A Parallel Multiplexed Temperature Sensor System Using Bragg-Grating-Based Fiber Lasers

A parallel multiplexed temperature sensor scheme using a Bragg grating-based fiber laser approach has been developed and evaluated. Multiple laser cavities were formed as the active gain media of the system using a common broadband chirped fiber Bragg grating (CFBG) and several normal FBGs, which were used as optical feedback elements, in conjunction with different lengths of erbium-doped fibers (EDFs). These gain media were externally pumped by light from a 1480-nm laser diode (LD) through a 1480-nm 1$times$4 splitter. Normal FBGs were used as the wavelength-selective and sensing elements of the laser system. Simultaneous laser action at three different wavelengths corresponding to channels 1, 3, and 4, respectively, was obtained using this scheme. The temperature was measured over the range from room temperature (27$^circhboxC$) to a maximum of 540$^circhboxC$, which shows the potential of the scheme for quasi-distributed sensor applications.

I. Introduction

Fiber-Optic laser-based sensor systems have shown considerable advantages over passive optical sensors using spontaneous emission due to the higher optical power delivered at the sensor head and the narrower linewidth associated with the measurand [1]. The additional advantage is their wavelength-encoded measurement information (compared to other intensity-based sensing schemes), thus having self-referencing and potential multiplexing capabilities. In many reported fiber Bragg grating (FBG)-based sensor schemes, the output power reflected from the narrowband FBG-based passive sensor systems is often quite weak, this leading to a poor signal-to-noise ratio (SNR) and reducing the potential accuracy of the detection system, thereby creating limitations on the number of FBGs that may be interrogated for multisensor applications. Several multiplexed fiber laser-based sensor systems have been developed for strain sensing applications [2]–[5]. Similarly, parallel multiplexed fiber laser-based sensor systems are also important for a range of simultaneous measurements including temperature (demonstrated in this paper), humidity [6], or chemical parameters [7] using coated FBGs. Murphy et al. [8] have reported a silica fiber extrinsic Fabry-Pérot (FP) strain sensor to measure temperatures up to 975 °C. Alavie et al. [9] have reported a serial multiplexed sensor system where each laser cavity was formed using an FBG and a broadband mirror, measuring the temperature from 20 °C to 160 °C. Kaddu et al. [10] have reported multiplexed optical fiber FP sensor systems to measure temperature and strain over the ranges from 20 °C to 70 °C and from 0 to , respectively. Peng et al. [11] have reported an FBG-based temperature sensor system using a fiber laser to measure temperature over the range from 0 to 40 °C.A Raman fiber laser probe has also been developed [12] for long-distance remote temperature sensing applications, typically reported for use over the temperature range from 30 to 100 °C. Recently, fiber laser-based sensor systems have been developed to measure temperatures up to 500 °C.in a single cavity configuration using a chirped FBG (CFBG) and a normal FBG in [13] and [14]. Additionally, some of the commercial manufacturing technologies are also available for temperature measurement applications [15], [16].