EDF ring laser using cascaded-chirped long period fiber grating for temperature measurement

Highly sensitive detection of low-concentration sodium chloride solutions based on polymeric nanofilms coated long period fiber grating

Long period fiber gratings (LPFGs) have special advantages in the detection of salt concentrations due to small volume, corrosion resistance and immunity to electromagnetic interference. However, it is very difficult to distinguish low-concentration salt solutions with usual LPFGs owing to the poor sensitivity. In this paper, the detection capability of the LPFG to low-concentration salt solutions was significantly improved by assembling salt-containing poly (diallyldimethylammonium chloride) (PDDA) and salt-containing poly (sodium-p-styrenesulfonate) (PSS). Experimental results showed that, the responsive wavelength range of the LPFG was remarkably broadened in low-concentration salt solutions after assembling nanofilms. The suitable detection range of the PDDA/PSS films coated LPFG for salt concentrations was 0-3%. In such a range, the average refractive index sensitivity and the average salinity sensitivity of the LPFG was as high as 29545.9 nm/RIU and 52.2 nm/% respectively. Compared with the LPFG without nanofilms, the discrimination ability of the PDDA/PSS films coated LPFG to 0-3% salt solutions increased by 568 times. The analysis demonstrated that PDDA and salt in the assembly solutions played a pivotal role in the above effects. The proposed sensor has extensive application prospects in the monitoring of salt concentration in many fields such as seawater, food processing, fermentation process, etc.

Simultaneous Measurement of Temperature and Refractive Index Using Michelson Interferometer Based on Waist-Enlarged Fiber Bitaper

An all-fiber temperature and refractive dual-parameter-sensing Michelson interferometer is designed based on the waist-enlarged bitaper. At 5 mm from the fiber end, the waist-enlarged bitaper is manually spliced and the probe is formed. Since the input light encounters the waist-enlarged bitaper, it will excite high-order modes to transmit in the fiber cladding, and there will be an optical path difference between the basic mode and the higher-order mode. The light transmitted in the core and cladding is reflected upon encountering the fiber end face and the interference occurs due to the optical path difference between basic mode and higher-order mode. Changes in temperature and refractive index at the fiber probe can be detected by monitoring the interference fringes. The refractive response sensitivity is −191.06 dBm/RIU from 1.351 RIU to 1.4027 RIU, and the temperature response sensitivity is 0.12 nm/°C from 11 °C to 98 °C. Through the sensitivity matrix equation, the superimposed refractive index and temperature signals can be effectively demodulated. The sensor has the advantages of multi-parameter measurement, compact structure, low cost, easy fabrication and high reliability.

Loss-Modulation-Based Wavelength-Range Shifting of Tunable EDF Ring Laser with Cascaded-Chirped Long-Period Fiber Grating for Temperature Measurement

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.

Temperature measurement using a multi-wavelength fiber ring laser based on a hybrid gain medium and Sagnac interferometer

In this paper, a multi-wavelength fiber ring laser (MWFRL) based on a hybrid gain medium and Sagnac interferometer (SI) used for temperature measurement has been proposed and experimentally demonstrated. Experiments have been carried out with polarization maintaining fibers (PMF) of different lengths, which are incorporated in the SI as sensing elements. Stable multi-wavelength oscillation at 1560 nm band is successfully achieved with the wavelength instability of ±0.08 nm and the signal-to-noise of 42 dB. The experimental results show that the wavelength change of the MWFRL with temperature variation has a good linear response and the temperature sensitivity of 1.8063 ± 0.00933 nm/^°C is obtained when the length of the PMF is 1.7 m. As the length of PMF increases, the sensitivity can be improved.

Asia-Pacific Optical Sensors Conference: focus issue introduction

This feature issue of Optics Express contains 17 articles expanding on recent advances in optical sensors presented at the eighth Asia-Pacific Optical Sensors Conference (APOS 2019) held in Auckland, New Zealand, from November 19 to 22, 2019. These articles span sensing for real-time positioning, refractive indices, strain, gas, and temperature using a variety of methods including photoacoustic computed tomography, coherent optical frequency-modulated continuous-wave interferometry, enhanced Bragg gratings, and phase-sensitive optical frequency-domain reflectometry.