Photonics

In this study, we presented a simple highly sensitive sensor based on commercially available solid-core photonic crystal fiber (PCF) and surface plasmon resonance (SPR) for measuring the refractive index (RI) of analytes. The numerical simulation based on the finite element method (FEM) has been examined to compute the optical properties such as confinement loss, power spectrum, and transmission intensity of the sensor. The most sensitive and inert plasmonic materials (gold and silver) have been assumed to be coated inside the fiber with the range of analyte RI from 1.32 to 1.40. The performance of the proposed sensor has been evaluated by tracing the several optical features like wavelength sensitivity, amplitude sensitivity, resolution of the sensor, and figure of merit. As a result, the comparative study between silver and gold elements has been carried out in which the maximum sensitivity received was 1.15 μm/RIU and 1.10 μm/RIU, respectively. Whereas, on the base of power spectrum, the obtained sensitivity was 513 μm/RIU for the gold layer. Moreover, the effect of other structural parameters (air holes and plasmonic layer thickness) on the sensing performance has been taken into an account. According to the simulation analysis and results, this sensor would have a great potential in various sensing applications of biomedical and liquid refractive index. Full article

In the paper we propose a method for characterizing VUV pulse(s) in a bichromatic ionization setup. The scheme is based on s-shell ionization by joint action of circularly polarized fundamental harmonic and linearly polarized second one. The advantage of the proposed approach is the existence of kinematic (geometrical) zeros of partial amplitudes which positions can be extracted with minimal number of theoretical (spectroscopic) assumptions and therefore they may serve as natural reference points in measuring the relative phase and amplitude of the harmonics. In the paper, we investigate a general possible geometry setup with more detailed consideration of the edge cases and present calculation and numerical stimulation for helium ionization as an illustrative example. Full article

Volumetric scattering prevents imaging modalities in biomedical optics from imaging deep inside tissue. The optimization of the incident wavefront has the potential to improve these imaging modalities. To investigate the optimization and light propagation of such beams inside scattering media rigorously, full-vectorial simulations based on solutions of Maxwell’s equations are necessary. In this publication, we present a versatile two-step beam synthesis method to efficiently simulate the scanning and phase optimization of a focused beam inside a static scattering medium. We present four different approaches to the phase optimization of the energy density and the absolute value of the Poynting vector. We find that these quantities have two regions with different, almost exponential decays over depth for a non-optimized beam. Optimization by conjugating the phase of the projected electric field in various directions at the focus shows an improvement below a certain penetration depth. Seeking global solutions to the optimization problems reveals an even better enhancement in the energy density and the absolute value of the Poynting vector in the focus. For Poynting vector optimization, the differences between the presented optimization approaches are more significant than for the energy density. With the presented method, it is possible to efficiently simulate different imaging methods improved by wavefront shaping to investigate their possible penetration depths. Full article

In atmosphere free-space optical communication (FSO) systems, the scintillation effect produced by turbulence effects increases the bit error rate (BER) of the communication system and reduces the system’s performance. However, a high correlation of turbulent noise occurs in the two transmission channels when a signal transmitted in the bidirectional atmospheric channel with channel reciprocity. The performance of the FSO system can be increased by extracting channel state information (CSI) in forward transmission and using adaptive power technology to reduce turbulence in inverse transmission. In this research, we propose a bidirectional atmospheric channel reciprocity-based adaptive power transmission (CR-APT) technique that lowers the bit error rate of the transmitted signal by using the CSI of the relevant channel. To verify the effectiveness of the technique, a bidirectional atmospheric channel with various turbulence intensities is built in the simulation program, along with various background sounds to vary the channel reciprocity, and the impact of reciprocity on signal transmission is examined. The simulation findings demonstrate that adaptive power transmission with high reciprocity is excellent under the weak turbulence condition, and its future development is promising. Full article

As a novel nanomaterial, the TiN/Ti₃C₂ heterojunction has been demonstrated to possess exceptional optoelectronic properties, offering significant potential for applications in fields such as communication, optical sensors, and image processing. The rapid evolution of the internet demands higher communication capacity and information processing speed. In this context, all-optical wavelength conversion, a pivotal technique in all-optical signal processing, holds paramount importance in overcoming electronic bottlenecks, enhancing wavelength utilization, resolving wavelength competition, and mitigating network congestion. Utilizing the idle light generated through the four-wave mixing (FWM) process accurately mimics the bit patterns of signal channels. This process is inherently rapid and theoretically capable of surpassing electronic bottlenecks with ease. By placing an optical filter at the fiber output end to allow idle light passage while blocking pump and signal light, the output becomes a wavelength-converted replica of the original bitstream. It has been verified that TiN/Ti₃C₂ heterojunction-coated microfiber (THM) exhibits outstanding third-order nonlinear coefficients. Building upon this, we achieved a THM-enhanced FWM all-optical wavelength converter, resulting in a ~4.48 dB improvement in conversion efficiency. Compared to conventional high-nonlinear fibers, this compact device significantly reduces fiber length and can be easily integrated into current high-speed optical communication networks. It demonstrates broad prospects in the realms of all-optical signal processing, robotic applications, ultra-high-speed communication, and beyond. Full article

