# Characterization of Chromatic Dispersion and  
Refractive Index of Polymer Optical Fibers  
[PERSON]  
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November 2  
In other applications, a detailed knowledge of the dispersion properties is also required. This happens, for instance, in the field of spectroscopy. As an example, POFs, and highly dispersive fibers in general, could be utilized to convert short broadband optical pulses into fast wavelength scans [10].  
There are three principal techniques in the literature to characterize the chromatic dispersion of optical fibers: interferometric, phase-shift, and time-of-flight [11]. Interferometric techniques require precise knowledge of the mechanical components employed in the set-up because slight deviations in the physical dimensions of the interferometer produce significant discrepancies in the measurement results. For this reason, the precision achievable with this method is very high in theory but not as high in practice, so the potential improvement in precision with respect to the other two methods is not so clear. Moreover, this technique is limited to very short fiber lengths. On the other hand, phase-shift techniques can be used with both short and long fiber lengths, but they require tunable light sources of known characteristics, since the phase shifts have to be determined from a sequence of individual wavelengths. A reference signal is usually used to overcome this problem. The precision of this technique depends on the stability of the tunable light sources, so it is not clear that its results are better than those obtainable with the other two techniques. Finally, the time-of-flight technique is comparatively easier to implement, due to the absence of a reference signal, its simplicity, and its speed of execution. Therefore, it is a very suitable technique for the measurement of the dispersion of optical fibers.  
Although there are some works that have characterized the chromatic dispersion and the refractive index of optical fibers by means of these techniques, all of them have focused on glass optical fibers [11; 12; 13; 14; 15]. However, there are only a few works that characterize the dispersive behavior of polymer fibers and, if they do, they get the values from the bulk material or from the fiber preform, instead of from the POF itself [16; 17; 18]. In addition, these works usually require hand-made experimental measurements, apart from some time-consuming data analyses. In contrast, the fibers by themselves serve in our work to characterize the refractive index and the chromatic dispersion of POFs. As a matter of fact, all the characterizations of fiber dispersion in POFs reported in the literature were based on measurements using the preform, but the results in this paper have been obtained from the drawn fiber instead of the perform. For this purpose, the pulse delays are measured by temporally and spectrally resolving propagated pulses at different excitation wavelengths. The measurements, which are based on a time-of-flight approach, have been carried out by using a tunable laser as the excitation source and a Streak Camera as the measuring device. As far as we know, this is the first time that this kind of characterization has been carried out in POFs. Moreover, the measurement system can be widely automated, and the data analysis is straightforward, so the POF samples can be characterized in a very brief period of time.  
This paper is organized as follows. First, the theoretical background is explained. Then, the experimental set-up is described, together with the characteristics of the optical fibers employed. Afterwards, the measuring techniques and the results are shown. Finally, the conclusions are summarized.