JPH04343491A - Optical transmitting circuit - Google Patents

Abstract

PURPOSE:To minimize a deterioration of an optical quenching ratio and a chirping penalty while an optical output power is held constant in the case where efficiency of LD is changed. CONSTITUTION:A driving current is supplied from a laser driving circuit 1 to an LD 31 of an LD module 3 integrated with a monitoring photodiode 32. An alternating current component of frequency f0 is superposed on the driving current from an oscillator 7 through a capacitor 71. A detecting signal derived from a photodiode 32 is supplied to a peak detecting circuit 74 through an APC circuit 5 and a lowpass filter 73. The driving current obtained from the laser driving circuit 1 is adjusted by an output of a peak detecting circuit 7. Also, an output of the APC circuit 5 is supplied to the LD 31 of the LD module 3 as a bias current.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter circuit, and more particularly to an optical transmitter circuit that can maintain an appropriate amount of light emission even in a light emitting module that has deteriorated over time.

0002

[Background Art] In the field of optical communication, data to be transmitted is
After being converted into an optical signal by an optical transmission circuit, it is sent to an optical transmission line.

FIG. 6 is a block diagram showing an example of the configuration of the conventional optical transmitting circuit. In the optical transmission circuit in FIG.
The electrical signal S is input to the laser drive circuit 11. The laser drive circuit 11 outputs a laser drive current IP. Laser drive current IP is input to a laser diode (LD) module 13. The LD module 13 includes a monitoring photodiode (PD) 32 in addition to a laser diode (LD) 31. The signal SM from the monitor PD 32 is input to the automatic output control (APC) 15. The APC 15 supplies a bias current IB to the LD module 13 in order to keep the optical output P0 of the LD 31 of the LD module 13 constant.

In such an optical transmission circuit, an electric signal S is converted into a laser drive current IP by a laser drive circuit 11 and supplied to an LD module 13 . The LD 31 outputs light according to the laser drive current IP, and a part of it is input to the monitoring PD 32.

The monitor PD 32 outputs a signal SM corresponding to the optical output power of the LD and inputs it to the APC circuit 15. The APC circuit 15 outputs the optical output P to which the LD 31 is set.
The bias current IB is outputted until it reaches 0, and is input to the LD module 13. As a result, LD module 1
The light output of 3 is kept constant.

[0006]

[Problems to be Solved by the Invention] In the conventional optical transmission circuit described above, the optical output of the LD is kept constant by adjusting the bias current, but when the efficiency of the LD decreases due to temperature changes, the bias current increases. When the current exceeds the threshold value, the LD emits light in the same state as if it were driven by direct current. As a result, the extinction ratio deteriorates. on the other hand,
In the conventional optical transmission circuit described above, when the efficiency of the LD increases due to temperature change, the bias current decreases and the spread of the optical spectrum increases. As a result, a chirping penalty occurs during transmission, and the error rate deteriorates.

As mentioned above, the efficiency of the LD changes due to changes in temperature, so as a countermeasure to this problem, a method has been considered that allows the bias current supplied to the LD module to have temperature characteristics so that it can be set to an appropriate value depending on the ambient temperature. It will be done. However, in such a method, the LD due to temperature change
Since the efficiency differs from element to element, the amount of light output from the LD changes when the temperature changes, and there is a problem in that the amount of light output from the LD cannot be kept constant.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an optical transmission circuit in which the amount of light emitted from a light emitting module is not affected by temperature, aging, etc.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the optical transmission circuit of the present invention includes a light emitting module incorporating a monitoring photodetector that outputs a detection signal according to the amount of light emitted, and a laser drive circuit that supplies a drive current to the module; and an automatic system that supplies a bias current to the light emitting module so that the amount of light emitted by the light emitting module is constant based on a detection signal from a monitoring photodetector of the light emitting module. An output adjustment circuit, and an AC signal is superimposed on the drive current from the automatic output adjustment circuit and applied to the light emitting module, and the amount of light emitted by the optical module is determined based on the AC component of the detection signal from the monitoring photodetector. The present invention is characterized by comprising a correction control circuit that adjusts the laser drive circuit until the value becomes a constant value.

The correction control circuit also includes an oscillator that can superimpose an AC signal on the drive current from the laser drive circuit via a capacitor, and a low-pass filter that extracts an AC component from the detection signal from the monitoring photodetector. and a peak detection circuit that takes in the AC component obtained through the low-pass filter and adjusts the drive current from the laser drive circuit so that the AC component reaches a constant value.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

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

The optical transmission circuit shown in FIG. 1 includes a laser drive circuit 1 and a laser diode (LD) which is a light emitting module.
It includes a module 3, an automatic output control (APC) circuit 5, and a correction control circuit 7, and is configured as follows. Here, the laser drive circuit 1 converts the input electric signal S into a laser drive current IP and outputs it. In addition to the LD 31, the LD module 3 includes a photodiode (PD) 32, which is a monitoring photodetector that outputs a detection signal according to the amount of light emitted from the LD 31. The APC circuit 5 is
Based on the detection signal from the photodiode 32, a bias current is supplied to the LD 31 so that the amount of light emitted from the LD 31 is constant. The correction control circuit 7 superimposes an AC signal on the output from the laser drive circuit 1 and applies it to the LD 31, and drives the laser from the AC component of the detection signal from the photodiode 32 until the amount of light emitted from the LD 31 reaches a constant value. Adjust circuit 1. The correction control circuit 7 also includes an oscillator 72 that superimposes an AC signal of frequency f0 on the output IP from the laser drive circuit 1 via a capacitor 71, and a low-pass filter 7 that extracts an AC component from the detection signal from the photodiode 32.
3, and a peak detection circuit 74 that takes in the AC component obtained through the low-pass filter 73 and adjusts the signal pulse current from the laser drive circuit 1 so that the AC component reaches a constant value.

