We simulate subcarrier-modulated (SCM) transmission over 300 m of 62.5-µm-core-diameter multimode fiber (MMF) using 1300-nm edge-emitting lasers and 850-nm vertical-cavity surface-emitting lasers (VCSELs) for beam offsets from 0 to 30 µm. We model 81"worst-case"fibers while scaling their bandwidth according to a differential modal delay (DMD) criterion of 2 ns/km for our analysis at a center wavelength of 1300 nm and a DMD of 4 ns/km for analysis at 850 nm, all in order to ensure that the worst 5% of the MMF is being modeled as per the Gigabit Ethernet standard. We consider SCM carrier frequencies from 1 to 9 GHz at data rates of 1.25 and 2.5 Gb/s. Results show that SCM transmission with eye-opening penalties (EOPs) below 3 dB is achievable at 2.5 Gb/s for both edge-emitting lasers and VCSELs. VCSELs are found to be better suited for center launch than offset launch while edge-emitting lasers are better suited for offset launch at radial offsets of 17 to 23 µm. The region of best performance for VCSELs under offset launch is from radial offsets of 17 to 30 µm at carrier frequencies of 0 to 8 GHz, over which we observed an EOP less than 5 dB, while for edge-emitting lasers we observed a region of best performance from 10 to 25 µm over carrier frequencies from 2.5 to 9 GHz. This means that if interchannel crosstalk was ignored, a theoretical aggregate maximum bit rate for VCSELs of \sim 7.5 Gb/s should be achieved for three channels using a single offset launch between 17 and 30 µm for a fiber length of 300 m in order to achieve an EOP less than 5 dB for each channel. For edge-emitting lasers, the theoretical maximum is \sim 5 Gb/s for two channels with each having an EOP of less than 3 dB for transmission over a fiber of length 300 m. We also demonstrate how SCM performance is influenced by the usable average slope (UAS) of the frequency response: a UAS greater than 0.6 x 10-8dB/Hz implies severe deterioration of SCM performance.
© 2005 IEEEPDF Article