The analysis reported in this paper shows that the homogeneous sensitivity of both fundamental rib waveguide modes, HE₀₀ and EH₀₀, can slightly exceed the sensitivity of the optimized parent slab waveguide. The most crucial difference in the behavior of these two polarizations is that the sensitivity of the HE₀₀ mode is the maximum for strip waveguides. In contrast, the sensitivity of the EH₀₀ mode can either decrease monotonically or not-monotonically with increasing rib height or behave like a homogeneous sensitivity characteristic of the slab waveguide’s EH₀ mode. The second important conclusion comes from comparing the sensitivity characteristics with the distributions of the fundamental mode’s optical power. Namely, the homogeneous sensitivity of the rib waveguide is at the maximum if, due to a slight variance in the cover refractive index, a variation in the weighted optical power carried by the mode is the maximum. Full article

In order to meet the requirements of dynamic monitoring from a bird’s eye view for typical rapidly changing processes such as mechanical rotation and photoresist exposure reaction, we propose a vertical high-speed Mueller matrix ellipsometer that consists of a polarization state generator (PSG) based on the time-domain polarization modulation and a polarization state analyzer (PSA) based on division-of-amplitude polarization demodulation. The PSG is realized using two cascaded photoelastic modulators, while the PSA is realized using a six-channel Stokes polarimeter. On this basis, the polarization effect introduced by switching the optical-path layout of the instrument from the horizontal transmission to the vertical transmission is fully considered, which is caused by changing the incidence plane. An in situ calibration method based on the correct definition of the polarization modulation and demodulation reference plane has been proposed, enabling the precise calibration of the instrument by combining it with a time-domain light intensity fitting algorithm. The measurement experiments of SiO₂ films and an air medium prove the accuracy and feasibility of the proposed calibration method. After the precise calibration, the instrument can exhibit excellent measurement performance in the range of incident angles from 45° to 90°, in which the measurement time resolution is maintained at the order of 10 μs, the measurement accuracy of Mueller matrix elements is better than 0.007, and the measurement precision is better than 0.005. Full article

In the present investigation, commercially pure titanium is welded to AISI 316L stainless steel by intermixing niobium as filler material in a lap joint configuration. For this purpose, a pulsed Nd:YAG laser with various pulse durations and pulse peak powers is employed to obtain different mixing conditions for the materials. It will be demonstrated that, despite the implementation of the filler material, the weld seams are characterized by a high affinity for cracking, which in turn can be attributed to the formation of hard intermetallic compounds. Nevertheless, utilization of optimized process parameters can yield crack-free specimens in a reproducible manner through equable intermixing of otherwise critical alloy elements. Lap-shear forces of up to 140 N can be achieved with a single weld seam measuring 2.5 mm in length. By increasing the joint area with four adjacent weld seams, maximum loads up to 320 N are attained, thus exceeding the yield strength of the applied stainless steel. Considering the biocompatibility of the niobium filler material used, this work provides the foundation for this dissimilar material combination to be implemented in future medical technology applications. Full article

Developing fast-response liquid crystals (LCs) is an essential way to achieve low cost, high resolution, and good visual experience for augmented reality (AR) displays. In this paper, we optimized one new nematic LC mixture SNUP01 to meet the requirements of fast-response phase-only liquid crystal on silicon (LCoS) devices in AR displays. The photoelectric performance of this new LC mixture and three commercial LC mixtures were further comparatively evaluated, and the 2π phase-change response speed of this new LC mixture was extrapolated. The research results indicate that SNUP01 possesses high birefringence, moderate dielectric anisotropy, low viscoelastic coefficient, low activation energy, and high figure of merit values. When using this LC mixture at 25 °C @ λ = 633 nm, a 2π phase change can be achieved at 5 V with a total response time of up to millisecond response. Widespread applications of this LC mixture for AR displays are foreseeable. Full article

