US 4,789,987 A · Automatic modulation control apparatus

Abstract

A circuit used in conjunction with RF modulating a laser diode and controlling the bias point is presented. The novel function is the amplitude and level shifting modulation of the drive signal at two different low (non-RF) frequencies. The light output is then detected to ascertain the relative amounts of the two different frequencies. The amplitude modulated signal appearing in the light output rises as there is increased distortion due to clipping on the threshold side or knee of the light current curve of the diode, and the amount of the level shifting modulation frequency signal drops with increased amounts of clipping. The two signals are used to derive a feedback signal to control the amplitude of the drive signal to maintain the relative detected amounts of the two signals appearing in the light output at a given ratio.

Claims5

Dependent claims

Optical laser apparatus comprising, in combination:

signal level clipping and modulating first means, including control input means and signal input and output means, for providing output signals adjusted in amplitude in accordance with signals supplied to said control input means thereof and amplitude modulated in accordance with a first alternating frequency signal which frequency is low compared to RF (radio frequency);
data signal second means for supplying an RF data signal of greater than a predetermined amplitude to said signal input means of said first means;
laser diode signal modulating third means, including RF signal input means, modulated optical signal output means and average DC current control input means, for converting signals applied to said RF signal input means to optical output signals;
signal modifying fourth means, connected between said first and third means, for level shifting the envelope of the signal passed from said first means to said third means in accordance with a second alternating frequency signal which frequency is low compared to RF;
and
detection fifth means, connected between said third means and control input means of said first means, for detecting components of the first and second frequency signals in accordance with the amount of distortion introduced in converting from RF to optical signals and applying a control signal to said first means which varies in accordance with the relative amplitudes of the detected first and second alternating frequency signals.

3 more elements

Dependencies are inferred from the claim text.

Automatic modulation control apparatus

Life of this patent

Automatic modulation control apparatus

Life of this patent

Abstract

Claims5