ABSTRACT
We propose a Vernier effect-based sensor for temperature and salinity measurements. This sensor utilizes the correlation speckle pattern generated by spatial multimode interference and has undergone testing to validate its effectiveness. The speckle demodulation method is used to solve the problem of inconsistent envelope measurement when tracking with different upper and lower envelopes. The device consists of two Fabry Perot interferometers (FPIs) created by connecting hole core fiber (HCF) and erbium-doped fiber (EDF) in series. The speckle image produced by the interferometers is analyzed using the Zero means normalized cross-correlation (ZNCC) technique. The ZNCC value demonstrates a linear relationship with salinity and temperature, allowing for the measurement of these parameters. The sensor exhibits a temperature detection sensitivity of -0.0224 /°C and a salinity detection sensitivity of -0.0439/%. The sensor offers several advantageous features, including its compact size, low-cost manufacturing, high sensitivity, stability, and convenient reflection measurements. These characteristics make it a valuable tool for various applications. The proposed Vernier effect-based temperature and salinity sensor shows great potential for simultaneous monitoring and measurement of temperature and salinity in environments such as marine settings or industrial processes where accurate control of these parameters is crucial.
ABSTRACT
It is still a challenge to realize the absolute optical path difference (OPD) demodulation of multi-interference systems with a narrow spectral interval and small OPD interval. In this paper, an iterative normalized cross-correlation algorithm is firstly proposed for demodulating the multiple absolute OPDs of a dual-interference system and applied to optical fiber sensing system. By constructing a template function in combined form, the optimal solutions of its components and OPDs are solved iteratively based on the reconstruction matrix method and cross-correlation algorithm, respectively. The simulation and experiment show that the demodulation accuracies near the OPDs of 560 µm and 660 µm are both up to 5â nm in different spectral intervals from 45 to 80â nm. The simulation results show that all demodulation precisions at the spectral interval of 55â nm do not exceed 4â nm when the OPD changes in the range of 650-670 µm. Besides, the experimental verification shows the temperature accuracy (0.125 °C) with 95% confidence of T-distribution is very close to the control accuracy (0.1 °C). The proposed algorithm can improve the multiplexing capability of optical fiber sensor system and reduce its cost.
ABSTRACT
A surface plasmon resonance (SPR) temperature sensor on the basis of depressed double cladding fiber (DDCF) is theoretically proposed and experimentally demonstrated for the first time. Simulation analysis implies that the SPR fiber optic structure consisting of a multimode fiber (MMF) inserted into an 8 mm long DDCF is highly sensitive to the refractive index (RI) of the surrounding environment, owing to their mismatched cores, large discrepancy in cladding diameters, and the depressed inner cladding in DDCF. The experimental results further verify that the highest RI sensitivity is 7002 nm/RIU established with a 50nm Au coated DDCF-SPR sensor. Additionally, the temperature sensitivity reaches up to -2.27 nm/°C within a wide working temperature range of -30 to 330 °C by combining polydimethylsiloxane (PDMS) film as the temperature sensitive material with DDCF-Au architecture. The integrated PDMS, Au and DDCF temperature sensor possesses high performance in terms of sensing capability and physical construction, opening a route to their potential applications in other types of sensors.
