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Input optical excitation and transmission parameters of multimode optical fibers
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Abstrakty
W pracy zaprezentowano model propagacji światła w światłowodach wielomodowych. Na podstawie tego modelu określono zależności teoretyczne podstawowych parametrów transmisyjnych światłowodu (pasmo i tłumienność) od sposobu jego pobudzenia. Zależności te zostały zweryfikowane doświadczalnie przy pomocy opracowanego w tym celu układu pomiarowego składającego się z przestrajanego generatora, analizatora widma oraz konwerterów E/O i O/E. Badania eksperymentalne zostały przeprowadzone zarówno dla światłowodów kwarcowo-polimerowych, jak również dla światłowodów kwarcowych. W pracy wykazano, że wpływ typu pobudzenia światłowodu na jego parametry transmisyjne jest tym istotniejszy im mniejszy jest współczynnik sprzężenia modów. Wskazano również na możliwość selektywnego pobudzania na wejściu różnych grup modów za pomocą przesunięć offsetowych.
The multimode (MM) optical fibers both silica and plastic are used nowadays in LANs for high bit rate data transmission (up to 10 Gbit/s) and distances of a few hundred meters. In this paper, the influence of the launching conditions on the MM fiber attenuation and bandwidth are investigated both theoretically and experimentally for various launch types. The partial differential equation of mode group power diffusion was solved numerically. Also the initial excitation of mode groups was found. The theory indicated that the influence of initial distribution of modes is the greatest when the MM fiber modes are not coupled. Restricted launches such as offset launches usually lead to the bandwidth increase for regular n(r) profiles as compared to the overfilled launches. The reason is that they excite fewer modes than the overfilled launch. The situation is reversed for the profiles with flaws (such as a central dip). Then some launch types may even lead to the bandwidth reduction below the values guaranteed by the manufacturer. In order to verify the theoretical results a series of measurements was taken. The measurement set up consisted of a tuned generator connected to an optical transmitter (with switched wavelengths 650 nm and 780 nm), and an optical receiver coupled to an electrical spectrum analyzer. An opto-mechanical mechanism made it possible to vary the launch offset by moving a position of the end of a single mode patchcord with regard to the MM fiber center. Two SM patchcords were used with diameters of 4-žm (truly monomode) and 9 žm (bimodal- LP01 and LP11 modes were observed experimentally). Two typical GI MM silica fibers with core diameters 50 žm and 62.5 žm, and numerical apertures of 0.2 and 0.275, respectively, were examined, as well as a silica core plastic cladding SI 200 žm fiber. For the 4 žm exciter the modal bandwidth is the greatest for central launches and decreases for offsets, whereas for the 9 žm exciter the bandwidth only slightly depends on offset. Furthermore, no matter the offset, the bandwidth for the 4 žm exciter is always greater than for the 9 žm one.
Wydawca
Czasopismo
Rocznik
Tom
Strony
153--183
Opis fizyczny
Bibliogr. 31 poz., wykr.
Twórcy
autor
- Instytut Telekomunikacji Politechniki Warszawskiej, ul. Nowowiejska 15/19, 00-665 Warszawa
autor
- Instytut Telekomunikacji Politechniki Warszawskiej, ul. Nowowiejska 15/19, 00-665 Warszawa
autor
- Instytut Telekomunikacji Politechniki Warszawskiej, ul. Nowowiejska 15/19, 00-665 Warszawa
Bibliografia
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Typ dokumentu
Bibliografia
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bwmeta1.element.baztech-article-BWA1-0011-0038