With the increasing use of lasers for short reach and high data rate transmissions on MM fibers, the need to characterize the spectra of these narrow coherent sources is also increasing. The impact on data transmission of launching conditions and of interference speckle patterns resulting from high coherence sources launched in MM fibers has been the subject of much study in the last few years. Information and references for such work can be found via the IEEE 802.3 10Gb / s on FDDI - grade MM fiber Study Group web site . However, launching conditions and speckle also affect the measurement of the source spectra when using common monochromator- based Optical Spectrum Analyzers (OSA); such effects are often misunderstood or neglected. Recently in 2003, modifications have been proposed by Tatum , in order to adapt the TIA procedure for spectral characterization of laser diodes, FOTP - 127 , that dates back to 1991. The proposed modifications are aimed at mitigating the effects of unstable spectra observed with coherent sources used in high-speed multimode transmissions like VCSELs. In order to understand these effects and how not taking them into account can result in improper spectral characterization, it is necessary to understand how grating-based scanning-monochromator OSAs work and how their operation is affected by various launching conditions and speckle pattern noise.
© 2005 Optical Society of AmericaPDF Article
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