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A novel tunable erbium-doped fiber ring laser (EDFRL) using a cascaded-chirped long period fiber grating (C-CLPG) as a wavelength selection element is proposed. The oscillation wavelength is determined by the one of the spectral peaks of the C-CLPG used, and the oscillation output provides a high signal to noise (S/N) ratio detection and a highly sensitive measurement of the temperature due to its high power and narrow spectral output. In the experiment, it is confirmed that the wavelength of the output shifts in accordance with the temperature-induced spectral shift of the C-CLPG transmittance spectrum and the temperature sensitivity is obtained to be ∼-0.2 nm/°C within the wavelength range of 1567.30 ∼ 1575.78 nm. The oscillation wavelength range is to be limited depending on the fringe spacing of the channeled spectrum of C-CLPG, which limits the temperature measurement range, but a data processing approach to solve this problem is additionally proposed and its availability is also presented.

An EDF-sigma laser for a strain sensor is devised using a double-pass cascaded-chirped LPG with a polarization compensation effect. In the experiment, the stable measurements and sensor operations with suppression of polarization-induced fluctuations are demonstrated.

A novel tunable Erbium-doped fiber ring laser (EDFRL) with a cascaded-chirped long-period fiber grating (C-CLPG) as a wavelength selection filter is proposed from the viewpoint of the sensor use, in which a variable optical attenuator (VOA) is employed as an intracavity loss modulator to change the oscillation wavelength region so that the resultant tuning wavelength range is widened. In the demonstrative experiment for temperature measurements, oscillation over the wavelength range of 12.85 nm (1557.62~1570.47 nm), which is more than three times range of the previously presented laser and is equivalent to 64 °C in terms of temperature change, was achieved, while a single-wavelength oscillation was maintained. In addition, a practical technique for realizing a temperature measurement by combining with the VOA control is also discussed.

A novel laser strain sensor based on a sigma-cavity configuration is developed, in which a double-pass cascaded-chirped long period fiber grating with a Faraday rotator mirror is employed in the sigma-branch as a strain-sensitive wavelength filter. © 2021 The Author(s)

In this paper we have investigated optical frequency-shift sensitivities of the transmittance channeled spectra of cascaded-chirped long period fiber gratings (C-CLPGs) to the applied strain and temperature change from the viewpoint of the sensor use. In the experiment, several kinds of C-CLPGs have been fabricated by changing the cascaded distance between CLPGs and the strain- or temperature-induced spectral shifts for three different order of the cladding modes are measured simultaneously by use of a cross-correlation technique which provides highly precise determination of the spectral shift. As a result, it is confirmed that the frequency-shift sensitivities of the C-CLPGs to the strain and temperature are larger with the higher order of cladding mode, while the dependences for the temperature sensitivity is much less than that for the strain. In addition, the dependences for the cascaded distance are also investigated.

We present a multipoint vibration sensing system using fiber Fabry-Perot interferometers consisting of low-reflective fiber Bragg gratings (FBG-FPI) and a current-modulated laser diode. The lasing wavelength of a laser diode can be modulated by changing the injection current. Therefore, high-speed current modulation makes possible to achieve high-speed wavelength sweep exceeding 100 kHz. Using a current modulated laser diode as the source for interrogation of FBG-FPI sensor array, high-speed multipoint vibration measurement can be realized.

We have investigated optical frequency-shift sensitivity of the transmittance channeled spectrum of cascaded-chirped long period fiber gratings (C-CLPGs) to an applied strain from the viewpoint of the sensor use. In the experiment, eight different kinds of C-CLPGs have been fabricated by changing the cascaded distance for two types of CLPGs and the strain-induced spectral shifts are measured by use of a cross-correlation technique which provides highly precise determination of the spectral shift. As a result, it is confirmed that the higher frequency-shift sensitivities of the C-CLPGs to the strain obtain with the higher order of cladding mode.

A novel tunable and switchable Erbium-doped fiber ring laser (EDFRL) is constructed from the viewpoint of sensor applications. The laser consists of a cascaded-chirped long period fiber grating (C-CLPG) and a variable optical attenuator (VOA). The oscillation wavelength is used for sensing a measurand. As a result, wavelength range selecting over about 1557.57 ~ 1570.68 nm with the tuning range within ~5.6 nm is demonstrated, and the sensitivity of ~ −0.22 nm/°C is recorded.

A fiber Bragg grating (FBG)-based multi-point sensing system for the simultaneous measurement of strain and temperature is proposed, with a Fabry-Perot interferometer (FPI) consisting of low reflective FBGs inscribed inside a polarization-maintaining (PM) fiber is introduced as a sensor head. A multi-point sensing method with high dynamic range and short measurement time can be realized by analyzing the reflection spectrum of low reflective FBG-FPIs, and a simultaneous measurement of strain and temperature using two orthogonal polarization modes is enabled by the high birefringence of a PM fiber. An experimental demonstration of multi-point measurement utilizing the proposed system is reported.