High-resolution label-free dual-mode full-field optical coherence tomography (FFOCT) is developed for simultaneous structural and functional imaging of mouse retinas, achieving both static contrasts gained from structural refractive index gradients and dynamic contrasts induced by endogenous cell motility. Imaging experiments on normal mouse retinas show that static FFOCT images better reveal the relative stationary structures like nerve fibers, vascular walls, and collagens, and dynamic FFOCT images show enhanced contrasts of cells with active intracellular metabolic motions, offering complementary information about major retinal layers. Specifically, dual-mode FFOCT imaging on early ischaemia/reperfusion (I/R) injured mouse retinas highlights the transparent ganglion cells at the cellular level without contrast agent labeling, visualizing their structural and dynamic alterations in early I/R injured retina.

We propose a method for realizing single-shot high-resolved quantitative birefringence microscopy by extending microsphere-assisted microscopy into polarization holographic microscopy. Based on our proposed imaging system and reconstruction algorithm, we are capable of simultaneously realizing high-resolved polarization holographic imaging and quantitative measurement of 2D birefringence information of dynamic samples. We demonstrated our proposed method by quantitatively imaging a birefringence resolution target, whose resolution (0.71 µm) exceeds the resolution limit of a microscope objective with a numerical aperture of 0.25. Experimental results of rotating holographic diffraction grating with 500 lp/mm further demonstrated the feasibility of our method in birefringence imaging of dynamic samples.

In this paper, a high-security three-dimensional carrierless amplitude and phase (3D-CAP) modulation technique is proposed, integrating deep learning with four-level masking. The 3D constellation geometry is optimized using an autoencoder (AE) with an additive white Gaussian noise (AWGN) channel model, reducing complexity by 40% compared to a variational autoencoder (VAE). Experimental validation on a 2 km seven-core fiber intensity modulation/direct detection (IM/DD) system shows a 1 dB improvement in receiver sensitivity. A 3D chaotic oscillator model is used for chaotic selective mapping, polynomial-like masking, constellation rotation, and subcarrier masking. The encrypted 3D-CAP signal achieves a key space of up to 10103, with strong anti-noise and confidentiality performance.

In this paper, a carrier-less amplitude and phase modulation passive optical network (CAP-PON) scheme is proposed based on dynamic probabilistic shaping (DPS) and Rubik’s cube encryption in optical access networks. The key is generated from a novel five-dimensional entangled chaos model for dynamic probabilistic shaping and Rubik’s cube encryption. To verify the performance of the encryption scheme, an experimental demonstration of 70 Gb/s (7 × 10 Gb/s) encrypted DPS-3D-CAP signal transmission over 2 km weakly coupled 7-core fiber is performed. The key space of the new five-dimensional entangled chaos model reaches 10173, and the interference level reaches 100%. Experimental results show that the receiver sensitivity increases by 1.47 dB compared to the conventional uniform 3D-CAP due to the introduction of dynamic probabilistic shaping.

In this paper, we demonstrate and experimentally verify a tunable, multi-wavelength switchable ring-cavity erbium-doped fiber laser (EDFL). The hollow-core anti-resonant fiber (HC-ARF) filters, which are based on polarization interference, are fabricated using a bent HC-ARF. These filters were incorporated into a ring-cavity EDFL, achieving a tunable laser output ranging from 1547 to 1561 nm with a tuning step of 3.5 nm, and all measured optical signal-to-noise ratios (OSNRs) exceeded 35 dB. Additionally, the laser system supports switching from single-wavelength to three-wavelength operation near the 1560 nm region.

Range-gated imaging has the advantages of long imaging distance, high signal-to-noise ratio, and good environmental adaptability. However, conventional range-gated imaging utilizes a single laser pulse illumination modality, which can only resolve a single depth of ranging in one shot. Three-dimensional (3D) imaging has to be obtained from multiple shots, which limits its real-time performance. Here, an approach of range-gated imaging using a specific double-pulse sequence is proposed to overcome this limitation. With the help of a calibrated double-pulse range-intensity profile, the depth of static targets can be calculated from the measurement of a single shot. Moreover, the double-pulse approach is beneficial for real-time depth estimation of dynamic targets. Experimental results indicate that, compared to the conventional approach, the depth of field and depth resolution are increased by 1.36 and 2.20 times, respectively. It is believed that the proposed double-pulse approach provides a potential new paradigm for range-gated 3D imaging.

