We present a compact in-fiber polarization beam splitter (PBS) implemented in a gold-coated dual-core photonic crystal fiber (DC-PCF), using finite element method (FEM). The octagonally arranged DC-PCF achieves enhanced birefringence through optimized structural design. Gold layers integrated within the two large air holes induce surface plasmon resonance (SPR), which modulates the optical response at the edges of the operational band and enhances polarization splitting efficiency. Numerical analysis shows that when the lattice gap Λ = 1.6 μm, diameters d1 = 1.2 μm, d2 = 0.5 μm, d3 = 2.1 μm, d4 = 0.7 μm, and a gold layer thickness of t = 50 nm, this PBS achieves a coupling length ratio (CLR) of 0.5 at 1.55 μm. It exhibits a shortest splitting length of 220 μm and a maximum extinction ratio (ER) of -133 dB over an operating bandwidth of 140 nm. The fabrication process and experimental setup are analyzed. It is worth anticipating that this polarizer will emerge as a crucial signal processing component in photonic integrated systems, driving the continuous advancement of communication systems and information technology.

A tri-axial magnetic field fiber optic sensor based on a whisk-shaped single-mode fiber (WSMF) coated with soft magnetic elastomer is proposed. The sensor operates by exploiting the magneto-straining effect of Fe3O4@polydimethylsiloxane (PDMS) composite under an external magnetic field, combined with two orthogonally arranged balloon-like single-mode fiber (BLSMF) structures. When the fiber is bent into a balloon-like shape, variations in the refractive index distribution of the cladding and core induce optical leakage, forming a Mach-Zehnder interferometer. Finite element analysis reveals that a single Fe3O4-PDMS-coated BLSMF exhibits anisotropic deformation characteristics under the magnetic field. By cascading two BLSMFs in orthogonal configuration, the dip shift of the resonant wavelength is correlated not only with the magnitude of the magnetic field but also with its direction. This demonstrates that the whisk-shaped SMF configuration enables three-dimensional magnetic field measurement. In this study, the mass ratio of Fe3O4 nanoparticles in preparing the magnetic elastomer was varied from 10% to 50%. The optimized tri-axial magnetic field sensor achieves a magnetic sensitivity of 242.1 pm/mT and a rapid response time of 0.28 s. The proposed sensor shows great potential for applications in intelligent robotic control and human-machine interactions.

In this paper, a refractive index (RI) sensor based on a Mach-Zehnder interferometer fabricated using tapered photonic crystal fiber (TPCF) is proposed and demonstrated. The sensor configuration comprises a segment of single-mode fiber (SMF) spliced between two sections of TPCF, forming an SMF-TPCF-SMF structure. A systematic experimental investigation is conducted on sensors with varying taper waist diameters (TWDs). The sensing mechanism is predicated on the alterations in optical path differences between the core and cladding modes, induced by fluctuations in the external RI. These changes manifest as a discernible shift in the interference spectrum, facilitating precise RI detection. Experimental results indicate that a reduction in TWD enhances light-matter interaction, thereby improving the RI sensitivity. For a TWD of 35.43 μm, a maximum sensitivity of 326.65 nm/RIU is achieved within the RI range of 1.3–1.4 at an operating wavelength of 1580 nm. Additionally, the sensor exhibits minimal temperature cross-sensitivity, with a temperature sensitivity of only 3.11 pm/℃. Benefiting from its compact structure, mechanical robustness, and cost-effectiveness, the proposed sensor holds significant potential for applications in environmental monitoring, biomedical diagnostics, aerospace engineering, and related fields.

