ThD1 Phenomenon of modal noise in fiber systems

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

“…The power-law or so-called -profile grading is of particular importance for minimized dispersion and has become commonly used at this purpose. Therefore, the multimode GRIN fibers whose dispersion will be examined here have a refractive index profile defined by for for (1) where offset distance from the core center; free space wavelength of the fiber excitation light; refractive index exponent ; refractive index in the center of the core; refractive index contrast between the core center and the cladding; core radius (i.e., the radius at which the index reaches the cladding value . It is to be noted that the core grading becomes parabolic for and converges to the step-index profile (uniform core) for .…”

“…It is clear that in the short-range applications where many junctions and connections between adjacent sections are often necessary, the multimode version is the most appropriate in consideration of whole system cost. Despite the above advantages, the use of multimode fibers has been resisted for some years by fiber-optic link designers in favor of single-mode fibers (SMF's) since Epworth discovered the potentially catastrophic problem of modal noise [1]. Modal noise in laser-based MMF links was recently more completely addressed and theoretical as well as experimental proofs showed that long-wavelength operation of MMF's is robust to modal noise [2], [3].…”

Measurement of optical fiber bandwidth in the frequency domain

“…or somewhat more generally using the shift theorem (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) This expression is probably most useful where f(t) is symmetrical about T, for then the argument of the integral on the right side of eq (2-20) is real and equal to the transform of h(t-T).…”

Statistical properties of modal noise in fiber–laser systems

“…2 The fact that different speckle patterns exhibit different transmission losses when a connector is inserted between two fibers has been recognized as an important possible source of noise in fiber communication links (modal noise). 3 To assist in understanding the effect quantitatively, a number of investigations of speckle patterns as they appear on a fiber exit face have been reported. Since such speckle patterns are usually time varying at random because of fluctuations both in the exciting source and in the fiber environment, statistical methods have quite naturally been used to advantage in the calculation of the ensemble average (equivalent to time averaging over a long time interval under the ergodicity hypothesis) of some important relevant statistical quantities, such as average power and the variance.…”