The supercontinuum generation and manipulation of Airy-Gaussian pulses in a photonic crystal fiber with three zero-dispersion points are studied using the split-step Fourier method. Firstly, the spectral evolution of Airy-Gaussian pulses in four photonic crystal fibers with different barrier widths was discussed, and the optimal fiber was determined after considering the factors of width and flatness. By analyzing the mechanism of supercontinuum generation in photonic crystal fibers with single, double and three zero-dispersion points, it is found that the photonic crystal fiber with three zero-dispersion points have a larger spectral width due to the component of tunneling solitons. Then, the effects of four characteristic parameters (truncation factor a, distribution factor χ₀, initial chirp C and central wavelength λ) on forming the supercontinuum spectrum of Airy-Gaussian pulses are analyzed in detail. The results show that the spectral width and energy intensity of the dispersive wave and tunneling soliton generation can be well controlled by adjusting the barrier width and initial parameters of the pulse. These research results provide a theoretical basis for generating and manipulating high-power mid-infrared supercontinuum sources. Full article

Three different stimulated Brillouin scattering (SBS) configurations in perfluorooctane were experimentally compared to achieve the ultimate compression of ~1.1 ns pulses from a commercially available Nd:YAG mini-laser. These schemes contained either a focusing lens and a plane feedback mirror, a spherical mirror, or variable pulse splitting to provide self-seeding of the SBS. In the optimal configuration with a focusing lens and return mirror, 93 ps pulses with an energy of 9.5 mJ were achieved at the output of the double-pass phase-conjugated Nd:YAG amplifier. The resulting diffraction-free, high-quality beams with M²~1.2 and excellent pointing stability are of practical interest for scientific, medical, and industrial applications. Full article

The modulation accuracy of Multi-Plane Light Conversion (MPLC) mainly depends on the positioning accuracy of the phase mask on the Spatial Light Modulator (SLM). To improve positioning accuracy, the impact of phase mask shift on modulation accuracy is investigated, and a position method is proposed. In order to investigate the influence of phase mask offset on the input light conversion effect, a convolution transmission model for the adjustable multi-pass cavity is established. Then, the positioning process for the phase masks is analyzed and simulated, and a method of positioning the phase masks is presented. This method reduces the positioning time and increases the positioning accuracy to 8 μm. Finally, experiments are performed to verify the feasibility of the method. Experimental results show that the similarity of the adjustable multi-pass cavity positioned by this method can reach 93.44%. Full article

The X-ray free-electron laser oscillator (XFELO) has received significant attention due to its ability to produce fully coherent, high-brightness, and highly stable X-ray beams. Despite these advantages, the operation of the XFELO can be impeded by the surrounding environment. Specifically, vibrations of the optical components within the cavity can lead to poor alignment, which can diminish the interaction between the light and electrons in the undulator. Consequently, the quality of the output X-rays may be compromised. This study aims to investigate the impact of mirror vibrations on the output laser at various vibration frequencies. Firstly, we develop three single-frequency vibration models at 10 Hz, 0.01 MHz, and 1.1 MHz to investigate the changes in energy, spectral width, beam size, and beam divergence angle of the output laser. Secondly, we build a more complex multi-frequency vibration model based on the single-frequency one to simulate the realistic vibration of the mirror. Finally, we utilize the multi-frequency vibration model to investigate the tolerance limits of the output laser to vibration amplitude at different vibration frequencies of the mirror. The results show that the tolerance of the amplitude near the low and middle frequencies has less effect on the output power, which is approximately 250 nrad or more. However, in certain particular instances, particularly in the vicinity of the resonant frequency, there will be deviations from the tolerance limit. These deviations can result in values that are excessively high or excessively low. The study could prove useful in the future installation of XFELOs. Full article

Single-phase samples of the Ba_1−xCe_xF_2+x solid solution (x = 0.3–0.4) were synthesized by directional crystallization in the form of single crystals and by co-precipitation from aqueous nitrate solutions using potassium fluoride as a fluorinating agent in the form of nanopowders. The cathodoluminescence of the pressed powder samples was studied in comparison with the BaF₂: Ce single crystals in 250–460 nm (2.7–5 eV) spectral range upon excitation by an electron accelerator. The cathodoluminescence spectra of the samples revealed a wide band in the range of 3.0–4.0 eV, which consists of two typical components of Ce³⁺ with decay time 23 ns in the case of single crystals and three decay times 27 ns, 140–170 ns, and ~600 ns in the case of pressed powders. The decay time of the short-wavelength component (27 ns) in the case of pressed powders is close to the lifetime of the excited state of the Ce³⁺ ion. The developed X-ray phosphors can be applied for embedding in diamonds for diamond–nanoparticle composite preparation. Full article

