × 24 mm, weighs 40 g, and features a lateral resolution of 8.7 µm, a field of view (FOV) of 3 mm in diameter, and a motorized adjustable focus for optimizing the imaging plane for different individuals. We recruited volunteers to wear the watch and the backpack and performed in vivo imaging of the vasculatures inside human wrists under the conditions of walking and human cuff…

For most imaging systems, there is a trade-off between spatial resolution, temporal resolution, and signal-to-noise ratio. Such a trade-off is particularly severe in single-pixel imaging systems, given the limited throughput of the only one available pixel. Here we report a real-time single-pixel imaging method that can adaptively balance the spatial resolution, temporal resolution, and signal-to-noise ratio of the imaging system according to the changes in the target scene. When scene changes are detected, the dynamic imaging mode will be activated. The temporal resolution will be given high priority and real-time single-pixel imaging will be conducted at a video frame rate (30 frames/s) to visualize the object motion. When no scene changes are detected, the static imaging mode will be activated. The spatial resolution and the signal-to-noise ratio will be progressively built up to resolve fine structures and to improve image quality. The proposed method not only adds practicability to single-pixel imaging, but also generates a new, to the best of our knowledge, insight in data…

Because of their ultra-light, ultra-thin, and flexible design, metalenses exhibit significant potential in the development of highly integrated cameras. However, the performances of metalens-integrated camera are constrained by their fixed architectures. Here we proposed a high-quality imaging method based on deep learning to overcome this constraint. We employed a multi-scale convolutional neural network (MSCNN) to train an extensive pair of high-quality and low-quality images obtained from a convolutional imaging model. Through our method, the imaging resolution, contrast, and distortion have all been improved, resulting in a noticeable overall image quality with SSIM over 0.9 and an improvement in PSNR over 3 dB. Our approach enables cameras to combine the advantages of high integration with enhanced imaging performances, revealing tremendous potential for a future groundbreaking imaging technology.

High-Q intrinsic quasi-bound states in the continuum (QBICs) require three-dimensional (3D) geometries with both in-plane and out-of-plane mirror symmetry breakings, hindering practical implementations due to the complex architectures. Here we demonstrate that high-Q intrinsic QBICs can be flexibly controlled by using the engineered 2.5D phase-change metasurfaces of Ge 2 Sb 2 Te 5 (GST). By introducing the additional out-of-plane perturbations of slant angle θ and azimuthal angle φ , highly efficient and high-Q intrinsic circular dichroism (CD) for both reflection and transmission can be realized. The spinning-selected magnetic dipole (MD) is responsible for the high-Q intrinsic chirality. The high-Q intrinsic CD is robust to the variation of structural parameters, and its Q-factor and resonance location can be tuned through the phase transition of GST.

We present a double-pass bismuth (Bi)-doped fiber amplifier (BDFA) providing high-gain wideband amplification from 1330 to 1480 nm. A peak gain of 38 dB with 4.7 dB noise figure (NF) was obtained at 1420 nm for a -23 dBm input signal, with >20 dB gain from 1335 to 1475 nm. We achieved 30 and 21.5 dB peak gains with 122 nm (1341-1463 nm) and 140 nm (1333-1473 nm) 6 dB-gain bandwidth for -10 and 0 dBm input signal, respectively. For a 0 dBm signal, the power conversion efficiency (PCE) reached 23.7%, and the in-band optical-signal-to-noise ratio (OSNR) across the wideband BDFA was >44 dB. Also, the absorption and luminescence characteristics have been studied for different Bi-doped phosphosilicate fibers (BPSFs) fabricated in-house.

To monitor the health of the fiber network and its ambient environment in densely populated access/metro network areas, in this Letter, an endogenous distributed acoustic sensing (DAS) has been proposed and achieved in a coherent digital subcarrier multiplexing (DSCM) system. Rather than specially allocating a sensing probe in general integrated communication and sensing schemes, the fractional Fourier transformed (FrFT) training sequence (TS) designated for time/frequency synchronization in DSCM coherent communications has been repurposed for sensing. While achieving excellent synchronization performance of communication, the FrFT-based TS can also be concurrently utilized to perform distributed vibration sensing. Experimental results demonstrate that the FrFT-based timing/frequency synchronization sequence is repurposed to achieve a DAS sensitivity of 70 p ε /Hz at a spatial resolution of 5 m, along with 100-Gb/s 16 quadrature amplitude modulation (QAM) DSCM transmission, without a loss of spectral efficiency.