The operation of such an embodiment will be explained below.

FIG. 2 is an explanatory diagram showing the waveform of drive current IPP on which frequency f0 is superimposed. 3 to 5 are explanatory diagrams showing the efficiency of electrical-to-optical conversion, in which the horizontal axis shows the drive current and the vertical axis shows the detection signal.

When the laser drive current IPP is supplied to the LD 31 of the LD module 3, the LD 31 outputs an optical signal. A part of the optical signal from this LD 31 enters a monitoring photodiode 32, and is sent to a low-pass filter 73 and AP as a detection signal SM corresponding to the amount of optical output of the LD 31.
The signal is input to the C circuit 5. The low-pass filter 73 extracts the AC component Sf0 of the frequency f0 of the oscillator 72,
This is input to the peak detection circuit 74. The peak detection circuit 7 generates a signal SP according to the amplitude of the AC component Sf0 as follows:
It is input to the laser drive circuit 1.

The laser drive circuit 1 outputs a laser drive current IP having a magnitude corresponding to an input signal SP. on the other hand,
The signal SM is also input to the APC circuit 6, and a bias current I is supplied to the LD 31 so that the optical output power is constant.
Adjust B.

Here, the efficiency of the LD 31 of the LD module 3 has decreased from the characteristics shown in FIG. 3 (high efficiency) to the characteristics shown in FIG. 4 (low efficiency) due to temperature changes and aging deterioration. As a result, as shown in FIG. 4, the amplitude of the AC component SM of the frequency fo superimposed on the laser drive current IPP becomes smaller during electro-optical conversion. This reduced detection signal SM is filtered by the low-pass filter 73.
It is input to the peak detection circuit 74 through. As a result, the signal SP from the peak detection circuit 74 is fed back to the laser drive circuit 1. In the laser drive circuit 1, L
In response to the decrease in the efficiency of D31, the signal S is increased so that the laser drive current IPP increases from the threshold current Ith to the set optical output amount P as shown in FIG.
There is a correspondence with P. Further, the APC circuit 5 feedbacks the bias current to a current value IB (which is equal to the threshold current Ith) obtained by subtracting the laser drive current IPP from the current value I0 at which the optical output amount P is obtained (this is equal to the threshold current Ith). I'm putting it on.

In this way, it is possible to prevent the efficiency of the LD 31 from changing due to temperature changes or deterioration over time.

[0020]

[Effects of the Invention] As explained above, in this embodiment, an alternating current component is superimposed on the laser driving current, and feedback is provided so that the optimum laser driving current is obtained according to the amplitude value of the alternating current component output from the monitoring photodiode. Therefore, even if the efficiency of the LD changes due to temperature changes, the amount of light output remains constant, there is no deterioration in the extinction ratio, and there is no chirping.
This has the effect of minimizing the penalty.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform obtained by superimposing an alternating current component on a laser drive current obtained in an example of the present invention.

FIG. 3 is a diagram showing the efficiency of electrical-to-optical conversion under normal conditions.

FIG. 4 is a diagram showing the efficiency of electrical-to-optical conversion under temperature and aging conditions.

FIG. 5 is a diagram of the efficiency of electrical-to-optical conversion shown to explain the operation of the present invention.

FIG. 6 is a block diagram of a conventional optical transmission circuit.

[Explanation of symbols]

1 Laser drive circuit 3 LD module 5 APC circuit 7 Correction control circuit 71 Capacitor 72 Oscillator 73 Low pass filter 74 Peak detection circuit

Claims (2)

[Claims] 1. A light emitting module incorporating a monitoring photodetector that outputs a detection signal according to the amount of light emitted; a laser drive circuit that supplies a drive current to the light emitting module;
an automatic output adjustment circuit that supplies a bias current to the light emitting module so that the amount of light emitted by the light emitting module is constant based on a detection signal from a monitoring photodetector of the light emitting module; superimposing an AC signal on a drive current and applying it to the light emitting module, and driving the laser drive circuit until the amount of light emitted from the optical module reaches a constant value based on the AC component of the detection signal from the monitoring photodetector; An optical transmission circuit comprising: a correction control circuit for adjusting. 2. The correction control circuit includes an oscillator that can superimpose an AC signal on the drive current from the laser drive circuit via a capacitor, and a low-pass filter that extracts an AC component from the detection signal from the monitoring photodetector. and a peak detection circuit that takes in the alternating current component obtained through the low-pass filter and adjusts the drive current from the laser drive circuit so that the alternating current component reaches a constant value. The optical transmission circuit described.