We propose and demonstrate a novel and compact optical-fiber temperature sensor with a high sensitivity and high figure of merit (FOM) based on surface plasmon resonance (SPR). The sensor is fabricated by employing a single-mode twin-core fiber (TCF), which is polished as a circular truncated cone and coated with a layer of gold film and a layer of polydimethylsiloxane (PDMS). Owing to the high refractive index sensitivity of SPR sensors and high thermo-optic coefficient of PDMS, the sensor realizes a high temperature sensitivity of $-4.13\mathrm{nm}/°\mathrm{C}$ to $-2.07\mathrm{nm}/°\mathrm{C}$ in the range from 20°C to 70°C, transcending most other types of optical-fiber temperature sensors. Owing to the fundamental mode beam transmitting in the TCF, the sensor realizes a high FOM of up to 0.034/°C, more than twice that of SPR sensors based on multimode fiber. The proposed temperature sensor is meaningful and will have potential applications in many fields, such as biomedical and biomaterial.

We propose and demonstrate a dual-channel surface plasmon resonance (SPR) sensor based on the side-polished D-type optical fiber, which is available for simultaneous measurement of refractive index (RI) and temperature. The single mode fiber (SMF) is side-polished to remove the fiber cladding and plated a layer of gold film on the polished surface to excite SPR effect. The RI sensing characters are researched by simulation and experiment. The sensitivity increases from 1543 nm/RIU to 6300 nm/RIU as RI increasing from 1.333 to 1.410. Besides, the resonance wavelength red-shifts about 40 nm as the gold film thickness increasing from 40 nm to 60 nm. Based on the above, we design the temperature compensated RI sensor by modifying the side-polished D-type fiber. One half of the side-polished region is applied for RI sensing and the other half is additionally coated a layer of polydimethylsiloxane (PDMS), which is high sensitive to temperature variation, for temperature sensing. In addition, the resonance wavelengths of two sensing channels can be controlled by adjusting the film thickness to avoid crosstalk. In the range from 1.333 to 1.390, the RI sensitivity reaches as high as 2260.1 nm/RIU. In the range from 20 °C to 60 °C, the temperature sensitivity reaches as high as -2.41 nm/°C. Finally, by temperature compensation, the RI measurement accuracy can be greatly improved.

We propose and demonstrate a novel surface plasmon resonance (SPR)-sensing approach by using the fundamental mode beam based on a twin-core fiber (TCF). Although normally in a fiber SPR sensor, a multimode fiber (MMF) has often been used to improve the coupling efficiency; for improving fiber SPR sensor sensitivity, single-mode beam is optimal. We provide a novel method to employ the single (fundamental)-mode beam to SPR sense based on the TCF. We grind the TCF tip to be a frustum wedge shape, and plate a 50-nm sensing gold film on the end face, and two 500-nm reflected gold films on the side faces of the wedge tip. By using this new configuration, we reduce the mode noise effectively and get a high testing sensitivity (the testing highest sensitivity reaches to 6463 nm/RIU). This SPR probe can be applied in a microfluidic chip and monitors the refractive index (RI) charges of the flow liquid in the microfluidic channel in real-time. The probe successfully monitors the refractive index of liquid ranged from 1.3333 to 1.3706, and the average sensitivity reaches to 5213 nm/RIU in the solution, which is much higher than most multimode SPR systems.

We propose and demonstrate a novel and compact optical fiber surface plasmon resonance (SPR) sensor for the simultaneous measurement of the refractive index (RI) and temperature. The sensor is fabricated by employing the eccentric-core fiber (ECF), which is polished to a V-shaped micro-structure optical fiber (MOF). One side of the MOF is used as the RI sensing channel, and the other side is used as the temperature sensing channel. Two sensing channels are independent without crosstalk. The sensor has high RI sensitivity up to the maximum of 3376 nm/RIU from 1.333 to 1.385 RIU, and high-temperature sensitivity up to $-2.65\mathrm{nm}/°\mathrm{C}$ from 20°C to 60°C. In addition, owing to the few-mode light in the ECF, the full width at half-maximum is smaller than other SPR sensors based on multimode fiber. This sensor will be extremely helpful to improve the RI measurement uncertainty caused by temperature disturbance.

We propose and demonstrate a whispering gallery mode (WGM) resonance-based temperature sensor, where the microresonator is made of a DCM (2-[2-[4-(dimethylamino)phenyl] ethenyl]-6-methyl-4H-pyran-4-ylidene)-doped oil droplet (a liquid material) immersed in the water solution. The oil droplet is trapped, controlled, and located by a dual-fiber optical tweezers, which prevents the deformation of the liquid droplet. We excite the fluorescence and lasing in the oil droplet and measure the shifts of the resonance wavelength at different temperatures. The results show that the resonance wavelength redshifts when the temperature increases. The testing sensitivity is 0.377 nm/°C in the temperature range 25°C–45°C. The results of the photobleaching testing of the dye indicate that measured errors can be reduced by reducing the measured time. As far as we know, this is the first time a WGM temperature sensor with a liquid state microcavity has been proposed. Compared with the solid microresonator, the utilization of the liquid microresonator improves the thermal sensitivity and provides the possibility of sensing in liquid samples or integrating into the chemical analyzers and microfluidic systems.

We propose and demonstrate a novel optical-fiber micro-displacement sensor based on surface plasmon resonance (SPR) by fabricating a Kretschmann configuration on graded-index multimode fiber (GIMMF). We employ a single-mode fiber to change the radial position of the incident beam as the displacement. In the GIMMF, the angle between the light beam and fiber axis, which is closely related to the resonance angle, is changed by the displacement; thus, the resonance wavelength of the fiber SPR shifts. This micro-displacement fiber sensor has a wide detection range of 0–25 μm, a high sensitivity with maximum up to 10.32 nm/μm, and a nanometer resolution with minimum to 2 nm, which transcends almost all of other optical-fiber micro-displacement sensors. In addition, we also research that increasing the fiber polishing angle or medium refractive index can improve the sensitivity. This micro-displacement sensor will have a great significance in many industrial applications and provide a neoteric, rapid, and accurate optical measurement method in micro-displacement.