The M66510 is a semiconductor laser diode driver that drives a semiconductor laser of the type whose cathode and the anode of monitor photodiode are connected to the stem. Laser driving current of up to 120mA can be set by applying constant voltage from outside to drive the laser diode. It operates from a 5V single power supply, allowing switching of laser driving current at a speed of 20M bits/sec. *: Our semiconductor laser is of R type.