A twin-core photonic crystal fiber sensor is proposed for measuring liquid refractive index (RI) and temperature simultaneously. The air holes of the sensor are arranged in a hexagonal pattern, and two planes are introduced by polishing in the cladding. On one side of the plane, the gold film is deposited for RI measurement, and on the other side, the gold film and polydimethylsiloxane are deposited for temperature measurement. We analyzed its sensing characteristics by using the finite element method. The numerical results show that the two channels for measuring RI and temperature have no mutual interference and the arrangement reduces the complexity of the sensing measurement. The maximum spectral sensitivity of the sensor is 20 000 nm/RIU and 9.2 nm °C⁻¹, respectively, when the liquid RI is in the range of 1.36–1.42 and the temperature is in the range of 0 °C–50 °C. The results also show the sensing accuracy was not very sensitive to the change of structural parameters, which makes the sensor very easy to fabricate. Our work is very helpful for implementation of a high sensitivity, easy fabrication and real-time multi-parameter surface plasmon resonance sensor.

For surface plasmon resonance (SPR) sensors, sensitivity and full width at half maximum (FWHM) are incompatible parameters, and it is difficult to realize a sensor with both high sensitivity and low FWHM. To weigh two parameters, we propose and demonstrate an SPR sensor based on a few-mode fiber (FMF) structure. The FMF is polished, which can enhance the evanescent wave leakage to excite the SPR effect. Since this FMF can transmit only five modes, the proposed sensor is characterized by high sensitivity and low FWHM. Refractive index sensing experiments were performed on it, and the results showed that the polishing length and depth did not affect the location of the SPR valley but the shape of the valley. In addition, we compared the proposed FMF structure with single-mode fiber (SMF) structure and multimode fiber (MMF) structure in terms of performance. We found that the FMF sensor has higher sensitivity and stronger mechanical strength than the SMF sensor and lower FWHM than the MMF sensor. Therefore, FMF is a compromise between SMF and MMF. The sensitivity of the proposed sensor is 5635 nm/RIU. The lowest FWHM is 127 nm. This study provides a new method for balancing sensitivity and FWHM.

A high-sensitivity temperature sensor based on gold-coated D-shaped photonic crystal fiber is proposed in this paper. To enhance the sensing performances, gold as the surface plasmon resonance material is coated on the polishing surface. The thermosensitive liquid consists of ethanol and chloroform, and it is placed on the outer layer of the photonic crystal fiber. As the phase-matching condition is satisfied, the core mode couples to the surface plasmon polariton mode, and energy transfer occurs. The influences of the structural parameters on the sensing characteristics were studied using the finite element method. The numerical results show the average sensitivity can reach up to 10.61 nm/°C, and the linearity $R^2=0.99341$ for the temperature sensing ranges of 0–60°C. Moreover, a good spectral shape can be realized by the proposed fiber. Compared with some previously reported temperature sensors, the proposed temperature sensor shows excellent performances in terms of the sensitivity, detection range, and fabrication.

As an essential biomarker for diagnosing and treating various diseases, low-cost, quantitative detection methods for complementary DNA (cDNA) have received much attention. The surface plasmon resonance (SPR) sensing technique is an effective measurement scheme, but the ambient temperature and pH variations have a non-negligible impact. In this work, we developed a triple-probe SPR sensing system for detecting cDNA concentration, temperature, and pH. In order to satisfy the triple parameter measurements, we used a microstructured optical fiber as the sensing platform, silver and gold films as the excitation layer, and a MoS2 film as the modulation layer. First, we explore the modulation mechanism of SPR and the conditions for excitation of triple SPR and demonstrate that the carrier concentration is a crucial factor affecting the resonance wavelength. Then, the feasibility of the sensing system for triple-probing is theoretically analyzed. Finally, in the experiment, the optimal parameters of the sensor were determined, and the triple parameter detection was successfully realized. The experimental results show that the three probes can work independently, and the hybridized DNA probe can realize the selective detection of cDNA with a sensitivity of 0.249 nm/(nmol/l). The maximum sensitivity of the pH probe and the temperature probe are 51.5 nm/pH and 6.14 nm/°C. In addition, the experimental results show that the sensing probes have excellent reproducibility. This paper’s innovation is using the fiber optic SPR effect to achieve quantitative detection for cDNA, temperature detection, and pH detection. Therefore, the sensor has a promising future in early diagnosis and biosensing.