Abstract: A method and system for bandwidth efficient optical transport in radio access networks using radio-over-fiber optical transport may directly transmit radio access signals over an optical fiber by frequency multiplexing multiple parallel streams of digital wireless signals into a serial stream of optical digital subcarrier signals. A radio-over-fiber transceiver to enable efficient optical transport in radio access networks may be implemented on remote radio head and baseband unit equipment as a plug-in digital coherent optics module or as an on-board internally mounted digital coherent optics module.

Abstract: A method for transmitting broadcast and narrowcast services in a system having a headend, a hub connected the headend, and a plurality of nodes connected to the hub. Instead of transmitting the signals directly from the headend to each node, the signals are transmitted from the headend to the hub. The signals transmitted from the headend to the hub include both broadcast services to be transmitted to each node and narrowcast services to be transmitted only to predetermined targeted nodes. The broadcast and narrowcast services are transmitted by optical signal beams operating at different wavelengths. Subscribers can transmit signals to the headend, via each node, on the reverse channel. The reverse channel information from subscribers is combined at each respective node into a single wavelength for each node. The narrowcast services are added at the headend instead of at the hub.

Abstract: A system and method for reducing Raman cross-talk between optical signals having different wavelengths in an optical communications system. Optical signals having wavelengths &lgr;1, &lgr;2, &lgr;3, and &lgr;4, respectively, are launched into an optical fiber at the headend of the system by an optical transmitter. Each wavelength &lgr; is preferably separated from each adjacent wavelength by the same amount, &Dgr;&lgr;. &lgr;1 and &lgr;2 have vertical polarizations and &lgr;3 and &lgr;4 have horizontal polarizations. Because there is no Raman cross-talk between orthogonally polarized optical signals, there will be no Raman cross-talk between &lgr;1 and &lgr;3, between &lgr;2 and &lgr;4, between &lgr;1 and &lgr;4, or between &lgr;2 and &lgr;3. However, there is Raman cross-talk between &lgr;1 and &lgr;2 because each is vertically polarized and also between &lgr;3 and &lgr;4 because each is horizontally polarized.

Abstract: A system for amplifying separate optical signals traveling in a forward path and a reverse path over an optical communications system used for CATV program distribution. A first and second optical circulator, each having a first, second, and third port, are connected to respective opposite sides of a bi-directional amplifier. The first port of the first circulator inputs a first optical signal traveling in the forward path. The second port of the first circulator is coupled to an input/output port of the amplifier. The third port of the first circulator outputs an amplified second signal traveling in the reverse path. The second circulator is similarly connected to the side of the amplifier. A first and second signal/signal WDM coupler, each having a pass port P, an add port A/D, and a common port C, are coupled to the first and second optical circulators, respectively.

Abstract: A distortion circuit for linearizing third-, fifth- and seventh-order distortion components in a non-linear optical communications system includes at least one group of series connected diodes coupled to a common input terminal for receiving a signal source at one end and to an inductor and a capacitor at the other end, a resistance coupled to the common input terminal and a bias source for providing a bias current to the group of series connected diodes. The distortion circuit may be implemented as a predistortion circuit in the headend of the optical communications system or as a postdistortion circuit at the receiving end.