JPH0541555A - Automatic optical output control circuit - Google Patents

Abstract

PURPOSE:To fix the pulse width of optical output and make the fixed value conform to the pulse width of a PFM modulated signal. CONSTITUTION:An electric signal which is the output of a PIN diode 5 is amplified to a connection configuration which comprises a PFM modulator 2, a laser drive circuit 3, a laser diode 4 and a PIN diode 5. This amplitude is compared with an amplifier 6 whose amplitude is identical to that of the PFM modulation signal and a first smoothing circuit 7 which smoothes the electric signal amplified by the amplifier 6, a second smoothing circuit 9 which smoothes the PFM modulation signal and the flattening output between the smoothing circuit 7 and the smoothing circuit 9. There is installed a compared 8, which feeds back the error portion of the voltage to the drive circuit 3. In the drive circuit, the drive circuit is controlled so that the error voltage portion to be fed back may come to naught.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission using a pulse frequency modulation (hereinafter, referred to as PFM modulation) signal having a constant pulse width, in which the pulse width of the optical output is constant.
The present invention relates to an automatic optical output control circuit (hereinafter referred to as an APC circuit) that can match the pulse width of an FM modulated signal.

[0002]

2. Description of the Related Art Conventionally, as an APC circuit, there is a circuit as shown in FIG. In the figure, 1 is a signal input terminal, 2 is a PFM modulator, 3 is a laser drive circuit, 4 is a laser diode, 5 is a PIN diode as a photoelectric converter, 10 is a smoothing circuit, 11 is a reference voltage setting terminal, 12 Is a comparator. In this APC circuit, an input signal such as an image signal given to the signal input terminal 1 is converted by the PFM modulator 2 into a PFM modulated signal having a constant pulse width and given to the laser drive circuit 3. Laser drive circuit 3 is PF
A drive current corresponding to the M modulation signal is generated. The drive current causes the laser diode 4 to emit an optical output corresponding to the PFM modulation signal. When the laser diode 4 emits an optical output, the PIN diode 5 receives the backward light of the laser diode 4, converts it into an electric signal, and outputs it. PIN
The electric signal output from the diode 5 is smoothed by the smoothing circuit 10. Then, the smoothed output (voltage value) of the smoothing circuit 10 is supplied to the comparator 12, compared with the reference voltage supplied via the reference voltage setting terminal 11, and the error voltage is fed back to the laser drive circuit 3. It In the laser drive circuit 3, the drive current is controlled based on the error voltage component fed back from the comparator 12 so that the error voltage becomes zero. As a result, the optical output of the laser diode 4 is made constant.

[0003]

However, in such a conventional APC circuit, when the laser diode 4 is driven by the PFM modulation signal having a constant pulse width, the response speed of the laser diode 4 is slow, so that the PFM modulation signal is reduced. There is a problem that the pulse width of the optical output becomes narrower than the pulse width of.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a PFM for converting an input signal into a pulse frequency modulation signal having a constant pulse width and generating it.
A modulator, a drive circuit which outputs a drive current corresponding to a pulse frequency modulation signal generated by the PFM modulator, a laser diode which is driven by the drive current output by the drive circuit and emits an optical output, and a rear side of the laser diode. A photoelectric converter that receives light, converts it to an electrical signal and outputs it, an amplifier that amplifies the electrical signal output by this photoelectric converter, and makes its amplitude the same as that of the pulse frequency modulation signal, and this amplifier amplifies A first smoothing circuit for smoothing the generated electric signal, and a second smoothing circuit for smoothing the pulse frequency modulation signal.
And a comparator for comparing the smoothed output of the first smoothing circuit and the smoothed output of the second smoothing circuit and feeding back the comparison result to the drive circuit.

[0005]

Therefore, according to the present invention, the drive current is controlled so that the smoothed output of the second smoothing circuit matches the smoothed output of the first smoothing circuit based on the comparison result fed back to the comparator. If so, it is possible to make the pulse width of the optical output of the laser diode constant and match the pulse width of the PFM modulation signal.

