This study discusses the development of a simple and cost-effective natural environment monitoring system constructed
using a hetero-core spliced fiber optic SPR sensor by which simultaneous data communications and sensing functions
can be achieved on the same line. In order to verify the data communication and sensing function of sensor in an
extensive-area of 2000 meters, laboratory experiments employ a SPR sensor with 50-3-50μm core type hetero-core
structure which is coated with gold (Au) at 25nm and tantalum pentoxide (Ta2O5) at 60nm. The proposed system has
been developed such that the data communication and sensing function are successfully demonstrated.
We aim at composing a novel remote monitoring system of the water level and soil humidity under the natural
environment with a hetero-core spliced fiber optic chemical sensor inserted into an existing communication line. This
paper demonstrates the fusion characteristics of an optical communications and a humidity sensing by means of a
hetero-core spliced fiber optic sensor that has been highly-vaunted from the practical perspective. However, this
humidity sensor leaks light and attenuates the optical signal power of a communication wavelength by intent on sensing
use. From the communications standpoint, this may lead to decrease intensity of optical signals sent to the receiver and
increase a bit error. In other words, there may be a trade-off relationship between communications quality and measuring
accuracy. We have proved the possibility of the co-existence of communication signals and measuring functions by
finding out the effect of humidity sensing on the communications is the optical loss and modal dispersion.
We have developed a fiber optic network combining communication and measurement using a hetero-core spliced fiber
optic sensor inserted into an existing communication line with a wavelength-division multiplexing (WDM) analogy.
Switch modules using the proposed sensor were inserted into an actual communication line and the influence on the
communication of the switch modules was examined. The communication link broke when approximately 21 dB is
inflicted a loss on the communication light of 1.31-μm wavelength by the switch modules, the WDM filters and a fiber-optic
coupler in the communication line. Because the amount of loss is the maximum allowable for a communication
instrument, the proposed sensor has been clarified to have only the loss characteristic. If the loss is controlled to within
tolerance for the communication wavelength, a measurement function can be added to a communication line by a
comparatively simple method. It was also shown that a combined optical fiber network can be achieved, where the
intensity of the communication light is measured. The combined method is highly cost effective, because it is not
necessary to have a separate light source for measurement, WDM filters, and other elements in the communication line.
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