Session-based recommendation aims to capture user’s short-term dynamic preferences based on the dependencies between items within a session, and then predicts the next item that the user is most likely to interact with. Currently, session sequences are typically modeled as single-view structures, which focus on learning the interaction between individual items. However, these methods lack rich contextual information and are difficult to understand the user’s intent from a higher dimensional perspective. To better leverage the associations between contexts, this work proposes a Contrast-enhanced Heterogeneous Multi-view Graph via Subsequence Units (CHMGSU) for session-based recommendation. The sequences are modeled as both single-view and heterogeneous multi-view structures, where the single-view graph is constructed at the level of individual items to learn information transfer between items, while the heterogeneous multi-view graph is built using multiple consecutive items to better grasp the user’s high-dimensional intent. A hybrid readout function extracts the intent of subsequences, and captures relationships with contextual relevance. Next, single-view graph attention networks and heterogeneous multi-view graph neural networks are employed to generate item-level and subsequence-level embeddings. By fusing these two types of information, a session-level embedding with information from different perspectives is formed. The prediction results are optimized using the sample-adaptive loss function and the contrastive control gate. In addition, CHMGSU introduces Tmall, Gowalla, Diginetica and Nowplaying datasets to verify the effectiveness of the model on different types of datasets, and experimental results demonstrate that CHMGSU achieves consistent improvements over state-of-the-art baselines, thereby highlighting the incremental yet meaningful advancements achieved.

The objective of session-based recommendation (SBR) is to predict the next item by leveraging a sequence of interactions. Accurately modeling the dependency of the user’s next click on the past action is crucial to improve the recommendation performance. Existing SBR models focus heavily on the user’s current interest represented by the most recent item in the sequence or the interaction between single items, without fully considering different levels of user’s interests. In addition, the sparsity of interaction sequence also limits the recommendation performance of the model. This work proposes contrastive learning enhanced multi-level interest-aware graph attention networks (CLEMI-GAT) for SBR. The session sequence is constructed as a multi-level interest-aware hypergraph, which utilizes interest-aware modules at different levels and hypergraph attention networks (HGAT) to learn deep interests of users. Simultaneously, a interaction graph is built to aggregate the long-term attention of users, and the intermediary node is added to acquire long-distance dependencies among items. A fusion gated network is employed to merge multi-level interests and long-term attention of users. In this work, repeat-exploration normalization (RENorm) is introduced to account for both exploration and repetition behaviors in predictions, which is to better distinguish items within and outside the session sequence. The auxiliary task, namely contrastive learning (CL), further enhances the item representation of our model CLEMI-GAT, thereby alleviating data sparsity. Extensive experimental results show that CLEMI-GAT is superior to the baseline models on the realistic datasets.

Anatabine, as an important alkaloid component in tobacco, has potential application value in flavor regulation and the development of characteristic tobacco products. However, traditional detection methods have limitations such as complex sample processing and weak anti-interference ability. In this regard, this study proposes a chiral molecular enantiomeric selectivity sensor based on double-hole optical fiber (DOF). Multi-parameter detection is achieved by integrating surface plasmon resonance (SPR) and Mach-Zehnder interferometer (MZI) technologies. It innovatively adopts a cascade structure of single-mode fiber (SMF)- multimode fiber (MMF)-DOF. Nano-metal films are deposited in the dual-hole fiber region to excite the SPR effect, and the UiO-66-NH2 metal-organic framework (MOF) is coated as the chiral recognition carrier. Au/R-Tar@UiO-66-NH2 and Au/TiO2/S-Tar@UiO66-NH2 composite films were respectively modified on both sides of the sensor to stimulate surface plasmon resonance 1 (SPR-1) and 2 (SPR-2) as sensing channels 1 and 2. This design can achieve specific recognition of liquid (R)-(+)-anatabine and (S)-(-)-anatabine. Moreover, single-mode optical fibers and dual-hole optical fibers can be combined to form MZI, which serves as the sensing channel 3 to eliminate temperature interference. The detection sensitivities of (R)-(+)-anatabine and (S)-(-)-anatabine are 51.743 pm/nM and 49.512 pm/nM respectively, and the minimum detection limit is 0.386 nM. This design provides an innovative detection solution for chiral drug enantiomer analysis in complex environments.

