Laser-diode for fast data transmission with servo output - uses photodiode to monitor and set threshold and modulator currents

摘要

A laser diode (3) is held at its extinction threshold with a bias current generator (5). A photodiode (2) monitors the laser output. The AC component is filtered out (1) and the DC component compared with a reference level (7) in a regulator (4) to maintain the bias current at the threshold level. Further compensation is introduced by comparing the regulator output with a second reference (10) and taking the difference (8) to set the modulator current (9) which is added to the bias current at the modulator switch (6). ADVANTAGE - Allows extinction threshold to be held over wider ranges of ambient-temp. and modulation frequency.