Abstract: A modular cross connect system for optical telecommunication networks has the optical unit divided in at least two main bodies with one section for connection comprising the collimators and a main commutation section with MEMS devices. The first section is a fixed part while the second section is a readily removable section. The two sections face each other through a window and, in the first section, optics are provided for steering all or part of the optical signals from and to the main MEMS unit to a MEMS standby or protection plane to allow replacement of the main MEMS unit without interrupting service.

Abstract: A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems with the compensator comprising a cascade of adjustable optical devices through which passes an optical signal to be compensated and comprising the steps of computing the Stokes parameters S0, S1, S2, S3 in a number Q of different frequencies of the signal output from the compensator, producing control signals for parameters of at least some of said adjustable optical devices so as to make virtually constant said Stokes parameters computed at different frequencies.

Abstract: A coding scheme of order n for digital communications, in particular optical communication, for obtaining a coded signal x(t) which represents binary data which are constituted by sequences of information bits {uk} with rate T, the scheme having N=2n states, named ?i, for i=1, 2, . . . , N, and comprising predetermined elementary signals si(t) which are combined in the signal x(t). According to the scheme, if, at the time t=kT, the coding is in a state ?m of the N states, the arrival of the information bit uk of the sequence {uk} forces a transition to the state ?q of the N states and the selection of the elementary signal si(t) as x(t), where q and i are given by the following equations: di=m?1 mod 2; d0=d1+ukmod 2; y=2(m?1)+d0; q=(r mod N)+1; and i=r+1 if r<N, or i=r?2N otherwise.

Abstract: In a communications system, especially an SDH DCN system in which most network elements (NEs) function as intermediate systems (ISs) rather than end systems (ESs), it is made possible to reduce the constraints on the DCN topology posed by the IS-IS routing protocol by configuring the gateway element (GNE) and the NEs directly connected to it in such a way that the non-gateway NEs appear as ESs to the rest of the system. This is achieved by setting up on each of the digital communication channels (DCCs) of the GNE manual end-system adjacencies for all the NEs reachable through that DCC; setting the “external domain” attribute of these DCCs to TRUE and setting the same attributes of the corresponding DCCs of those NEs which are immediate neighbors of the GNE likewise TRUE; and supplying those DCCs with length-zero reachable address prefixes (RAPs) and configuring the neighbor NEs as level 2 Intermediate Systems.

Abstract: A Raman amplifier for amplifying WDM radiation propagating along an optical fiber, the WDM radiation comprising a plurality of radiation components each having a selected waveband, comprises a plurality of optical radiation generators operable to generate pump radiation of a selected wavelength and power, the radiation being coupled into the fiber to optically amplify the WDM radiation. The generators are wavelength tuneable, and the power of the radiation components of the WDM radiation is measured after it has propagated along the fiber and has been amplified. The wavelength and power of operation of the generators are controlled in dependence upon the measured powers such as to make the measured powers substantially equal in magnitude and of a selected magnitude.

Abstract: A device wavelength division multiplex optical transmission system has the wavelengths of the optical carriers arranged so as to reduce the effect of in-band crosstalk which results from unwanted side bands to the carriers. Possible wavelengths are placed on an equally spaced wavelength grid, and the transmitted channels are organized into groups of three each of which is placed on four adjacent grid positions, one of which is unused. Adjacent groups are spaced apart by two or more vacant grid positions.

Abstract: A method of detecting polarization mode dispersion (PMD) indicative parameters of an optical fiber link comprising at least one transmission channel in which is transmitted a first wideband optical signal with a bandwidth divided into sub-bands. For each sub-band is produced a second reference optical signal with which to find a third optical signal by superposition. For each of the third signals are calculated first parameters considered indicative of the PMD thereof, and with the first parameters of all the sub-bands are calculated second parameters considered indicative of the PMD of the first wideband signal. The method can be used as part of a PMD compensation method for a transmission system employing the parameters calculated for feedback piloting of a PMD compensator.

Abstract: To perform routing in telecommunications networks it is proposed to partition the network, create a reduced graph on the partitions in a preprocessing step in which a dual graph of the network is constructed and the graph is reduced using connections determined by the characteristics of the apparatuses. The routing is then performed on the converted graph. Graph updating techniques to keep it coherent are also described. Each time a routing is requested for a type of traffic not yet considered, a reduced graph for that traffic is constructed while canceling the arch of the original graph which does not support that traffic. For each type of traffic only the reduced graph developed by graph partitioning as described above is kept in memory with considerable resource savings.

Abstract: An optical assembly has a number of optical fibers which terminate at connectors which connect to short lengths of optical fibers which connect, in turn, to an optical back plane mounted within a housing. The connectors are withdrawn from the housing for inspection. A plurality of movable guides is provided for the short fibers to determine a number of optical paths which remain of constant length as the connectors are withdrawn from the housing.

Abstract: Data transmitted on optical fiber over long distances is subject to the introduction of errors at the receiving end, caused by distortions and alterations of the original data. Raising the transmission power to increase the level of signals at the receiving end also increases errors due to non-linear characteristics of the fiber. The invention optimizes launch power by assessing error rates due to amplified spontaneous emissions and due to four wave mixing, so that signal to noise ratios due to these causes exceed threshold levels while enabling launch power to be maximized.

Abstract: An equipment assembly includes a housing and a sub-unit each having a large array of electrical contacts which mate when the sub-unit is inserted into the housing. The sub-unit has a plurality of threaded bolts which extend through the sub-unit to engage with cooperating threaded nuts secured to the housing. The plurality of bolts is linked together mechanically, so that all bolts engage simultaneously with their respective nuts, and draw the sub-unit into engagement with the housing as the bolts are rotated.