SMC - 17 Fibre Optical Sensors

Topics

Interferometric Sensors
Intensity Sensors
Mach-Zehnder Interferometer
Temperature Sensor
Stress and Pressure Sensor
Current Sensor
Computer Control


 

Basic Concept

The past two decades have shown a rapidly growing interest in the field of fibre optic sensors. This increase in interest has been enabled mainly by the progress made in the related fields like opto-electronics and signal processing. The main reasons for the popularity of optical fibre based sensor systems are their small size, light weight and immunity to electromagnetic interference (EMI). Furthermore, the widespread use of optical fibre communication devices in the telecommunication industry has dropped optical fibre sensor cost. Optical fibre sensors have been developed for a variety of applications in industry, medicine, defence and research. Some of these applications include gyroscopes for navigation systems, and for the measurement of various physical and electrical parameters like temperature, pressure, liquid level, acceleration and voltage in mains power plants.
The response of all optical fibre sensors is a change in either polarization, phase, frequency, intensity or a combination of all. Optical fibre sensors can be classified according to their operating. Two major kinds exist: an intensity or an interferometric based type. Intensity based sensors are inherently simple and require simple electronics. Interferometric based types require relatively more advanced signal processing but have extremely high sensitivity.

Experimental Set-up

Within this experiment both types of sensors are applied. For the intensity based ones, a temperature sensor with a GaAs tip is selected. The response light of the sensor is monitored under varying temperatures. For this purpose the fibre sensor is placed into a small oven which is operated by a Peltier’s element in the range of 15° to 60°C. The attached temperature controller provides an accuracy of ± 1 °C
The interferometric based sensor consists of a fibre coil into which tension stress can be manually introduced. The sensor is connected to a Mach-Zehnder interferometer and the fringes are either displayed on an optional oscilloscope or counted with the frequency counter.