The main issue with the circuit you've shared is transients.

Some linear regulator circuits will tend to overshoot on turn-on, or allow input transients to pass through to the load. Here's the ripple rejection curve for TI's LM317:



You can see that the LM317 will do very little to protect the laser from transients with characteristic times below about 1 us. And an ESD event can easily have a pulse width as short as 1 ns.

And many laser diodes are quite sensitive to over-voltage and over-current. They may also respond very quickly to transients compared to other devices that you might connect to an LM317.

A good laser driver circuit should have ESD protection, transient protection, and a slow-start behavior.

These things are more important if you are driving a low-cost CD laser, or a high-speed telecommunications laser than if you are driving a high-power material processing laser. They may also be less important today than they were 20 years ago due to improvements in the robustness and reliability of newer laser designs.

most basic laser diode driver?
I have a pfSense setup with two WANs (WAN1 and WAN2) and one LAN network. The two WANs are setup for failover.

However, QoS has recently been an issue for Skype calls in our office (about 30 people) so we want to dedicate WAN2 for Skype traffic (we use Skype for all VOIP calls, etc.)

As Skype is notoriously difficult to deal with, does anyone have any suggestions on how I should deal with this? A simple rule based on ports will not work, and using layer 7 inspection with a Skype profile on all incoming LAN packets doesn't seem like the way to go either. Here is a related pfSense forum post: Multi-WAN, single LAN; Route VOIP/Skype traffic over one WAN
