JPS61236181A - Driving circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain stable photo output, by installing a current-voltage conversion circuit and a peak value detecting circuit which detects the peak value of the output voltage of the conversion circuit, between the anode of semiconductor laser and the earth. CONSTITUTION:When the pulse signal voltage is not impressed, the current determined by the bias current controlling voltage flows through the semiconductor laser diode 3. The potential of one end point P of the resistor R4 descends, and the condenser C5 is charged by the current flowing through the diode D5, whose potential becomes equal to that of the point P. When the pulse signal voltage is impressed and becomes 'H', the potential of the point P descends furthermore, and the voltage of the condenser C5 also descends. When the pulse signal voltage turns to 'L', the potential of the point P ascends, and the diode D5 turns OFF. If the resistance value of R4 is sufficiently large, the voltage of the capacitor C5 is maintained, and the detected peak value is output form the terminal Q as the peak value. By selecting adequately the time constant C5R5, the peak value of laser current can be detected independently of the mark ratio of the pulse signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a driving circuit for a semiconductor laser used in an optical communication system.

[Conventional technology]

In an optical communication system using a semiconductor laser, a bias current of -4 is added and a pulse signal current is superimposed on this to perform the change W4. Since the oscillation threshold current changes greatly due to temperature fluctuations and deterioration of the semiconductor laser, the bias current is usually automatically controlled to stabilize it. The target value to be automatically controlled is the peak value of the waveform obtained by multiplying the bias current by 1 tatami of the pulse signal current.

By the way, since the semiconductor laser drive circuit to which the present invention is directed is one in which a bias current control circuit and a pulse signal voltage/current conversion circuit are provided in parallel between the cathode of the semiconductor laser and the negative voltage source, The superimposed current cannot be detected directly, so the average value of the pulse signal current is detected by some method, this value is converted to a peak value, and then added to the bias current value to obtain the peak value of the superimposed current and stabilized. I was trying to do something.

[Problem that the invention seeks to solve]

In the above method of calculating and adding the average pulse signal current value and bias current value individually, if the mark rate of the input pulse signal voltage changes, the average pulse signal current value changes, so the correct beam value cannot be determined. However, there was a drawback that the semiconductor laser current could not be stabilized.

An object of the present invention is to provide a circuit that eliminates the above drawbacks, incorporates a peak current value detection circuit directly into a semiconductor laser drive circuit, and can obtain stable optical output regardless of the mark rate K of the pulse signal voltage. It's about doing.

[Means for solving problems]

The semiconductor laser drive current circuit that is the subject of the present invention has a first
As shown in the figure, a pulse signal voltage/current conversion circuit 1 and a bias current control circuit 2 are connected in parallel between the cathode of a semiconductor laser 3 and a negative voltage source (-E). In the present invention, a current/voltage conversion circuit 4 and a peak value detection circuit 5 for detecting the peak value of the output voltage of the conversion circuit 4 are provided between the anode of the semiconductor laser 3 and the ground. The output value of the peak value detection circuit 5 is supplied as a target value to an automatic control loop that controls the bias current.

[Function] In the circuit of the present invention, a current in which a bias current and a pulse signal current are superimposed flows on the anode side, and a peak current value can be directly detected from this current. By controlling the bias current of the semiconductor laser using this detected value as a target value, it is possible to stabilize the voltage even if the mark rate of the pulse signal voltage changes.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a circuit diagram of the embodiment.

Pulse signal voltage/current conversion circuit 1 is transistor TR1
An emitter follower consisting of a transistor T and a resistor Rt.
The pulse signal current is changed by applying a pulse signal voltage to the base terminal of the RI. The bias current control circuit 2 is an emitter follower consisting of a transistor TRz and a resistor R-, and applies a bias current control voltage to the pace terminal of the transistor T&. The current/voltage conversion circuit 4 that changes the semiconductor laser current into voltage simply uses the voltage of the resistor R4. The peak value detection circuit 5 is a capacitor C
This is a circuit in which one end of a parallel circuit of IS+resistance R5 is connected to one end of resistor R4 via a diode 5.

In the circuit of the present invention, when the pulse signal voltage is not applied, a current determined by the bias current control voltage flows through the semiconductor laser 3, the potential at one end of the resistor R4 at point P decreases, and the capacitor C5 is a current flowing through the diode Ds. When the capacitor C5 is charged and the voltage becomes equal to the potential at point P, charging ends and becomes a constant value.

Next, when a pulse signal voltage is applied and becomes "H", the potential at point P further decreases, so the voltage of capacitor Cs also decreases. When the pulse signal voltage reaches 1L'', the potential at point P rises and the diode D5 turns off.If the resistor R5 is high enough, the voltage of the capacitor CS is maintained and the peak detected value is output from the terminal Q as the peak value. By appropriately selecting the time constant CIIRB, the peak value of the rape current can be detected regardless of the margin j' ratio of the pulse signal.

〔Effect of the invention〕

As described above in detail, in the semiconductor laser drive circuit of the present invention, the peak value voltage is always output, and furthermore, this value is unrelated to the mark rate of the input pulse signal.

Therefore, it is possible to easily stabilize the semiconductor laser current by utilizing this peak value voltage, which is extremely effective in improving the reliability of the optical communication system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is a circuit diagram of one embodiment. DESCRIPTION OF SYMBOLS 1... Pulse signal voltage/current conversion circuit, 2... Bias current control circuit, 3... Semiconductor laser, 4... Current/voltage conversion circuit, 5... Peak value detection circuit.

Claims (1)

[Claims] In a semiconductor laser drive circuit, the anode of the semiconductor laser is connected to ground, and a pulse signal voltage/current conversion circuit and a bias current control circuit are connected in parallel between the cathode of the semiconductor laser and a negative voltage source, A semiconductor laser drive circuit comprising: a current/voltage conversion circuit connected between the anode of the semiconductor laser and ground; and a peak value detection circuit for detecting the peak value of the output voltage of the conversion circuit.