JPS592392B2 - Laser equipment for optical communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser device for optical communication equipped with an optical output stabilization mechanism.

Semiconductor lasers oscillate when supplied with a current equal to or higher than a threshold current, and are normally driven with a modulation current obtained by superimposing a signal current on a DC bias current.

The threshold current has a strong temperature dependence, so if the modulation current is kept constant, the emitted optical power will vary with changes in ambient temperature.

Further, as it is used for a long time, it gradually deteriorates and the optical output power decreases.

For this reason, in order to ensure stable signal transmission in optical communications laser devices that use semiconductor lasers as light sources, the optical output is controlled by an optical output stabilization (APC) mechanism that keeps the transmitted optical power constant. It is essential and usually
A bias current control method with a simple circuit configuration and easy control is used.

FIG. 1 is a block diagram showing the configuration of a laser device for optical communication equipped with a conventional APC circuit having a protection function for a semiconductor laser.

In FIG. 1, a modulation current obtained by weighting a bias current from a DC bias circuit 2 with a signal current from a drive circuit 3 is applied to a semiconductor laser 1, and from the semiconductor laser 1,
Signal light is emitted in both the front and rear directions.

Now, it is assumed that the signal light 4 emitted in the forward direction is used for transmission, and the signal light 5 emitted in the rear direction is used for control.

At this time, the signal light 5 emitted in the backward direction is received by the light receiving element 6, and passed through the amplifier T to obtain a signal proportional to the power of the emitted light.

This detection signal is compared with a reference signal from a reference signal generation circuit 8 that sets the emitted light power using a comparison circuit 9, and the bias current of the DC bias circuit 2 is increased or decreased in proportion to the comparison signal. The optical power of the signal light 4 emitted in the direction is controlled to be constant. At this time, a current limiting circuit 10 composed of a Zener diode and a resistor is connected between the comparator circuit 9 and the DC bias circuit 2 to prevent an overcurrent exceeding the maximum rated value from flowing into the semiconductor laser 1. ing.

However, in conventional optical communication laser devices with the above configuration, when the ambient temperature rises beyond the permissible operating temperature range of the semiconductor laser and the DC bias current is below its maximum rated value, the bias current decreases. further increased, and semiconductor lasers rapidly deteriorated due to thermal damage, resulting in the serious drawback that the semiconductor lasers were destroyed.

In order to eliminate these drawbacks, the present invention connects a current limiting circuit consisting of a temperature detection circuit, two stages of differential amplifier circuits, and a Zener diode to the input side of the DC bias circuit, so that the ambient temperature can be set. The DC bias current is automatically cut off when the operating temperature is exceeded. FIG. 2 shows an embodiment of a laser device for optical communication according to the present invention.

In FIG. 2, 1 to 10 are the same as in FIG. 1, and signal light is emitted from the semiconductor laser 1 in both forward and backward directions. Of these, the optical power of the signal light 5 emitted in the backward direction is The detection signal is used to operate the DC bias circuit 2 to increase or decrease the bias current, thereby controlling the optical power of the signal light 4 emitted in the forward direction to be constant.

At this time, the comparison signal from the comparison circuit 9 is passed through a current limiting circuit 10 composed of a Zener diode and a resistor to limit the bias current so that it does not exceed its maximum rating.

On the other hand, a detection signal from a temperature detection circuit 11 using a thermistor, thermocouple, etc. as a temperature sensor and a setting signal from a reference signal generation circuit 12 for setting an allowable operating temperature value are input to a differential amplifier circuit 13. .

The output signal from the differential amplifier circuit 13 is input to the next stage differential amplifier circuit 16 through a Zener diode 15 connected between the output terminal of the differential amplifier circuit 13 and the power supply 14. The device is configured such that the output signal from the operational amplifier 16 and the signal from the current limiting circuit 10 are input to the arithmetic circuit 17, and the DC bias circuit 2 is operated using the output signal.

In the optical communication laser device according to the present invention having such a device configuration, the detection signal voltage from the temperature detection circuit 11, the setting signal voltage from the Etl reference signal generation circuit 12, and the Zener voltage of the Erl Zener diode 15 are used. E
Assuming that the power supply voltage of the Zl power supply 14 is the offset voltage from the EZl offset voltage generation circuit 18 as Ez, the output signal voltage EO from the differential amplifier circuit 16 is given by equation (1).

