| Comparing with the cable, the plastic optical fibers(POFs) possess a number of advantages, such as high bandwidth and immunity to electromagnetic interference. Thus, in the short range communication and local area networks(LANs) field, the POFs will be gradually employed as the preferred media. At present, many institutions have engaged in the investigations on the manufacture, the communication and the sensor of POF. Lots of remarkable achievements have been obtained. However, little of the research into on-line measurement technique for the POF attenuation coefficient has been reported. It should be pointed that such an on-line measurement technique is significant to the POF manufacture. Hence, the nondestructive light injection and extraction method, which are based on the fiber macrobending and refractive index matching technique, are studied in this dissertation. With these two methods, the light from the source can be injected into the fiber core via the cladding, and the light transmitted in the fiber core can be extracted out of the fiber. With the aid of these two methods, a novel nondestructive method for measuring POF attenuation coefficient is proposed and studied. Note that this method has the potential for realizing on-line measurement technique. In addition, the liquid-level sensor technique based on POF is also investigated. The main research contents and innovative achievements can be listed as follow:(1) A 3D theoretical model which is based on the ray tracing method is proposed to study the light propagation characteristic in the POF. With the help of this model, the nondestructive light injection method, which is based on the fiber macrobending and the refractive index matching technique, is studied. The influence of the bending radius, the original incidence position and angle of the beam, as well as the refractive index of the surrounding medium on the light injection efficiency is investigated. By constructing the experimental platform, the correlated experiment is performed and the theoretical predictions are verified. The maximum light injection efficiency is 30 % in our experiment.(2) Based on the power flow equation and ray tracing method, the evolvement of inner angular power distribution at various locations along the POF is studied theoretically. The power distribution under the steady state distribution(SSD) condition is finally acquired. With the aid of the experimental platform, the power distribution under the SSD condition is observed in the experiment.(3) Based on the power distributions under the SSD condition, the macrobending loss under various bending radii is studied. According to the theoretical results, it can be found that the power loss ratio caused by macrobending loss is invariable provided that the bending radius is a certain value and the light power distribution is close to the SSD condition.(4) By utilizing the nondestructive light injection and extraction method, a novel nondestructive method for measuring the POF attenuation coefficient is proposed. For confirming the feasibility of this method, the light injection module and extraction module are both designed and fabricated, and the correlative experiments are performed. By comparing with the measured results from the cut back method, this nondestructive method is proved to be feasible. The measurement error of this nondestructive method for measuring the POF attenuation coefficient is less than 8 %.(5) A low-cost and simple multipoint liquid level sensor with POF is proposed. The core sensing element consists of a group of POF segments which are aligned coaxially and spaced equally. When the spacing between every two adjacent fiber segments is filled with liquid, the light power will be easier to couple from one segment to the next. This is the operation principle of this intensity-based sensor. The theoretical studied on this sensor is performed with ray tracing method. Then, a series of experiments are performed to examine the theoretical predictions while different liquid are selected as specimens. Moreover, the stability and reproducibility of this sensor are proved to be satisfying according to the experimental results. The response time is less than 1 s.
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