The term amplifier is used below to describe a device which can be used to increase the intensity of an optical beam.
FIG. 1 shows a segment of a section of optical waveguide. An optical waveguide L is connected via an optical connector S to an optical amplifier V. Optimum noise behavior of an optical amplifier, in particular an erbium doped fiber amplifier, results if the amplifier does not have isolators on the input side. Amplified spontaneous emission ASE caused by the optical amplifier spreads counter to the direction of spread of the optical signal on the optical waveguide and is, for example, reflected via a connector S and fed back to the input of the amplifier.
In order to achieve safety shutdown of the optical amplifier in the event of interruption, components of the optical signal directed to the input of the optical amplifier V can be fed to a monitoring unit via an optical coupler in appropriate transfer systems. This monitoring unit is, for example, made up of a filter, particularly a band-pass filter, and a signal monitor downstream from this. If the measured power is below a predefined threshold value, it is assumed that the optical waveguide section is interrupted, which, for example, triggers safety shutdown of the optical amplifier. If the measured power is above the predefined threshold value, safety shutdown does not take place, as it is assumed that optical signals have reached the measuring device via the optical waveguide section and, therefore, there can be no interruption.
In the case of interruption, however, a power reading above the predefined threshold value may be measured under certain circumstances due to reflection of the amplified spontaneous emission ASE at a connector S at the input of the amplifier and this is interpreted as the input signal, so the mandatory safety shutdown does not take place.
To ensure shutdown in the event of an interruption, optical amplifiers are therefore fitted with isolators on the input side.
This has the advantage that amplified spontaneous emission ASE spreading counter to the direction of spread of the optical data signal is avoided.
The use of an isolator, however, such as a passive element, has the disadvantage that the noise level increases and, as a result, the intervals between the regenerators along the optical transfer section are reduced.
An object of the present invention is to specify a circuit and a method for safety shutdown of an optical amplifier.