Temperature Sensing in Seawater Based on Microfiber Knot Resonator

Abstract

Ocean internal-wave phenomena occur with the variation in seawater vertical temperature, and most internal-wave detections are dependent on the measurement of seawater vertical temperature. A seawater temperature sensor based on a microfiber knot resonator (MKR) is designed theoretically and demonstrated experimentally in this paper. Especially, the dependences of sensing sensitivity on fiber diameter and probing wavelength are studied. Calculated results show that sensing sensitivity increases with the increasing microfiber diameter with the range of 2.30–3.91 μm and increases with the increasing probing wavelength, which reach good agreement with results obtained by experiments. By choosing the appropriate parameters, the maximum sensitivity measured can reach to be 22.81 pm/°C. The seawater temperature sensor demonstrated here shows advantages of small size, high sensitivity, easy fabrication, and easy integration with fiber systems, which may offer a new optical method to detect temperature of seawater or ocean internal-wave phenomenon and offer valuable reference for assembling micro sensors used for other parameters related to seawater, such as salinity, refractive index, concentration of NO3− and so on.

A Review of Microfiber-Based Temperature Sensors

“…Cascaded KRs were used to demonstrate high-precision and simultaneous multi-point temperature sensing [ 101 ]. A seawater temperature sensor based on a KR was demonstrated in [ 102 ]. Results show that sensing sensitivity increases with the increasing MF diameter from 2.30 μm to 3.91 μm, which was attributed to the larger overlap with seawater associated with MFs with smaller diameters.…”

Salinity sensing based on microfiber knot resonator

“…Compared to the above approaches, optical sensors based on microfibers have attracted more and more attention due to their advantages of smaller size, higher sensitivity, faster response, lower cost and simpler fabrication, which have been widely used in physical [11][12][13][14] and biochemical sensing fields [15,16]. As a typical structure of microfiber sensor, microfiber knot resonator (MKR) has been proved sensitive to the surroundings and been successfully used in refractive index (RI) [17][18][19], humidity [20,21], temperature [22,23], magnetic field [24], electric current [25] and UV [26] sensing. Recently, seawater salinity sensing based on microfiber loop resonator has been proposed and modeling on the performance of the salinity sensor has been reported, which proved to be a new optical method to measure seawater salinity with high sensitivity, low detection limit and miniaturized sizes [27].…”

Water Temperature and Salinity Measurement Using Frequency Comb

“…However, the premise of the experiment is that the dye concentration and laser intensity should be constant and stable, which is hard to satisfy. In recent years, optical fibers [18][19][20][21][22] are widely used in temperature and salinity sensing. However, this type of fiber is not appropriate to be applied in harsh circumstances.…”