This work presents a compact broadband in-fiber polarization filter using gold-deposited square-lattice photonic crystal fiber (PCF) numerically. The finite element method (FEM) is utilized to analyze the transmission characteristics of this PCF. The simulation results indicate that when the cladding hole diameter is 1.5 mu m, the large hole diameter is 2.1 mu m, the long axis of elliptical holes is 1.96 mu m, the short axis of elliptical holes is 0.98 mu m, the pitch is 2 mu m, and the gold layer thickness is 50 nm, the x-polarized mode can interact with two plasmonic modes, and two surface plasmon resonance (SPR) processes at two common communication windows can be achieved. The length of this PCF filter is set as 0.5 mm, exhibiting the maximum extinction ratio (ER) of -51.4 dB at 1.31 mu m and -47.3 dB at 1.55 mu m, and the operating bandwidth of >860 nm. Additionally, the estimated splice losses are similar to 2.22 dB at 1.31 mu m and similar to 1.42 dB at 1.55 mu m. It is expected that this small-size PCF-SPR filter, characterized by its efficient filtering performance and wide bandwidth, will serve as a promising candidate for building integrated networks that combine optical fiber communication, sensing, and computing capabilities.

A Mach-Zehnder interferometer (MZI) coated with graphene oxide (GO) for relative humidity (RH) measurement has been proposed in this paper. The proposed sensor is fabricated using microstructured single-mode fiber and leverages the exceptional hydrophilicity of GO to achieve highly sensitive RH detection. Specifically, a microsphere-misalignment structure is first created by splicing to excite higher-order modes, followed by a tapering process to further enhance the interaction between the evanescent field and the surrounding environment. A GO film is then deposited on the tapered region via a physical deposition method to augment the response to water molecules. When ambient RH changes, RI of GO film correspondingly alters, leading to a shift in the phase difference. This phase shift ultimately manifests as a shift of resonant wavelength in interference spectrum. Experimental results demonstrate that with a waist diameter of 18 mu m, the sensor achieves a sensitivity of 194.54 pm/%RH and a response time of 12.7 s within RH range of 37 % to 65 %. The proposed structure exhibits highly sensitivity, straightforward fabrication, and cost-effectiveness, showing promising potential for applications in chemical and biochemical sensing.

The high-performance terahertz polarizer is critically required to establish advanced terahertz (THz) communication networks. This work presents a hollow-core anti-resonant fiber polarizer featuring an asymmetric cladding design to achieve both high polarization loss ratio (PLR) and low transmission loss. Semi-circle nested tubes with dual-gradient wall thickness are integrated along one direction to enhance resonant coupling between the x-pol core guided mode and cladding modes, while a three-layer nested anti-resonant structure is employed along the orthogonal direction to ensure ultra-low loss transmission of the y-pol core guided mode (YCGM). The filtering characteristics are analyzed using the powerful finite element method by evaluating geometric parameters. The numerical results show that this fiber polarizer can achieve a maximum PLR of 6.76 & times; 104 at 1.18 THz, with an ultra-low confinement loss of 7.78 & times; 10-5 dB m-1 for the YCGM. Meanwhile, a stable bandwidth of 0.13 THz can be obtained, where the PLR exceeds 100. Besides, fabrication tolerance analysis indicates that the device maintains robust performance under a wall thickness deviation of +/- 2%. We believe that this in-fiber polarizer can be one of the key candidate photonic devices in THz communication, sensing, and other related fields.

