Patent ID: 8139956

Claim:
A signal transmission system incorporating an optical sub-assembly, the optical sub-assembly comprising: a dual-purpose pin for propagating an analog signal out of the optical subassembly and for providing an access point whereby an external element may be coupled to the optical sub-assembly for modulating the analog signal, the modulated analog signal being used thereon to generate a control signal inside the optical sub-assembly; a photodetector configured to receive light and generate therefrom, a first electrical signal indicative of an intensity of the received light; a signal transmitter circuit coupled to the photodetector and configured to convert the first electrical signal into the analog signal that is transmitted out of the dual-purpose pin; a signal receiver circuit configured to monitor the modulated analog signal present at the dual-purpose pin and generate therefrom, the control signal inside the optical sub-assembly; and wherein the analog signal is a current output signal, wherein the signal transmitter circuit is configured to maintain the current output signal at a quiescent current level when the first electrical signal falls below a threshold level, wherein the external element is a switching element located external to the optical sub-assembly, the switching element operable to generate the modulated analog signal by coupling the dual-purpose pin to a ground potential for a selected period of time whereby the analog signal is transitioned to a Low logic level for the selected period of time.