[0006]

The APC circuit according to the present invention will be described in detail below.

FIG. 1 is a block circuit diagram showing an embodiment of this APC circuit. In the figure, the same reference numerals as those in FIG. 2 indicate the same or equivalent components, and the description thereof will be omitted.

This APC circuit amplifies the electric signal output from the PIN diode 5 and makes its amplitude the same as that of the PFM modulation signal, and a first smoothing the electric signal amplified by this amplifier 6. Smoothing circuit 7, a second smoothing circuit 9 for smoothing the PFM modulated signal, the smoothing output of the first smoothing circuit 7 and the smoothing output of the second smoothing circuit 9 are compared, and the error voltage Comparator 8 for feeding back to the drive circuit 3
It has and.

In this APC circuit, the signal input terminal 1
An input signal such as an image signal given to the above is converted by the PFM modulator 2 into a PFM modulated signal having a constant pulse width, and given to the laser drive circuit 3. The laser drive circuit 3 is a PFM
A drive current corresponding to the modulation signal is generated. The drive current causes the laser diode 4 to emit an optical output corresponding to the PFM modulation signal.

On the other hand, the PFM modulation signal output from the PFM modulator 2 is branched and given to the second smoothing circuit 9. The second smoothing circuit 9 smoothes the PFM modulated signal and supplies the smoothed output (voltage value) to the comparator 8.

When the laser diode 4 emits a light output,
The rear light of the laser diode 4 is transmitted to the PIN diode 5
Is received, converted into an electrical signal and output. The electric signal output from the PIN diode 5 is given to the amplifier 6 and amplified, and its amplitude is made the same as that of the PFM modulation signal. The amplified electric signal output from the amplifier 6 is
Smoothed by the first smoothing circuit 7, and the smoothed output (voltage value) is given to the comparator 8.

The comparator 8 compares the smoothed output of the first smoothing circuit 7 with the smoothed output of the second smoothing circuit 9, and feeds back the error voltage component to the drive circuit 3.

In the laser drive circuit 3, based on the error voltage component fed back from the comparator 8, the error voltage is set to zero, that is, the smoothed output of the second smoothing circuit 9 is used as a reference. The smoothing output 7 of the first smoothing circuit 7
The drive current is controlled so as to match
As a result, the pulse width of the optical output of the laser diode 4 becomes constant and matches the pulse width of the PFM modulation signal.

[0014]

As is apparent from the above description, according to the present invention, the smoothing output of the first smoothing circuit is added to the smoothing output of the second smoothing circuit based on the comparison result fed back from the comparator. If the drive current is controlled so as to match the pulse width of the PFM modulation signal, the pulse width of the optical output of the laser diode can be made constant, and the optical output can be compared with the pulse width of the PFM modulation signal. It becomes possible to solve the problem that the pulse width of is narrowed.

[Brief description of drawings]

FIG. 1 is a block circuit configuration diagram showing an embodiment of an APC circuit according to the present invention.

FIG. 2 is a block circuit configuration diagram showing a conventional APC circuit.

[Explanation of symbols]

 2 PFM modulator 3 laser drive circuit 4 laser diode 5 PIN diode 6 amplifier 7 first smoothing circuit 8 comparator 9 second smoothing circuit

Claims (1)

[Claims] 1. A PFM modulator which converts an input signal into a pulse frequency modulation signal having a constant pulse width and outputs the pulse frequency modulation signal, and this PF
A drive circuit that generates a drive current according to the pulse frequency modulation signal output from the M modulator, a laser diode that emits an optical output driven by the drive current generated by this drive circuit, and an electric power that receives the backward light of the laser diode A photoelectric converter that converts and outputs the signal, an amplifier that amplifies the electric signal output by the photoelectric converter and has the same amplitude as the pulse frequency modulation signal, and an electric signal amplified by this amplifier A smoothing output for smoothing the pulse frequency modulated signal, a smoothing output for the first smoothing circuit, and a smoothing output for the second smoothing circuit. An automatic optical output control circuit, comprising: a comparator for comparing and feeding back the comparison result to the drive circuit.