To satisfy the high-performance and wide-bandwidth filtering requirements of optical communication systems, this work presents a broadband dual-window in-fiber polarization filter based on gold layer deposited photonic crystal fiber (PCF), using finite element method. There are two coupling mechanisms in this device. This allows the bandwidth to cover two communication windows of 1.31 and 1.55 μm, while simultaneously featuring high filtering capabilities. The numerical results indicate that when the appropriate structural parameters are determined, two SPR coupling mechanisms will occur within the proposed PCF, which is beneficial for the gold-deposited PCF to achieve superior filtering performance. The 1-mm-long all-fiber filter possesses the maximum extinction ratios (ERs) of − 46.7 dB at 1.31 μm and − 55.1 dB at 1.55 μm, with an operating bandwidth of > 820 nm (> 1.28 μm) in the investigated band. Additionally, the PCF filter has ease of manufacture. This high-performance in-fiber filter is anticipated to play a significant role in modern communication networks, including multiplexing/demultiplexing, wavelength selection, optical add-drop multiplexing, and fully optical signal processing at network nodes.

Lung cancer with heterogeneity has a high mortality rate due to its late-stage detection and chemotherapy resistance. Liquid biopsy that discriminates tumor-related biomarkers in body fluids has emerged as an attractive technique for early-stage and accurate diagnosis. Exosomes, carrying membrane and cytosolic information from original tumor cells, impart themselves endogeneity and heterogeneity, which offer extensive and unique advantages in the field of liquid biopsy for cancer differential diagnosis. Herein, we demonstrate a Gramian angular summation field and MobileNet V2 (GASF-MobileNet)-assisted surface-enhanced Raman spectroscopy (SERS) technique for analyzing exosomes, aimed at precise diagnosis of lung cancer. Specifically, a composite substrate was synthesized for SERS detection of exosomes based on Ti3C2Tx Mxene and the array of gold-silver core-shell nanocubes (MGS), that combines sensitivity and signal stability. The employment of MXene facilitates the non-selective capture and enrichment of exosomes. To overcome the issue of potentially overlooking spatial features in spectral data analysis, 1-D spectra were first transformed into 2-D images through GASF. By using transformed images as the input data, a deep learning model based on the MobileNet V2 framework extracted spectral features from higher dimensions, which identified different non-small cell lung cancer (NSCLC) cell lines with an overall accuracy of 95.23%. Moreover, the area under the curve (AUC) for each category exceeded 0.95, demonstrating the great potential of integrating label-free SERS with deep learning for precise lung cancer differential diagnosis. This approach allows routine cancer management, and meanwhile, its non-specific analysis of SERS signatures is anticipated to be expanded to other cancers.

Polarization filters are key components driving the widespread adoption of new photonic integration technologies. This work demonstrates a broadband and high-extinction plasmonic polarization filter using photonic crystal fiber with dual graphene-coated elliptical silver layers. The finite element method is employed to analyze in-fiber transmission behavior. The graphene-silver layers are introduced to stimulate the surface plasmon resonance effect, significantly enhancing the difference in signal strength across different polarization directions. The numerical results indicate that when the lattice constant is 1.6 mu m, the diameter of the cladding hole is 1.2 mu m and the larger diameter of holes near core region is 1.45 mu m, the length of elliptical hole long axis is 2.0 mu m, the length of elliptical hole short axis is 0.60 mu m, the thickness of silver layer is 50 nm, and the thickness of graphene layer is 17 nm, the intensity difference between the two polarization signals reaches 12712 times. The 400 mu m-long PCF filter, supporting single mode single polarization transmission, exhibits the maximum extinction ratio of -249.1 dB, with an ultra-broad band of greater than 880 nm, covering two common communication windows of 1.31 and 1.55 mu m. Boasting excellent comprehensive performance, this all-fiber polarizer is anticipated to be a candidate device for further optimization of photonic signal processing, optical communication, and optical computing technologies.

