Laser driver configuration with 5MHz modulation and current monitoring
It seems to me that your best option is to drive the laser with a current source and use the in-built monitor photodiode to regulate the light output to the average level you desire by using feedback techniques to modify the current. This is the standard approach because it overcomes such issues as the laser output extinguishing (as it warms) because the threshold lasing current alters with temperature: -



Picture source

Of course it does require you to have kept a record of what the specific sensitivity of the photodiode was when you bought the device. The data sheet gives very wide limits but a lot of supplier's of higher-end lasers will have calibrated it. If not then you need to get the photodiode calibrated.

Regards the picture, where it says "input pulses" this is where you would feed your modulation - it can be digital in nature or an analogue signal - it all depends on how you would design the pulsing and biasing circuit. I'm not sure what your modulation is so I can't help much more on this except to say that there are two methods that I know of.


For injection of high speed data you can use an inductor in series with the current feed and inject a small p-p voltage on-top of the forward voltage applied to the laser. Inductors are used so that you are not reliant on the current source's transistor's capacitance slowing the data edges down too fast.
You can superimpose slow speed data (5 MHz falls into this bracket) directly to the output of the "adder" shown in the picture.


There are many ways to skin a cat.

THIS ANSWER GIVES NO SAFETY RECOMMENDATIONS REGARDING SAFE OUTPUT LEVELS FROM LASER DIODES - SAFETY IS IMPORTANT WITH LASERS AND YOU NEED TO RESEARCH THIS SEPERATELY.