Referencing Schemes for Intensity Modulated Optical Fiber Sensor Systems

Abstract

For nearly two decades, intensity modulation has remained as one of the most extensively investigated forms of optical signal modulation for sensing applications [1–10]. The simple reason for the extensive and diversified usage of this modulation scheme is a multitude of potential benefits that include the inherent simplicity, reliability, flexibility and relatively low costs. Although intensity modulated optical fiber sensors have been fabricated in many different designs and with varying degrees of complexity, the essential building blocks of a simple optical fiber sensor system are depicted in figure 5.1. Light from an optical source, such as an LED, is coupled into an optical fiber for transmission to the optical sensor where it can be modulated in accordance with the state of a measurand. When using reflection-mode sensing the modulated optical signal is retroreflected into the same optical fiber for transmission to the photodetector [8]. However, in transmission-mode sensing a second optical fiber is normally used for the transmission of the modulated signal to the photodetector.