Circuit arrangement with a laser diode for transmission of communication signals through a light waveguide

Claim 1

A circuit arrangement with a laser diode for the transmission of communications signals through a transmission link comprising a light waveguide, a transmitting device, a modulator in said transmitter, said laser diode in said modulator and connected to one end of said light waveguide, a receiving device connected to the second end of said light waveguide, a regulating device connected to said laser diode for controlling the optical output power, a return channel connected between said transmitting device and said receiving device, an analysis device in said receiving device which analyses the mean value or the peak value of the received communication signal which is characteristic of the optical transmitted power, and depending upon the characteristic value forms a control signal, means for transmitting said control signal through said return channel to said transmitting device from said receiving device, and said regulating device receiving said control signal to control the optical output power of the laser diode as a function of the received control signal, and characterized in that a signalling device is provided for analyzing both the control signal received by way of the return channel and the bias current of the laser including first means for producing an output when said return signal is less than a preset limit and second means for producing an output when said laser exceeds a predetermined limit, gate means connected to said first and second means, and an indicator connected to said gate means.