Basic Concept

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 the costs of optical fibre sensor. They 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 operatins. Two major types exist: an intensity based and an interferometric based. The intensity based sensors require simple electronics. The interferometric based type requires advanced signal processing and has an 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 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.