Hetero-core fiber optic binary sensors based on pulse loss change with tandem connection for security network

A hetero-core fiber optic sensor has the capability of combining sensing and communication signals in a single fiber transmission line and has many advantages for environmental information monitoring such as home-security. This is because its cost-effectiveness due to its temperature independency and intensity based measurement. We have developed a hetero-core fiber optic binary sensor that can be connected in tandem to detect the number of doors and windows that are opened or closed. In this paper, we propose a new improved method for using hetero-core fiber optic binary sensors, which are regarded as binary switches, with tandem connection. A unique pulse loss change enables the connected switch system to identify the states of the switches. As a result, the total optical loss in the transmission line is reduced. Therefore, the number of binary switches connected in tandem can be increased on a single transmission line. The unique pulse peaks in loss can be induced by the flat spring flipping and, in addition, achieved by means of adjusting the position of the flat spring inside the binary switch module. The typical pulse peak and insertion loss of each binary switch are estimated to be changed with ranging from 0.13 to 0.75 dB in positive, from −0.47 to −0.03 dB in negative sides and from 2.23 to 2.61 dB, respectively, with the position of the hetero-core portion within the binary switch module. Two binary switches are successfully demonstrated tandem connected monitoring along a single transmission line by the optical loss change. Results of our experiments show that the number of binary switches connected in tandem can be increased significantly on a single transmission line.