Light intensity subtractor, optical A-D converter, and method for subtracting light intensity

A method for subtracting light intensity, the method comprising:

• inputting input light to a light subtracting unit;
• outputting first output light and second output light from the light subtracting unit;
• and
• receiving the second output light output from the light subtracting unit and generating a control voltage in accordance with light intensity of the received second output light,
• wherein the light subtracting unit generates the first output light by subtracting light intensity of the second output light from light intensity of the input light in accordance with the control voltage.

A light intensity subtractor comprising:

• a light input port where input light is input;
• a first light output port where first output light is output;
• a second light output port where second output light is output;
• a light subtracting means for receiving the input light through the light input port, outputting the first output light to the first light output port and outputting the second output light to the second light output port;
• and
• a feedback circuit that is connected to the light subtracting means through the second light output port, and outputs a control voltage in accordance with light intensity of the received second output light,
• wherein the light subtracting means generates the first output light by subtracting light intensity of the second output light from light intensity of the input light in accordance with the control voltage.