The emerging field of optical vortex beams having fractional topological charges (TCs) is of high interest due to its usefulness in various applications. The efficiency of the result depends on the precise measurement of the orbital angular momentum information tied to the fractional TC. This Letter demonstrates, to our knowledge, a novel and simple technique to measure the fractional TC of optical vortex beams through a hybrid digital-optical correlator with the help of auto-correlation between fork-shaped interference patterns corresponding to integer and fractional TCs. Unlike machine learning-based approaches, the proposed method does not require a complex architecture, which lowers computational cost and enables real-time implementation.

The bound states in the continuum (BICs) have attracted much attention in designing metasurface due to their high Q-factor and effectiveness in suppressing radiational loss. Here we report on the realization of the third harmonic generation (THG) at a near-ultraviolet wavelength (343 nm) via accidental BICs in a metasurface. The absolute conversion efficiency of the THG reaches 1.13 × 10 −5 at a lower peak pump intensity of 0.7 GW/cm 2 . This approach allows the generation of an unprecedentedly high nonlinear conversion efficiency with simple structures.

We investigate the temperature tunable dual quasi-bound states in the continuum (qBICs) in a silicon/vanadium dioxide (Si/VO 2 ) hybrid metasurface with Q -factor being as large as 9.3 × 10 6 and 2.8 × 10 7 by breaking the in-plane C 2 symmetry. The far-field scattering of multipoles and near-field distributions confirm that the toroidal dipole and magnetic quadrupole dominate the dual qBICs resonance. The high performance of slow light with ultralarge group index exceeding 5.6 × 10 5 and the inverse quadratic law between the group index and asymmetric parameter are achieved. By temperature tuning of the VO 2 thin film at the sub-10 K scale, a modulation depth of 90% and the ON/OFF ratio exceeding 12.8 dB are obtained. The proposed temperature tunable dual qBICs have potential applications in the fields of tunable slow light, temperature switches, and sensors.

The Mpemba effect (ME) is the counterintuitive phenomenon in statistical physics for which a far-from-equilibrium state can relax toward equilibrium faster than a state closer to equilibrium. This effect has raised great curiosity for a long time and has been studied extensively in many classical and quantum systems. Here, it is shown that the Mpemba effect can be observed in optics as well. Specifically, the process of light diffusion in finite-sized photonic lattices under incoherent (dephasing) dynamics is considered. Rather surprisingly, it is shown that certain highly localized initial light distributions can diffuse faster than initial broadly delocalized distributions. The effect is illustrated by considering the random walk of optical pulses in fiber-based temporal mesh lattices, which should provide an experimentally accessible setup for the demonstration of the Mpemba effect in optics.

Bound states in the continuum (BICs) have emerged as a powerful platform for boosting light–matter interactions because they provide an alternative way of realizing optical resonances with ultrahigh quality( Q -) factors, accompanied by extreme field confinement. In this work, we realized an optical biosensor by introducing a quasi-BIC (qBIC) supported by an elaborated all-dielectric dimer grating. Thanks to the excellent field confinement within the air gap of grating enabled by such a high- Q qBIC, the figure of merit (FOM) of a biosensor is up to 18,908.7 RIU −1 . Furthermore, we demonstrated that such a high- Q grating can help push the limit of optical biosensing to the single-particle level. Our results may find exciting applications in extreme biochemical sensing like COVID-19 with ultralow concentration.

In this Letter, a modulated-symbol domain matched filtering scheme based on orthogonal frequency division multiplexing (OFDM) is proposed for the photonic-assisted W-band integrated sensing and communication (ISAC) system. The photonic-assisted ISAC system based on a single OFDM waveform is experimentally demonstrated. By using the single OFDM waveform, it can improve the spectrum efficiency and achieve dual functionalities of communication and radar detection simultaneously. The optical heterodyne scheme is used to generate the W-band OFDM signal for the ISAC system. The experimental results show that the data rate of OFDM is up to 4.56 Gbit/s; meanwhile, it can achieve the radar ranging with a ranging resolution of 1.88 cm and a ranging error of millimeter level in the OFDM-ISAC system.

