A novel, high-resolution, high-speed fiber-optic temperature sensor for oceanographic applications

Abstract

A novel fiber-optic thermometer based on a thick silicon Fabry-Pérot interferometer (FPI) realized on the tip of a cleaved single-mode fiber has been designed and implemented, in order to achieve high resolution and high sampling rate necessary for studying underwater turbulent microstructures. The choice of silicon for its large thermal-optic coefficient and thermal expansion coefficient enables a high sensitivity of 84 pm/°C. A new data processing method, using average wavelength tracking, is proposed to reduce the wavelength noise. The high sensitivity along with the low wavelength noise results in a temperature resolution as high as 0.0009 °C. Furthermore, the good thermal conductivity of silicon endows the proposed sensor with a response time ~ 2 ms, which allows a sampling frequency of 500 Hz. By further optimizing the sensor structure, e.g. size of the silicon FPI, a better temperature resolution and quicker response can be expected. This novel temperature sensor significantly augments underwater sensing capabilities, especially those related to microstructure turbulence mixing process in the ocean. A preliminary experimental demonstration is presented, where the sensor was used to measure the highly dynamic temperature variations induced by a sharp thermo-gradient underwater.

Finely tunable laser based on a bulk silicon wafer for gas sensing applications

“…and T are the refractive index, the reflectivity and the temperature of the silicon wafer respectively; λ is the wavelength and θ is the angle of incidence. Hence, as the FPI cavity length is fixed ( ) d therefore the fringes can be shifted by taking advantage of the temperature dependency of silicon's refractive index [8][9][10][11][12][13]. Thus by varying slightly the refractive index of the wafer a phase shift can be induced, which consequently shifts the overall FPI spectrum.…”

Fast-Response Fiber-Optic FPI Temperature Sensing System Based on Modulated Grating Y-Branch Tunable Laser

“…And condition monitoring systems must have the ability to detect sudden deterioration, so there is sufficient time to intervene appropriately before a major failure [5]. In addition, monitoring and exploration of seawater are becoming increasingly important, the water temperature is one of the fundamental parameters of ocean measurement, and timely and accurate acquisition of the seawater temperature is important for fisheries, disaster warnings, and military security [6][7][8]. The seawater mass boundaries are superimposed on each other, and temperature gradients exist at different levels, so the sensitivity and response time of the sensors must be considered when using the ocean sensors to measure seawater temperatures [9,10].…”