To explore the potential of new information transmission windows, this work presents a broadband plasmonic filter based on gold-deposited silicon photonic crystal fiber (PCF) operating in mid-infrared regime numerically, using the finite element method (FEM). The simulation results indicate that the interaction between the high-refractive-index pure silicon material and the gold layer can cause a shift of the resonance central point to the mid-infrared band, which provides the prerequisite for mid-infrared filtering. When the cladding holes’ diameter is 1.3 µm, the inner holes’ diameter is 1.04 µm, the diameter of the holes located on both sides of the core region is 2.08 µm, the gold-coated holes’ diameter is 2.08 µm, the lattice constant is 2 µm, and the gold thickness is 50 nm, this PCF can operate in the mid-infrared band near the central wavelength of 3 µm. The 1 mm long PCF polarizer exhibits a maximum extinction ratio (ER) of −43.5 dB at 3 µm and a broad operating bandwidth of greater than 820 nm with ER better than −20 dB. Additionally, it also possesses high fabrication feasibility. This in-fiber polarization filter, characterized by its comprehensive performance and ease of fabrication, aids in exploring the development potential of high-speed and large-capacity modern communication networks within new optical bands and contributes to new photonic computing and sensing.

Lead sulfide (PbS) colloidal quantum dots (CQDs) are of great interest for short-wave infrared (SWIR) optoelectronic devices due to their tunable bandgaps across the whole SWIR spectra. PbS CQD inks synthesized directly at room temperature (RT) and ready for the fabrication of various SWIR devices are highly demanded. There are currently no available protocols for RT synthesis of PbS CQDs with absorption beyond 1200 nm. Here, we report on the first synthesis of PbS CQDs at RT with an absorption beyond 1800 nm. There is a delicate balance between nucleation of new seeds and growth of existing dots regulated by the lead-to-sulfur (Pb/S) precursor ratio in the reaction medium, and a proper Pb/S ratio ranging from 1.1 to 2 should be maintained to keep the continuous growth. Photodiodes based on PbS CQDs with a 1550 nm excitonic absorption are fabricated to demonstrate their suitability for device applications. The resulting devices achieve a high photo responsivity of 0.635 A/W, a specific detectivity of 1.01 x 1011 Jones, and a fast response with rise and fall times of 1.08 and 1.10 mu s, respectively.

In the field of interferometric fiber-optic sensing, the phase-shifting technique is well known as a highly efficient method for retrieving the phase signal from the interference light intensity. The rectangular-pulse binary phase modulation (RPBPM) method is a typical phase-shifting method with the advantages of high efficiency, low complexity, and easy array multiplexing. Exploring the impact of the parameters on the performance is of great significance for guiding its application in practical systems. In this study, the influence of the sampling interval and modulation depth deviation involved in the method is analyzed in detail. Through a comparative simulation analysis with the traditional heterodyne and phase-generated carrier methods, the superiority of the RPBPM method is effectively validated. Meanwhile, an improved method based on the ellipse fitting of the Lissajous figure is proposed to compensate for the error and improve the signal-to-noise-and-distortion ratio (SINAD) from 26.3 dB to 37.1 dB in a specific experiment. Finally, the experimental results guided by the above method show excellent performance in a practical vibration system.

The demand for high-performance photonic filters is steadily on the rise in the information age. This work proposed a simple-structure and high-extinction plasmonic polarization filter using gold-deposited photonic crystal fiber (PCF), by the mature finite element method (FEM). The numerical results indicate that once the structural parameters are reasonably ascertained, the operating center of this PCF filter can be verified to be at the 1.55 μm communication window. The 1-μm-long PCF filter possesses a maximum extinction ratio (ER) of −109.9 dB, with a broad operating bandwidth of 620 nm, ranging from 1.35 to 1.97 μm, and a low insertion loss (IL) of 0.3 dB. In addition, this device has an ease of fabrication based on the existing processing techniques. It is reasonable to believe that with its compact structure, comprehensive filtering performance, and high-feasibility, this all-fiber filtering device is likely to assume a crucial role in various fields, including laser technology, sensing, biomedicine, and nonlinear optics.

