Remote temperature sensing with low-threshold-power using erbium-doped fiber laser

Remote temperature sensing is of significant interest nowadays as it can continuously monitor structures located at tens or hundreds of kilometers away from a central location. With remote sensing, any damage of structures can be detected immediately, thus appropriate action can be taken quickly. Optical fiber laser temperature sensor is one of technologies that can be used for the implementation of remote temperature sensing. Few developments have been reported regarding the use of fiber laser for remote temperature sensing. However, in general they use Raman amplifiers which have relatively high threshold power of higher than 1 W to trigger the laser and this consequently increases the total cost for the implementation. Motivated to achieve a lower threshold power, this thesis presents a remote temperature sensor that utilizes erbium-doped fiber laser (EDFL). The configuration of the laser cavity is linear, comprising a fiber mirror reflector at one end, and the other end is formed by a fiber Bragg grating (FBG) with central wavelength of 1560 nm as the sensor head. A 30 km single mode fiber is placed before the FBG to serve as a transmission channel for remote sensing and erbium-doped fiber amplifier (EDFA) as the gain medium. The EDFA is used because it can operate using low pump power owing to the high gain efficiency of the doped-fibers. Based on this proposed design, experimental results indicate that it has a low threshold pump power of only 12 mW. In comparison to the previous study, the obtained threshold power presents an improvement of 98.8%. In addition, the laser has good stability with power fluctuations of less than 1.2 dB over a 30 minute duration, OSNR of 49 dB and power efficiency, up to 0.07%. With this fiber laser, a temperature sensor with a sensitivity of 10.6 pm/°C is realized for a temperature range from 30 °C to 90 °C which has potential to be applied in the oil and gas field. This sensitivity value is comparable with those obtained with Raman-based fiber lasers, albeit with the requirement of lower threshold pump power. The 98.8% reduction of the threshold power requirement presents opportunity for more cost effective operation in the implementation of remote temperature sensing

Application of Sagnac Interferometer for Temperature Monitoring: Experimental Study

Temperature sensors have been widely used in industries and they have found applications in food processing units, medical devices, chemical handling processes, automotive and agriculture. In the market, there currently exist many varieties of temperature sensors including thermocouples, resistor temperature detectors, infrared sensor, thermistor, thermometer and optical temperature sensor. Of these technologies, optical temperature sensors have the edge in that they are free from electromagnetic interference, low weight, compact, high sensitivity, high signal-to-noise ratio and excellent stability. In this work, optical temperature sensor based on Sagnac interferometer is experimentally demonstrated. The Sagnac interferometer consists of a 3.5 cm polarization maintaining fiber that acts as a sensor head, a polarization controller and a 3 dB coupler. Experiments are carried out in which an amplifier noise being the input light for the Sagnac interferometer and the transmission spectrum of the output light is observed for the output. Throughout the experiment, the sensor head is placed in an oven for temperature variation. Based on the measurements on the output spectrum, it is found that the spectrum dips shifts to the shorter wavelength from 1554.96 nm to 1528.56nm as the temperature is varied from 30 °C to 45 °C. The spectrum dip is found to be inversely proportional to the temperature with the obtained sensitivity of 1.766 nm/°C. This Sagnac-based optical sensor is promising for detecting temperature especially in the harsh environment

Ammonia detection in water with balloon-like plastic optical fiber sensor

This work presents the demonstration of a plastic optical fiber(POF)-based ammonia sensor. The sensor head is formed by bending an unclad fiber optic sensor into a balloon-like structure. The bending radius of the balloon-like bent fiber optic sensor is varied from 1.0 to 2.5 cm. The performance of each sensor is tested using ammonia solution with concentration ranging from 0 to 15 mg l−1 . Results show that the optimized performances of the proposed sensor occur when the bending radius is fixed at 1.5 cm. At this bending radius, the sensor illustrates the sensitivity of − 0.0024 (mg/l) −1with linearity of 0.97 and resolution of − 4.17 mg l−1 . For comparison, the bent sensor is compared to the straight sensor and performances of the former is found to be more superior. In addition, the balloon-like bent sensor is further tested with real water samples. The sensor sensitivity is found to be − 0.0022 (mg/l) −1with linearity of 0.95 and resolution of − 4.54 mg l−1 . The result shows that the sensor has comparable performance in the ammonia detection for both pure ammonia and real water samples. In essence, this balloon-like bent sensor functions without additional coating on the sensor head, making it favorable in terms of the simplicity of the design