JPH0484479A - Ld driving circuit - Google Patents

Abstract

PURPOSE:To stably supply light output power regardless of changes in the threshold value current of LD caused by, in particular, temperature changes, by comprising a pulse current supply circuit for activating laser diodes, a bias circuit, a bias current control circuit and a pulse current amplitude control circuit. CONSTITUTION:First, fixed light output power P2 is obtained as a result of setting pulse current I by a pulse current supply circuit 10 and setting bias current IP2' by a bias circuit 15 at a temperature of 25 deg.C with respect to I-L characteristics of a PIN diode 5a of an LD module 5. In this condition. when the temperature changes to 0 deg.C or 60 deg.C, the bias current is controlled so as to control maintain light output power L2 at a constant. At this time, if pulse currents IP1', IP3' have the same amplitude as that of pulse current IP2' at 25 deg.C, there occurs a case where light output power is not fixed due to the threshold value current of LD, the inclination of the I-L characteristics of the LD module 5, or the like. In such a case, a control voltage (-V1) corresponding to temperature change is applied to a control terminal 12a by means of a pulse current amplitude control circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an LD drive circuit for driving a laser diode (hereinafter referred to as LD).

[Conventional technology]

Conventionally, this type of LD drive circuit causes the LD to emit light directly using a pulse current sent from a pulse current supply circuit, and monitors the optical output power. and,
Based on the monitoring results, the bias current control circuit (AP
By controlling the bias current of the LD with respect to external conditions such as temperature changes using the C circuit) and making it follow the change in threshold current due to its I (current) - L (optical power output) characteristic, the optical output power can be increased. It was designed to be stable.

[Problem to be solved by the invention]

However, in the conventional LD drive circuit described above, when the threshold current of the LD changes due to a temperature change, it may become impossible to control the bias current depending on the IL characteristics. To explain this using the 1-L characteristic diagram in Figure 3, in a state of 25°C, the pulse current supply circuit generates a pulse current IP2, and the bias circuit generates a bias current I.
By setting B2, a constant optical output power L2 can be obtained. In this state, the temperature is 0℃ or 60℃
, the bias current is controlled by the bias current control circuit and the bias circuit so as to keep the optical output power L2 constant. However, in the conventional LD drive circuit, the pulse current IP output from the pulse current supply circuit
I+ IF5 has the same amplitude as the pulse current IP2 at 25°C, and the threshold current of the second iLD and the LD
The optical output power L depends on the slope of the I-L characteristic of the module.
+, L3 may have a different value from L2. That is, there is a problem in that stable operation cannot be achieved if the optical output power is controlled only by the conventional bias current.

The present invention has been made in view of these problems.

The purpose of this is to compensate for the I-L characteristics of the LD even when bias current control becomes impossible due to changes in the threshold current of the LD due to temperature changes, and to drive an LD that can stably supply optical output power. The purpose is to provide circuits.

[Means to solve the problem]

The LD drive circuit according to the present invention includes a pulse current supply circuit that supplies a pulse current for driving a laser diode, a bias circuit that supplies a bias current to the laser diode, and a current that monitors the output power of the laser diode. a bias current control circuit that outputs a control signal for stabilizing the bias current to the bias circuit;
and a pulse current amplitude control circuit that changes the amplitude of the pulse current in accordance with temperature changes.

With such a configuration, in the LD drive circuit of the present invention, the amplitude of the pulse current changes according to temperature changes.
It is possible to compensate for the IL characteristics of the LD and supply stable optical output power.

Further, the LD drive circuit according to the present invention further includes an impedance circuit that passes the DC component of the monitor current,
The output of this impedance circuit is configured to be input to the bias current control circuit, thereby making it possible to supply a stable bias current to the laser diode.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an LD drive circuit according to an embodiment of the present invention. In the figure, 1 is an input terminal, and a pulse current for driving the LD is input to this input terminal 1. Input terminal 1 has coupling capacitor 2, PI
It is connected to the cathode side of one PIN diode 5a of the LD module 5 via an N diode 3 and a coupling capacitor 4. A connection point between the PIN diode 3 and the coupling capacitor 4 is connected to the cathode side of the PIN diode 7 via the coupling capacitor 6.

The anode side of this PIN diode 7 is grounded. Further, the connection point between the PIN diode 3 and the coupling capacitor 4 is connected to a power source (-■) 16 via a resistor 8. Further, a connection point between the coupling capacitor 2 and the PIN diode 3 is connected to the cathode side of the PIN diode 7 via a resistor 9. The PIN diode 3.7, the coupling capacitor 2.6, and the resistor 8.9 constitute a pulse current supply circuit 10.
The pulse current input to the input terminal 1 is driven with a constant current, and the constant pulse current is supplied to the PIN diode 5a of the LD module 5.

