This study mainly compares two optimized interrogation techniques for an interferometric fiber-optic surface plasmon resonance (SPR) sensor. For this sensor, both SPR and interference effects are excited in a single fiber structure and they can be applied for dual-parameter measurement. On the other hand, the interference fringe patterns are mixed into the SPR transmission spectra, and the novel interrogation technique should be evaluated. In this study, two optimized interrogation techniques are proposed and their performances are compared. For the first one, the non-linear least square method is used to filter out the interference components and only retain the SPR signal. For the second one, the wavelength-distributed spectra are converted into the spatial frequency-distributed spectra, hence SPR components and the interference components can be discussed individually. The advantages and disadvantages of the two interrogation techniques are discussed thoroughly.
This study proposes a novel fiber-optic interferometer based on the single-mode fiber-no core fiber-single mode fiber structure with the coated polydimethylsiloxane (PDMS). The no core fiber is the key carrier to excite the modal interference, and the PDMS that covers onto the fiber cascade structure is able to enhance the sensor sensitivity and also protect the sensor structure. The experimental results verify that the proposed sensor owns a high temperature sensitivity and the strain sensitivity, and it is particularly suitable for multi-parameter measurements.
This study proposes a novel interferometric fiber optic SPR sensor which is able to realize both the temperature and the strain sensing with high sensitivity. Firstly, it is fabricated by splicing a no core fiber between two single-mode fibers to form the multimode interference structure. Then, half-length of the no core fiber is deposited by the gold film layer to form the classic three-layer SPR sensor. Finally, PDMS is covered onto the whole surface of the no core fiber, which performs as a medium to convert the external temperature changes into its refractive index variations. When compared with the other fiber optic sensors, the proposed sensor realizes the temperature and strain measurements based on two independent sensing mechanisms, particularly speaking, the temperature sensing is realized based on the SPR mechanism, and the strain sensing is realized based on the multimode interference. Hence, its inherent cross-sensitivity can be largely suppressed since the two sensing mechanisms are independent of each other. Besides, the proposed sensor shows both high-temperature sensitivity (1.13 nm/℃) and strain sensitivity (54.1 pm/με), which is suitable for the dual-parameter measurements.
We investigate the Fresnel zone plate (FZP) inscribed on multimode fiber endface using femtosecond laser ablation and its application in sensing. The mode transmission through fiber tips with FZP is investigated both by the beam propagation method theoretically and by measuring the beam images with a charge-coupled device camera experimentally, which show a good agreement. Such devices are tested for surface-enhanced Raman scattering (SERS) using the aqueous solution of rhodamine 6G under a Raman spectroscopy. The experimental results demonstrate that the SERS signal is enhanced benefiting from focal ability of FZP, which is a promising method for the particular biochemical spectra sensing applications.
A simple and compact interferometer for temperature and pressure discrimination is proposed and demonstrated experimentally. It consists of a short section of high-birefringence photonic crystal fiber (Hi-Bi PCF) and a cascaded fiber Bragg grating (FBG). In the Hi-Bi PCF, two orthogonal polarized modes are employed as optical arms to construct, such as a Michelson interferometer. Combined with a cascaded FBG, pressure and temperature measurements are discriminated by a matrix method, and the pressure sensitivity of Hi-Bi PCF is determined to be around 3.65 nm/MPa. The proposed Michelson interferometer is easy-to-fabricate, flexible, and low-cost, which shows great potential in future applications of remote sensing.
The thermo-optic coefficient of standard single mode fiber (SMF) is researched in the temperature range from 20 to 1000 °C by using a fiber-optic intrinsic Fabry-Pérot interferometer. Polynomial fit of the interference fringe shift indicates that the thermo-optic coefficient increases with temperature, and is estimated to reach its peak at ~1144 °C. The error of the temperature measurements is also analyzed when taking the thermo-optic coefficient value as a constant.
Laser pulse width is the limiting factor for high spatial resolution measurement with Raman distributed temperature sensor (RDTS). Typically a 10 ns laser pulse provides a spatial resolution of 1 m. Path delay multiplexing can be used to overcome this limitation. This paper presents formalism for two path delay multiplexing, taking into account the point response function (PRF) of the RDTS.
We propose an ultrasensitive temperature sensor based on an in-line liquid-filled photonic crystal fiber (PCF) Mach-
Zehnder interferometer. It consists of a small piece of index-guiding PCF fully infiltrated by fluid and two standard
single-mode fibers offset spliced with the PCF. Two core modes of LP01 mode and LP11 mode are conveniently utilized
as optical arms to form an in-line Mach-Zehnder-type interferometer. Experimental and theoretical investigation of its
response to temperature confirms that and a high temperature sensitivity up to -0.244nm/(oC-mm) could be realized by
such a compact inline liquid-filled PCF Mach-Zehnder interferometer.
In this paper, we present a novel optical fiber fluorescent temperature sensor based on photonic crystal fiber(PCF) and its
theory of forward stimulated fluorescence emission in PCF. It is realized by liquid filling in hollow-core PCF, the liquid
is of higher temperature coefficient of refractive index than that of silicon, and is mixed with fluorescent material.
Stimulating light and fluorescence propagating in the fiber are in the same direction. Because the band gaps of PCF are
modulated by temperature, besides the sensitivity of fluorescence, the stimulating light passing through the photonic
crystal fiber is also sensitive to temperature. Experiment results and theory modulation show that when PCF length is
shorter than an optimum length, stimulating light in fiber will increase and fluorescence will decline gradually with the
increase of temperature.
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