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• Metal oxides with high RI will improve the sensing performance of fiber sensors. • Compared to silver-based sensors, the maximum sensitivity of TiO 2 composite film sensors has increased by 16.92 %. • Compared to silver-based sensors, the maximum sensitivity of ZnO composite film sensors has increased by 4.62 %. • The maximum temperature sensitivity of the two composite membrane sensors is 4.9 nm/℃ and 4.3 nm/℃, respectively. With the widespread application of fiber surface plasmon resonance (SPR) sensors in the field of biochemical sensing, especially in the detection of large molecules such as proteins, the sensitivity of traditional fiber SPR sensors has made it difficult to meet the requirements of detection accuracy in practical applications. This article proposes and proves an effective method for selecting the optimal metal oxide material to improve the sensing performance of SPR sensors. Metal oxides (TiO 2 and ZnO) can improve the sensitivity by enhancing the evanescent field of fiber SPR phenomenon. Through simulation, it was found that when the metal oxide film of the composite film sensor maintains the same thickness, the metal oxide with a high effective refractive index (RI) has a better improvement effect on the sensitivity of the SPR sensor. Experimental results show that the maximum RI sensitivity of TiO 2 composite film sensors and ZnO composite film sensors in the RI range of 1.333–1.420 is 15,200 nm/RIU and 13,600 nm/RIU, respectively. Compared to silver-based sensors, RI sensitivity has increased by 16.92 % and 4.62 %, respectively. To further verify the enhancement effect of different metal oxides on fiber sensors, another layer of PDMS film is deposited on TiO 2 and ZnO films. Within the temperature sensing range, the maximum temperature sensitivity of these two composite film temperature sensors is 4.9 nm/°C and 4.3 nm/°C, respectively. Overall, metal oxides with high RI can improve the sensing performance of fiber optic sensors. [ABSTRACT FROM AUTHOR]

• A novel air-hole array and trench (HAT) structure is proposed. • The 6-core 2-LP fiber with a 125 μm cladding, which is compatible with the current optical fiber communication network. • This fiber exhibits an ICXT is below −38.23 dB/100 km, which is sufficiently low to neglect IMXT. • Compared to SMF, the communication capacity of this fiber has increased by 18 times. In order to be compatible with the current optical fiber communication network, we propose a 125 μm diameter heterogeneous six-core two linear polarization modes fiber with air-hole array and trench (HAT) structure. The coupled power theory and finite element method (FEM) are used to investigate inter-core crosstalk (ICXT), bending loss, and other properties. The HAT structure can effectively suppress ICXT; and the maximum ICXT is less than −38 dB/100 km in C + L band. The effective refractive index difference (Δ n eff) between modes is greater than 3 × 10-3, inter-mode crosstalk (IMXT) can be ignored. The maximum intrinsic loss is 0.187 dB/km; relative core multiplicity factor reaches 32.21. The relative spatial efficiency is 18 times that of traditional single-mode fibers. This fiber can be produced by chemical vapor deposition and existing optical fiber manufacturing technology. The designed fiber can be directly connected to the communication network to reduce the cost of equipment renewal, and the communication capacity can be increased by 18 times. [ABSTRACT FROM AUTHOR]

A method of fabricating dual-core photonic crystal fiber(PCF) using secondary drawing technique is presented. The diameter of fiber core can be reduced to 4 μ m by placing the thin preform into glass sleeve for secondary drawing. Dual-core PCF, partial dual-core PCF and non-centrosymmetric dual-core PCF are successfully prepared by secondary drawing technology combined with air pressure regulation. A curvature sensing system is built. When the length of partial dual-core PCF is 105 mm, the measured curvature sensitivity is − 3.79944 nm/m−1. Through the water bath temperature experiment, the measured temperature sensitivity is 21 pm/ ∘ C, and the cross interference caused by temperature value on curvature value is very small. When the length of non-centrosymmetric dual-core PCF is 207 mm, the curvature sensitivity measured by forward bending and negative bending is 4.68429 nm/m−1 and − 4.68808 nm/m−1, respectively. The measured temperature sensitivity is − 13 pm/ ∘ C, and the cross interference of temperature on curvature can be ignored. • The secondary drawing technology is proposed to prepare PCF. • In the process of preparing PCF, the problem of pore collapse is solved. • Dual-core PCFs are prepared, and the core diameter is reduced to below 4 um. • The sensing system is established, and curvature and temperature are measured. • The cross-interference of temperature on curvature is very small. [ABSTRACT FROM AUTHOR]