We numerically establish the controllable conversion between Laguerre-Gaussian and Hermite-Gaussian solitons in nonlinear media featuring parabolic and cross-phase potential wells. The parabolic potential maintains the stability of Laguerre-Gaussian and Hermite-Gaussian beams, while the actual conversion between the two modes is facilitated by the cross-phase potential, which induces an additional phase shift. By flexibly engineering the range of the cross-phase potential well, various higher-mode solitons can be generated at desired distances. Beams carrying orbital angular momentum can also be efficiently controlled by this method. In addition, other types of beams, such as sine complex-various-function Gaussian and hypergeometric-Gaussian vortex beams, can be periodically transformed and manipulated in a similar manner. Our approach allows the intricate internal relationships between different modes of beams to be conveniently revealed.

Dynamically manipulating the spectra and polarization properties of thermal radiation is the key to counter an infrared polarization imaging system (IPIS) under the different background environments. In this Letter, we propose a phase-change metasurface thermal emitter (PCMTE) composed of vanadium dioxide (VO 2 ) dipole antenna arrays to dynamically manipulate polarized radiation spectra in the long-wave infrared (LWIR) region of 8–14 µm. During the thermally induced and reversible insulator-to-metal transition (IMT) in VO 2 , by simulating the LWIR images at different polarization angles for the PCMTE and background plates, the PCMTE can realize dynamically tunable LWIR camouflage; then, their degree of linear polarization (DoLP) can be calculated, which can demonstrate that the PCMTE can also achieve dynamically tunable LWIR polarization camouflage at the specific radiation angles and backgrounds. Our proposed PCMTE provides an effective scheme for adaptive IR polarization camouflage.

Polarization and wavelength multiplexed metalenses address the bulkiness of traditional imaging systems. However, despite progress with numerical simulations and parameter scanning, the engineering complexity of classical methods highlights the urgent need for efficient deep learning approaches. This paper introduces a deep learning-driven inverse design model for polarization-multiplexed metalenses, employing propagation phase theory alongside spectral transfer learning to address chromatic dispersion challenges. The model facilitates the rapid design of metalenses with off-axis and dual-focus capabilities within a single wavelength. Numerical simulations reveal a focal length deviation of less than 5% and an average focusing efficiency of 43.3%. The integration of spectral transfer learning streamlines the design process, enabling multifunctional metalenses with enhanced full-color imaging and displacement measurement, thus advancing the field of metasurfaces.

With ongoing advancements in photothermal therapy, achieving efficient tumor cell eradication while minimizing damage to healthy tissues necessitates a highly effective and non-invasive real-time temperature monitoring technique for human tissues. Herein, we report a near-infrared (NIR)-II optical temperature sensing nanoprobe featuring rare-earth-doped gadolinium oxide nanocrystals (RENCs) attached to the dumbbell mesoporous silica-coated gold nanorods (AuNRs). The composite nanoprobe presents an intense absorption in the NIR region, and NIR-II photoluminescence (PL) increases by 97.2 to 102-fold compared to pure RENCs upon 980 nm irradiation. The localized electric field generated through surface plasmon resonance effects of AuNRs demonstrated a dumbbell-shaped distribution that aligns with the structure of nanoprobes, maximizing the PL enhancement of RENCs. Moreover, the NIR-II emissions are changed with the rising temperature, with an exceptional relative sensitivity of 7.25% K −1 at 338 K based on PL lifetime, indicating the nanoprobe is highly potential for optical temperature…

A full-field swept-source optical coherence tomography (FF-SS-OCT) for in vivo murine retinal imaging is demonstrated. The on-axis FF-SS-OCT system was built in a Mach-Zehnder interferometer configuration employing a tunable laser source with an adjustable sweep rate and sweep range in conjunction with a fast 2D-CMOS camera. A large field retinal (coherent) illumination was accomplished using an imaging interface comprised of a short-focal length imaging lens and a contact lens. The magnification between the camera and retina (spatial sampling) was appropriately chosen to record the microscopic structural features of the retina in the image. A pupil stop was employed in the detection path to reject unwanted backscattering from the mouse eye and other sources and limit aberrations distorting the retinal images. In vivo mouse retinal imaging was performed at a sweep rate of 150 Hz to acquire volumes unaffected by the system vibrations, which predominated at lower frequencies. Operating the FF-SS-OCT at this speed yielded an effective axial scan rate of 20 million A-scans/s and a field…

