JPS6250070B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a laser diode (hereinafter referred to as LD).
The output of the laser diode is monitored by a photodetector, and this output is negatively fed back to the laser diode drive circuit to change the DC bias current of the LD to stabilize the optical output.The circuit applies DC bias to the LD only when all power supplies are on. This invention relates to a DC bias circuit for a laser diode that prevents the LD from emitting unnecessary light and deteriorating by flowing current.

Figure 1 shows how the output light of a conventional LD is monitored, and this output is negatively fed back to the laser diode drive circuit.
This shows a circuit that stabilizes the optical output by changing the DC bias current of the LD.

In the figure, D ₁ is LD, D ₂ is PIN diode, T _r1 , T _r
2 , T _r3 are transistors, 1 is an inverting amplifier, 2 is a chiyoke coil, C ₁ , C ₂ are capacitors, R ₁ to _{R 10}
is a resistor, S _IN is a signal input terminal, and +5V and -5V indicate positive and negative 5 volt power supplies.

The transistors T _r1 and T _r2 are configured as a current switch circuit, and perform a switch operation based on the difference between the voltage at point a, which is obtained by dividing -5V by resistors R ₁ and R ₂ , and the voltage applied to the signal input terminal SIN. That is, if the input signal to the signal input terminal S _IN is "1", the transistor T
_r2 is turned on and no current flows through LDD _1. If the input signal is "0", transistor T _r1 is turned on.
Power flows to LDD ₁ and it emits light. This converts electrical signals into optical signals and performs optical communication. in this case
In order to maintain the optimal operating point of LDD ₁ , the DC bias current is connected to the coil 2 transistor T _r3 resistor R ₃
circuit, while the PIN diode _D2
Amplifier 1 receives the light from LDD ₁ and inverts the received light current.
By inputting the inverted and amplified signal to the base of the transistor _Tr3 , negative feedback is applied to change the DC bias current of LDD ₁ and stabilize the optical output. This circuit uses +5V and -5V power supplies, but if we consider the case where only +5V is disconnected,
The light-receiving current of the PIN diode _D2 does not flow, and the output voltage of the inverting amplifier 1 becomes the ground level, and the transistor T _r3 is turned on. Therefore, the collector current of the transistor T _r3 becomes large, and even though LDD ₁ is emitting light, a large DC bias current flows regardless of it, and the +5V cutoff causes an unnecessary reduction in the amount of light even though optical communication is naturally not possible. LD emits a large light
It had the disadvantage of accelerating deterioration.

The purpose of the present invention is to eliminate the above-mentioned drawbacks by passing a DC bias current to the LD only when all power supplies are on, without emitting unnecessary light with a large amount of light.
The purpose of the present invention is to provide a DC bias circuit that prevents deterioration.

In order to achieve the above object, the present invention comprises a laser diode drive circuit and a monitor circuit that monitors the output of the laser diode with a light receiving element and feeds back this output negatively to the laser diode drive circuit. In a circuit that stabilizes optical output by changing the DC bias current of the laser diode, the DC bias current flows to the laser diode only when all power supplies are on between the output terminal of the monitor circuit and the input terminal of the laser diode drive circuit. This is a DC bias circuit for a laser diode, which is characterized in that Zener diodes having such a breakdown voltage are inserted in series.

Embodiments of the present invention will be described below with reference to the drawings. Figure 2 shows a circuit that monitors the output of an LD in an embodiment of the present invention using a light receiving element _D2 , feeds this output back to the LD drive circuit, and stabilizes the optical output by changing the DC bias current of the LD. It is.

Components in the figure that have the same functions as those in FIG. 1 are indicated by the same symbols. 3 is a Zener diode, R ₁₁ , R ₁₃ and R ₁₄ are resistors, and R ₁₂ is a potentiometer.

The difference from Fig. 1 is that a Zener diode 3 with a reverse breakdown voltage of 5V is inserted at the input of _{the transistor Tr3 to} correspond to the power supply voltage of the transistor Tr3 of -5V, thereby lowering the input voltage of the transistor _Tr3 by 5V. On the other hand, a voltage is applied to the (-) side input of the inverting amplifier 1 by adjusting the potentiometer R ₁₂ to compensate for the voltage drop caused by the Zener diode 3 when the output of the inverting amplifier 1 is normal. It is.

Therefore, the operation in the normal case is the same as that shown in FIG. However, if +5V is disconnected, the output voltage of the inverting amplifier 1 becomes the ground level, but the 5V potential decreases at the Zener diode 3, so the base potential of the transistor T _r3 becomes -5V and the transistor T
_r3 is OFF and no DC bias current flows to the LD. Therefore, the LD can be used without emitting an unnecessarily large amount of light.
can prevent deterioration.

As explained in detail above, according to the present invention, the DC bias current of the LD flows only when all the power supplies are on, so if only some of the power supplies are turned off, the LD does not emit a large amount of light unnecessarily and the LD deteriorates. It has the effect of preventing

[Brief explanation of the drawing]

In both Figures 1 and 2, the output of the LD is monitored by a light receiving element, and this output is negatively fed back to the LD drive circuit.
FIG. 1 shows a conventional example of a circuit that stabilizes the optical output by changing the DC bias current of an LD, and FIG. 2 shows an embodiment of the present invention. In the figure, D ₁ is an LD, D ₂ is a PIN diode, and T _r1 to _{T r3}
is a transistor, 1 is an inverting amplifier, 2 is a choke coil, C ₁ , C ₂ are capacitors, R ₁ to R ₁₁ , R ₁₃ ,
_R14 is a resistor, _R12 is a potentiometer, 3 is a Zener diode, S _IN is a signal input terminal, +5V, -5
V indicates a positive and negative 5 volt power supply.

Claims (1)

[Claims] 1 Consists of a laser diode drive circuit and a monitor circuit that monitors the output of the laser diode with a light receiving element and feeds back this output negatively to the laser diode drive circuit, and changes the DC bias current of the laser diode with the output of the monitor circuit. In a circuit that stabilizes optical output by using a circuit, the circuit has a reverse breakdown voltage between the output terminal of the monitor circuit and the input terminal of the laser diode drive circuit such that a DC bias current flows through the laser diode only when all power supplies are on. A laser diode DC bias circuit characterized by a Zener diode inserted in series.