Abstract: The network monitoring system comprises a network router with built-in monitoring data gathering. The network router includes channels through which data pass in packets. Each of the packets includes a packet header. The network router additionally includes a header copier and a packet generator. The header copier generates a header copy from the packet header of at least some of the packets. The packet generator receives the header copies and forms monitoring data packets from them. Each monitoring data packet additionally represents temporal data relating to the header copies included in it. A method of obtaining performance data relating to a data transmission network that includes a node passes data through the node in packets. Each of the packets includes a packet header. At least some of the packet headers are copied to obtain respective header copies as monitoring data from which monitoring data packets are formed.

Abstract: A partial optical regenerator for use in high bit-rate optical systems and useful in WDM applications employing soliton transmission. The regenerator essentially comprises a saturable optical element in a main optical path and a resonant optical circuit coupled to the element. A resonant pulse can be generated from an input data pulse in a number of ways. (A) an input data pulse may be coupled directly to the resonant optical circuit before entering the element; (B) the input data pulse may first saturate the element, resulting in the creation of a counter-propagating pulse; (C) the data pulse may pass through the element and be coupled to the resonant optical circuit upon exit. The resonant pulse travels around the resonant circuit and repeatedly returns to the saturable optical element after an integer multiple of the symbol duration or after an odd integer multiple of half the symbol duration.

Abstract: Loss of optical signal is detected in a synchronous communications system by detecting features of a monitor signal occurring at a detection frequency corresponding to the frame rate. Since the frame rate is substantially less than the bit rate, monitoring and detection can be performed at a lower bandwidth than the bit rate. An auto-correlation circuit utilises delays which are an integral multiple of the frame rate and produces a detection value which is compared with a threshold value. Alternatively, detection may be based on a power measurement of a band pass filtered monitor signal by setting the lower bandwidth limit above zero frequency and normalizing the measurement of power relative to an average power measurement. A loss of signal may then be detected by a change in power measurement relative to a threshold and can be used for asynchronous systems as well as synchronous systems.

Abstract: At a receiver a 20 Gbit/s soliton bit stream is demultiplexed into two 10 Gbit/s bit streams using a 2-way splitter, a clock extraction circuit, and a pair of polarization insensitive amplitude modulators exhibiting positive chirp. The outputs of the modulators are fed to detectors via lengths of optical fiber exhibiting normal dispersion thereby producing bit streams with increased mark/space ratio and reduced timing jitter.

Abstract: An add/drop multiplexer/demultiplexer (ADM) for switching, modulating and attenuating optical signals in a fiber optic network employing wavelength division multiplexing (WDM) is disclosed. The ADM is equipped an optical multiplexer for splitting an input WDM signal into individual optical signals, leading to respective 2.times.2 switches. Each switch has another input originating from a plurality of "add lines", and selects one of its inputs to be dropped and the other to continue along a main signal path. The retained signals may be modulated and attenuated prior to being tapped and finally multiplexed together by a WDM multiplexer. The tapped signals are optoelectronically converted and fed back to a controller, preferably a digital signal processor running a software algorithm, which controls the switching, modulation and attenuation.

Abstract: An add/drop multiplexer/demultiplexer (ADM) for switching, modulating and attenuating optical signals in a fiber optic network employing wavelength division multiplexing (WDM) is disclosed. The ADM is equipped an optical multiplexer for splitting an input WDM signal into individual optical signals, leading to respective 2.times.2 switches. Each switch has another input originating from a plurality of "add lines", and selects one of its inputs to be dropped and the other to continue along a main signal path. The retained signals may be modulated and attenuated prior to being tapped and finally multiplexed together by a WDM multiplexer. The tapped signals are optoelectronically converted and fed back to a controller, preferably a digital signal processor running a software algorithm, which controls the switching, modulation and attenuation.

Abstract: An optical transmission system utilizing at a transmitter (100) continuous phase frequency shift keyed modulation of a laser (14) and a coherent heterodyne receiver (200) therefor, the system including at the transmitter means for imposing (18,12) a low frequency modulation on the transmitter optical power and frequency deviation and at the receiver means for extracting (28) from the receiver AGC control signal a replica of the low frequency modulation, means for demodulating (32) the modulated frequency deviation of the received optical signal synchronously with respect to the extracted low frequency signal, means for deriving (34) from the demodulated signal an error signal and a control system responsive to the error signal to control the receiver local oscillator (22) frequency.