A tunable polarization-independent comb filter based on high-order mode fiber

et al. 2019

IEEE Sensors J.

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This paper studied the relationship between the temperature/strain wavelength sensitivity of a fiber optic in-line Mach-Zehnder Interferometer (MZI) sensor and the wavelength separation of the measured wavelength to the critical wavelength (CWL) in a CWL-existed interference spectrum formed by interference between LP01 and LP02 modes. The in-line MZI fiber optic sensor has been constructed by splicing a section of specially designed few-mode fiber (FMF), which support LP01 and LP02 modes propagating in the fiber, between two pieces of single mode fiber. The propagation constant difference, Δβ, between the LP01 and LP02 modes, changes non-monotonously with wavelength and reaches a maximum at the CWL. As a result, in sensor operation, peaks on the different sides of the CWL then shift in opposite directions, and the associated temperature/strain sensitivities increase significantly when the measured wavelength points become close to the CWL, from both sides of the CWL. A theoretical analysis carried out has predicted that with this specified FMF sensor approach, the temperature/strain wavelength sensitivities are governed by the wavelength difference between the measured wavelength and the CWL. This conclusion was seen to agree well with the experimental results obtained. Combining the wavelength shifts of the peaks and the CWL in the transmission spectrum of the SFS structure, this study has shown that this approach forms the basis of effective designs of high sensitivity sensors for multi-parameter detection and offering a large measurement range to satisfy the requirements needed for better industrial measurements.

Section: Temperature Sensitivies Of Peaksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Studies on Temperature and Strain Sensitivities of a Few-Mode Critical Wavelength Fiber Optic Sensor

et al. 2019

IEEE Sensors J.

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“…close to the CWL, whether on the left or right side [14]. Previous studies by some of the authors [12][13][14][15] indicate that an exclusive value of the CWL may exist in the transmission spectrum of a SFS structure employing a specially designed FMF, which supports only two modes, LP01 and LP02 [16] and the interference between these two modes may produce a stable and polarization-independent transmission spectrum [17]. The peaks closest to the CWL on each side exhibit maximum strain/temperature sensitivities and they shift in opposite directions, with different strain/temperature sensitivities.…”

mentioning

confidence: 99%

Simultaneous Measurement of Strain and Temperature With a Few-Mode Fiber-Based Sensor

et al. 2018

J. Lightwave Technol.

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This paper proposes a novel detection scheme simultaneously to measure strain and temperature, based on a simple to construct device using a section of a specially designed few mode fiber (FMF). The parameters and index profile of the FMF used as the key sensor element are such that the fiber supports only the LP01 and LP02 modes. The propagation constant difference between LP01 and LP02 modes, Δβ, has a maximum corresponding to the critical wavelength (CWL) in the fiber transmission spectrum. Because the two peaks located closest to the CWL from both sides, Left Peak 1 and Right Peak 1, shift in opposite directions, with different sensitivities under axial strain and temperature variations, the FMF device is capable of measuring the strain and temperature simultaneously. A theoretical analysis has been carried out as part of the design process and the experimental results obtained are found to agree well with the theoretical predictions. The characteristics of this sensor scheme is discussed in light of other competing approaches to simultaneous temperature and strain monitoring and is found to show advantages which suit several practical applications including compactness, ease of fabrication and implementation, relatively high sensitivities and low cost.

“…This is different from the conventional few mode fiber approach, in which several higher order core modes (e.g., LP11) are supported. Here the DMF used in this sensor structure is superior in its polarization behavior [24] and it is stable, even with the variation of the contaminants experienced in the underwater environment. As reported in our previous work [25], the propagation constant difference between the LP01 and the LP02 modes, Δβ, has a maximum corresponding to the critical wavelength (CWL) in the transmission spectrum.…”

Section: Introductionmentioning

confidence: 99%

Underwater Pressure and Temperature Sensor Based on a Special Dual-Mode Optical Fiber

Lei

et al. 2020

IEEE Access

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In this paper, an all fiber optic sensor based on a Mach-Zehnder interferometer (MZI) has been proposed for the simultaneous measurement of underwater pressure and temperature, utilizing a dualmode fiber (DMF) which has been specially designed, and supporting only the LP01 and LP02 modes propagating in the fiber. In this design, an in-line MZI sensor that was constructed by splicing a DMF between two pieces of single mode fibers, shows a critical wavelength (CWL) which exists in the transmission spectrum of the LP01-LP02 mode interference. Since the two peaks, located closest to the CWL (and from both lower and higher wavelengths), shift in opposite directions and show different sensitivities under temperature and water pressure variations, the DMF-MZI sensor is capable of measuring both the water pressure and the temperature simultaneously. The CWL-based interference spectrum is stable with the variation of underwater salinity or impurities seen around the fiber surface and independent of the polarization states of the transmission light. As a result, in the operation of the DMF-MZI sensor, underwater pressure and temperature sensitivities increase significantly, when the peak wavelengths are close to that of the CWL. A theoretical analysis has been developed and used to predict that the sensitivities of this specific DMF-MZI structure which can be further improved by increasing the physical length of the DMF and by adjusting the position of the first left/right peak to be closer to the critical wavelength. This co-located, multi-parameter all-fiber sensor developed in this way and showing relatively high sensitivity is easy to implement in the underwater environment. It does not require a complex shell design and the peaks nearest to a CWL are convenient, allowing easy identification and detection, thereby providing a large measurement range to satisfy the requirements of practical marine and fresh water measurements. INDEX TERMS fiber sensor, temperature, pressure, dual mode fiber, Mach-Zehnder interferometer.