The possibility of making new SMF-NCF-SMF- long period fiber grating (SNS-LPG) by periodically embedding no-core fiber (NCF) is demonstrated. It is shown that an 11-period SNS-LPG can exhibit an extremely high loss resonant dip (>20 dB). The theoretical analysis shows good agreement with the measured transmission spectrum. We investigated the refractive index and temperature sensitivity of SNS-LPG, and achieved the average wavelength sensitivity of 141.837 nm/RIU in the range of 1.333-1.400 RIU. The sensor also exhibits a lower temperature sensitivity (-6.43 pm/°C and 0.005 dB/°C).

The polarization characteristics of the multifunctional integrated optic chip (MFIOC) are fully evaluated with high accuracy by using optical coherence domain polarimetry based on white light interferometer. Two polarization maintaining (PM) fibers, serving as extended fibers, are spliced to the PM pigtails of the MFIOC with polarization axes aligned. By launching light at 45° to the birefringence axes of the lead-in extended PM fiber, the beams along the fast and slow axes of the birefringent waveguides interfere after a 45° polarization analyzer and an optical path correlator. The polarization extinction ratio (PER) and birefringence of the LiNbO3 Y-waveguide, the birefringence of the PM pigtails, and the crosstalks at the connection points between the Y-waveguide and the PM pigtails can be simultaneously obtained from the amplitudes and positions of the corresponding interference peaks. The characteristic peak of the Y-waveguide's PER is shifted out of the interference peak of the light source ripple by selecting proper length of the extended fibers. The extended fibers also brings in two additional cross-coupling points at the ends of the PM pigtails, which are used for calculating the birefringence of the PM pigtails. In addition, the alignment type between the PM pigtails and the birefringent Y-waveguide is identified according to the position of the characteristic peak of the Y-waveguide's PER. Theoretical model based on Jones matrix is built to describe the characteristic peaks of the MFIOC. Two MFIOCs with different alignment angle between the PM pigtails and the Y-waveguide are experimentally tested. Results show that the PER resolution of the proposed method can achieve nearly -90 dB and the dynamic range of the test system is about 90 dB.

Calibration-free wavelength modulation spectroscopy (WMS) is an efficient technique for trace gas monitoring. It is widely used due to its resistance to light intensity fluctuations, strong suppression of low-frequency noise, fast response time, and excellent environmental adaptability. The calibration-free WMS often employs the Levenberg–Marquardt algorithm for spectral fitting to retrieve gas characteristics. However, to the best of our knowledge, an analysis of the main factors affecting the operational effectiveness of the Levenberg–Marquardt algorithm in calibration-free WMS has merely been reported. In this paper, we have systematically analyzed the Levenberg–Marquardt algorithm’s operating mechanism in WMS-2f/1f. The results show that the number of parameters and the estimation errors of the initial parameters are the main factors limiting the retrieval accuracy of the algorithm, which provides some important guidelines for the subsequent optimization of the spectral fitting scheme.

In this paper, a new sensor based on SnO₂–ZnO nanohybrids modified glassy carbon electrode for simultaneous electrochemical determination of catechol (CC) and hydroquinone (HQ) has been investigated. The SnO₂–ZnO nanohybrids was synthesized via a simple one-pot hydrothermal method and characterized by SEM, XRD and FTIR. Cyclic voltammetry and differential pulse voltammetry were employed to investigate the electrocatalytic performance towards the CC and HQ redox. The combined advantages of SnO₂ and ZnO provide excellent electrochemical catalytic activity toward CC and HQ. Under the optimized condition, the response peak currents of the modified electrodes were linear over ranges from 0.5 to 500 μM for both CC and HQ. In addition, the proposed sensor also showed excellent sensitivity with the detection limit of 0.07 μM and 0.09 μM for CC and HQ, respectively. Moreover, the sensor also exhibited excellent reproducibility and stability.

A new type of Mach-Zehnder interferometer (MZI) is proposed to measure twist and temperature. The sensor contains a pretwisted taper and a ball. The pretwisted taper is made by pretwisted, and then, thermally tapering along a single-mode fiber, to induce permanent spiral distortion in the fiber. The experimental results indicate that the sensor has higher twist sensitivity. Twisting the sensor for counterclockwise and clockwise direction, the twist sensitivities of Dip 1584 nm are -0.378 and 0.083 nm/(rad/m), respectively, and the twist sensitivities of Dip 1685 nm are -0.117 and 0.089 nm/(rad/m), respectively. Meanwhile, the twist direction can be determined by the value of the twist sensitivities. The temperature sensitivities of Dip 1584 and Dip 1685 nm are 63 pm/°C and 74 pm/°C, respectively. The feasibility of measuring the torsion and temperature characteristics has been experimentally confirmed. Thus, the proposed MZI sensor can be used to measure twist and temperature and discriminate twist direction.

We present a D-shaped photonic crystal fiber (PCF) plasmon sensor based on a large-hole self-reference channel for applications in biological and chemical sensing. Both the Plasmon’s fundamental linear-polarization LP01 and high-order LP11 modes are excited at the interface between the analyte and the silver film based on results of the numerical calculation method. We obtained the transmitted spectrum of the guided mode LP01 in the D-shaped PCF. We found that the peak spectral wavelength of the sensor increases when the refractive index of the analyte increases. The spectral sensitivity clearly increases with the silver film’s thickness on the sensor’s platform, although it is unaffected by other variations of the PCF’s geometry. We obtained an optimal spectral sensitivity for the sensor of 3191.43nm/RIU for a silver film thickness of 50nm.