JPS59145587A - Direct current bias circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent overcurrents, and to obviate a breakdown by overcurrents of a semiconductor laser by connecting a Zener diode between a control terminal and an output terminal for a constant-current circuit. CONSTITUTION:A DC bias circuit 5 is formed in constitution in which a Zener diode 53 is connected between a base of a transistor 51 constituting a constant- current circuit and negative power supply voltage and a control signal (a) from a comparison circuit 3 is inputted to the base of the transistor 51 through an operational amplifier 52. Since the Zener diode 53 protects so that the base voltage of the transistor 51 does not reach a fixed value or more at that time, high currents do not flow through a semiconductor laser 1 even when a large signal is applied to the DC bias circuit 5 due to a short circuit, etc., and the breakdown of an element can be prevented. The DC bias circuit is very effective when it is applied to an APC circuit.

Description

[Detailed description of the invention] The present invention relates to a DC bias circuit for a semiconductor laser.

Semiconductor lasers (LDs) are nonlinear light-emitting devices that have a threshold current, but the threshold value changes depending on the temperature.
When obtaining digitally modulated output light using a semiconductor laser, currently APC (Auto Power
Control) circuit is required.

This APC circuit changes the direct current bias value of a semiconductor laser so that the laser output light becomes stable, and usually has a circuit configuration as shown in FIGS. 1 and 2. The first illustrated circuit obtains a control signal 8 by comparing it with the monitor electric No. 41 of the semiconductor laser drive circuit 4, and adds this control signal 8 to the control terminal of the DC bias circuit 5 to control the DC bias value of the semiconductor laser 1. It is configured to change. This method is not limited by any signal format since the %11 signal of the monitor light and the driving electrical signal are directly compared at their average or peak values. On the other hand, the second illustrated circuit converts the monitor light of the semiconductor laser 1 into an electric signal by the monitor circuit 2, detects its peak value by the peak detection circuit 6, and compares this peak value with the reference voltage V0. It obtains the control signal 8,
Since the peak value is compared with the reference voltage, the problem is limited by the p1 code format when there are continuous 0'' signals, but the configuration is relatively simple.

Incidentally, semiconductor lasers are easily destroyed by overcurrent, so sufficient care must be taken when driving semiconductor lasers. However, since conventional APC circuits have no countermeasures against overcurrents, for example, if a short circuit occurs in the circuit section that generates the control signal 8, such as the comparator 3, a large signal may be applied to the DC bias circuit 5. When inputted, a large current flows through the semiconductor laser 1, which has the drawback of causing destruction of the device.

The present invention improves these conventional drawbacks.
The purpose is to provide a DC bias circuit for a semiconductor laser that can prevent overcurrent that could lead to element destruction of the semiconductor laser.

Examples will be described in detail below.

FIG. 3 is an electrical circuit diagram representing an embodiment of the present invention.
1 is a transistor constituting a constant current circuit, 52 is a voltage amplifier, 53 is a Zener diode, 54 is a resistor, and -f. 1 is a power source, and the same reference numerals as in FIGS. 1 and 2 indicate the same parts.

As shown in the figure, the DC bias circuit 5 of this embodiment has the following features:
A Zener diode 53 is connected between the base of the transistor 51 constituting the constant current circuit and the negative power supply voltage, and a comparison circuit 6 is connected.
The control signal 8 is inputted to the transistor 51 via a p-amplifier 52. In this case, the Zener diode 56 protects the base voltage of the transistor 51 from exceeding a certain value, so that even if a large signal is applied to the DC bias circuit 5 due to a short circuit or the like, the Zener diode 56 will not cause the semiconductor laser 1 to become Current will no longer flow, and destruction of the element can be prevented.

As described above, the present invention has a structure in which a Zener diode is connected between the control terminal and the output terminal of a constant current circuit in a DC bias circuit for a semiconductor laser, and the superiority of the Zener diode prevents overcurrent. This has the effect of preventing the semiconductor device from being destroyed by overcurrent. Therefore, it is very effective to apply the DC bias circuit of the present invention to an APC' circuit.

[Brief explanation of the drawing]

1 and 2 are electrical circuit diagrams showing the general structure of an APC circuit, and FIG. 3 is an electrical circuit diagram showing an embodiment of the present invention. 1 is a semiconductor laser, 2 is a monitor circuit, 6 is a comparator, 4 is a semiconductor laser drive circuit, 5 is a DC bias circuit, 6 is a peak detection circuit, 51 is a transistor, 52 is an operational amplifier, 53 is a Zener diode, 54 is a It is resistance. Applicant: Sumitomo Electric Industries Co., Ltd. Patent attorney Gobe Tamamushi

Claims (1)

[Claims] In a DC bias circuit that changes the DC bias to stabilize the laser output light based on the control signal obtained by processing the semiconductor laser's monitor light, the control terminal of the constant current circuit that applies DC bias to the semiconductor laser. and negative power box,
A DC bias circuit for a semiconductor laser, characterized in that a Zener diode is connected between the positive terminals and the control signal is input to the control terminal.