Abstract: A frequency division multiplexing (FDM) node used in optical communications networks provides add-drop multiplexing (ADM) functionality between optical high-speed channels and electrical low-speed channels. The FDM node includes a high-speed system and an ADM crosspoint. The high-speed system converts between an optical high-speed channel and its constituent electrical low-speed channels through the use of frequency division multiplexing and preferably also QAM modulation. The ADM crosspoint couples incoming low-speed channels to outgoing low-speed channels, thus implementing the ADM functionality for the FDM node.

Abstract: Return-to-zero (RZ) formatted data is recovered and transmitted using non-return-to-zero (NRZ) devices. A NRZ clock and data recovery device (CDR) interprets the clock rate of a RZ formatted signal as twice its actual clock rate. Due to this interpretation, extra zeroes will be inserted in the data stream. The extra zeroes introduced by the NRZ interpretation of the data are discarded, and the interpreted clock rate is divided resulting in preserving the values of the original data stream of the RZ formatted signal. A NRZ encoded data stream at a specific clock rate is processed so that when the data stream is transmitted to a recipient expecting RZ formatted data, the recipient interprets the correct data.

Abstract: A frequency division multiplexing (FDM) node used in optical communications networks provides add-drop multiplexing (ADM) functionality between optical high-speed channels and electrical low-speed channels. The FDM node includes a high-speed system and an ADM crosspoint. The high-speed system converts between an optical high-speed channel and its constituent electrical low-speed channels through the use of frequency division multiplexing and preferably also QAM modulation. The ADM crosspoint couples incoming low-speed channels to outgoing low-speed channels, thus implementing the ADM functionality for the FDM node.

Abstract: A frequency division multiplexing (FDM) node used in optical communications networks provides add-drop multiplexing (ADM) functionality between optical high-speed channels, and low-speed tributaries. The FDM node includes a high-speed system and an ADM crosspoint. The high-speed system converts between an optical high-speed channel and its constituent electrical, low-speed channels through the use of frequency division multiplexing. The ADM crosspoint couples any incoming low-speed channels and any incoming tributaries to any outgoing low-speed channels and tributaries, thus implementing the ADM functionality for the FDM node.

Abstract: In an optical communication network, a variable rate or non-uniform input rate signal is converted to a “pseudo” signal comprising a uniform or standard data rate for the optical communication system. At the receiver, the original non-uniform rate signal is recovered.

Abstract: Overhead information is transmitted from a first node to a second node in an optical fiber communications system using a separate frequency band. A control channel containing the overhead information is frequency division multiplexed with electrical low-speed channels to form an electrical high-speed channel, which is converted from electrical to optical form to form an optical high-speed channel. The optical high-speed channel is transmitted over the optical fiber to the second node. In one embodiment, the control channel has a narrow bandwidth and/or is located at lower frequencies than the electrical low-speed channels, thus making the control channel more robust to impairments in the optical fiber.

Abstract: Return-to-zero (RZ) formatted data is recovered and transmitted using non-return-to-zero (NRZ) devices. A NRZ clock and data recovery device (CDR) interprets the clock rate of a RZ formatted signal as twice its actual clock rate. Due to this interpretation, extra zeroes will be inserted in the data stream. The extra zeroes introduced by the NRZ interpretation of the data are discarded, and the interpreted clock rate is divided resulting in preserving the values of the original data stream of the RZ formatted signal. A NRZ encoded data stream at a specific clock rate is processed so that when the data stream is transmitted to a recipient expecting RZ formatted data, the recipient interprets the correct data.