Abstract: The invention concerns a method of protecting a label switching path in an MPLS network comprising a plurality of nodes connected by IP links, the said path commencing with an ingress node and ending in an egress node of the said network, passing through a given series of nodes and links in the said network, referred to as elements of the said path. When the said ingress node requires the protection of an element of the path, in a first phase a node on the said path, referred to as the PLR point, upstream of the said element to be protected, determines a back-up path, referred to as the bypass tunnel, joining the path upstream of the said element to be protected at a node, referred to as the PM point, and, in a second phase, network resources are reserved on each of the links of the bypass tunnel in order to back up the said path in the event of failure of the said element.

Abstract: Label switching paths in an MPLS network having plural nodes connected by IP links, each path passing through a series of network nodes and links called “elements of the path,” are protected. An element of a first path is protected by a bypass path starting from a node of the first path upstream and ending in a node of the first path downstream of the element to be protected. A certain number of resources of the network are reserved for the bypass path. An element of a second path is protected by a bypass path of the second path starting from a node of the second path upstream of the second element and ending in a node of the second path downstream of the second element. The bypass path of the second path includes at least one part of the resources reserved for the first bypass path.

Abstract: Light diffraction device using reconfigurable spatial light modulators and the fractional Talbot effect. This device comprises two liquid crystal, electrically addressable spatial light modulators (M1, M2) on a semiconductor substrate and at least one polarizing beam splitter (2), the optical path between the modulators being equal to (2k+1) Z.sub.T /4.sup.n in which k and n are natural integers, n differing from zero, and Z.sub.T is the Talbot distance relative to a biperiodic hologram obtained by means of one of the modulators and at one of the periods equal to double the other, which makes it possible to obtain a reconfigurable hologram having four phase levels. Application to optical telecommunications.