All 6 photodiodes are connected to a common point which during operation has a DC bias voltage on it typically around 5 V. 2V datasheet is max reverse laser diode reverse voltage. Laser diode substrate is like a square, a box, it emites for two. They range from super cheap (or even free if you can find one in an old CD player!) to more expensive. Most types are really easy to use too, once you learn the basics. In the end, I'll show you how. A laser diode is a specific type of light-emitting diode, in which a high proportion of the light generated in the semiconductor chip is reflected by partially reflecting mirrors at each end of the chip so that its intensity builds up. If you see a few hundred mV or less, there is likely a problem.