Lung cancer exhibits strong heterogeneity, and its early diagnosis and precise subtyping are of great importance, as they can increase the ability to deliver personalized medicines by tailoring therapy regimens. Tissue biopsy, albeit the gold standard, is invasive, costly and provides limited information about the tumor and its molecular landscape. Exosomes, as promising biomarkers for lung cancer, are a heterogeneous collection of membranous vesicles containing tumor-specific information for liquid biopsy to identify lung cancer subtypes. However, the small size, complex structure, and heterogeneous molecular features of exosomes pose significant challenges for their effective isolation and analysis. Herein, we report a deep learning-driven microfluidic chip with surface-enhanced Raman scattering (SERS) readout to characterize the differences in exosomes for the early diagnosis and molecular subtyping of non-small cell lung cancer (NSCLC). This integration comprises a processing unit for exosome capture and enrichment using polystyrene microspheres (PS) binding gold nanocubes (AuNCs) and anti-CD-9 antibody (denoted as PACD), and an optical sensing unit to trap the PACD and detect SERS signals from these exosomes. This system achieved a maximum trapping efficiency of 85%, and could distinguish three different NSCLC cell lines from the normal cell line with an overall accuracy of 97.88% and an area under the curve (AUC) of over 0.95 for each category. This work highlights the combined power of deep learning, SERS, and microfluidics in realizing the capture, detection, and analysis of exosomes from biological matrices, which may pave the way for clinical exosome-based cancer diagnosis and prognostication in the future.

This work presents a compact polarization beam splitter using liquid crystal infiltrated dual-core photonic crystal fiber with gold layers. The finite element tool is utilized to analyze the in-fiber coupling characteristics, aiming to investigate the beam splitting performance and sensing capabilities. Simulation results indicate that when the appropriate structural parameters are determined, the coupling length ratio at 1.55 mu m is approximately equal to 2 and the minimum length of 14.43 mu m can be achieved. Both cores exhibit excellent beam splitting performance. In core A, the maximum extinction ratio of 89.04 dB is achieved with a bandwidth of 180 nm covering the S, C, and L bands. In core B, the maximum extinction ratio of 80.03 dB is achieved with a bandwidth of 240 nm fully covering the S, C, L, and U bands. Simultaneously, as a temperature sensor, it has a sensitivity of 2.1 nm/degrees C and a high linearity of 0.99573. Additionally, with the use of the existing process, this splitter can be manufactured. There are reasons to believe that this multifunctional all-fiber device is anticipated to be one of key components in photonic integration, all-optical networks, and distributed sensing.

We propose an egg-beater like single mode fiber (EBSMF) structure for highly sensitive three-dimensional (3D) micro-displacement measurement. The EBSMF features a simple and effective structure, constructed by cascading two vertically distributed elliptic single mode fibers (SMFs). Each elliptic SMF is fabricated by bending a SMF to different radii, thereby altering the refractive index (RI) distribution in both the core and cladding, which enhances the evanescent field. This structure can be regarded as a Mach-Zehnder interferometer. Under external micro-displacement, the radius of the elliptic SMF changes, leading to variations in the RI of the core and cladding, which in turn causes shifts in the resonance dips. The deformation of a single elliptic SMF along the axis of symmetry and perpendicular to the axis of symmetry results in opposite resonance dip shifts. By vertically stacking two elliptic SMFs with different radii, we exploit two distinct dip shift directions to enable precise recognition of displacements along the X, Y, and Z axes. To evaluate the performance of the proposed sensor, four samples with varying radii were fabricated. Experimental results demonstrate displacement sensitivities of 20 pm/mu m (X-axis), 27 pm/mu m (Y-axis), and 337 pm/mu m (Z-axis) within displacement ranges of 0-180 mu m (X, Y) and 0-60 mu m (Z). The proposed sensor offers advantages in terms of ease of fabrication, high sensitivity and linearity, making it a promising candidate for tactile sensing applications. Additionally, when packaged with a flexible material, the proposed sensor can predict object surface morphology, mimicking the sensing capabilities of human fingers. Notably, the tactile sensor achieves a minimum resolution of 50 mu m and response time of 0.9 s, which is comparable to that of human touch.