The layered MoS₂ has recently attracted significant attention for its excellent nonlinear optical properties. Here, the ultrafast nonlinear optical (NLO) absorption and excited carrier dynamics of layered MoS₂ (monolayer, 3-4 layers, and 6-8 layers) are investigated via Z-scan and transient absorption spectra. Our experimental results reveal that NLO absorption coefficients of these MoS₂ increase from -27 × 10³cm/GW to -11 × 10³cm/GW with more layers at 400-nm laserexcitation, while the values decrease from 2.0 × 10³ cm/GW to 0.8 × 10³ cm/GW at 800 nm. In addition, at high pump fluence, when the NLO response occurs, the results show that not only the reformation of the excitonic bands, but also the recovery time of NLO response decreases from 150 ps to 100 ps with an increasing number of layers, while the reductive energy of A excitonic band decreases from 191.7 meV to 51.1 meV. The intriguing NLO response of MoS₂ provides excellent potentials for the next-generation optoelectronic and photonic devices.

The excitation mechanism of surface plasmon polaritons (SPPs) in a surface plasmon sensor with a one-dimensional (1D) Au diffraction grating on a glass substrate is studied herein. The sensitivity of the sensor for application to a refractometer is also characterized. The SPPs are excited at the following two types of interface: one between the Au grating and the glass substrate and the other between the Au grating and the medium. The simulation data for the transmittance spectra and the transmittance mapping are consistent with the experimental data even when the refractive index of the solution medium is 1.700. Therefore, the excitation mechanism of the SPPs in a surface plasmon sensor is capable of detecting the medium (n = 1.700), in which the sensor is used and clarified.

We propose a novel structure and unique sensing mechanism bio-chemical sensor which is fabricated by a polymer long-period waveguide grating with the detection liquid directly as the waveguide cladding. Quantitative detection is realized from analyzing the output absorption spectrum and resonant wavelength shift related to the liquid detection concentration. The proposed polymer long-period waveguide grating based liquid refractive-index sensor is developed experimentally, the high sensitivity of 1.01 × 10⁴ nm/RIU is achieved, and the temperature stability coefficient is 1.47 nm/℃. Theoretically and experimentally, this work has been demonstrated to have potential application in chemical and biological detections and may provide an important technical support for solving today’s increasingly serious civil problems such as food safety and drug safety, which will also have the important scientific significance and application prospects.

A high-sensitivity all-fiber temperature sensor based on a Sagnac interferometer is demonstrated by splicing a section of polarization maintaining fiber (PMF) between two sections of standard single mode fibers (SMFs). In this sensor, the SMF-PMF-SMF structure in the Sagnac loop is bent into a circle to enhance the sensitivity. The length and curvature of the PMF in the loop are investigated and can be optimized to further increase the temperature sensitivity of the sensor. Results show that the radius of the circle has an important effect upon temperature sensitivity due to the bend-induced birefringence variation of the PMF. The SMF-PMF-SMF structure bent into a circle with a radius of 30 mm exhibits a high-sensitivity temperature of 1.73 nm/℃. The sensor is provided with the advantages of easy fabrication, low-insertion loss, and high sensitivity, which may find potential applications in the field of high precision temperature measurement.

An idea of the surface plasmon resonance (SPR) has been utilized for the design of highly sensitive sensors based on the wagon-wheel fiber technology. Such sensors are sensitive to changes in the refractive index of sample analyte. In this study, a three-strut wagon-wheel structure, coated with the gold layer of nano-sized thickness, has been proposed as the SPR sensor. Finite element method is employed to simulate and tune the proposed SPR’s design, which leads to a highly sensitive and multichannel plasmonic sensor with the ability for a dual reading on a single analyte or simultaneous identification of two analytes. In this design, suitable thickness values for the gold layer and core struts are determined. Sensitivities of the detector due to the first resonance peak, second resonance peak, and the difference in resonance peaks are calculated to be 1120 nm/RIU, 1540 nm/RIU, and 420 nm/RIU, respectively, when analytes are placed in all three channels of the fiber. Sensitivity of the detector with respect to the second resonant peak for analyte in Channels 2 and 3 is also found to be 1252 nm/RIU when Channel 1 is filled with the reference. The sensitivity and resolution of the sensor increase as the refractive index of the analyte increases by almost a linear proportion. If the sensor is utilized to detect the difference in two peaks, it would substantially reduce the noise, and the best result is expected. The thicknesses of the struts and the gold layer are proper parameters to be tuned in designing the detector.

