Optical fiber sensor system design utilizing the field programmable gate array

This paper presents the design of a system that is aimed to provide a flexible, portable and low cost solution for optical fiber based sensor systems. The field programmable gate array (FPGA) provides the digital logic to implement the system and ability to reconfigure the system operation. It aims to support different optical fiber sensing requirements by the ability to reconfigure the digital circuitry used. It is therefore a hardware configured alternative to a software programmed processor based approach. The work discussed in this paper focuses on the architecture of the FPGA based system with additional circuitry to implement the light source using a light emitting diode (LED), sensor signal sampling using a photodiode and the digital functions implemented using the Xilinx Artix-7 FPGA. The system also includes serial communications to an external computer that allows the system to be used as part of a larger sensor network. In this paper, system control and sensor data visualization on a personal computer (PC) is undertaken using the Python open source programming language.

I. Introduction

Optical fiber sensor (OFS) systems use a fiber optic cable as the medium for sensor signal propagation between the sensor itself and the sensor electronics using light rather than electrical signals. A range of different optical fiber sensors have been studied (e.g., [1], [2]) and different design implementations have been proposed and developed. Applications of such sensors have included environmental [3] and medical [4]. OFS systems are composed of several parts which include the sensor itself along with a light source, light receiver, electronic circuits for sensor interfacing, results analysis and communications (readout of sensor data) functions. The inert nature of the optical fiber is valuable to perform in-situ measurements in harsh environments whilst the sensitive electronic circuits can be shielded at appropriate location and remotely from the environment being sensed. Fig. 1 shows the simplified architecture of a typical OFS system. Here, the light source provides the required optical signal to apply to the sensor via the optical fiber cable. The sensor, either a separate device connected to the fiber or actually the fiber itself, modifies the light signal and the result is captured by the optical receiver. The source and receiver are then connected to a computing device that provides the interface, communications and data analysis. Fig. 1

Simplified architecture of an OFS system.