A nanonewton force sensor using a U-shape tapered microfiber interferometer.

Nanomechanical measurements, especially the detection of weak contact forces, play a vital role in many fields, such as material science, micromanipulation, and mechanobiology. However, it remains a challenging task to realize the measurement of ultraweak force levels as low as nanonewtons with a simple sensing configuration. In this work, an ultrasensitive all-fiber nanonewton force sensor structure based on a single-mode-tapered U-shape multimode-single-mode fiber probe is proposed and experimentally demonstrated with a limit of detection of ~5.4 nanonewtons. The use of the sensor is demonstrated by force measurement on a human hair sample to determine the spring constant of the hair. The results agree well with measurements using an atomic force microscope for the spring constant of the hair. Compared with other force sensors based on optical fiber in the literature, the proposed all-fiber force sensor provides a substantial advancement in the minimum detectable force possible, with the advantages of a simple configuration, ease of fabrication, and low cost.

[Role and mechanism of gut microbiota and its metabolites in host defense against infection].

The interaction of gut microbiota and its metabolites with the host not only plays an important role in maintaining gut homeostasis and host health, but also is a key link in responding to pathogen infections. A thorough understanding of the changes in gut microbiota and its metabolites during infection, as well as their role and mechanism in host defense against infection, is helpful to guide anti-infection treatment. This review focuses on the role of gut microbiota and their metabolites in host defense against bacterial, fungal, and viral infections, and reveals that they can exert anti-infection effects through resistance mechanisms (inducing antimicrobial substances, training immunity, inhibiting pathogen respiration, directly neutralizing pathogens, immune regulation) and tolerance mechanisms (altering energy metabolism patterns of microbiota, cell proliferation and tissue damage repair, maintaining physiological signal transduction in extraintestinal organs, inflammation regulation, maintaining the integrity of the intestinal barrier), and also summarizes measures to regulate gut microbiota against pathogen infections, in order to provide more ideas for novel anti-infection prevention and treatment strategies targeting gut microbiota and its metabolites.

D-shaped photonic crystal fiber sensor based on the surface plasmon resonance effect for refractive index detection.

In this paper, a photonic crystal fiber (PCF) sensor based on the surface plasmon resonance (SPR) effect for refractive index (RI) detection is proposed. We design a D-shaped polished PCF structure consisting of air holes arranged in a hexagonal lattice. The silver film is coated on the middle channel of the polished surface of the PCF. The finite element method is used to analyze the propagation characteristics of the proposed D-shaped SPR-PCF sensor. Simulation results show that the proposed D-shaped SPR-PCF sensor has a maximum wavelength sensitivity of 30,000 nm/RIU, an average wavelength sensitivity of 6785.71 nm/RIU, and a maximum resolution of 3.33×10-6 R I U in the RI range of 1.22-1.36. Owing to the high wavelength sensitivity in the considered RI range, the proposed D-shaped SPR-PCF sensor is suitable for applications in water contamination detection, liquid concentration measurement, food safety monitoring, etc.

A label-free fiber ring laser biosensor for ultrahigh sensitivity detection of Salmonella Typhimurium.

The rapid detection of low concentrations of Salmonella Typhimurium (S. Typhimurium) is an essential preventive measure for food safety and prevention of foodborne illness. The study presented in this paper addresses this critical issue by proposing a single mode-tapered seven core-single mode (STSS) fiber ring laser (FRL) biosensor for S. Typhimurium detection. The experimental results show that the specific detection time of S. Typhimurium is less than 20 min and the wavelength shift can achieve -0.906 nm for an S. Typhimurium solution (10 cells/mL). Furthermore, at a lower concentration of 1 cell/mL applied to the biosensor, a result of -0.183 nm is observed in 9% of samples (1/11), which indicates that the proposed FRL biosensor has the ability to detect 1 cell/mL of S. Typhimurium. In addition, the detection results in chicken and pickled pork samples present an average deviation of -27% and -23%, respectively, from the measured results in phosphate buffered saline. Taken together, these results show the proposed FRL biosensor may have potential applications in the fields of food safety monitoring, medical diagnostics, etc.