Existing two-step Fourier single-pixel imaging (FSPI) suffers from low noise-robustness, and three-step FSPI and four-step FSPI improve the noise-robustness but at the cost of more measurements. In this Letter, we propose a method to improve the noise-robustness of two-step FSPI without additional illumination patterns or measurements. In the proposed method, the measurements from base patterns are replaced by the average values of the measurement from two sets of phase-shift patterns. Thus, the imaging degradation caused by the noise in the measurements from base patterns can be avoided, and more reliable Fourier spectral coefficients are obtained. The imaging quality of the proposed robust two-step FSPI is similar to those of three-step FSPI and four-step FSPI. Simulations and experimental results validate the effectiveness of the proposed method.

Imaging through scattering media remains a formidable challenge in optical imaging. Exploiting the memory effect presents new opportunities for non-invasive imaging through the scattering medium by leveraging speckle correlations. Traditional speckle correlation imaging often utilizes a random phase as the initial phase, leading to challenges such as convergence to incorrect local minima and the inability to resolve ambiguities in object orientation. Here, a novel method for high-quality reconstruction of single-shot scattering imaging is proposed. By employing the initial phase obtained from bispectral analysis in the subsequent phase retrieval algorithm, the convergence and accuracy of the reconstruction process are notably improved. Furthermore, a robust search technique based on an image clarity evaluation function successfully determines the optimal reconstruction size. The study demonstrates that the proposed method can obtain high-quality reconstructed images compared with the existing scattering imaging approaches. This innovative approach to non-invasive single-shot imaging through strongly scattering media shows potential for applications in scenarios involving moving objects or dynamic scattering imaging scenes.

Aiming at low-loss terahertz (THz) fiber fabrication, we propose a negative curvature terahertz tube fiber (NC-TF). Simulation results show that the NC-TF has similar transmission losses (TLs) to the recognized half-ring fiber but with a significantly simpler fabrication structure. NC-TF samples are fabricated by extruding polymers from a specially designed mold, presenting a novel approach for obtaining fibers with shaped boundaries. Experimental data demonstrate that the NC-TF exhibits TLs below 3 dB/m in transmission bands, with a minimum TL of 0.2 dB/m at 0.6 THz. The simplicity and practicality of the NC-TF enable its application in various THz transmission or sensing scenarios.

Optical coherence tomography (OCT) offers a direct and precise measurement of keyhole depth in laser welding, facilitating its application for quality assurance and control. Nevertheless, in high-speed welding, the keyhole lags behind the processing beam, leading to a reduction in OCT measurement accuracy. In this paper, OCT is utilized to monitor keyhole morphology by employing a scanner to deflect the measuring beam and the keyhole lag is quantitatively analyzed. Bead-on-plate welds were conducted on stainless steel and aluminum alloys at varying welding speeds. Real-time OCT data collection was performed and reconstructed to generate keyhole morphology. The aluminum alloy exhibited fluctuating keyhole morphology and irregular seam surfaces. The determination of the keyhole lag was based on the longitudinal view of keyhole morphology. Results indicated a proportional increase in keyhole lag with welding speed, and this trend was consistent for both materials.

In this work, a 4H-SiC-based soft X-ray single photon detector with photon energy resolution capability is demonstrated. The 4H-SiC p-i-n detector with an 80-μm-thick epi-layer and low intrinsic doping exhibits a low leakage current of ∼1.8 pA at -180 V, guaranteeing superior dark current performance for single photon detection with low electronic noise. An amplification strategy employing an active switch in the charge-sensitive amplifier has also been developed, where feedback-resistance-related thermal noise has been well eliminated, contributing to lower electronic noise in the amplification stage. By tuning the shaping time in the analog-to-digital circuit for precise signal processing, an optimal photon energy resolution has been achieved with a duration time within 6.4 µs, achieving an energy analysis standard deviation below 5.7%. Ultimately, superior linearity has been obtained between the output pulse amplitude and the characteristic photon energy by utilizing a series of different metal targets, opening a new opportunity for advanced soft X-ray detection technology based on wide bandgap semiconductors.

