JPS60171778A - Driving device for semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a driving device, which is simple and highly reliable and also superior in safety, for a semiconductor laser, by a method wherein a limited signal generating circuit capable of generating continuously a dummy photoelectric signal for a constant time since a point when a power source has been turned-ON is added in between the photo output detector and the current control circuit of the semiconductor laser. CONSTITUTION:Parts 3 of laser lights are incided in a photo output detector 4, the parts 3 are amplified in an amplifier 5 and an optical intensity signal 6 is obtained. A limited signal generating circuit 7 has been provided in between the amplifier 5 and a current control circuit 2. A signal 9 obtained by adding the optical intensity signal 6 to the output voltage 8 of this limited signal generating circuit 7 is compared with an optical intensity set value 10, and after that, the signal 9 is turned into an error signal 11 and the error signal 11 controls the output current of the current control circuit 2. Here, it is assumed that (to) is a non-control time, which is decided by the rise characteristics of the amplifier 5 and so forth, and Vo is an optical intensity set value. Under this condition, when a dummy photoelectric signal of a larger optical intensity value than the Vo is made to generate at least for a longer time than the (to), the output current of the current control circuit 2 dwindles into zero during the time. Accordingly, there is no possibility that a semiconductor laser 1 is broken even for a momentary turning-ON of a power source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present disclosure relates to a driving device used to control the light intensity of a semiconductor laser.

With the advancement of semiconductor lasers, various types of semiconductor lasers have come into widespread use as compact and powerful coherent light generating devices, and various systems have been proposed for their driving devices. Generally, as shown in Figure 4, semiconductor lasers have the characteristic that when the driving current is increased, the light intensity increases rapidly when the current value exceeds the carry-in current value (oscillation starting current value). Furthermore, this characteristic changes greatly depending on temperature, and phenomena such as instantaneous destruction of the semiconductor laser occur when the light intensity exceeds a certain level, so it is extremely important to control the drive current appropriately. be.

The commonly used method for controlling the drive current is to detect a portion of the light from the semiconductor laser with a photodiode and control the drive current so that the output voltage is constant. There was a concern that excessive current would flow through the semiconductor laser when the power was turned on. In other words, when the power is turned on instantaneously, a certain R-open is required before the photodiode detection signal begins to control the drive current, so an uncontrolled excessive current flows during this short period of time, destroying the semiconductor laser. There are things to do. In addition, semiconductor lasers are often used by modulating the light intensity with high frequency, but a simple and reliable modulation method is required. Since the presence of light is not visible to the naked eye, appropriate safety measures are required.

The present invention has been made to solve the above problems, and its purpose is to provide a semiconductor laser drive device that is simple, highly reliable, and has excellent safety.
The invention will now be described in detail with reference to embodiments illustrated in the accompanying drawings.

First, FIG. 1 is an overall configuration diagram of a driving device, in which reference numeral 1 denotes a semiconductor laser, the driving current of which is controlled by a current control circuit 2. As shown in FIG. Part 3 of the laser beam is transmitted to a light output detector (
The light enters a light beam (hereinafter simply referred to as a detector) 4 and is amplified by an amplifier 5 to obtain a light intensity signal 6. A time signal generation circuit 7 is provided between the amplifier 5 and the current control circuit 2, and a signal 9 obtained by adding the output voltage 8 of the time signal generation circuit 7 and the light intensity signal 6 is the light intensity. It is compared with a set value 10 and becomes an error signal 11 to control the output current of the current control circuit 2. Note that a photodiode is used as the detector 4.

Considering the case where the one-time signal generation circuit 7 is not provided in the above configuration, when the power is turned on momentarily, the light intensity signal 6 is not generated for a certain period of time determined by the rise characteristics of the amplifier 5, etc., so the current Is the output current of control circuit 2 I? There is a possibility that the damage will reach a maximum in time and destroy the semiconductor laser 1. Therefore, a time signal such as that shown at A or B in FIG. 2 is used as a pseudo light detection signal, and this is added to the light intensity signal 6. In FIG. 2, if to is the uncontrolled time determined from the rise characteristics of the amplifier 5, and Vo is the light intensity setting value, then if a pseudo photodetection signal larger than VQ is generated between at least FRs longer than to, then during this period , the output current of the current control circuit 2 has become zero.

