A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900 nm corresponds to PDMS refractive index at 20 °C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4 nm/RIU and −2.850 nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.

Simultaneous measurement of refractive index and temperature using a SPR-based fiber optic sensor

Surface plasmon resonance has established itself as an immensely acclaimed and influential optical sensing tool with quintessential applications in life sciences, environmental monitoring, clinical diagnostics, pharmaceutical developments and ensuring food safety. The implementation of sensing principle of surface plasmon resonance employing an optical fiber as a substrate has concomitantly resulted in the evolution of fiber optic surface plasmon resonance as an exceptionally lucrative scaffold for chemical and biosensing applications. This perspective article outlines the contemporary studies on fiber optic sensors founded on the sensing architecture of propagating as well as localized surface plasmon resonance. An in-depth review of the prevalent analytical and surface chemical tactics involved in configuring the sensing layer over an optical fiber for the detection of various chemical and biological entities is presented. The involvement of nanomaterials as a strategic approach to enhance the sensor sensitivity is furnished concurrently providing an insight into the diverse geometrical blueprints for designing fiber optic sensing probes. Representative examples from the literature are discussed to appreciate the latest advancements in this potentially valuable research avenue. The article concludes by identifying some of the key challenges and exploring the opportunities for expanding the scope and impact of surface plasmon resonance based fiber optic sensors.

[INVITED] Recent advances in surface plasmon resonance based fiber optic chemical and biosensors utilizing bulk and nanostructures

A new sensing method for simultaneous measurement of seawater temperature and salinity by C-type micro-structured fiber was proposed. The C-type fiber structure formed by removing the outer wall of one pore from a six holes micro-structured fiber, which would bring in birefringence and broke original pattern of degeneracy. By optimizing the parameters of this fiber structure, X polarization and Y polarization of fundamental mode were separate. Therefore, it could be used for double parameter measurement. Besides, gold film coated on the surface of structure to enhance sensing sensitivity by Surface Plasmon Resonance (SPR) principle. In this study, finite element analysis method was used to analyze the spectral transmission characteristics of C-type micro-structured optical fiber. The surface of wedge-shaped defect was contacted with seawater directly to feel salinity; meanwhile, thermo-optic material filled into pores to detect the temperature of seawater. Through model analysis, it was proved that the proposed filling structure could produce two SPR loss valleys, which had different responses to temperature and salinity. Under optimized structure, maximum salinity sensitivity of 1.402 nm/‰ was obtained for X-polarization and maximum temperature sensitivity of −7.609 nm/ °C was obtained for Y polarization, which demonstrated that the designed scheme could not only solve the cross sensitivity problem of two parameters but also achieve high sensitivity. In addition, C-type micro-structured fiber is non-cascade integrated, strong stability, and flexibility in design, which has great potential for sensing applications.

Theoretical analysis of high-sensitive seawater temperature and salinity measurement based on C-type micro-structured fiber

A hydrogel-coated optical fiber surface plasmon resonance (SPR) sensor based on MMF-SMF-MMF structure has been fabricated for pH measurements. When the solutions with difference pH values contacting the sensing probe, the amount of the dissociated carboxylic ions in the hydrogel will change according to the pH value of the solution. This process will modify the volume and refractive index of the hydrogel, which results in a shift of the SPR wavelength. The experimental sensor is able to indicate pH variations in a wide pH range from 1 to 12, and the maximum pH sensitivity of the proposed sensor can reach 13 nm/pH at higher pH region (8–10 pH). The influence of temperature (in the range of 20 °C–40 °C) on SPR wavelength is found to be weak. Further, the sensor possesses remarkable repeatability and excellent stability. Due to the wide measuring range and simple fabrication process, the sensor is promising to be used for the pH measurements.

Smart hydrogel-based optical fiber SPR sensor for pH measurements

A Review of advancements (2007–2017) in plasmonics-based optical fiber sensors

A high sensitivity D-shaped hole double-cladding fiber temperature sensor based on surface plasmon resonance (SPR) is designed and investigated by a full-vector finite element method. Within the D-shaped hole double-cladding fiber, the hollow D-section is coated with gold film and then injected in a high thermo-optic coefficient liquid to realize the high temperature sensitivity for the fiber SPR temperature sensor. The numerical simulation results show that the peaking loss of the D-shaped hole double-cladding fiber SPR is hugely influenced by the distance between the D-shaped hole and fiber core and by the thickness of the gold film, but the temperature sensitivity is almost insensitive to the above parameters. When the thermo-optic coefficient is −2.8×10−4/°C, the thickness of the gold film is 47 nm, and the distance between the D-shaped hole and fiber core is 5 μm, the temperature sensitivity of the D-shaped hole fiber SPR sensor can reach to −3.635  nm/°C.

