Apparatus and method for monitoring received optical power in an optical receiver over a wide range of received power with high accuracy

A received power monitoring (RPM) apparatus for use in an optical receiver for monitoring optical power received in the optical receiver, the apparatus comprising:

• an amplifier circuit configured to receive an electrical signal produced by an optical detector in response to light received by the optical detector, the amplifier circuit being configured to amplify the electrical signal and to output the amplified electrical signal;
• an adjustable resistor circuit configured to receive the amplified electrical signal at an input terminal of the adjustable resistor circuit and to produce an analog voltage signal, VMON, at an output terminal of the adjustable resistor circuit, the adjustable resistor circuit providing a resistance value that is adjustable between at least a first resistance value, RL1, and a second resistance value, RL2, wherein RL1 is greater than RL2;
• and
• a controller having an analog-to-digital converter (ADC), the ADC having an input port that receives the analog VMON signal and an output port that outputs a multi-bit digital value, VMON—DIG, the ADC having ADC circuitry that converts the analog VMON signal into the digital VMON—DIG value that is output from the output port of the ADC, wherein the controller IC is configured to perform a received power monitoring (RPM) algorithm that analyzes the digital VMON—DIG value output from the output port of the ADC to determine whether or not the digital VMON—DIG value indicates that the resistance value provided by the adjustable resistor circuit needs to be adjusted, wherein if the RPM algorithm determines that the digital VMON—DIG value indicates that the resistance value of the adjustable resistor circuit needs to be adjusted, the RPM algorithm causes the adjustable resistor circuit to be adjusted to provide one of the first resistance value RL1 and the second resistance value RL2.