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.

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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.

In this work, we have constructed an Erbium-doped fiber sigma laser (EDFσL) using a double-pass cascaded-chirped long-period fiber grating (C-CLPG) from the viewpoint of the sensor applications. The double-pass C-CLPG is composed of a C-CLPG and a Faraday rotator mirror (FRM) and works as a comb-like wavelength selection element as well as a sensor section in the sigma-branch of the laser cavity. Further, due to the FRM reflection scheme, the double-pass C-CLPG compensates for birefringence variation in the sigma-branch during the sensing. In the experiment, the sensor section near the C-CLPG is intentionally deformed to induce birefringence variation assuming the external disturbances; nevertheless, it is confirmed that the double-pass C-CLPG provides stable polarization states. Then, under the birefringence variation, it is demonstrated that the proposed EDFσL can achieve a stable oscillation and resultant precise measurements in contrast to the simple EDF ring laser using the singlepass C-CLPG. In addition, for the demonstration of the sensor with external force to the fiber, the oscillation wavelength of EDFσL in response to axial strain is investigated, and a linear response with sensitivity ~0.32 pm/µε is obtained.

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.