The terahertz absorption fingerprint spectrum is crucial for qualitative spectral analysis, revealing the rotational or vibrational energy levels of numerous biological macromolecules and chemicals within the THz frequency range. However, conventional sensing in this band is hindered by weak interactions with trace analytes, leading to subtle signals. In this Letter, an all-dielectric metasurface array is proposed to enhance the absorption fingerprint spectrum using quasi-bound states in the continuum (BIC) resonance. The observable quasi-BIC resonance is achieved by breaking the symmetry of the C 2 v structure. The periodic dimensions of the structure are adjusted to excite quasi-BIC resonances at different frequencies, thereby enhancing the fingerprint spectra of four different substances. By exploiting the correlation between the Q -factor and absorption across different frequencies, calibration of the molecular absorption fingerprint spectrum obtained through metasurface sensing yields precise enhanced absorption fingerprint spectra for various substances within the 0.55–1.6 THz…

A compact underwater lidar system, utilizing a single-photon detection technology, is proposed to effectively eliminate interference from the sea–air interface and enhance the accuracy of water optical property measurements. However, the high sensitivity of the single-photon detector poses challenges, including daytime operation difficulties due to strong solar radiation noise and detector saturation from near-field lidar signals. To address these issues, the laser and optical receiver of the lidar are optimized to suppress solar radiation noise, and a dual-telescope structure is introduced to improve the dynamic measurement range beyond 70 dB. In addition, a Monte Carlo simulation establishes the relationship between beam attenuation coefficients ( c ) and lidar attenuation coefficients ( K lidar ), enabling the retrieval of c profiles from K lidar . A field experiment conducted in the South China Sea, spanning from inshore to offshore waters, demonstrates the effectiveness of the lidar. The results highlight its potential applications, including the assessment of subsurface…

A high security physical layer encryption scheme for dual-mode orthogonal frequency division multiplexing with index modulation (DM-OFDM-IM) in magnetic induction communication is proposed. The scheme utilizes DM-OFDM-IM, where subcarriers within each subblock are divided into two groups, each modulated by distinct signal constellations. DM-OFDM-IM leverages the sequential information from the modulated constellation to transmit extra information, leading to a substantial enhancement in spectral efficiency. In order to improve the security of DM-OFDM-IM magnetic communication system, a 4D hyperchaos model is used to generate four columns of chaotic sequences for specific encryption, frequencies, and symbols scrambling of transmitted data to prevent attacks from illegal receivers. A DM-OFDM-IM magnetic communication signal encrypted by 23.76 kb/s is experimentally transmitted on a 36 cm magnetic induction coil. Due to the use of geometric shaping, the communication distance is increased by 0.316 cm compared with the traditional 8QAM modulation at the hard-decision FEC BER limit of…

All-dielectric metasurface (ADM) absorbers driven by quasi-bound states in the continuum (BIC) are critical for high-performance optoelectronic devices due to their ability to offer high Q -factor absorption. However, these all-dielectric metasurfaces usually require the aid of degenerate critical coupling schemes or back-metal reflective layers to achieve high absorption, which often suffers from limitations such as sensitive geometrical parameters, ohmic losses, and low Q -factors. This work presents an ADM for high- Q near-perfect light absorption, which consists of double Si nanorods and SiO 2 /Ta 2 O 5 multilayers. By breaking the symmetry of the length of the Si nanorods, this ADM can excite a single quasi-BIC resonance corresponding to the electric dipole. Without introducing a metal layer, we realize the highly asymmetric coupling of quasi-BIC by only 6 layers of SiO 2 /Ta 2 O 5 films. It is theoretically and numerically demonstrated that the quasi-BIC has more than 98% absorption at 943.68 nm and a Q -factor as high as 2842. In addition, the ADM exhibits excellent tolerance…

We experimentally demonstrate a liquid crystal (LC)-integrated EIT metasurface for active THz polarization conversion and asymmetric transmission. By controlling the LC orientation under static magnetic field anchoring and an adjustable electric field, the device realizes the active control from the OFF state to the ON state, corresponding to the orthogonal polarization excitation modes of the EIT metasurface. Furthermore, based on the different polarization responses at forward and backward incidences, we achieve asymmetric transmission at the EIT peak and two nearby resonances, with its isolation actively manipulated by the external electric field. This study on dynamic polarization conversion and asymmetric transmission by a LC-integrated metasurface offers a promising route for active THz devices, applicable to THz communication, switching, and sensing systems.