The coupling capacitor 2 of this pulse current supply circuit 10 and the PI
A control terminal 12a is connected to the connection point with the N diode 3 via a resistor 11, and a pulse current amplitude control circuit 12 is connected to the control terminal 12a. The pulse current amplitude control circuit 12 applies a control voltage (-V, ) to the control terminal 12a according to the temperature change, and supplies a control DC current voltage to the pulse current supply circuit 10, whereby the pulse It is designed to control the amplitude of the current.

The other PIN diode 5b of the LD module 5 is for monitoring, and its cathode side is grounded, and its anode side is connected to a bias current control circuit (APC circuit) 14 via a DC passing type impedance circuit 13. There is. The bias current control circuit 14 inputs the DC component of the output current of the PIN diode 5b that has passed through the impedance circuit 13, converts it into a voltage, compares it with a reference voltage, amplifies the DC current, and adjusts the threshold current due to temperature changes. It outputs a control signal so that the optimum bias current can be obtained by following the current. Nokuiasu circuit 15 is P
It is connected to the cathode side of the IN diode 5a, and receives a control signal from the bias current control circuit 14 to input the PIN.
A bias current is supplied to the diode 5a.

Next, the operation of this LD drive circuit will be explained with reference to FIG. First, the pulse current I P2' is set by the pulse current supply circuit 10, and the bias current IB2' is set by the bias circuit 15, with respect to the L characteristic of the PIN diode 5a of the LD module 5 in a state of 25°C. A constant optical output power P2 can now be obtained from the diode 5a. In this state, when the temperature changes to 0° C. or 60° C., the bias current is controlled by the bias current control circuit 14 and the bias circuit 15 so as to keep the optical output power L2 constant. At this time, as mentioned above, the pulse current I.

If rps' has the same amplitude as the pulse current 112' at 25° C., the optical output power may not be constant due to the threshold current of the LD and the slope of the IL characteristic of the LD modular 5. On the other hand, in the LD drive circuit of this embodiment, the Noculus current amplitude control circuit 12 applies a control voltage (-V,
) is applied. As a result, a control DC current 11 2 corresponding to the temperature change is supplied to the pulse current supply circuit 10, and this current 11 changes the forward internal resistance of the PIN diode 3.7, thereby changing the amplitude of the pulse current.

In this way, the forward internal resistance of the PIN diode 3.7 changes the IL characteristics of the LD module 5 with respect to temperature changes, so that the pulse current I PI' changes at each temperature.
The amplitudes of IP2' and IP3' vary as shown in FIG. This pulse current I.

', IP2' and IP3' drive the PIN diode 5a. Then, the DC component of the monitor current of the other PIN diode 5b is transferred to the impedance circuit 1.
3 to the bias current control circuit 14. As a result, a control signal is output from the bias current control circuit 14, and based on this control signal, the bias currents I B+', L2', and I B are output from the bias circuit 15.
3' follows changes in the threshold current of the LD module 5 and always becomes the optimum bias current. Therefore, the optical output power P2 can be kept constant at each temperature.

〔Effect of the invention〕

As explained above, according to the LD drive circuit according to the first aspect, since the amplitude of the pulse current for driving the laser diode is changed according to the temperature change, the threshold current of the laser diode changes due to the temperature change. Even if bias current control becomes impossible, the IL characteristics of the laser diode can be compensated and optical output power can be stably supplied.

Further, according to the LD drive circuit according to claim 2, since the LD drive circuit further includes an impedance circuit that passes the DC component of the monitor current, a stable bias current can be supplied to the laser diode, and a more stable optical output can be achieved. Can supply electricity.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an LD drive circuit according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the circuit of FIG. 1, and FIG. 3 is an explanatory diagram of the operation of a conventional LD drive circuit. 1...Input terminal, 2.4.6...Coupling capacitor, 3.7...
...PIN diode, 8.9.11...Resistor 5...LD module, 12...Pulse current amplitude control circuit, 13...
... Impedance circuit, 14 ... Bias current control circuit (APC circuit), 5 ... Bias circuit 1st section 2nd figure 3rd section

Claims (1)

[Claims] 1. A pulse current supply circuit that supplies a pulse current for driving a laser diode; a bias circuit that supplies a bias current to the laser diode; and a monitor current for the output power of the laser diode. The present invention is characterized by comprising a bias current control circuit that outputs a control signal for stabilizing the bias current to the bias circuit, and a pulse current amplitude control circuit that changes the amplitude of the pulse current according to temperature changes. LD drive circuit. 2. The LD drive circuit according to claim 1, further comprising an impedance circuit for passing a DC component of the monitor current, and configured to input an output of the impedance circuit to the bias current control circuit.