Laser interface: Testing, known bugs and fixes

• The feedback amplifier for the monitor photodiode may have to be adjusted depending on the laser diode used. Replace R5 with a value appropriate for the amount of monitor current produced in the laser diode at the operating power.

• Resistor R6 should be removed.

• The feedback amplifier for the monitor photodiode was designed for use with SDL 5400 series laser diodes, which use a type A configuration for the anodes and cathodes. This creates a problem when using Sanyo laser diodes with a type C configuration because the monitor photodiode is reversed in this case. The transconductance amplifier on the interface board(U2A) is currently configured to operate only single supply, and so can't amplify the negative signal produced by the Sanyo diodes. A revised version of the circuit suitable for type C laser diodes is available here.