Abstract: A method of automatic gain control for use in an optical amplification device comprising a variable optical attenuator and an optical amplifier connected downstream of the optical attenuator includes the steps of measuring the power at the input of the amplification device, determining the number of channels at the input of the amplification device as a function of the measured power knowing the attenuation value of a span upstream of the device, and modifying the gain of the amplifier as a function of the number of channels determined in this way.

Abstract: The invention relates to a method of providing protected transmission between two nodes (1, 2) of a wavelength-division multiplexed network. The invention proposes to have loss of signal over the main line (3) detected by a node, and then to interrupt transmission of data over the main line by said node. By interrupting transmission, it is thus possible to force loss of signal on the other node: the other node then switches its transmission of protected data over to the backup line (4). Interrupting the transmission of data can be achieved by switching off the laser of said node. The invention also describes a method of testing with a view to re-using the main line (3). The invention provides means for switching the protected data over to the backup path that are particularly simple in terms of protocol.

Abstract: An optical device that measures and dynamically compensates power loss variations in an optical fiber based on supervisory signals. An injector injects supervisory signals having a predefined optical power downstream of the fiber entry end and a detector extracts the supervisory signals at the exit end of the fiber to detect their optical power. Based on the detected optical power and the predefined optical power, the optical power loss of the supervisory signals in the fiber is determined. The optical power loss and the nominal power loss in the fiber are compared to determine a variation in the power loss in the optical fiber. A controller coupled to the detector and to the exit end of the fiber modifies the power of primary signals delivered by the exit end of the fiber as a function of the detected variation in power loss.

Abstract: An optical system is dedicated to dynamically measuring power loss in an optical fiber (FO) having a first end (E1) and a second end (E2) respectively adapted to receive and to send primary optical signals. The system comprises injection means (3) adapted to inject supervisory signals into the second end (E2) of the optical fiber (FO) at a selected optical power and detection means (5) adapted to extract the supervisory signals at the first end (E1) of the optical fiber (FO) in order to determine their optical power and to deduce therefrom and from the selected optical power primary information representative of the optical power loss of the supervisory signals in the optical fiber (FO), and where applicable to compare the primary information to a value representative of a nominal power loss in the optical fiber (FO) in order to supply secondary information representative of a variation of the power loss in the optical fiber.

Abstract: An optical system dynamically measures power loss in an optical fiber (2) having an entry end (E) adapted to receive optical signals and an exit end (S) adapted to deliver the signals. The system comprises modulation means (4) upstream from the entry end (E) and adapted to modulate the amplitude of the optical signals with a low-frequency modulation signal having a modulation index inversely proportional to the input power (Pe) of the optical signals, and detection means (7) downstream from the exit end (S) and adapted to extract from the modulated optical signals primary information representative of the output amplitude of the modulation signal and to deduce from the primary information secondary information representative of a variation in the power loss in the fiber.

Abstract: It is described a WDM optical communication method based on the use of a plurality of wavelength specific channels defining a spectrum for the transmission of optical signals through an optical communication network. These optical signals will be coupled at a sender side into a common optical fiber of said network, to be amplified by optical amplifiers along said network. The power of optical signals per channel will be tuned at said sender side to build an uniform—flat—spectrum throughout said optical communication network.

Abstract: A method of automatic gain control for use in an optical amplification device comprising a variable optical attenuator and an optical amplifier connected downstream of the optical attenuator includes the steps of measuring the power at the input of the amplification device, determining the number of channels at the input of the amplification device as a function of the measured power knowing the attenuation value of a span upstream of the device, and modifying the gain of the amplifier as a function of the number of channels determined in this way.

Abstract: An optical system dynamically measures power loss in an optical fiber (2) having an entry end (E) adapted to receive optical signals and an exit end (S) adapted to deliver the signals. The system comprises modulation means (4) upstream from the entry end (E) and adapted to modulate the amplitude of the optical signals with a low-frequency modulation signal having a modulation index inversely proportional to the input power (Pe) of the optical signals, and detection means (7) downstream from the exit end (S) and adapted to extract from the modulated optical signals primary information representative of the output amplitude of the modulation signal and to deduce from the primary information secondary information representative of a variation in the power loss in the fiber.

Abstract: The optical device is for measuring and dynamically compensating power loss variations in an optical fiber (2). It includes injector means (4) adapted to inject supervisory signals having a chosen optical power downstream of the fiber entry end (E) and detector means (5) adapted to extract the supervisory signals at the exit end (S) of the fiber (2), to determine their optical power, to deduce therefrom and from said chosen optical power primary information representative of the optical power loss of the supervisory signals in the fiber, and to compare said primary information and a value representative of a nominal power loss in the fiber to deliver secondary information representative of a variation in the power loss in the optical fiber (2). Control means (11) coupled to the detector means (5) and to the exit end (S) of the fiber (2) modify the power of the primary signals delivered by the exit end of the fiber (2) as a function of the detected variation in power loss.

Abstract: A current limiter circuit receiving an input current having a non-zero DC component whose value lies in a wide range of current values, and delivering a limited output current whose value lies in a narrower range of current values. The limiter comprises a series connection of a first asymmetrical conductivity element followed by a second asymmetrical conductivity element which is followed in turn by a resistive element, the series connection extending between two poles of a voltage source so that a bias current flows through the asymmetrical conductivity elements and makes them conductive. The input current is applied to the common point between the two asymmetrical conductivity elements and the current-limited output is taken from the common point between the second asymmetrical conductivity element and the resistive element.