By Jack Koscinski, General Optronics Corporation
Fiber optic supertrunks have already demonstrated the capability of transporting 8-16 video channels/wavelength over path distances greater than 20 km (repeaterless). These systems have traditionally utilized wideband FM as the RF modulation technique. Wideband FM provides the dual benefits of 1) signal to noise improvement and 2) high immunity to intermodulation distortion.
While the performance of these fiber optic (FO) links is impressive, they are also relatively costly (>$5K/channel not including FO cable). Additionally, the use of FM modulation requires a potential modulation conversion (AM/FM/AM) at both ends of the FO link with the attendant costs for AM modulators and demodulators. For.many broadband transportation applicatlons these costs are prohibitive and have prevented the widespread usage of FO links.
The ability to use multi-channel VSB/ AM transmission is highly desirable. The ideal scenario would be to accept a broadband signal (bridger output etc.) and transport these signals directly over the fiber optics links without any modulation conversion. The scope of this paper reviews the following areas:
- A Multi-channel VSB/AM Fiber Optic System Block Diagram.
- Basic VSB/AM System Considerations.
- Performance of a Multi-channel VSB/AM FO Link.
- Feasibility of Optimizing the mance and Number of Channels on FO Links.