E1.3 A precise optical signal source can control the output power level to within 1% [32]. A laser is controlled by an input current to yield the power output. A microprocessor controls the input current to the laser.

The microprocessor compares the desired power level with a measured signal proportional to the laser power output obtained from a sensor. Complete the block diagram representing this closed-loop control system shown in Figure E1.3, identifying the output, input, and measured variables and the control device.

i(t) Error Current Input Device Laser Output Sensor Measured variable