Visual analysis of image-guided radiation therapy based on bibliometrics: A review.

Radiation therapy plays an important role in tumor treatment. The development of image-guided radiation therapy (IGRT) technology provides a strong guarantee for precise radiation therapy of tumors. However, bibliometric studies on IGRT research have rarely been reported. This study uses literature collected from the Web of Science during 1987 to 2021 as a sample and uses the bibliometric method to reveal the current research status, hotspots, and development trends in IGRT. Based on 6407 papers published from the Web of Science during 1987 to 2021, we utilized Microsoft Excel 2007 and cite space software to perform statistical analysis and visualization of IGRT. A total of 6407 articles were included, this area of IGRT has gone through 4 stages: budding period, growth period, outbreak period, and stationary period. The research category is mainly distributed in Radiology Nuclear Medicine Medical Imaging, which intersects with the research categories of Materials, Physics, and Mathematics. Yin FF, Tanderup K, and Sonke JJ are highly productive scholars who are active in IGRT research, while Jaffray DA, van Herk M and Guckenberger M are authors with high impact in this field. The team of scholars has close cooperation within the team and weak cooperation among teams. The League of European Research Universities, University of Texas System, University of Toronto, and Princess Margaret Cancer are the main research institutions in this field. The United States has the most research literature, followed by China and Germany. Six thousand four hundred seven articles are distributed in 712 journals, and the top 3 journals are Med Phys, Int J Radiat Oncol, and Radiather Oncol. Precise registration, intelligence, magnetic resonance guidance, and deep learning are current research hotspots. These results demonstrate that the research in this field is relatively mature and fruitful in the past 35 years, providing a solid theoretical basis and practical experience for precision radiotherapy.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus.

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 105, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 105 CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Design of Compact and Broadband Polarization Beam Splitters Based on Surface Plasmonic Resonance in Photonic Crystal Fibers.

In this work, a polarization beam splitter (PBS) based on surface plasmonic resonance is proposed and realized in a designed photonic crystal fiber (PCF). The PCF consists of two kinds of air holes with different diameters. Two solid silica cores near the center of the PCF are established by removing the cladding air holes. A gold film is plated at the external surface of the central air hole of the PCF to excite the surface plasmonic resonance. In order to minimize the length and improve the operation bandwidth of the PBS, the influences of the transversal structural parameters of the PCF are investigated in the context of both X and Y polarization beams. It was found that a 123.6-µm-long PBS with an operation bandwidth of 314 nm could be realized after the global optimization of five structural parameters. The proposed PBS may have potential applications in micro-/nano-optical systems for sensing and communications.

Post chemical etching of tapered seven-core fiber sensor for enhanced figure of merit.

A post chemical etching process to a tapered seven-core fiber (TSCF) is proposed and experimentally demonstrated to effectively adjust the mode profiles of high-order supermodes, aimed to improve the figure of merit (FOM). The experimental results show that the FOM of an etched TSCF is as high as 1431.36 1/RIU, a 7.32-times enhancement compared with that of TSCF without etching, provided the TSCF has the same taper waist diameter of 19.20 µm. The proposed method opens a new, to the best of our knowledge, method for optimizing optical fiber sensor performance.

A Surface Plasmon Resonance-Based Photonic Crystal Fiber Sensor for Simultaneously Measuring the Refractive Index and Temperature.

In this paper, a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) sensor is proposed for simultaneously measuring the refractive index (RI) and temperature. In the design, the central air hole and external surface of the proposed PCF are coated with gold films, and an air hole is filled with the temperature-sensitive material (TSM). By introducing the inner and outer gold films and TSM, the RI and temperature can be measured simultaneously at different wavelength regions. The simulation results show that the average wavelength sensitivities of the proposed SPR-based PCF sensor can reach 4520 nm/RIU and 4.83 nm/°C in the RI range of 1.35~1.40 and a temperature range of 20~60 °C, respectively. Moreover, because of using the different wavelength regions for sensing, the RI and temperature detections of the proposed SPR-based PCF sensor can be achieved independently. It is believed that the proposed SPR-based PCF RI and temperature sensor has important applications in biomedicine and in environmental science.

