In this work, we proposed a high-resolution D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor based on gold grating. Gold grating is introduced to modulate the resonance wavelength and enhance the refractive index (RI) sensitivity. Structure parameters of PCF and gold grating are analyzed by the finite element method for optimizing the SPR sensor. The simulation results indicate that air hole pitch, air hole diameter, and gold thickness and grating constant have little influence on the sensitivity of the refractive index, which reduces the requirement of precise processing. For improving the resolution of RI sensing, a two-feature (2F) interrogation method, which combines wavelength interrogation and amplitude interrogation, is used. The maximum theoretical resolution of the SPR sensor reaches to $5.98\times {10}^{-6}\mathrm{RIU}$ in the range of 1.36–1.38, and the wavelength sensitivity reaches to 3340 nm/RIU. The proposed SPR sensor shows potential applications for developing a high-sensitivity, real-time, and fast-response SPR-RI sensor.

We experimentally demonstrated a high sensitive gas pressure sensor, which also has more concise processing steps and lower cost. The sensor was fabricated by splicing the single-mode fiber (SMF) and a short section of hollow-core fiber (HCF) which was filled with a Polydimethylsiloxane (PDMS) film to form an enclosed air microcavity with the length of 55 μm. The thin PDMS film also plays a role in reflecting the beam. The thermo-optical effect and the thickness of PDMS film can affect the cavity that is sensitive to external pressure. When the thickness of the PDMS membrane is 3 μm, the measured gas pressure sensitivity reaches to 52.143 nm/Mpa, the linearity is 99.86%, and the cross-sensitivity of the gas pressure over temperature is lower than 2.51 × 10 ⁻³ Mpa/°C. Moreover, the compact structure, high sensitivity, high mechanical strength, and convenient fabrication make it suitable for measuring gas pressure in harsh conditions.

An optical vortex carrying orbital angular momentum (OAM) with a fractional topological charge (TC) is a good complement to a traditional integer optical vortex and has many potential applications. However, the fractional optical vortex (FOV), which breaks the orthogonality of OAM, makes the precision measurement of the FOV complicated and difficult when using a conventional method. Thus, we propose an accurate and effective FOV detection method by using a two-dimensional multifocal array consisting of different integer vortices. Theoretically, FOV beams could be decomposed into a Fourier series of integer optical vortex beams, and the average OAM of the FOV can be calculated via the energy of these integer optical vortices, which can be accurately measured by a commercial photoelectric detector. For improving the measurement accuracy, a compensation iteration algorithm is employed to correct the detected average OAM of the FOV. Experimental results show that the error of average OAM detection is less than 0.025. This alternative FOV TC detection method is sufficient for a wide range of real-time requirements in optical manipulation, imaging, and quantum optics.

Vernier-effect has been widely employed in interferometer-based optical fiber sensors to improve the sensitivities greatly. However, the influence of the Vernier-effect on detection limit (DL) that is more important for evaluating the actual performance of the sensor has not been discussed. Two gas pressure fiber sensors (a typical Fabry-Perot interferometer-based sensor and a Vernier sensor) are used to compare the DL of them by experiments. Both the theoretical analysis and the experimental results show that, though the Vernier-effect magnifies the spectrum shift sensitivity, it also magnifies the value of the smallest detectable wavelength shift. As a result, the actual DL of the sensor is not improved by employing the Vernier-effect. If the contrast ratio of the Vernier envelope is not optimized enough for most of the reported sensors, the DL can even degenerate greatly.

A simple fiber-optic sensor for simultaneous measurement of high pressure and high temperature was proposed. The sensor was simply fabricated by splicing two sections of silica capillary tubes (SCTs) with different inner diameters to the single-mode fiber. The thick core SCT functions as a Fabry-Perot (FP) micro-cavity and an anti-resonant reflecting waveguide at the same time. The two different sensing mechanisms lead to the high contrast sensitivity values of pressure and temperature (‒3.76 nm/MPa, 27.7 pm/°C and 4.24 nm/MPa, 0.82 pm/°C). We also proposed a simple and effective method to evaluate the actual sensitivities of two-parameter sensors by using linear programming, which shows that our sensor is more sensitive than others in high pressure and high temperature simultaneous detection. Besides, low cost, good mechanical property and convenient reflective probe make the sensor more competitive in actual application.

We proposed a simple and efficient method to create a 2D perfect optical vortex (POV) array based on the Fourier shift theorem and a 2D POV array hexadecimal encoding/decoding method to realize high capacity data transmission. The encoding data sequence contains the position and topological charge information of each POV, which can be modulated by adding a phase shift factor to a specially designed hybrid phase-only grating. Based on the position and topological charge information, the 2D POV array can realize spatial division multiplexing and orbital angular momentum shift keying. The hexadecimal encoding/decoding method was investigated both theoretically and experimentally. The experimental results show that this method has potential applications in high capacity optical communications.