You keep talking about :-
constant voltage over the lens of an optical drive
I don't know what that means. A lens is made of non conducting material so it makes little sense applying a voltage to it.
You have still not said what sort of voltage and what sort of current you need. It is vital to know this before you can start to make even the block diagram of a design let alone specify the sort of D/A that you need.
you could be better off looking for Arduino code to work with a chip, rather than choosing a chip and then looking for code.
I would strongly disagree with that. Interface code for a D/A is almost trivial, you need it to do the right thing first.