Highly coherent and multi-octave mid-infrared supercontinuum generations in a reverse-strip AlGaAs waveguide with three zero-dispersion wavelengths.

In this paper, a reverse-strip AlGaAs waveguide with three zero-dispersion wavelengths (ZDWs) is designed. The corresponding three ZDWs are located at 3.74, 6.56, and 8.89 µm. The nonlinearity coefficient of the proposed reverse-strip AlGaAs waveguide is calculated as 2.09W-1m-1 at wavelength 4.9 µm. The effects of pump pulse parameters, waveguide length, and noise coefficient on the nonlinear dynamics of supercontinuum (SC) generation are investigated. When the hyperbolic secant pump pulse with a wavelength of 4.9 µm, peak power of 900 W, and duration of 100 fs is launched into the proposed waveguide and propagated after a 3 mm length, highly coherent and multi-octave mid-infrared (MIR) SC spanning from 2.2 to 14.5 µm (more than 2.7 octaves, at -40dB level) is generated. Finally, a possible fabrication process of the reverse-strip AlGaAs waveguide is introduced. Our research results have important applications in MIR photonics, MIR spectroscopy, optical precision measurement, and more.

A Novel Gold Film-Coated V-Shape Dual-Core Photonic Crystal Fiber Polarization Beam Splitter Covering the E + S + C + L + U Band.

In this paper, a novel gold film-coated V-shape dual-core photonic crystal fiber (V-DC-PCF) polarization beam splitter (PBS) based on surface plasmon resonance effect is proposed. The coupling lengths of the X-polarization (X-pol) and Y-polarization (Y-pol) and the corresponding coupling length ratio of the proposed V-DC-PCF PBS without gold film and with gold film are compared. The fiber structure parameters and thickness of the gold film are optimized through investigating their effects on the coupling lengths and coupling length ratio. As the propagation length increases, the normalized output powers of the X-pol and Y-pol of the proposed V-DC-PCF PBS at the three wavelengths 1.610, 1.631, and 1.650 µm are demonstrated. The relationships between the extinction ratio (ER), insertion loss (IL) and wavelength for the three splitting lengths (SLs) 188, 185, and 182 µm are investigated. Finally, it is demonstrated that for the proposed V-DC-PCF PBS, the optimal SL is 188 µm, the ILs of the X-pol and Y-pol are less than 0.22 dB, and the splitting bandwidth (SB) can cover the E + S + C + L + U band. The proposed V-DC-PCF PBS has the ultra-short SL, ultra-wide SB, and ultra-low IL, so it is expected to have important applications in the laser, sensing, and dense wavelength division multiplexing systems.

Hollow-Core Negative Curvature Fiber with High Birefringence for Low Refractive Index Sensing Based on Surface Plasmon Resonance Effect.

In this paper, a hollow-core negative curvature fiber (HC-NCF) with high birefringence is proposed for low refractive index (RI) sensing based on surface plasmon resonance effect. In the design, the cladding region of the HC-NCF is composed of only one ring of eight silica tubes, and two of them are selectively filled with the gold wires. The influences of the gold wires-filled HC-NCF structure parameters on the propagation characteristic are investigated by the finite element method. Moreover, the sensing performances in the low RI range of 1.20-1.34 are evaluated by the traditional confinement loss method and novel birefringence analysis method, respectively. The simulation results show that for the confinement loss method, the obtained maximum sensitivity, resolution, and figure of merit of the gold wires-filled HC-NCF-based sensor are -5700 nm/RIU, 2.63 × 10-5 RIU, and 317 RIU-1, respectively. For the birefringence analysis method, the obtained maximum sensitivity, resolution, and birefringence of the gold wires-filled HC-NCF-based sensor are -6100 nm/RIU, 2.56 × 10-5 RIU, and 1.72 × 10-3, respectively. It is believed that the proposed gold wires-filled HC-NCF-based low RI sensor has important applications in the fields of biochemistry and medicine.

