Optical amplifiers

A method of controlling an optical amplifier having a plurality of gain stages in order to compensate for the effect of amplified spontaneous emission (ASE), the method comprising:

• (i) detecting an optical input signal to a first gain stage,
• (ii) detecting an optical output signal from the first gain stage,
• (iii) controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (iv) detecting an optical input signal to a last gain stage,
• (v) detecting an optical output signal from the last gain stage,
• (vi) controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (vii) compensating for the effect of amplified spontaneous emission (ASE) in the first and last gain stages by applying a correction factor based on the ASE outputted by the first gain stage, the output power of the first gain stage, the ASE originating in the last gain stage and the output power of the last gain stage.

An optical amplifier having a plurality of controllable gain stages separated by loss means and including first and last gain stages, the amplifier comprising:

• (i) gain control means for controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (ii) power control means for controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (iii) compensating means for compensating the gain control means for the effect of amplified spontaneous emission (ASE) in the first gain stage, the compensating means applying a correction factor based on the ASE outputted by the first gain stage and the output power of the first gain stage,
• wherein the gain control means is arranged to control the drive current supplied to the first gain stage so as to zero in on an error signal of the general form:
• (Total Power at B−Stage 1 ASE)−(A+Stage 1 Gain)
• where Total Power at B is a signal representing the power of the output signal from the first gain stage,
• Stage 1 ASE is a signal representing the ASE outputted by the first gain stage determined during a calibration step in a gain control mode,
• A is a signal representing the input signal of the first gain stage, and
• Stage 1 Gain is a signal representing the gain of the first gain stage.

An optical amplifier having a plurality of controllable gain stages separated by loss means and including first and last gain stages, the amplifier comprising:

• (i) gain control means for controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (ii) power control means for controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (iii) compensating means for compensating the gain control means for the effect of amplified spontaneous emission (ASE) in the first gain stage, the compensating means applying a correction factor based on the ASE outputted by the first gain stage and the output power of the first gain stage,
• wherein the power control means is arranged to control the drive current supplied to the last gain stage so as to zero in on an error signal of the general form:
• (Total Power at E−Stage 2 ASE)−(D+Stage 2 Gain)
• where Total Power at E is a signal representing the power of the output signal from the last gain stage,
• Stage 2 ASE is a signal representing the ASE outputted by the last gain stage,
• D is a signal representing the input signal of the last gain stage, and
• Stage 2 Gain is a signal representing the gain of the last gain stage.

A method of controlling an optical amplifier having a plurality of gain stages in order to compensate for the effect of amplified spontaneous emission (ASE), the method comprising:

• (i) detecting an optical input signal to a first gain stage,
• (ii) detecting an optical output signal from the first gain stage,
• (iii) controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (iv) detecting an optical input signal to a last gain stage,
• (v) detecting an optical output signal from the last gain stage,
• (vi) controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (vii) compensating for the effect of amplified spontaneous emission (ASE) in the first gain stage by applying a correction factor based on the ASE of the first gain stage and the output power of the first gain stage,
• wherein a calibration step is performed in which the correction factor is calibrated in the gain control mode of the amplifier, the correction factor subsequently being applied in a power control mode of the amplifier.

A method of controlling an optical amplifier having a plurality of gain stages in order to compensate for the effect of amplified spontaneous emission (ASE), the method comprising;

• (i) detecting an optical input signal to a first gain stage,
• (ii) detecting an optical output signal from the first gain stage,
• (iii) controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (iv) detecting an optical input signal to a last gain stage.
• (v) detecting an optical output signal from the last gain stage,
• (vi) controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (vii) compensating for the effect of amplified spontaneous emission (ASE) in the first gain stage by applying a correction factor based on the ASE of the first gain stage and the output power of the first gain stage,
• wherein the drive current supplied to the first gain stage is controlled so as to zero in on an error signal of the general form:
• (Total Power at B−Stage 1 ASE)−(A+Stage 1 Gain)
• where Total Power at B is a signal representing the power of the output signal from the first gain stage,
• Stage 1 ASE is a signal representing the ASE outputted by the first gain stage,
• A is a signal representing the input signal of the first gain stage, and
• Stage 1 Gain is a signal representing the gain of the first gain stage.

A method of controlling an optical amplifier having a plurality of gain stages in order to compensate for the effect of amplified spontaneous emission (ASE), the method comprising:

• (i) detecting an optical input signal to a first gain stage,
• (ii) detecting an optical output signal from the first gain stage,
• (iii) controlling the drive current supplied to the first gain stage in dependence on the optical input signal to the first gain stage,
• (iv) detecting an optical input signal to a last gain stage,
• (v) detecting an optical output signal from the last gain stage,
• (vi) controlling the drive current supplied to the last gain stage to maintain the output power of the last gain stage substantially constant, and
• (vii) compensating for the effect of amplified spontaneous emission (ASE) in the first gain stage by applying a correction factor based on the ASE of the first gain stage and the output power of the first gain stage,
• wherein the drive current supplied to the last gain stage is controlled so as to zero in on an error signal of the general form:
• (Total Power at E−Stage 2 ASE)−(Required signal output power)
• where Total Power at E is a signal representing the power of the output signal from the last gain stage,
• Stage 2 ASE is a signal representing the ASE outputted by the last gain stage determined during a calibration step in a gain control mode.