Surface-Plasmon-Resonance-Based Optical Fiber Curvature Sensor with Temperature Compensation by Means of Dual Modulation Method

Highly sensitive SPR curvature sensor based on graded-index fiber

At present, fiber curvature sensors based on surface plasmon resonance (SPR) are mostly of the multimode fiber core type or cladding type. These types have many SPR modes, resulting that the sensitivity cannot be adjusted and is difficult to improve. In this Letter, a highly sensitive SPR curvature sensor based on graded-index fiber is proposed. The light-injecting fiber is eccentrically connected with the graded-index fiber to inject single-mode light. Due to the self-focusing effect, the light beam propagates in the graded-index multimode fiber with a cosine trajectory, and the cosine beam contacts the flat grooved sensing region fabricated on the graded-index fiber to generate SPR. Due to the single transmission mode of the proposed fiber SPR sensor, the curvature sensing sensitivity is greatly improved. By changing the light injection position of the graded-index multimode fiber, the sensitivity can be adjusted. The proposed curvature sensing probe has a high sensitivity and can identify the bending direction. When bending in the X direction, the sensitivity reaches 5.62 nm/m^-1, and when bending in the - X direction, the sensitivity reaches 4.75 nm/m^-1, which provides a new scheme for highly sensitive and directionally identifiable curvature measurement.

Research Advances on Fiber-Optic SPR Sensors with Temperature Self-Compensation

The fiber-optic surface plasmon resonance sensor has very promising applications in environmental monitoring, biochemical sensing, and medical diagnosis, due to the superiority of high sensitivity and novel label-free microstructure. However, the influence of ambient temperature is inevitable in practical sensing applications, and even the higher the sensitivity, the greater the influence. Therefore, how to eliminate temperature interference in the sensing process has become one of the hot issues of this research field in recent years, and some accomplishments have been achieved. This paper mainly reviews the research results on temperature self-compensating fiber-optic surface plasmon sensors. Firstly, it introduces the mechanism of a temperature self-compensating fiber-optic surface plasmon resonance sensor. Then, the latest development of temperature self-compensated sensor is reviewed from the perspective of various fiber-optic sensing structures. Finally, this paper discusses the most recent applications and development prospects of temperature self-compensated fiber-optic surface plasmon resonance sensors.

Fiber SPR two-dimensional micro displacement sensor based on the coaxial double waveguide with a conical structure

Fiber SPR micro displacement sensor cannot be used for two-dimensional displacement sensing at present. In this paper, we proposed and demonstrated a fiber SPR two-dimensional micro displacement sensor based on the coaxial double waveguide with a conical structure. The coaxial double waveguide is fused into a cone as the light injection fiber, and two different forms of outgoing light fields can be obtained through two cores of the fiber. The horn shaped light field emitted by the ring core of the coaxial double waveguide can cooperate with the sensing fiber to realize the micro displacement sensing in the x-axis direction. And the straight beam emitted by the middle core of the coaxial double waveguide can cooperate with the sensing fiber to realize the micro displacement sensing in the y-axis direction. Through simulation analysis and experimental test, its average wavelength sensitivity and light intensity sensitivity of the x-axis displacement are 0.0537nm/µm and 0.000124a.u./µm, respectively. And that of the y-axis displacement are 0.315nm/µm and 0.00277a.u./µm, respectively. The proposed fiber sensor realizes the two-dimensional displacement sensing based on SPR, which can be widely used in the fields of two-dimensional micro displacement measurement and two-dimensional position precision positioning.

Single-mode fiber curvature sensor based on SPR

A fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index measurement, but there is less research on curvature measurement. In this paper, a single-mode fiber curvature sensor based on SPR is designed and fabricated. By employing bending, the transmitted light in the fiber core leaks into the cladding. A 50 nm gold film is coated outside the cladding, and the evanescent field of the cladding after bending contacts the gold film to cause SPR. When the curvature changes, the coupled cladding mode and intensity are different; that is, the SPR incident angle and evanescent field intensity are different, so as to realize the dual parameters of SPR resonance wavelength and depth of the resonance valley changing with curvature. By experiments, the influence of different cutoff wavelengths of single-mode fiber on the performance of the sensor is studied. The testing results indicate that with the decrease in cutoff wavelength of the single-mode fiber, the valley depth sensitivity of the sensor increases, and the half height width (FWHM) decreases. When the cutoff wavelength of the single-mode fiber is 630 nm, the valley depth sensitivity of the sensor is 0.0088a.u/m^-1, the wavelength sensitivity is 0.26nm/m^-1, and the average FWHM is only 21 nm. The proposed single-mode fiber curvature sensor based on SPR has a narrow FWHM and an opening threshold. It can also realize no opening threshold by introducing a coreless fiber, which provides a new solution, to the best of our knowledge, for the diversified detection of fiber SPR sensors.

Recent Advances in Plasmonic Sensor-Based Fiber Optic Probes for Biological Applications

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field.