Study On The Transmission Properties Of Polymer Optical Fiber

Plastic optical fibers (POFs) are being considered for high-performance fiber links at very short distances because of their low-cost, robustness and ease of preparation and connection. With the extending application of POFs, to increase the bandwidth of POFs and predict it exactly are of great importance in the practice. To clarify the parameters that affect the bandwidth of POFs helps to choose the raw materials of POFs, to improve the preparation technology and to choose reasonable methods to increase the bandwidth of POFs. The theoretical bandwidth properties of the POFs with different refractive index profiles disagree to some extent with those measured. However, the reason of the disagreement still remains a puzzle. In addition, the precise predicting tool for bandwidth of POFs is still absence at present time. The simulation models developed for glass optical fibers (GOFs) systems some decades ago appear to be invalid in consideration of POFs. In this paper, the factors affecting the bandwidth of POFs with different refractive index profiles were systematically analyzed. A new dispersion model was developed to predict precisely the bandwidth of POFs.Determination of the refractive index profiles of POFs is of great importance in the evaluation of performance, and design, manufacture of the fibers. Two sets of the equipments for measuring the refractive index of POFs were designed and manufactured on the basis of the measuring principle of both the focusing method and the refracted near-field method. The applicability and the advantages and disadvantages of these two methods were analyzed theoretically and verified by experiments.With the help of the far-field pattern of the POFs, the mode coupling effects in both the SI-POF and the GI-POF were systematically analyzed. The coupling length of both the SI-POF and the GI-POF was obtained. As for the SI-POF, the larger the numerical aperture (NA) of the incident rays is, the easier the mode coupling happens. When the NA of the incident rays is 0.1, mode coupling happens after transmitting for 5-10 in; whilst the NA of the incident rays is 0.4, mode coupling happens only after transmitting for 2.5 m. After transmitting for about 30 m, mode coupling finishes and the equilibrium mode distribution is established. As for the GI-POF, mode coupling happens after transmitting for 1 m and finishes after transmitting for 10 in.The effect of different sources to cause mode coupling for the POFs with different refractive index profiles was analyzed by comparison of mode coupling coefficient of both the SI-POF and the GI-POF. It is shown that the mode couplingcoefficient of the SI-POF decreases first with the increasing mode number and then increases quickly when the mode number approaches the cutoff value. As for the GI-POF, the mode coupling coefficient does not change significantly with the increasing mode number. Furthermore, the mode coupling coefficient of SI-POF is 3-4 orders larger than that of the GI-POF. According to the mode coupling theory of POFs, all the mechanisms to cause mode coupling can be represented by a general refractive index perturbation. Coupling between neighboring modes occurs only if the perturbations with a spatial frequency component a> equals to the difference in the propagation constants between these two modes. Assuming that the refractive index profile of POFs meets the power-law, the larger the power index a is, the wider the perturbation period A spectrum of perturbations contributing to the mode coupling, that is, the easier the mode coupling happens. Considering both the probability and the level of the mode coupling, its effect on the properties of the SI-POF is found to be greater than on the GI-POF. Thus, when considering the dispersion property of the SI-POF, the effect of mode coupling cannot be neglected; while for the GI-POF, it is ignorable.The differential mode attenuation (DMA) profile of both the SI-POF and the GI-POF was obtained by the cut-back method. With the increasing mode number, the DMA properties of...