Abstract: An optical amplifier comprises an active fiber (1) a pump unit (2) spaced from the active fiber and adapted to give a nominal, continuous pump power in an operational state, and a pump fiber (3) adapted to transfer optical pump power from the pump unit (2) to the active fiber (1). Moreover, in a safety state, the pump unit (2) is adapted to give a pulsed pump power whose mean power is lower than a prescribed safety limit. A method of preventing emission of optical power exceeding a prescribed safety limit on interruption of an optical fiber (3) which transfers pump power from a pump unit (2) to an active fiber (1), comprises changing the mean power of the pump power in response to a signal received from the active fiber (1) so that the mean power assumes a value below said safety limit if said signal is not received, and assumes a nominal value if said signal is received.

Abstract: A method for ensuring that modules (3, 4) to be connected to an apparatus comprising a processor of a specific type, includes providing these modules (3, 4) with a code circuit (6, 7, 13, 21, 24) capable of outputting one or more code words on request. When a module has been connected to the system, the processor of the apparatus reads one or more of the code words from the code circuit (6, 7, 13, 21, 24) of the module, compares the read code word or words with reference code words stored in the apparatus (2), and rejects the module if the read code word or words do not correspond to the reference code words. A large number of different code words are stored in the code circuit (6, 7, 13, 21, 24) of the specific type, and the code circuit is moreover adapted such that a code word can be output correctly only after the lapse of a prefixed period of time, which is considerably longer than a normal output time determined by the implementation of the code circuit, after a previous output of a code word.

Abstract: In a method of setting up connections for the transfer of information in the form of calls between at least two arbitrary subscribers in a teletransmission network (1), it is detected at a subscriber interface on the basis of an identification associated with a given call whether the call is of a first type or of a second type. Then the connection is set up via a first transmission path comprising one or more exchanges (2) in case of calls of the first type, and via a second transmission path bypassing the exchange or exchanges (2) in case of calls of the second type. A detector unit (25; 41), for use in the setting up of connections in such a teletransmission network (1) comprises circuitry (32, 33; 43) for detecting on the basis of an identification associated with a given call whether the call is of the first type or of the second type.

Abstract: In a method of amplitude equalization of a plurality of optical signals having mutually different wavelengths, the optical signals are launched into a first end of an optical fiber (5). The optical signals are amplified, before being launched into the fiber (5), to a level at which at least one of the signals exceeds a stimulated Brillouin scattering (SBS) threshold value (TSBS) characteristic of the fiber, so that part of the signal energy in the fiber is transferred to a Stokes signal propagating in the fiber (5) in a direction opposite to said optical signals. An apparatus for amplitude equalization of a plurality of optical signals having mutually different wavelengths comprises an optical fiber (5) having an input end (6) where said optical signals may be supplied to the fiber, and an output end (10) where said optical signals may be tapped from the fiber after equalization.

Abstract: The invention relates to a method and a modulator circuit for modulating light in a modulator circuit. The modulator circuit comprises a Mach-Zehnder modulator (12) having at least one optical input and at least one optical output, said Mach-Zehnder modulator (12) modulating light, which is fed to the input of the Mach-Zehnder modulator (12) in response to applied electrical modulation signals from a driver circuit (15). According to a method of the invention, the applied modulation signal on the electrodes of the Mach-Zehnder modulator is superimposed by a pilot tone which is thus superimposed by the modulated light emitted by the Mach-Zehnder modulator. In response to the emitted modulated light, an electrical feedback circuit (30) generates bias control signals for the bias circuit (16) and driver control signals for the driver circuit (15) for regulating the bias signal and the driver signal fed to the Mach-Zehnder modulator (12).

Abstract: A method of transmitting data signals via an optical fiber between two network elements (14, 36, 43, 56) in a digital data transmission network comprises using a transmission protocol, wherein, in addition to said data signals, first control and/or monitor signals in the form of overhead signals are transmitted. An optical fiber amplifier (23) is inserted in the optical fiber between the two network elements. Additionally, second control and/or monitor signals in a format corresponding to said overhead signals are transferred between the optical fiber amplifier and at least one of the two network elements. An amplifier unit (22, 48) comprising an optical fiber amplifier (23) is adapted to be inserted in an optical fiber for the transmission of data signals between two network elements (14, 36, 43, 56) in such a data transmission network.