At this time, when the ambient temperature is T1 and the allowable operating temperature is Tc, the detection signal voltage Et and the setting signal voltage Er are given by equations (2) and (3), respectively.

However, θ is a constant. Therefore, the output signal voltage EO from the differential amplifier circuit 16 is given by equation (4), and the temperature dependence of the signal voltage EO is as shown in FIG. 3a.

When the output signal of the differential amplifier circuit 16 is input to the DC bias circuit 2 through the arithmetic circuit 17, the DC bias current 1B changes depending on the ambient temperature T as shown in FIG. 3B. Here, if the DC bias current in the temperature range where the ambient temperature T is lower than the allowable operating temperature Tc is IB (m), as the ambient temperature T exceeds the allowable operating temperature Tc, B
(m) The DC bias current decreases at a ratio of θ/Ez, and the cut-off state is automatically established, allowing current limitation. Note that in the temperature range of T<Tc, the output signal of the arithmetic circuit 17 changes in proportion to the detection signal of the emitted light power of the semiconductor laser, whereas in the temperature range of T≧Tc, the output signal of the arithmetic circuit 17 changes in proportion to the detection signal of the output power of the semiconductor laser. It will vary proportionally to the output signal from circuit 16.

That is, in the optical communication laser device according to the present invention, T
In the temperature range <Tc, the current limiting circuit 10 operates to suppress the DC bias current below the maximum rated value, and when the temperature range becomes T>=Tc, the two-stage differential amplifier circuit 13 operates.
, 16 and the Zener diode 15 operates to automatically cut off the DC bias current, which has the advantage of preventing thermal damage to the semiconductor laser.

In addition, in the laser device for optical communication according to the present invention, the signal transmission function does not stop due to thermal damage to the semiconductor laser, so by limiting the DC bias current, the optical power emitted from the semiconductor laser can be adjusted to the set value. Even if it decreases below this value, the S/N ratio of the signal transmission system only decreases, and in this case, there is an advantage that the original state can be restored by providing means for lowering the ambient temperature. Although the above description has been made of the case of an optical communication laser device that is driven by superimposing a pulse or analog signal current as a modulation signal on a DC bias current, the present invention is not limited to this. Needless to say, it can also be applied to the case of superimposed driving.

As described above, in the optical communication laser device according to the present invention, a part of the signal light emitted from the semiconductor laser is detected, the detection signal is used to control the bias current supplied to the semiconductor laser, and the emitted light power is The input of this bias circuit is being stabilized! By installing a circuit in which two stages of differential amplifier circuits are connected in cascade on the side, and a Zener diode is connected between the output terminal of the operational amplifier in the previous stage and the power supply, when the ambient temperature exceeds the allowable differential temperature, the bias Since the current is automatically cut off, there is an advantage that the semiconductor laser can be prevented from being thermally damaged, causing rapid deterioration and damage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional optical communications laser device equipped with an output stabilization mechanism, FIG. 2 is a configuration diagram of an embodiment of the optical communications laser device according to the present invention, and FIGS. b
FIG. 2 is a characteristic diagram for explaining the operating characteristics of the present invention. In the figure, 1 is a semiconductor laser, 2 is a bias circuit, 3 is a 1 drive circuit, 4 is a signal light emitted in the forward direction, 5 is a signal light emitted in the rear direction, 6 is a light receiving element, 7 is an amplifier, 7 is a Reference signal generation circuit, 9 a comparison circuit, 10 a current limit circuit, 11
12 is a temperature detection circuit, 12 is a reference signal generation circuit, 13, 16
1 is a differential amplifier circuit, 14 is a power supply, 15 is a Zener diode, and 17 is an arithmetic circuit.

Claims (1)

[Claims] 1 Optical output stabilization that detects a part of the signal light emitted from the semiconductor laser and uses the detection signal to control the bias current supplied to the semiconductor laser to keep the power of the signal light emitted from the semiconductor laser constant. In a laser device for optical communications equipped with a switching mechanism, a current control circuit consisting of a temperature detection circuit, a Zener diode, and a differential amplifier circuit is installed in the bias current supply circuit, so that when the ambient temperature exceeds the set operating temperature, A laser device for optical communication, characterized in that a bias current flowing through the semiconductor laser is sometimes in a cut-off state.