High sensitivity D -shaped hole fiber temperature sensor based on surface plasmon resonance with liquid filling

A dual-parameter sensor based on a photonic crystal fiber (PCF) concatenated with a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of magnetic field and temperature. Novel magnetic fluids (MF) with different concentration and surfactant are filled in the air holes of PCF. The magnetic field measurement property is only determined by PCF, while the temperature is co-determined by PCF and FBG. Experimental results show that the wavelength shift has a good linearity corresponding with temperature and magnetic field. Temperature and magnetic field sensitivity are proportional to concentration of MF and are affected by different surfactants. For PCF point, when polyethylene glycol is used as a surfactant and the magnetic fluid concentration is equal to 0.15, the highest magnetic field sensitivity is up to 924.63 pm/mT. The proposed sensor has a high sensitivity as well as cross-sensitivity resistance, which provides a promising candidate for dual-channel filtering or multi-parameter measurement applications.

Magnetic field and temperature dual-parameter sensor based on magnetic fluid materials filled photonic crystal fiber

A novel fiber sensor based on surface plasmon resonance (SPR) is designed to realize the simultaneous measurement of temperature and refractive index (RI). In order to obtain the SPR effect both in x- and y-polarized directions, the fiber is double-side polished and covered with gold and silver on horizontal and vertical polished surfaces, respectively. The numerical simulation results demonstrate that the temperature sensitivities of x- and y-polarized loss spectrums are 0.1371 and 0.04736 nm/°C, respectively. The RI sensitivities of x- and y-polarized loss spectrums are 561.4286 and 457.1429 nm/RIU, respectively. Therefore, the variation of temperature and RI can be measured simultaneously by monitoring the resonant wavelength shifts of x- and y-polarized loss spectrums.

Double-Side Polished Fiber SPR Sensor for Simultaneous Temperature and Refractive Index Measurement

A tunable polarization beam splitter (PBS) is proposed based on a dual-core photonic crystal fiber (DCPCF). The DCPCF is filled with magnetic fluids in the air holes, whose refractive index varies with the magnetic field strength. The two polarized modes are separated into the two cores at the output ports in a magnetic-free condition. When magnetic field is applied, the output intensities of the two polarized modes would fluctuate. The polarized modes can be ported out with arbitrary proportion by adjusting the magnetic field intensity. Moreover, the polarized mode would be completely converted at some magnetic field strength. The properties of the DCPCF are investigated by the finite element method (FEM), including mode-conversion magnetic field strength, extinction ratio, fabrication tolerance of the PBS, and the performance of PBS at various temperatures. The numerical results show that at 1550-nm wavelength, the length of the tunable PBS is 8.13 mm. The polarized mode converts at a magnetic intensity of 25 mT with a high extinction ratio greater than −100 dB. In addition, the tunable PBS sustains a fabrication tolerance of at least 0.5% and works well at temperatures in the range of 0–55 °C by adjusting the magnetic field strength.

A Tunable Polarization Beam Splitter Based on Magnetic Fluids-Filled Dual-Core Photonic Crystal Fiber

An ultrashort polarization beam splitter (PBS) is proposed based on liquid-filled dual-core photonic crystal fiber (DCPCF). The two cores of DCPCF are formed by two side elliptical holes and a central circular hole in the horizontal direction. The properties of the PBS are analyzed first with a non-filled DCPCF by the finite element method. Then, the performances of the PBS are discussed when the DCPCF is filled with liquids in the central hole. As a result, an ultrashort PBS is realized with a length of 78 μm when glycerol solution with a concentration of 37% is filled in the central hole. In this case, an extinction ratio of 87 dB is obtained at 1550 nm wavelength. The significantly short device shows a great advantage when being integrated in ultra-compact optical systems.

Jianshuai Wang

Papers

High sensitivity D -shaped hole fiber temperature sensor based on surface plasmon resonance with liquid filling

Magnetic field and temperature dual-parameter sensor based on magnetic fluid materials filled photonic crystal fiber

Double-Side Polished Fiber SPR Sensor for Simultaneous Temperature and Refractive Index Measurement

A Tunable Polarization Beam Splitter Based on Magnetic Fluids-Filled Dual-Core Photonic Crystal Fiber

Ultrashort polarization beam splitter based on liquid-filled dual-core photonic crystal fiber.