초록 ▼

A fiber-optic communication system for data bursts includes a plurality of nodes, each including a laser diode transmitter. In order to reduce the noise floor of the system, each laser diode receives bias current only when it is transmitting data. Due to the propagation delay between nodes, there is

A fiber-optic communication system for data bursts includes a plurality of nodes, each including a laser diode transmitter. In order to reduce the noise floor of the system, each laser diode receives bias current only when it is transmitting data. Due to the propagation delay between nodes, there is a dead time between data bursts received by each node during which no data signals are received. The bias current of the laser diode is adjusted following each data transmission, so that the light attributable to laser operation during the setting of bias is received during the dead time. The adjustment is accomplished by stepping an up-down counter by one clock pulse following transmission of each data burst.

대표청구항 ▼

A knee bias control circuit for a light emitting device, for a data transmitter adapted for burst communications in a local area fiber optic communications system, wherein said light emitting device has a light-versus-drive-current characteristic including a first portion in which the light emitted

A knee bias control circuit for a light emitting device, for a data transmitter adapted for burst communications in a local area fiber optic communications system, wherein said light emitting device has a light-versus-drive-current characteristic including a first portion in which the light emitted as a function of drive current increases relatively slowly from zero to a first level which occurs at a knee point, and also including a second portion in wich the light emitted as a function of drive current increases relatively quickly for drive currents exceeding the drive current correponding to said knee point, said ciruit comprising: a controllable bias current source coupled to the light emitting device for applying bias current thereto, said controllable bias current source being enabled in response to an enable signal applied to a bias current enable terminal of said current source, the magnitude of said bias current supplied by said current source is established in response to a magnitude signal applied to a magnitude input terminal of said current source; a source of burst digital data signals; enable signal generating means coupled to said source of signals and to said controllable bias current source for generating said enable signal during an interval equal to the sum of the duration of said burst digital data and an additional time and for applying said enable signal to said enable terminal of said controllable bias current source, whereby bias signal is applied to said light emitting device during the time said burst digital data signals are transmitted but said bias current is not applied to said light emitting device during most of the time between bursts of said burst digital data signal, which reduces residual light in said local area fiber optic communications system and noise resulting therefrom; and bias current setting means coupled to said enable signal generating means and to said controllable bias current source for generating said magnitude signal, for updating said magnitude signal during said additonal time and for applying said magnitude signal to said magnitude input terminal of said controllable bias current source, whereby said residual noise on said local area system is reduced, and the bias point of each data transmitter is reset without significant effect on the noise of the system.