Using spread-spectrum in a high-capacity fiber-optic local network

A local fiber-optic communications network capable of supporting tens of thousands of simultaneous users, each requiring on the order of 10-Mb/s continuous data rate, is proposed. The system uses coherent optical techniques to fully utilize the vast bandwidth offered by single-mode optical fibers (tens of thousands of GHz) a spread-spectrum technique is used to circumvent the problem caused by the instabilities of present-day semiconductor lasers. These include difficulty in reliably setting a laser's frequency with an accuracy better than several hundred GHz, and phase noise in the laser output, which would otherwise result in excessive amounts of interference among the various users. The method proposed is a variant of code-division multiple access (CDMA) that is called random-carrier (RC) CDMA, since the modulated carriers can be assumed to be completely randomly placed in the available optical band.<
>