The frequency-swept laser (FSL) is applied widely in various sensing systems in the scientific and industrial fields, especially in the light detection and ranging (Lidar) area. However, the inherent nonlinearity limits its performance in application systems, especially in the broadband frequency-swept condition. In this work, from the perspective of data-driven control, we adopt the reinforcement learning-based broadband frequency-swept linearization method (RL-FSL) to optimize the control policy and generate the modulation signals. The nonlinearity measurement system and the system simulator are established. Since the powerful learning ability of the reinforcement learning algorithm, the linearization policy is optimized off-line and the generated modulation signals reduce the nonlinearity almost 20 times, compared to the case without control. In the long-term operation, the regular updated modulation signals perform better than the traditional iteration results, demonstrating the efficiency of the proposed data-driven control method in application systems. Therefore, the RL-FSL method has the potential to be the candidate of optical system control. Full article

This paper presents the results of studying the process of laser formation of microstructures from silver nanoparticles in nanoporous quartz glasses. Glass samples were impregnated with organometallic molecules Ag(hfac)COD in a supercritical carbon dioxide environment. The formation of point and linear microstructures was carried out by high-frequency (70 MHz) femtosecond laser radiation with a wavelength of 525 nm and energy in the pulse up to 1 nJ. It was found that the formation of microstructures occurs due to photo- and thermal decomposition of precursor molecules with the formation of plasmonic silver nanoparticles. It is shown that the developed temperatures can exceed the melting point of glass, which leads to the appearance of microstructures with altered refractive index. A qualitative model explaining the individual stages of cluster formation in the glass volume under point laser impact is presented. Full article

Wide-range crystal spectrometers are important tools for performing X-ray spectroscopic measurements of medium- and high-Z tracer elements in research on laser-driven inertial confinement fusion (ICF) plasmas. In this paper, we propose a wide-range high-resolution crystal spectrometer based on a tandem array of crystals that have the same geometric parameters. We have developed a three-channel crystal spectrometer that covers the range of 8–18 keV by combining Ge<311>, Ge<331>, and Ge<531> crystals. Here, we report the design, optical simulations, and X-ray test experiments of this spectrometer. The calibration results indicate that the spectral resolution E/ΔE is greater than 2800 at 8.048 keV. By selecting appropriate Bragg angles, crystal materials, orientations, or other geometrical parameters, the wide-range crystal spectrometer developed in this paper can also be used to make measurements in other energy ranges. Full article

This paper proposes a novel method to improve the anti-dispersion ability of the all-optical orthogonal frequency division multiplexing (AO-OFDM) system. By replacing the Sinc-shaped filter with a Gauss-shaped filter for sub-carrier generation and inserting a cyclic prefix (CP), the impact of dispersion on the system can be significantly mitigated. Formula derivation and numerical analysis of the pulse-shaping function of the AO-OFDM system in the time domain for each cycle indicated that the pulse-shaping function generated by the Gauss-shaped filter was less affected by the dispersion effect than that of the Sinc-shaped filter. Meanwhile, less inter-carrier crosstalk between carriers was also observed. After carrying out system transmission simulations employing these two different filters, we found that the AO-OFDM system based on the Gauss-shaped filter could greatly improve the anti-dispersion ability compared with the system based on a Sinc-shaped filter. When the parameter settings in both schemes were identical, that is, the number of subcarriers was 32 and the power of a single subcarrier was −13 dBm, the bit error rate (BER) of the system based on the proposed Gauss-shaped filter after 60 km SMF transmission was only 1.596 × 10⁻³, while the BER of the traditional Sinc-shaped filter based system scheme was as high as 8.545 × 10⁻². Full article

Twist sensors have emerged as crucial tools in the field of structural health monitoring, playing a significant role in monitoring and ensuring the integrity of critical infrastructure such as dams, tunnels, bridges, pipelines, and buildings. We proposed and demonstrated an all-fiber in-line twist sensor which was based on a capillary fiber spliced between two single-mode fibers with a transverse offset. Through a series of experiments, the sensor’s performance was evaluated and quantified. The results showcased remarkable twist sensitivities in both clockwise and anticlockwise directions. With a transverse offset of 8.0 µm, the sensor exhibited twist sensitivities of −0.077 dB/° and 0.043 dB/° in the clockwise and anticlockwise directions, respectively, in the measured twist range from 0 to 90°. Furthermore, it was also demonstrated that the sensor was temperature insensitive at the chosen wavelength of 1520 nm, which can assist in increasing measurement accuracy. Our sensor’s low cost, simplicity of manufacture, and improved performance will push forward its adoption in future engineering applications such as structural health monitoring in dams, tunnels, and buildings. Full article