MFD measurement - Mode Field Diameter Measurements in...

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Mode Field Diameter Measurements in Single-Mode Optical Fibers M. ARTIGLIA, G. COPPA, P. DI VITA, M. POTENZA, AND A. SHARMA (Invited Puper) Abstract-The role of the mode field diameter in the characterization of single-mode fibers is examined. The most relevant definitions of this parameter are reviewed and a comparative analysis of its measurement methods is performed. Eniphasis is also given to the requirements posed by the new fiber designs, such as the polarization-maintaining struc- tures. I. INTRODUCTION INGLE-MODE fibers (SMF) are being more and more S widely used in optical communication links, as they offer very large bandwidths and low attenuations. After the first generation of SMF, commercially available since 1982, a second generation of “special purpose” fibers has recently followed, such as dispersion-shifted (DS) and dispersion-flattened (DF) fibers [ 11, to meet the issues of large transmission capacity over very long distances. Moreover, to fully exploit the capabilities of coherent transmission, a new family of optical fibers has been in- troduced-the polarization-maintaining (PM) fibers- which are able to preserve the state of polarization of the propagating mode [2]. A simple and effective characteri- zation of the transmission properties of SMF’s has thus become of paramount importance for system designers, suppliers, and customers. After a great deal of theoretical and experimental work it has been found that for circularly symmetric fibers a simple and useful characterization can be made by intro- ducing the mode field diameters (MFD’s), parameters re- lated to the optical field distribution in the fiber. In fact, it has been shown that the MFD’s provide useful infor- mation about the cabling performances of the guide, i.e., possible joint, macrobending, and microbending losses. Moreover, if the MFD spectral behavior is known, the fiber chromatic dispersion, which is related to the band- width, can be obtained and the cutoff wavelength of the first higher order mode can also be determined. However, to obtain PM fibers, noncircular geometries are to be used and therefore a suitable generalization of the MFD concept is needed to characterize this new type Manuscript received January 27. 1989: revised March 3. 1989. M. Artiglia, P. Di Vita, and M. Potenza are with Centro Studi E La- G. Coppa is with the Dipartimento di Energetica. Politecnico di Torino. A. Sharma is with the Department of Physics. lndian Institute of Tech- IEEE Log Number 8928819. boratori Telecomunicazioni (CSELT), Torino, Italy. Torino, Italy. nology Delhi, New Delhi. 110016 India. of structures. This topic is at present a matter of discus- sion both from a theoretical point of view and as far as standardization procedures are concerned. Up to now several different definitions of MFD have been proposed. This work reviews the most meaningful definitions and the corresponding measurement tech- niques together with their applications. The definition of the various MFD’s for circularly symmetric fibers will be discussed first. Then the corresponding measurement techniques will be described. Finally, the generalization
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MFD measurement - Mode Field Diameter Measurements in...

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