Okay, I'm building a serial link cable for my TI calculator and the plans call for two zener diodes. What exactly is a zener diode? Is that just a regular diode, because I have some diodes, and if ...

The resistor and 10 uF capacitor are already forming a low-pass filter, which should prevent any spikes in either current/voltage. I don't know much about laser diodes though, so I am not sure what ...