equivalent step index method - JOURNALOF LIGHTWAVE...

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JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 11, NO. 10, OCTOBER 1993 1523 Equivalent Step-Index-Fiber Method for Multicladding Fibers Yan Fang Abstract-In this paper, an equivalent step-index-fiber method (ESFM) has been extended to multicladding fibers. Upon defining the refractive-index prome for the multicladding preform, the transmission parameters, especially the cutoff wavelength of the Sber drawn from the preform can be predicted directly before fiber-drawing, saving time, and energy. Comparison between the theory and results from experimental fibers shows an accuracy of 5% in predicted cutoff wavelengths. nv optimum bea line ............. ...~~ ....... .. nu .. . ?: f I. INTRODUC~~ON N general, if the refractive-index profile of a single-mode I step-index fiber preform is measured and plotted, the cutoff wavelength of the fiber drawn from the preform with standard fiber diameter (125 pm) can be accurately determined. How- ever, if the fiber investigated is a graded-core fiber, the same problem can be settled by using the equivalent stepindex fiber method [ 11 - [4]. Consequently, the method is developed to fibers with cladding index variation such as fibers with raised inner cladding, fibers with raised inner cladding and bamer layer, fibers with depressed inner cladding, and so on [5]-[8]. In recent years, with the development and application of the HB special fibers (double-cladding elliptical fiber, panda fiber and bow-tie fiber), the fiber with multicladding structure have brought people wide interests. Therefore, if the fiber diameter or cutoff wavelength can not be calculated in advance, the fiber-drawing process will not be carried out. So, the only method one can do for finally deterinining the parameter mentioned above should be done by “trial and error” between fiber-drawing and cutoff-wavelength measuring procedures. In that case, much vigor and financial resources are wasted. Thus, it is necessary to extend the equivalent step-index fiber method into multicladding fibers in order to determine the fiber-drawing diameter or cutoff wavelength in advance while avoiding extra heavy and complicated task. Besides this, the method extended is required to meet the needs of engineering application, to guarantee enough accuracy and to calculate conveniently, which is the object of this paper.
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This note was uploaded on 03/01/2010 for the course ELECTRONIC 12345 taught by Professor Xyz during the Summer '10 term at Punjab Engineering College.

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equivalent step index method - JOURNALOF LIGHTWAVE...

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