A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusionspliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA, and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors.

In this paper, a V-shape photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR) effect is proposed. With the full vector finite element method, the V-shape photonic crystal fiber polarization filter is designed, and the coupling characteristics between the core mode and surface plasmon polariton mode are analyzed. The simulation results show that the fiber parameters have significant effects on the shift and strength of the SPR wavelength. Moreover, the losses of the core modes along the Y and X polarization directions are 68904 dB/m and 858 dB/m at the SPR wavelength of 1550 nm, respectively. Finally, the extinction ratio and error-tolerant rate of extinction ratio are also analyzed. The proposed V-shape PCF polarization filter can achieve good filtering effect in the communication band and is easy to integrate with existing optical fiber communication and sensing systems.

Chongxiu (2020) Highly sensitive temperature sensing based on all-solid cladding dual-core photonic crystal fiber filled with the toluene and ethanol. Optics Communications, 477. p. 126357.

In this paper, a hollow-core negative curvature fiber (HC-NCF) with high birefringence is proposed for low refractive index (RI) sensing based on surface plasmon resonance effect. In the design, the cladding region of the HC-NCF is composed of only one ring of eight silica tubes, and two of them are selectively filled with the gold wires. The influences of the gold wires-filled HC-NCF structure parameters on the propagation characteristic are investigated by the finite element method. Moreover, the sensing performances in the low RI range of 1.20–1.34 are evaluated by the traditional confinement loss method and novel birefringence analysis method, respectively. The simulation results show that for the confinement loss method, the obtained maximum sensitivity, resolution, and figure of merit of the gold wires-filled HC-NCF-based sensor are −5700 nm/RIU, 2.63 × 10−5 RIU, and 317 RIU−1, respectively. For the birefringence analysis method, the obtained maximum sensitivity, resolution, and birefringence of the gold wires-filled HC-NCF-based sensor are −6100 nm/RIU, 2.56 × 10−5 RIU, and 1.72 × 10−3, respectively. It is believed that the proposed gold wires-filled HC-NCF-based low RI sensor has important applications in the fields of biochemistry and medicine.

Chongxiu (2020) Design of diamond-shape photonic crystal fiber polarization filter based on surface plasma resonance effect. Chinese Physics B, 29 (3). 034208.