Apparatus and method for laser diode calibration

A method of biasing a photodiode of a laser illumination device, the method comprising:

• connecting a cathode of a laser diode to a cathode of a photodiode;
• connecting an output of a laser diode driver to an anode of the laser diode;
• connecting an anode of the photodiode to a feedback input of the laser diode driver;
• connecting a variable resistor with a selectable resistance value between the anode of the photodiode and ground;
• and
• selecting a resistance value of the variable resistor to maintain a reference voltage on the anode of the photodiode to reverse bias the photodiode.

A method of calibrating a laser illumination device, the method comprising:

• connecting a cathode of a laser diode to a cathode of a photodiode;
• connecting an output of a laser diode driver to an anode of the laser diode;
• connecting an anode of the photodiode to a feedback input of the laser diode driver;
• connecting a variable resistor with a selectable resistance value between the anode of the photodiode and ground;
• for each of a plurality of different selected resistance values of the variable resistor, determining a photodiode current and a laser diode current;
• for each pair of adjacent values of the plurality of different selected resistance values of the variable resistor, calculating a ratio of (i) a difference between the photodiode current at a second selected resistance value and the photodiode current at a first selected resistance value and (ii) a difference between the laser diode current at the second selected resistance value and the laser diode current at the first selected resistance value;
• determining a maximum one of the calculated ratios;
• determining a target photodiode current by multiplying the maximum one of the calculated ratios by a photodiode reference current value within an operating range of the photodiode;
• and
• calculating an operating resistance value of the variable resistor using the target photodiode current.