Abstract: An optical amplifier comprises an active fiber (1), a pump unit (2) spaced from the active fiber and adapted to give a nominal, continuous pump power in an operational state, and a pump fiber (3) adapted to transfer optical pump power from the pump unit (2) to the active fiber (1). Moreover, in a safety state, the pump unit (2) is adapted to give a pulsed pump power whose mean power is lower than a prescribed safety limit.

Abstract: A method of transmitting data signals via an optical fiber between two network elements (14, 36; 43, 56) in a digital data transmission network comprises using a transmission protocol, wherein, in addition to said data signals, first control and/or monitor signals in the form of overhead signals are transmitted. An optical fiber amplifier (23) is inserted in the optical fiber between the is two network elements. Additionally, second control and/or monitor signals in a format corresponding to said overhead signals are transferred between the optical fiber amplifier and at least one of the two network elements. An amplifier unit (22; 48) comprising an optical fiber amplifier (23) is adapted to be inserted in an optical fiber for the transmission of data signals between two network elements (14, 36; 43, 56) in such a data transmission network.

Abstract: A digital phase-locked loop (1) has a counter (4) which counts pulses from a voltage controlled oscillator (8). The counter (4) is latched periodically with a period which is determined by an input signal (I) to the counter (4). The latched value is supplied to a compensation unit (5) which deducts a value which approximately corresponds to half the count counted by the counter circuit (4) when the phase lock is locked correctly. The compensated counts are supplied from the output of the compensation unit (5) to an integrator (6) and counter (9) which applies a control signal to the voltage controlled oscillator (8) via a D/A converter.

Abstract: A data transmission system is used for the transmission of a large number of telephone channels between nodes in a transmission network built as a Synchronous Digital Hierarchy (SDH), where a pulse frame (e.g. STM-1) contains a large number of bytes, each of which can be used for the transmission of a telephone channel or of overhead signals for the administration of the system, and where signals from a Plesiochronous Digital Hierarchy (PDH) are introduced into the pulse frame of the Synchronous Digital Hierarchy, so that the signals from the Plesiochronous Digital Hierarchy when introduced do not occupy all the bytes in said pulse frame. At least some of the bytes of the pulse frame which are not occupied by introduction, are used for the transmission of user-specified data signals.

Abstract: A receiver unit for a data transmission system, where transmitted data signals are accompanied by overhead signals, comprises processor means with one or more processors for processing said overhead signals as well as RAM type storage means, in which the processor means can store the data which are obtained by the processing of the overhead signals. Further, between the arriving overhead signals and the processor means there is a buffer circuit, in which the overhead signals can be temporarily placed prior to their processing, and from which the processor means can fetch the signals as the processor means become ready to process the signals.

Abstract: In a method of measuring on an optical fibre (2), a pulse is launched into the fibre, and the temporal course (8, 9) of the echo of this pulse is measured. Then, a signal level representing the background noise present in the fibre is subtracted in a subsequent signal processing of the echo signal. The signal level representing the present background noise is calculated on the basis of the instantaneous value (20) of the background noise which it assumes during the measurement of the echo signal. In a first embodiment the background noise is measured at a wavelength different from the wavelength of the emitted pulse. In a second embodiment wherein several successive pulses (25, 26) are launched into the fibre, optical power (27) is launched into the fibre at a wavelength other than the pulse wavelength during the intervals between said pulses.

Abstract: A method for desynchronization in a receiver in a digital transmission system, where justification is performed as required by introducing or removing a single bit in the transmitted bit flow on the transmission side when placing telephone calls in the transmission system, and where, on the transmission side, adjustments are moreover made in the transmission system as required by introducing or removing groups of bits in the transmitted bit flow, smooths the effect of the introduced and removed bits in the receiver by the desynchronization. The effect of the introduced and removed bits in the receiver is smoothed in two stages, so that in one stage just the effect originating from said groups of bits is smoothed, and in the other stage just the effect originating from said individual bits is smoothed.