Columbia University

International Business Machines Corporation

Thomas E Stern

Andre E Desblache

Philippe Emmanuel Thirion

George Nicos Ellinas

Georgios Ellinas

A system for accessing a wavelength-division-multiplexed ('WDM'), bidirectional optical fiber ring network having first and second network fibers for carrying WDM signals in opposite directions. The system includes a network node intersecting the first and second fibers of the ring network. The network node is coupled to a network access station through a single pair of access fibers. The network access station has a single array of receiving elements and a single array of transmitting elements. The network node has two wavelengths add drop multiplexers ('WADMs') each having a first input, a second input, a first output and a second output. The WADMs can be each individually set to a bar state or cross state for each one of the wavelengths on the ring network.

System for accessing a wavelength-division-multiplexed bidirectional optical fiber ring network

A system and method of automatic protection switching for a network ( ) which protect against link or node failure. The protection fibers ( ) in the links are pre-arranged into protection cycles so that if a link failure occurs, protection switches in the network nodes ( ) connected in the failed link will switch the working fiber data path onto an alternate path comprised of protection fibers ( ). Data can then be transmitted through the protection cycle around the fault to reach the node on the other side of the failed link. The same protection fibers ( ) can be used to protect a priority connection against center switch failure in a network. The protection switches in each node ( ) which connect working fibers ( ) to protection fibers ( ) are very fast and their settings do not depend on the state of the network.

Automatic protection switching system in a network

A system and method for automatically restoring a network which contains a node with a failed switch. Protection cycles are generated for the network to be restored and cyclegroups are generated from the protection cycles. Each node is provided with protection switches which internally interconnect the input/output ports to connecting links via interconnecting protection fibers. The selection of which internal protection fibers upon which to switch transmitted information onto allows the node to be configured to create merged cyclegroups. Thus if a failure in the central switch is detected, the transmitted information is diverted to a selected protection fiber corresponding to a merged cyclegroup so that the information can be automatically passed around the failed switch via the protection fibers. Each protection switch has associated mapping data which defines which protection fiber will be switched to based upon the input and output link for the transmission that is required to be sent through the node. The system and method applies to non-planar networks as well as planar networks.

Network switch failure restoration

Optical communications systems and methods are disclosed which involve routing optical signals through communications nodes which are controlled such that optical power arriving at input ports is linearly distributed to output ports. Such distribution may be realized by electro-optical, acousto-optical, or electro-mechanical controllable linear divider-combiner devices. Preferred systems including optical fiber links can be designed to make maximum use of physically realizable bandwidth, and to achieve high reliability in case of faults.

Optical communications system and method

A digital phase filter including two decision filters connected in cascade or parallel for minimizing the noise components in a received phase modulated digital signal. The first decision filter cancels the residual noise component representing the phase intercept component and the phase shift component introduced by frequency shift, and the second decision filter minimizes the random noise component representing phase jitter and white noise.

Phase filter for reducing the effects of the noise components altering

The feature of the invention is an adaptive equalizer for modulated carrier transmission systems in which a received signal is subjected to a Hilbert transformation to obtain a second signal having a 90.degree. phase shift for all components. The two signals are then passed through a pair of filters each and the outputs are cross-combined to generate the cartesian coordinate signals of an equalized signal. The coordinate signals are combined in a polar converter and are then decoded to detect the amplitude and phase data components of the received signal. The equalizers are made adaptive by determining at each sampling time, the phase and amplitude errors in the signal and using these errors to modify the coefficients of the equalizing filters. The phase and amplitude errors are recoded into Cartesian coordinates and multiplied by the values of the samples at each tap of the filters to generate four error signals for each tap. A cross combination of these signals is time averaged and used to adjust the corresponding coefficients at the associated taps of the equalizer.

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Riverdale, NY, United States of America

Thomas E Stern