Integrated photonic spectrographs could provide a new generation of low-cost, highly integrated, high-performance optical terminal instruments for astronomical observations. However, these spectrographs still face the challenge of high spectral resolution. In this Letter, we demonstrate a cascaded phase-modulated waveguide array (CPMWA) spectrograph, with designed and measured spectral resolutions of 100,000 and 68,000, respectively. A spectral reconstruction method is proposed to minimize the influence of the phase error induced during the chip fabrication process and increase the spectral contrast to 20 dB. This type of spectrograph demonstrates promising potential for high-resolution spectrum observations in astronomy.

We propose a dual feed-forward neural network (DFNN) model, consisting of a cavity parameter feature expander (CPFE) and a dynamic process predictor (DPP), for predicting the complex nonlinear dynamics of mode-locked fiber lasers. The output of the CPFE, following layer normalization, is combined with the pulse complex electric field amplitude and then fed into the DPP to predict the dynamics. The pulse evolution process from the detuned steady state to the steady state under different cavity configurations is rapidly calculated. The predicted results of the proposed DFNN are consistent with the numerical split-step Fourier method (SSFM). The simulation speed has been greatly improved with low computational complexity, which is approximately 152 times faster than the SSFM and 4 times faster than the long short-term memory recurrent neural network (LSTM) model. The findings provide a new low computational complexity and efficient machine learning approach to model the complex nonlinear dynamics of mode-locked lasers.

In this Letter, we report a 2-kW all polarization-maintaining (PM) fiber ultrafast laser from a single fiber link, which has a center wavelength of 1064 nm and a repetition rate of 1.39 GHz. To the best of our knowledge, this is the highest average power from all PM fiber lasers at 1.0 µm. Its beam quality (M2) is measured to be <1.2, and the pulse width after compression is measured to be ∼855 fs.

In this paper, to reduce the damage or absorption caused by radiation to optical fibers, we study lightweight and flexible anti-radiation films based on optical precision deposition technology. At first, anti-radiation composite thin films based on Kapton, ITO, and Cu (or Al) are designed and homemade with different structures. Subsequently, polarization-maintaining (PM) Yb-doped fiber (Yb-fiber) samples protected by these different kinds of anti-radiation films are irradiated with a dose of ∼150 kGy. At last, we comparatively investigate (1) the radiation-induced attenuation (RIA) of these PM Yb-fiber samples and (2) the lasing performance (threshold and slope efficiency) and gain performance of a 1064 nm fiber laser and amplifier using these irradiated PM Yb-fibers as the gain medium, respectively. The results show that such a film can reduce the RIA of the irradiated Yb-fiber by up to 2.84 dB/m and increase the output power by up to 75.3% at most. In addition, we also study the optical recovery of the PM Yb-fibers after radiation.

In this Letter, a homemade bismuth-doped germane silica fiber (BGSF) with a high gain coefficient is fabricated. Based on this fiber, a single-frequency fiber laser (SFFL) operating at 1440 nm is successfully realized. A ring cavity with a short BGSF of 10 m and two cascaded sub-ring cavities ensures the single-longitudinal-mode (SLM) operation. The maximum SLM laser output power of about 6 mW is obtained with the optical signal-to-noise ratio (OSNR) of more than 75 dB. The linewidth of the stable SLM laser is about 745 Hz, measured by the delayed self-heterodyne method. To the best of our knowledge, this is the first SFFL operating at 1440 nm based on the bismuth-doped fiber (BDF), demonstrating the great potential of BDF in expanding the operating band of SFFL.

