US 5,448,629 A · Amplitude detection scheme for optical transmitter control

Abstract

An amplitude control scheme for a high bit rate digital optical transmitter is disclosed. The data to be transmitted by the laser is pulse-width modulated by a low frequency signal. The pulse-width modulated signal is applied to the laser via a laser driver and to a mark density reference generator. The magnitude of the low frequency components from the mark density reference generator is a signal indicative of the desired amplitude of the laser light pulses. A back-face photodiode converts a portion of the laser light into an electrical signal, the magnitude of the low frequency portion thereof being a signal indicative of the actual amplitude of the laser light pulses. The actual amplitude of the laser light pulses is compared to the desired amplitude and the laser driver output amplitude may then adjusted to compensate for variations in the laser performance.

Claims10

Dependent claims

An apparatus for monitoring and controlling the amplitude of a digital laser light output signal, comprising:

a pulse width modulator for modulating a high bit rate input data signal with a low frequency modulating signal to form a pulse width modulated data signal;
a laser driver, responsive to the pulse width modulated data signal and a control signal, for generating a drive signal to a laser, the amplitude thereof being substantially determined by the control signal;
photodetection means, responsive to an optical output signal from the laser and creating an electrical representation thereof, for generating a light amplitude control signal from the low frequency AC component of the electrical representation;
and
means for comparing the light amplitude control signal to a reference signal and providing as an output an amplitude error signal indicative of any difference in value between the light amplitude control and reference signals;
wherein the amplitude error signal may be applied as the control signal input of the laser driver to control the amplitude of the laser light.

3 more elements

A digital lightwave transmitter comprising:

a laser diode responsive to both a digital modulation signal and a bias signal for forming an optical digital output signal therefrom;
a monitor photodetector coupled to the back-face of the laser diode for coupling a portion of the optical digital output signal and deriving an electrical control signal I.sub.MON therefrom;
means for driving the laser diode with the digital modulation signal;
and
bias control means responsive to a DC reference signal from the driving means and a DC monitor signal from the photodiode for providing a corrective bias signal in response to a difference in value between the applied DC signals;
a low frequency oscillator, for producing a modulating signal at a predetermined low frequency;
a pulse width modulator responsive to both an input digital data signal and the modulating signal for providing as an output a pulse width modulated digital data signal, wherein the pulse width modulated digital data signal is applied as an input to the means for driving the laser diode;
means for extracting the AC component of the driving means output signal and multiplying the AC component with the low frequency reference signal to form a light amplitude reference signal;
means for extracting the AC component of the monitor photodiode output signal and multiplying the AC component with the low frequency reference signal to form a light amplitude monitor signal indicative of the amplitude of the digital output signal;
and
means for comparing the light amplitude reference signal to the light amplitude monitor signal and providing an output control signal indicative of any difference between the light amplitude signals, wherein the output control signal is applied as an input to the driving means to adjust the amplitude of the digital data signal applied as an input thereto.

8 more elements

Dependencies are inferred from the claim text.

Amplitude detection scheme for optical transmitter control

Life of this patent

Amplitude detection scheme for optical transmitter control

Life of this patent

Abstract

Claims10