In underwater computational ghost imaging, the presence of scattering and absorption introduces significant degradation, leading to blurring and distortion of illuminating patterns. This work proposes an anti-degradation underwater computational ghost imaging (AUGI) method based on the physical degradation model of underwater forward degradation caused by scattering and absorption. Through AUGI, we can enhance the quality of a reconstructed image by about 10% compared to differential ghost imaging (DGI) as measured by peak signal-to-noise ratio (PSNR) and structural similarity (SSIM), as a result of simulations. We experimentally demonstrate the superior effectiveness of this method in the artificial submarine environment. Additionally, benefitting from its simplicity, this method is expected to be applied across a wide range of underwater ghost imaging applications.

Recent advances in learning-based computer-generated holography (CGH) have unlocked novel possibilities for crafting phase-only holograms. However, existing approaches primarily focus on the learning ability of network modules, often neglecting the impact of diffraction propagation models. The resulting ringing artifacts, emanating from the Gibbs phenomenon in the propagation model, can degrade the quality of reconstructed holographic images. To this end, we explore a diffraction propagation error-compensation network that can be easily integrated into existing CGH methods. This network is designed to correct propagation errors by predicting residual values, thereby aligning the diffraction process closely with an ideal state and easing the learning burden of the network. Simulations and optical experiments demonstrate that our method, when applied to state-of-the-art HoloNet and CCNN, achieves PSNRs of up to 32.47 dB and 29.53 dB, respectively, surpassing baseline methods by 3.89 dB and 0.62 dB. Additionally, real-world experiments have confirmed a significant reduction in ringing…

The existing methods for the generation of arbitrary vector vortex beams often involve complex optical setups or intricate fabrication methods. In this Letter, we propose a novel, to the best of our knowledge, and simplified approach for the efficient generation of vector vortex beams using a polarization-multiplexed hologram fabricated on an azo-carbazole polymer using a simple double-exposure technique. The hologram generates a vector vortex beam when simply illuminated by a collimated beam and also allows for a seamless traversal across the entire higher-order Poincaré sphere (arbitrary vortex beam generation) just by modulating the polarization of an illuminating beam.

The advancement demands of high-speed wireless data link ask for higher requirements on visible light communication (VLC), where wide coverage stands as a critical criterion. Here, we present the design and implementation of a transmitter structure capable of emitting a high-power wide-coverage white light laser. This laser source exhibits excellent stability, with an irradiation range extending to a half-angle of 20°. Its high brightness satisfies the needs of indoor illumination while maintaining excellent communication performance. Utilizing bit-loading discrete multi-tone modulation, a peak data transmission rate of 3.24 Gbps has been achieved, spanning 1 to 5 m. Remarkably, the data rates exceed 2.5 Gbps within a 40° range at a distance of 5 m, enabling a long-distance, wide coverage, high-speed VLC link for future mobile network applications.

All-dielectric high-Q metasurface absorbers based on quasi-bound states in the continuum (QBICs) are essential for optical and photonic devices. However, achieving perfect absorption requires adding back reflectors at the bottom or placing at least four asymmetric elements in each unit of monolayer metasurfaces, which will increase the design complexity. This work proposes a honeycomb structure with units periodically arranged as a hexagonal lattice. Each unit cell is made of two nanopost elements. By only tuning the radius difference of two elements to break the in-plane symmetry, two orthogonal QBIC modes corresponding to toroidal dipole (TD) and electric dipole (ED) modes are excited, respectively. The maximum absorption reaches 92.3% at 955 nm with a Q factor of 1501, breaking the monolayer limit of 50% by the degenerate critical coupling. Our work may provide a promising route for designing high-Q all-dielectric metasurface absorbers applied in ultrafast optoelectronic devices.

We experimentally establish a 3 × 3 cross-shaped micro-ring resonator (MRR) array-based photonic multiplexing architecture relying on silicon photonics to achieve parallel edge extraction operations in images for photonic convolution neural networks. The main mathematical operations involved are convolution. Precisely, a faster convolutional calculation speed of up to four times is achieved by extracting four feature maps simultaneously with the same photonic hardware's structure and power consumption, where a maximum computility of 0.742 TOPS at an energy cost of 48.6 mW and a convolution accuracy of 95.1% is achieved in an MRR array chip. In particular, our experimental results reveal that this system using parallel edge extraction operators instead of universal operators can improve the imaging recognition accuracy for CIFAR-10 dataset by 6.2% within the same computing time, reaching a maximum of 78.7%. This work presents high scalability and efficiency of parallel edge extraction chips, furnishing a novel, to the best of our knowledge, approach to boost photonic computing speed.