US 4,733,398 AGranted

Apparatus for stabilizing the optical output power of a semiconductor laser

AssigneeKabushiki Kaisha Tohsiba

InventorsTaro Shibagaki, Osamu Kinoshita

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Abstract

A drive circuit supplies a semiconductor laser with current pulses corresponding to an input pulse signal. A current supply feeds a d.c. bias current to the laser. A monitoring photodiode produces a light detection signal indicative of the actual laser output level. The detection signal is supplied to a subtraction device, to which the pulse signal is also supplied via a low-pass filter. The subtraction device detects the difference between the two signals to produce an error signal. Integration devices produce average value signals, which are compared by comparators with reference voltages to obtain control signals. The current supply and the current drive circuit are responsive to these control signals to independently modulate the d.c. bias current and the amplitude of the drive pulses applied to the laser, whereby the laser output level can be stabilized to remain at a constant level.

Claims20

Dependent claims

An apparatus for stabilizing an optical output level of an electro-optical converter, said apparatus comprising:

modulator means for supplying said converter with drive pulses corresponding to an electrical input pulse signal, said modulator means further feeding a d.c. bias current to said converter;
light sensitive means for producing a first electrical signal indicative of the actual optical output level of said converter;
signal processing means for receiving said pulse signal to produce a second electrical signal indicative of an ideal optical output level of said converter;
subtraction means for detecting a difference between integration values of said first and second signals to produce as an error signal a third electrical signal indicative of a change in the actual optical output level of said converter;
and
temperature-compensation means for receiving said electrical input pulse signal and said third signal, for applying a multiplication operation to said pulse signal and said third signal to extract a pulse component from said third signal, for generating a wave-shaped error signal in which a pulse component of said third signal is emphasized, and for producing first and second feedback signals based on said wave-shaped error signal to feed these feedback signals to said modulator means, said modulator means being responsive to said first and second feedback signals to independently modulate said d.c. bias current and the amplitude of said drive pulses applied to said converter, whereby the actual optical output level remains substantially constant.

3 more elements

An apparatus for stabilizing an optical output level of an electro-optical converter, said apparatus comprising:

modulator means for supplying said converter with drive pulses corresponding to an electrical input pulse signal, said modulator means further feeding a d.c. bias current to said converter:
light sensitive means for producing a detection signal indicative of the actual optical output level of said converter;
difference detector means for receiving said detection signal and a reference signal indicative of an ideal optical output level of said converter, and for detecting a difference between integration values of said detection signal and said reference signal to produce an error signal indicative of a change in the actual optical output level of said converter;
waveform-shaping means connected to said difference detector means, for delaying said electrical input pulse signal to produce a delayed pulse signal, and for applying a multiplication operation to said delayed pulse signal and said error signal so as to produce a wave-shaped error signal having a waveform which is reformed to emphasize a pulse component of said error signal;
and
temperature-compensation means connected to said waveform-shaping means, for producing first and second feedback signals based on said wave-shaped error signal to feed these feedback signals to said modulator means;
said modulator means being respective to said first and second feedback signals to independently modulate said d.c. bias current and the amplitude of said drive pulses applied to said converter, whereby the actual
optical output level remains substantially constant.

5 more elements

Dependencies are inferred from the claim text.