We demonstrate a high power linearly polarized Raman fiber laser (RFL) pumped by an amplified spontaneous emission (ASE) source. Temporal-stable operation of RFL could be ensured owing to the employment of ASE, which mitigates the inherent intensity noise compared with the classic scheme adopting laser oscillator as pump source. In this experiment, the RFL has up to 119.5 W output power, with central wavelength of 1129.2 nm, and full width at half maximum (FWHM) linewidth of about 4.18 nm. The polarization extinction ratio (PER) of the Raman laser is about 23 dB. Moreover, this laser has excellent long-term and short-term stabilities in terms of the output power and time domain.

High efficiency and precision of the pot center detection are the foundations of avionics instrument navigation and optics measurement basis for many applications. It has noticeable impact on overall system performance. Among them, laser spot detection is very important in the optical measurement technology. In order to improve the low accuracy of the spot center position, the algorithm is improved on the basis of the circle fitting. The pretreatment is used by circle fitting, and the improved adaptive denoising filter for TV repair technology can effectively improves the accuracy of the spot center position. At the same time, the pretreatment and de-noising can effectively reduce the influence of Gaussian white noise, which enhances the anti-jamming capability.

A fiber-optic Raman spectrum sensor system is used for the fast diagnosis of esophageal cancer during clinical endoscopic examination. The system contains a 785 nm exciting laser, a Raman fiber-optic probe with 7 large core fibers and a focus lens, and a highly sensitive spectrum meter. The Raman spectrum of the tissue could be obtained within 1 second by using such a system. A signal baseline removal and denoising technology is used to improve the signal quality. A novel signal feature extraction method for differentiating the normal and esophageal cancer tissues is proposed, based on the differences in half-height width (HHW) in 1200 cm^-1 to 1400 cm^-1 frequency band and the ratios of the spectral integral energy between 1600 cm^-1 - 1700 cm^-1 and 1500 cm^-1 - 1600 cm^-1 band. It shows a high specificity and effectivity for the diagnosis of esophageal cancer.

The deposition of tetrakis (4-sulonatophenyl) porphyrin (TPPS) thin film on optical fibers presents many possibilities for sensing applications. The J-form aggregation with a narrow and sharp spectral feature at about 490 nm and its sensitivity to humidity have been discussed; a fast change of wavelength occurs according with variation in the humidity level. The reproducibility and high sensitivity of TPPS-coated fibers, along with the capabilities of optical fibers, suggest the device as a good candidate for humidity sensing in harsh environments.

In this paper, a photonic crystal ring resonator based bio sensor is designed to sense different blood constituents in blood in the wavelength range of 1530 nm-1615 nm for biomedical applications. The blood constituents such as hemoglobin white blood cell, red blood cell, blood sugar, blood urea, albumin, serum bilirubin direct, and ammonia are sensed for the corresponding transmission output power, Q factor, and refractive index changes. As the blood constituent has unique refractive index, the resonant wavelength and output power are varied from one to another, which are used to identify the blood constituents.

This paper firstly and experimentally demonstrates an in-fiber axial micro-strain sensing head, combined with a Mach-Zehnder interferometer (MZI) based on the concentric multilayer elliptical-core fiber (CMECF). This MZI with a high extinction ratio (about 15 dB) is successfully achieved with a CMECF-single mode fiber-CMECF (CSC) structure. The MZI sensor theory and the resonance demodulation technology are systematically described in this paper. In this CSC structure, two sections of the CMECF have a role as the mode generator and coupler, respectively. LP01 and LP11 even, which have similar excitation coefficients, are two dominated propagating mode groups supported in the CMECF. On account of the distinct dual-mode property, a good stability of this sensor is realized. The detected resonance in the MZI shifts as the axial micro-strain variated due to the strong interaction between higher order modes. High sensitivity of ~1.78 pm/με is experimentally achieved within the range of 0 με - 1250 με, meanwhile, the intensity fluctuation is below 0.38 dB.

A simple method for the estimation of the wavelength of a fiber laser system is proposed. The method is based on the use of a high-birefringence-fiber loop mirror (HBFLM). The HBFLM exhibits a periodic transmission/reflection spectrum whose spectral characteristics are determined by the length and temperature of the high-birefringence fiber (HBF). Then, by the previous characterization of the HBFLM spectral transmission response, the central wavelength of the generated laser line can be estimated. By using a photodetector, the wavelength of the laser line is estimated during an HBF temperature scanning by measuring the temperature at which the maximum transmitted power of the HBFLM is reached. The proposed method is demonstrated in a linear cavity tunable Er/Yb fiber laser. This method is a reliable and low-cost alternative for laser wavelength determination in short wavelength ranges without the use of specialized and expensive equipment.