Temperature Self-Compensated Refractive Index Sensor Based on Fiber Bragg Grating and the Ellipsoid Structure.

In this paper, a temperature self-compensated refractive index sensor based on fiber Bragg grating (FBG) and the ellipsoid structure is demonstrated. The ellipsoid can excite the cladding modes and recouple them into the fiber core. Two well-defined wavelength bands are observed in the reflection spectrum of the proposed sensor, i.e., the Bragg resonant peak and the cladding resonant peaks. By measuring the wavelength shift of the cladding resonant peak, the surrounding refractive index (SRI) can be determined, and the wavelength shift of the Bragg resonant peak can be used as a reliable reference to self-compensate the temperature variation (temperature sensitivity of 10.76 pm/°C). When the SRI changes from 1.3352 to 1.3722, the cladding resonant peak redshifts linearly with an average sensitivity of 352.6 pm/RIU (refractive index unit). When the SRI changes from 1.3722 to 1.4426, an exponential redshift is observed with a maximum sensitivity of 4182.2 pm/RIU. Especially, the sensing performance is not very reliant on the distance between the FBG and the ellipsoid, greatly improving the ease of the fabrication.

Multi-octave mid-infrared supercontinuum and frequency comb generation in a suspended As2Se3 ridge waveguide.

In this paper, we numerically investigate the mid-infrared supercontinuum (SC) generation in a suspended ${{\rm As}_2}{{\rm Se}_3}$As2Se3 ridge waveguide, which is designed with the two zero-dispersion wavelengths. Simulation results show that when the pump pulses at wavelength 3.3 µm with width of 100 fs and peak power of 900 W are launched into the anomalous dispersion region of the designed waveguide with a length of 0.87 mm, the SC can be generated in the wavelength range from 1.76 to 14.42 µm (more than three octaves), extending deep into the "fingerprint" region. The stability of the generated SC is confirmed by the first-order coherence. Moreover, we demonstrate the performance of the SC-based frequency comb by assuming a 50 pulse pump source at a repetition rate of 100 MHz.

Ultrasensitive biosensor based on magnetic microspheres enhanced microfiber interferometer.

A critical barrier for the successful development of fiber sensors for bio-chemical processes is their limitedly improved sensitivity, restricted by the sensor structural design. To solve this, in this paper, a novel concept was proposed using functionalised modified magnetic microspheres (MMSs) to "amplify" the effect of target bio-chemical analytes to significantly improve the fiber sensor's sensitivity, which has been demonstrated using human chorionic gonadotropin (hCG) as an example. Two types of antibody hCG, (ß and α, both can specifically bind with hCG), were adhered on the surface of fibre sensor and MMSs respectively. Both hCG and MMSs will be specifically captured by the fibre sensor, where MMSs act as an "amplifier" to improve the sensor sensitivity. Experimentally immunomagnetic detection limit of 0.0001 mIU/mL has been achieved, which is the highest reported so far. This newly developed methodology opens a new direction for sensitivity improvement and could be further explored to applications require ultrahigh sensitivity detections such as earlier medical diagnostics.

Highly coherent supercontinuum generation in a polarization-maintaining CS2-core photonic crystal fiber.

In this paper, we design a polarization-maintaining CS2-core photonic crystal fiber (PM-CCPCF). The two air holes in the x direction are infiltrated with C2H5OH in order to introduce birefringence. By optimizing the structure parameters of the PM-CCPCF, it is demonstrated that the x-polarization fundamental mode has an all-normal dispersion profile and the corresponding y-polarization fundamental mode has an anomalous dispersion profile for a pump wavelength of 1.76 µm. Then, we investigate the supercontinuum (SC) generations when different fiber lengths, pump peak powers, and pump pulse widths are chosen, respectively. Simulation results show that for the x-polarization and y-polarization fundamental modes, highly coherent SCs can be generated by appropriately choosing the fiber length and pump pulse parameters. Finally, nonlinear propagation dynamics are analysed when the optimized fiber length and pump pulse parameters are used. The bandwidth of the SCs generated for the x-polarization and y-polarization fundamental modes can be up to 0.82 and 1.26 octave, respectively.

