Mode Coupling Effects in Graded-Index Optical Fibers

Abstract

Mode coupling theory is applied to the study of multimode optical fibers with graded-index cores. For coupling caused by random bends in the waveguide axis, the results predict the dependence of the induced losses on the fiber's characteristics. The impulse response is determined for fibers with random bends having several different power spectra. The results are used to predict the transmitted power, the delay time, and the rms pulse width in fibers with graded-index cores.

Calculation of the frequency response and bandwidth in low numerical aperture step-index plastic optical fiber using time-dependent power flow equation

“…is, as it is stated, also mode-dependent (Olshansky, 1975), but mode-independent coupling constant D has been used frequently by other authors ( (Gloge, 1973), (Drljaca et al, 2009)…”

Influence of core diameter on the 3-dB bandwidth of graded-index optical fibers

“…Each mode propagates at its own velocity resulting from its particular propagation constant. From the WKB analysis the modal propagation constant was approximately derived as [12] (2) where is the principal mode number and is the total number of mode groups given by (3) The principal mode number (or mode group number) appearing in (2) is defined as , in which the parameters and are referred to as radial and azimuthal mode number, respectively. Physically, and have the meaning that they count the number of maximum intensities that may appear in the radial and azimuthal direction in the field intensities of a given mode.…”

“…This appears to be a general result within the weak guidance rule ( ), which a posteriori demonstrates the validity of our assumptions. Another comment that should be made from (12) to (14) is that for a fiber operated at a zero material dispersion wavelength, the chromatic contribution to bandwidth is not necessarily negligible because of the presence of the dispersion slope. Therefore, this term cannot systematically be ignored.…”

“…So far, different factors have clearly been identified to influence the information-carrying capacity, namely, the material dispersion (in combination with the spectrum of the exciting source) [6], [36], [7], the launching conditions [8], [9], as well as the mode-dependent characteristics (i.e., delay [6], [36] attenuation [10], and coupling-coefficient [10]- [12]). Unfortunately, the achievements, so far accomplished, are not quite complete to enable precise bandwidth prediction if an arbitrary operating condition is to be considered.…”

“…But because this theory treated only the particular case of uniform overfilled launching (EOFL), and additionally neglects the differential mode attenuation (DMA) as well as the mode-conversion, it needs reconsideration. The analysis of the mode-conversion was given in [12], but it ignores the DMA and no longer associates the contribution of material dispersion. Consequently, these results can efficiently be applied only at long enough transmission length under fiber operation at a zero width wavelength region.…”