After the opening time, if the pseudo signal is gradually decreased, the light intensity setting value is 10 while the current control based on the photodetection signal is activated.
The intensity of the laser beam increases as it approaches the target, and is controlled at a constant level when it reaches the set value.

Therefore, according to the present driving device to which the time signal generating circuit 7 is added, there is no risk of destroying the semiconductor laser 1 even when the power is turned on momentarily.

Further, in FIG. 1, a drive circuit 13 for a warning lamp 12 is connected to the output side of the detector 5, that is, a light intensity signal 6, so that the warning lamp 12 can be turned on immediately if a laser beam is generated. . With this configuration, safety can be particularly improved when using an infrared-emitting semiconductor laser.

Next, to explain the configuration for high-frequency modulating the light intensity of the semiconductor laser 1, in FIG. 1, 14 is a modulation signal source;
5 is the impedance of the modulation signal source 14, 1G is a high frequency coaxial cable, 17 is a resistor, 18 is a capacitor,
These members constitute a transmission circuit system 19 that supplies the 111 frequency modulation signal to the output side of the current control circuit 2 described above. Therefore, when transmitting high frequency signals, it is generally necessary to match the input and output impedance to the impedance of the cable. Voltage of semiconductor laser 1 -
Since the current characteristics are nonlinear as shown in Figure 3, RL-Δ
As V/ΔI, a resistor 17 such that the sum with this RL becomes the characteristic impedance of the coaxial cable and a capacitor 18 for cutting the DC component are connected. By constructing such a circuit A, the 1lffi current of the semiconductor laser 1 changes in proportion to the high frequency modulation signal. Also,
Since the average light intensity is controlled to the light intensity setting value by the detector 4 and the current control circuit 2, there is almost no fear that the semiconductor laser 1 will be destroyed even if an excessive modulation signal is applied.

The present invention is as described above, and the semiconductor laser is
Of course, you can control the light intensity without worrying about
It is possible to provide a drive device that can easily perform high-frequency modulation, and also ensures sufficient safety during use, and its practical value (such as greatly contributing to the spread of semiconductor lasers) It is extremely large.

[Brief explanation of drawings]

The first figure is a configuration diagram of an embodiment of the present invention, the second figure is an explanatory diagram of a time signal, the third figure is a voltage-current characteristic diagram of a semiconductor laser, and the fourth figure is a diagram of a semiconductor laser current-light intensity characteristic. It is a characteristic diagram. In the figure, 1 is a semiconductor laser, 2 is a current control circuit, 4 is an optical output detector, 7 is a time signal generation circuit, 12 is a warning lamp, 13 is a drive circuit, and 19 is a transmission circuit system. Patent applicant Yama 1) Hidehiko Figure 1 Q Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) In a semiconductor laser drive device consisting of a semiconductor laser optical output detector and a current control circuit that controls the current flowing through the semiconductor laser so that the output of the detector is constant, 1. A semiconductor laser driving device characterized in that a time-limited signal generation circuit is added between the circuits to generate a pseudo photodetection signal for a certain period of time after power is turned on. (2) In a semiconductor laser drive device that includes a semiconductor laser optical output detector and a current control circuit that controls the current flowing through the semiconductor laser so that the output of the detector is constant, the detector and the current i ! A time signal generation circuit that generates a pseudo light detection signal for a certain period of time after the power is turned on is connected to the fi11 circuit, and a drive circuit that lights up a warning lamp is added to the output side of the detector. A semiconductor laser drive device characterized by comprising: (3) In a semiconductor laser drive device consisting of a semiconductor laser optical output detector and a current control circuit that controls the current flowing through the semiconductor laser so that the output of the detector is constant, the detector and the current control circuit are provided. A time-limited signal generation circuit that generates a pseudo photodetection signal for a certain period of time after power-on is connected between the circuit and the output side of the current control circuit, and a transmission circuit that supplies a high-frequency modulation signal to the output. A semiconductor laser drive device characterized in that it is formed by adding systems.