Simultaneous Vector Bend and Temperature Sensing Based on a Polymer and Silica Optical Fibre Grating Pair.

The bending response of polymer optical fibre Bragg grating (POFBG) and silica optical fibre Bragg grating (SOFBG) mounted on a brass beam have been systematically studied and compared. The results indicate that POFBG has higher (almost twice as much) bend sensitivity than SOFBG. Based on the difference between the bend and temperature sensitivity of POFBG and SOFBG, a new method of measuring vector bend and temperature simultaneously was proposed by using a hybrid sensor head with series connection of one POFBG and one SOFBG with different Bragg wavelengths. It provides high sensitivity and resolution for sensing bend and temperature changes simultaneously and independently. The proposed sensor can find some applications in the fields where high sensitivity for both bend and temperature measurements are required.

Transmitter and receiver DSP for 112 Gbit/s PAM-4 amplifier-less transmissions using 25G-class EML and APD.

The transmission performance of 112 Gbit/s PAM-4 signal with commercial 25 G-class EML and APD is experimentally studied by using advanced digital signal processing (DSP) algorithms, i.e. pre-equalization (Pre-EQ), error-table based pre-correction (ETC), least-mean square (LMS) based equalization, direct detection faster than Nyquist (DD-FTN) algorithm. Among them, Pre-EQ and ETC are implemented at the transmitter, and ETC is a symbol-pattern-dependent pre-compensation algorithm based on the look-up-table approach. In order to obtain these pre-compensated parameters readily, a joint equalization and error table generation (JEEG) module is proposed. Employing the combination of ETC, LMS, and DD-FTN, a single line 112 Gbit/s PAM-4 40 km amplifier-less transmission with a record receiver sensitivity of -16.6 dBm (at 7% HD-FEC threshold) is experimentally demonstrated. In addition, the computational complexities of different DSP schemes are analyzed and discussed in detail. The receiver computational complexity can be effectively reduced by employing appropriate ETC and Pre-EQ in the transmitter.

A simple all-fiber comb filter based on the combined effect of multimode interference and Mach-Zehnder interferometer.

A polarization-dependent all-fiber comb filter based on a combination effect of multimode interference and Mach-Zehnder interferometer was proposed and demonstrated. The comb filter was composed with a short section of multimode fiber (MMF) fusion spliced with a conventional single mode fiber on the one side and a short section of a different type of optical fiber on the other side. The second type of optical fiber is spliced to the MMF with a properly designed misalignment. Different types and lengths of fibers were used to investigate the influence of fiber types and lengths on the performance of the comb filter. Experimentally, several comb filters with free spectral range (FSR) values ranging from 0.236 to 1.524 nm were achieved. The extinction ratio of the comb filter can be adjusted from 6 to 11.1 dB by varying polarization states of the input light, while maintaining the FSR unchanged. The proposed comb filter has the potential to be used in optical dense wavelength division multiplexing communication systems.

Deterministic generation of single soliton Kerr frequency comb in microresonators by a single shot pulsed trigger.

Kerr soliton frequency comb generation in monolithic microresonators recently attracted great interests as it enables chip-scale few-cycle pulse generation at microwave rates with smooth octave-spanning spectra for self-referencing. Such versatile platform finds significant applications in dual-comb spectroscopy, low-noise optical frequency synthesis, coherent communication systems, etc. However, it still remains challenging to straightforwardly and deterministically generate and sustain the single-soliton state in microresonators. In this paper, we propose and theoretically demonstrate the excitation of single-soliton Kerr frequency comb by seeding the continuous-wave driven nonlinear microcavity with a pulsed trigger. Unlike the mostly adopted frequency tuning scheme reported so far, we show that an energetic single shot pulse can trigger the single-soliton state deterministically without experiencing any unstable or chaotic states. Neither the pump frequency nor the cavity resonance is required to be tuned. The generated mode-locked single-soliton Kerr comb is robust and insensitive to perturbations. Even when the thermal effect induced by the absorption of the intracavity light is taken into account, the proposed single pulse trigger approach remains valid without requiring any thermal compensation means.