Laser transmitter for light wave (fiber optic) communication espectially of AM modulated CATV signals having means . . . against damage

摘要

A laser transmitter utilizes a laser diode which is biased to its stimulated (laser) emission mode of operation by the application of current from a source of one or more operating voltages. The failure of any of these voltages and over temperature conditions of the laser are detected by an optical AND gate which switches the operating voltage off when any one of them is absent. The temperature of the laser is also detected and applied to one of the optos in the chain of the AND gate such that an over temperature condition also results in the switching off of the operating voltage and shut down of the laser. The temperature detection is by way of a circuit having hysteresis such that the optical AND gate is not enabled until the temperature the laser decreases below the initial cut off temperature. Operating current for biasing the laser for laser emission is applied gradually over a period from one to five seconds by connecting the switched operating voltage source to the laser through a slow start circuit. The laser operating current and also the level of the modulating signal (an RF modulating signal carrying a plurality of CATV channels) is applied to the laser through a switching circuit which cuts off the modulating signal when either the current to the laser or the modulating signal level is below predetermined limits.