Signal Transmission of Multichannel Fiber-optic Sensors in Wavelength-division Multiplexing Technology

The article proves the possibility of signal transmission of multichannel fiber-optic polarization sensors via an optical single-mode route, with using polarization-division and wavelength-division multiplexing techniques. Fiber-optic polarization sensors can be placed in dangerous environments with the high possibility of explosion, with chemical vapours and at all places where it is necessary to have lightweight, inertness and non-electric elements for monitoring temperature changes. Polarization-division multiplexing, operating at one wavelength, multiplies the volume of transmitted data due to the orthogonality of signals. This technique allows transmission of the sensor's reaction, but single-mode optical route negatively affects these signals by its polarization non-maintaining properties. Signal polarization is randomly changed in the end, which causes incorrect polarization demultiplexing. This article solves the problem by connecting a polarization controller at the end and deals with the influence of wavelength-division multiplexing techniques for future utilization. Wavelength 1550.12 nm was used for power-supply of the sensor and wavelengths 1556.56 nm, 1555.75 nm and 1554.94 nm were used for proof of independence of wavelength-division multiplexing. The circuit was tested in a laboratory with a constant temperature of 24 °C by using a container of water at 0 °C, 48 °C, and pendulum swinging with a bob cooled to 0 °C.

I. Introduction

The use of optical fibers is nowadays widespread throughout the world. Fibers are used in communication systems, especially as data transmission medium. But it is not necessary to restrict the usage to only communication purposes, because different types of fibers can be used for sensing purposes as well. Polarization fiber-optic sensors are capable to react to many external influences such as stress, temperature changes, vibration [1] and many others, so they can help control conditions in industrial infrastructure [2] and rock missives [3]. The sensor is also capable of reacting to big temperature changes, which is described in the article [4]. But our research is devoted to monitoring small temperature changes in the ambient environment and using the sensor as the monitoring element in security systems. Physical principles and phenomena are described in the article [5]. Sensors advantages are also non-electricity, inertness to its surroundings, light weight, and simple structure, so this type of sensor can be placed in dangerous environments with a high risk of explosion, in gas reservoirs, in ammunition depots, or in the medical industry for controlling purposes.