Abstract:
Mining of precious metals and construction rocks has grown tremendously in Kenya and
across the globe. It is a significant source of employment for Kenyans, playing a key role
in reducing poverty and dependency rates. Although it acts as a source of livelihood to
many, it poses high risks including deaths owing to mine collapse, inhalation of poisonous
gases and rock bursts among others. This study aims at developing a fiber optical sensor
(FOS) for strain, stress and tensional force measurement. This was achieved by
experimental work. A laboratory test-bed was built where by the Fiber Under Test was
subjected to strain/stress/tension as power and polarization were monitored. The
transmission performance of a distributed feedback (DFB), wave division multiplexing
(WDM) and Mach-Zehnder modulator (MZM) laser sources over various fiber links was
investigated to enhance maximum coverage of the risk potential area. A 10 Gbps pseudo
random bit stream (PBRS) error free transmission of 75 km was achieved on an MZM
source while the DFB and WDM source managed to transmit up to 50 km. The effect of
mechanical disturbance/stress on power and states of polarization (SOPs) of a signal
transmitted through an optical fiber was investigated both in a linear and coiled fiber
orientation. Four fiber types namely; G652 Corning, G655 Corning, G655 OFS and PMF
Corning were considered. Power fluctuations and SOPs were monitored using the power
meter and polarization analyzer respectively when a fiber section was subjected to
mechanical stress. It was noted that as loading was done gradually there was a significant
decrease in power. The power loss was established after loading the fibers with 18 kg at
different times so as to establish their sensitivities kg-1
. The achieved states of polarization
were analyzed offline by digital signal processing (DSP) so as to establish the SOP speeds.
This was enabled by the use of MATLAB software. The optimal laser-fiber combination
for the design was MZM and G655 OFS, with a strain sensitivity of 0.024 dB/kg and SOP
speed of 7.29 0
/s. To trigger the alarm, the threshold values were set for the designed sensor.
The thresholds for power change and polarization fluctuation were set at 0.2 dB and 1000
respectively. It is through this automation that the designed FOS is expected to give an early
alert of the change in soil profile of mines, enabling communication between the miners
and the monitors. This will facilitate appropriate emergency response and safety of miners.
