Telefonaktiebolaget Lm Ericsson (publ)

Cisco Technology, Inc.

Cisco Systems (sweden) Aktiebolag

Dag Bonnedal

Bengt Johansson

Gunnar S Forsberg

Lars Egnell

Johan Sandell

Fredrik Lindgren

Ola Hulten

Bo Lagerstr&ouml;m

Stefano Piciaccia

Magnus Sundelin

Magnus &Ouml;berg

Fredrik Liden

Fredrik Linden

Fransisco Martinez

Information about optical amplifier ASE power is propagated down a link. Each amplifier along the link can learn of the ASE power at its input and take this input ASE power into account in controlling its own per channel output power. Each amplifier can also pass along to the next amplifier an indicator that represents its output ASE power taking into account both its input ASE power and own generated ASE power. Intermediate optical add/drop multiplexers (OADMs) adjust the ASE power indicator to account for losses and the spectral characteristics of each filter.

Optical channel power control in WDM networks

An add/drop node of an optical WDN-network which has two fiber paths for light of a plurality of channels propagating in opposite directions comprises two add/drop modules () for each of the channels. All the modules are identically constructed. Each module comprises an add device () for adding light to one of the paths and a drop device () for deflecting a portion of light from a second one of the paths. A module comprises a house () enclosing the add device and the drop device. A first fixed connector () is attached to the house for connection in the first path and to a an optical fiber () which extends freely from the house and has a first free connector () at its free end to be attached to the fixed connector of a neighboring add/drop module for continuing the first path through the considered add/drop module to the neighboring module. In the same way a second fixed connector is attached to the house for connection in the second path and to a second optical fiber which extends freely from the house and has a second free connector at its free end to be attached to the fixed second connector of a neighboring add/drop module for continuing the second path through the considered add/drop module to the neighboring module.

Connection of on an add/drop node

An add/drop node used in an optical network having two fiber paths for carrying light corresponding to a plurality of channels in opposite directions may include a pair of add/drop modules that correspond to one of the plurality of channels. This arrangement advantageously provides a simple approach for connecting the components of an add/drop node.

Connection of an add/drop node

An optical fiber amplifier has a length of active optical fiber into which pump light from a pump laser is injected. The pump laser is locally controlled by a laser monitor diode, the pump laser and the laser monitor forming a pump laser module. The overall amplification of the amplifier is controlled by two control loops: a feed forward loop and a feed back loop. These two control loops also control the pump laser. The feed forward loop gives a fast response and receives an input signal from an input monitoring diode. The feed back loop gives a slower response and sets the overall gain of the amplifier. The feed back loop receives an input signal from an output monitoring diode. In the feed forward loop, the input power level is biased and controlled by a set offset values from sources to provide a signal corresponding to a pump power reference level which maintains the desired gain. The offsets of characteristic curves indicating an overall behavior of the optical amplifier. The pump power reference level is further modified in accordance with the pump monitor signal locally controlling the pump laser. This gives a very fast and accurate control in spite of the non-linear behavior of the optical fiber amplifier.

Optical fiber amplifier control

An optical amplifier device intended for WDM light signals comprises a preamplifier ( ) and a power amplifier ( ) of the optical fiber amplifier type, which are connected in series and have gain curves dependent on the wavelength. A controllable attenuator ( ) is connected between the amplifiers ( and ) and is controlled by a control device ( ). The signal input to the preamplifier ( ) has a low power and is amplified to provide an output signal where the signals of the input channels have been amplified with different gains. The input signal of the power amplifier ( ) then has a larger power resulting in a gain characteristic different from that of the preamplifier ( ). By adapting the attenuation of the attenuator ( ) for variations in the input signal the gain characteristic of the power amplifier ( ) can be set so that the signal output from the amplifier device has a spectral dependence that is the same as the original spectral dependence obtained without variations. Also, the same spectral dependence can be maintained when the pump light power of the power amplifier is changed and then the total amplifier gain is changed, by adapting the attenuation of the attenuator ( ) so that the gain of the power amplifier is not changed. In the amplifier the lower possible noise from the preamplifier stage is added to the input signal and the full output power is always available from the power amplifier. If the input signal is e.g. increased the SNR of the signals passing through the amplifier is correspondingly improved. This improves the performance of an optical network in which the amplifier is used.

Optical fiber amplifier having variable gain

The present invention relates to an optical system comprising firstly an optical amplifier (,), which comprises at least one input and at least one output, secondly a control circuit for regulating the output power of the amplifier (,) with the aid of a feed-forward process demand signal (PF), said control circuit comprising a feed-forward block (,) and a first means (,) for tapping light from the input of the amplifier (,) to the feed-forward block (,). According to the invention, the feed-forward block (,) is arranged to measure the total optical input power.

System with optical amplifier

The present invention relates to an optical system with an optical amplifier having at least one input and output, a control circuit for controlling the output power of the amplifier with the aid of an output process demand signal (PD) from a control means. The control circuit comprises control means, a detector block and a means for tapping off light from an input or an output of the optical amplifier to the detector block. According to the invention, at least one check signal (A) is disposed to be sent in at least one check signal channel which passes through the optical amplifier. The detector block is configured to measure the amplitude of the control signal(s).

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