In this work, we report on the recent research progress on watt-level all-solid-state single-frequency Pr:LiYF4 (YLF) lasers in the orange spectral region. Combining dual-end pumping and ring-cavity technologies, we have achieved a maximum single-frequency output of 1.19 W at 607 nm with a linewidth of about 20.3 MHz. Based on this study, by inserting a 0.15 mm etalon inside the ring cavity, we find that the 607 nm lasing can be completely suppressed and a single-frequency laser at 604 nm with a 0.69 W output power and a linewidth of about 16.7 MHz can also be obtained. Moreover, the wavelengths of the two single-frequency lasers can be tuned from 607.16 to 607.61 nm and from 603.99 to 605.02 nm, respectively. Furthermore, the single-frequency Pr:YLF laser can also operate in a state of the two orange wavelengths, simultaneously, with a maximum output power of 0.97 W. We believe that this is the highest output power of a direct generation of single-frequency orange lasers and the first demonstration of the wavelength-tuned operation of the achieved single-frequency orange lasers, which could bring opportunities for the application of single-frequency orange lasers.

We propose and experimentally demonstrate the monolithic dual-waveguide (DW) distributed feedback (DFB) laser with tunable wavelength spacing. The differences in the chirp sampled grating with various index modulation amplitudes are theoretically elaborated. The wavelength spacing properties of the DW laser at different Bragg spacings are compared and analyzed. To validate the numerical investigation, the DW laser consisting of three sections is fabricated and implemented, where the chirp sampled grating with two equivalent π phase shifts is located. The simulated relationship between the Bragg wavelength spacing and the mode spacing is consistent with the experimental results. Owing to the prominent contribution of the three-section structure and chirp sampled grating, the tuning range of the wavelength spacing is extended significantly, and the cavity of the DW laser becomes compact. The experimental results indicate that the proposed scheme achieves a tuning range from 59.50 to 116.25 GHz. The proposed scheme paves an extraordinary avenue for the integration of laser devices in the applications of optical sensing and THz communication.

Atomic spectroscopy serves as the basis for quantum precision measurements, where frequency-stabilized lasers are crucial for obtaining accurate atomic spectra. This work introduces a compact laser frequency stabilization system that employs a multifunctional metasurface to adjust the polarization, amplitude, and propagation direction of incident light. By combining with a Rb atomic vapor cell, the system achieves a tunable sub-Doppler spectrum for laser frequency stabilization. The experimental result demonstrates that a laser frequency stability of 3 × 10-11 is attained from 1 to 200 s at 780 nm with the input power at 20 µW. The devices hold significant potential for compactness, integration, and mass production, making them highly suitable for quantum measurement applications.

High-aspect-ratio structures with heights or depths significantly exceeding their lateral dimensions hold broad application potential across various fields. The production of these structures is challenging, requiring meticulous control over materials, scale, and precision. We introduce an economical and efficient approach for fabricating high-aspect-ratio nanostructures using a two-photon polymerization process. This approach achieves feature sizes of around 37 nm with an aspect ratio of 10:1 using commercial photoresists. Offering advantages over traditional techniques, our approach simplifies operation and enhances design flexibility, facilitating the creation of smaller, more complex, and high-aspect-ratio structures. The capabilities of this approach are demonstrated by producing arrays of three-dimensional microstructures that exhibit sub-micron scales, extensive periodicity, and pronounced aspect ratios. These developments open new possibilities for applications in biomedical, precision engineering, and optical microdevice manufacturing.

Ge2Sb2Se4Te1, a newly developed phase change material derived from Ge2Sb2Te5, has garnered significant interest among researchers due to its numerous advantages. Here, its phase change characteristics under the electron beam evaporation method are thoroughly investigated, and a layered tunable color structure is proposed. Based on the low intrinsic absorption of Ge2Sb2Se4Te1 material, it exhibits excellent dynamic tunability along with vivid color appearance including high brightness and high purity. In experiments, five representative colors—red, green, blue, yellow, and purple—were successfully prepared. The peak reflection of these samples averaged 92%, and when heated to 320°C, the temperature at which the phase transition of Ge2Sb2Se4Te1 occurred, reflection loss was barely observed. In addition, after phase transition, the sideband reflection at non-target wavelengths decreased by 30%, bringing high-purity crystalline-state colors and noticeable color changes. Therefore, it is believed that the structural color scheme proposed here will contribute to the development of many fields including smart glasses, artificial retinal devices, high-resolution displays, and beyond.

The photonic Ising machine, a promising non-von Neumann computational paradigm, offers a feasible way to address combinatorial optimization problems. We develop a digital noise injection method for spatial photonic Ising machines based on smoothed analysis, where noise level acts as a parameter that quantifies the smoothness degree. Through experiments with 20736-node Max-Cut problems, we establish a stable performance within a smoothness degree of 0.04 to 0.07. Digital noise injection results in a 24% performance enhancement, showing a 73% improvement over heuristic Sahni–Gonzales (SG) algorithms. Furthermore, to address noise-induced instability concerns, we propose an optoelectronic co-optimization method for a more streamlined smoothing method with strong stability.

Optical gyroscopes in microcavity platforms have attracted much attention for their vast applications. For Sagnac effect enhancement, the exceptional surface (ES) concept holds the potential to stabilize exceptional points (EPs), allowing for EP splitting amplification and robustness in sensors. We propose a new optical microcavity gyroscope near the ES. Under the mechanical mode assistance, theoretical analysis reveals its prominent advantages compared with conventional gyroscopes, especially achieving higher levels for extremely low rotational speeds. This breakthrough opens possibilities in high-precision angular velocity measurement, facilitating the development of more accurate and stable sensor technologies.

The quantum eraser effect exemplifies the distinctive properties of quantum mechanics that challenge classical intuition and reveal the wave-particle duality of light. Whether the photon exhibits particle-like or wave-like behavior depends on whether the path information is discernible. In this paper, we propose a novel quantum eraser scheme that utilizes photonic phase structures as the which-way indicator. This scheme is implemented using a Mach–Zehnder interferometer (MZI), where one arm is configured with orbital angular momentum (OAM) to establish predetermined which-way information. Consequently, at the output ports of the MZI, the photon displays particle-like characteristics when the which-way information is retained. However, the introduction of an additional spiral phase plate (SPP) to eliminate the phase structure from the output photon of the MZI unveils distinct interference patterns. This result enhances our understanding of the quantum erasure effect.

Since the working conditions of classical and quantum signals are very different, how to effectively integrate classical and quantum communication networks without affecting their respective performance has become a great challenge. In this paper, we proposed a scheme to realize classical communication and continuous-variable quantum key distribution (CV-QKD) based on frequency-division multiplexing (FDM), and we verified the feasibility of simultaneously realizing CV-QKD and classical optical communication data synchronous transmission scheme under the same infrastructure. We achieved a 0 bit error rate in 50 frames and a 20 Mb/s bit rate for the classical signal and an average secret key rate of around 5.86 × 105 bit/s for the quantum signal through a 4 dB fiber channel. This work provides a scheme to establish a QKD channel by only reserving a small passband in the entire optical communication instead of an entire wavelength, increasing efficiency and simplifying the integration of QKD and classical communication.

Freestanding Zr filters are important devices for improving spectral purity in the extreme ultraviolet range of 7–20 nm, and their irradiation resistance directly determines their life and efficiency. We prepared multilayered Zr/B4C and Zr/Si filters using magnetron sputtering. Their transmittance reached a maximum of 23% (λ = 13.5 nm). Microwatt-radiation-induced structural changes in the filters were investigated at the metrology beamline (BL08B) of the National Synchrotron Radiation Laboratory. The aging of the Zr filters was measured and analyzed. The experimental results revealed that the damage was noticeable on the irradiated filter surfaces with different states, suggesting that the main factors causing the degradation of the filters were oxidation and carbon contamination at the surfaces. Furthermore, the thermal stability of the Zr filters was studied by annealing, and the heat accumulation during the damage process was estimated using finite-element numerical simulations and X-ray photoelectron spectroscopy measurements. Silicide formation at the Zr-Si-O system interfaces was found to be key to enhancing the stability of the filters.