JPH04264785A - Semiconductor laser driver - Google Patents

Abstract

PURPOSE:To contrive to miniaturize a device and reduce costs by a method wherein a semiconductor laser driving circuit is spatially separated from a semiconductor laser without causing a hindrance in driving of the semiconductor laser and only the semiconductor laser having small calorific value is controlled in a temperature. CONSTITUTION:A semiconductor laser module 1b having an optical fiber 1a is spatially separated from a circuit substrate 2a to which a semiconductor laser driving circuit is mounted. A cooler of which a constitutive element is a Peltier element 4b is fitted to the separated semiconductor laser module 1b to solely perform temperature control for the semiconductor laser module 1b. The circuit substrate 2a is electrically connected to the semiconductor laser module 1b through a coaxial cable 10. A resistor 13 is inserted into at least an output end of input and output ends of the coaxial cable 10 to perform impedance matching at the output end of the coaxial cable 10. Thus, the semiconductor laser is driven without causing a deformation strain of a pulse waveform.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for a semiconductor laser, and more particularly to a driving device for a high-output semiconductor laser that requires highly accurate temperature control.

0002

2. Description of the Related Art FIG. 4 shows a conventional example of a high-output semiconductor laser driving device. A semiconductor laser module 1b having an optical fiber 1a for extracting laser light is attached in close contact with a circuit board 2a on which a semiconductor laser drive circuit for pulse-driving the semiconductor laser module 1b is mounted. And the whole is made of resin 3 with good thermal conductivity.
It is molded with. A temperature sensor 9 for detecting the temperature of the semiconductor laser module 1b is embedded in the resin 3, and the optical fiber 1a described above is taken out from the front surface of the resin 3.

Further, on the back side of the resin 3, there is a Peltier element 4a for controlling the temperature of the drive circuit and semiconductor laser inside the resin 3.
are attached closely together. A heat sink 5a for heat radiation is attached to this Peltier element 4a, and a fan 6 for heat radiation of this heat sink 5a is further attached. A temperature controller 8 is connected to the Peltier element 4a, and the temperature controller 8 controls the current flowing through the Peltier element 4a based on the temperature detected by the temperature sensor 9.

[0004] A high voltage power supply 7 for applying a high voltage to the semiconductor laser drive circuit and a synchronization signal generating section 2b for providing a synchronization signal are connected to the circuit board 2a from outside the resin 3.

[0005]

[Problems to be Solved by the Invention] By the way, in the above-mentioned high output device, the pulse signal generated by the semiconductor laser drive circuit has a very high frequency of several hundred MHz.
In order to drive the semiconductor laser efficiently in terms of signal transmission, it is preferable to closely connect the circuit board 2a and the semiconductor laser module 1b. However, when they are brought into close contact, heat generated by the electronic components on the circuit board 2a is transmitted to the semiconductor laser module 1b, causing significant fluctuations in the oscillation wavelength, output, etc. of the semiconductor laser light output.

For this reason, in the conventional device, the circuit board 2a and the semiconductor laser module 1b are molded with resin, and the temperature of these is collectively controlled to stabilize the semiconductor laser light output.

However, by controlling the temperature all at once, in addition to the semiconductor laser module that originally needs to be controlled, the circuit board 2a, which generates a larger amount of heat, has to be controlled, which requires a large-scale control device. There was a drawback.

Furthermore, since the area to be temperature controlled is as wide as the entire mold resin, delicate temperature control is not possible, and it is difficult to effectively suppress fluctuations in the oscillation wavelength, output, etc. of the optical output.

Furthermore, since the temperature sensor 9 is located far from the semiconductor laser module 1b, which is the main heating element,
It was not possible to detect instantaneous temperature changes in the semiconductor laser whose temperature should be controlled.

[0010] In particular, these drawbacks become more noticeable as the output of semiconductor lasers increases, and a solution to these problems has been strongly desired.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art by independently controlling the temperature of the semiconductor laser, to facilitate delicate temperature control of the semiconductor laser, and to stabilize the optical output of the semiconductor laser. An object of the present invention is to provide a semiconductor laser driving device that can achieve the following objectives.

0012

[Means for Solving the Problems] A semiconductor laser driving device of the present invention spatially separates a semiconductor laser serving as a heating element and a semiconductor laser driving circuit also serving as a heating element. A semiconductor laser and a semiconductor laser drive circuit for driving the semiconductor laser are electrically connected through a line having a characteristic impedance equivalent to the impedance of the semiconductor laser. Furthermore, the temperature of the semiconductor laser is independently controlled. Generally, a semiconductor laser is handled as a semiconductor laser module, and a semiconductor laser drive circuit is handled as a circuit board on which electronic components such as a pulse drive circuit are mounted.

[0013] Here, if the characteristic impedance line is a coaxial cable, it can be constructed most simply and inexpensively. A plurality of coaxial cables may be connected in parallel to match impedance.

Furthermore, when the characteristic impedance of the characteristic impedance line does not match the impedance of the semiconductor laser or the output impedance of the drive circuit, an appropriate impedance element, such as It is desirable to insert a resistance element in series, in parallel, or in a combination of both to match the impedance at one end or both ends of the characteristic impedance line.

Furthermore, in order to accurately detect the temperature of the semiconductor laser and control the temperature with high precision, it is desirable to incorporate a temperature sensor, for example a thermistor, into the module housing the semiconductor laser.

[0016]

[Operation] Even though they are the same heating element, the amount of heat generated by the semiconductor laser is much smaller than that of the semiconductor laser drive circuit, and furthermore, the temperature of the semiconductor laser is directly related to fluctuations in the oscillation wavelength, output, etc. of the optical output. Therefore, it is desirable to control the temperature of only the semiconductor laser. To do this, first of all, it is necessary to spatially separate the two without impairing the drive performance of the semiconductor laser.

As in the present invention, when the circuit board for the driving circuit, which is a heating element, and the semiconductor laser are connected by a line having the same characteristic impedance as the impedance of the semiconductor laser, for example, a coaxial cable, a single wire or twisted wire having different impedance characteristics can be connected. Unlike the case where the pulse waveform is connected, the pulse waveform can be transmitted to the semiconductor laser without distortion. In particular, when using a coaxial cable, the transmission signal corresponds to a high frequency, so matching the characteristic impedance to the impedance of a semiconductor laser, which is several ohms, is most effective against negative effects such as loss and reflection of the transmission signal. can be prevented.

[0018] As described above, since the circuit board and the semiconductor laser can be spatially separated without causing any trouble in driving the semiconductor laser, it is possible to separate and control the temperature of only the semiconductor laser that generates a small amount of heat. As a result, the device can be made smaller and lower in cost.

[0019]

Embodiments Examples of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows the configuration of the semiconductor laser driving device of this embodiment. A semiconductor laser module 1b having an optical fiber 1a for extracting laser light is spatially separated from a circuit board 2a on which a semiconductor laser drive circuit for pulse driving is mounted. The circuit board 2a and the semiconductor laser module 1b are electrically connected by a coaxial cable 10, so that the semiconductor laser can be driven without causing distortion of the pulse waveform. The semiconductor laser module 1b is closely connected to a temperature control Peltier element 4b that controls the temperature of the semiconductor laser, and a Peltier element heat sink 5b is attached to the Peltier element 4b. Since the cooling capacity required of the Peltier element 4b to cool the semiconductor laser is not so large, a heat dissipation fan is not required.

A synchronizing signal generator 2b and a high-voltage power supply 7 are connected to the circuit board 2a, and when a synchronizing signal is input from the synchronizing signal generator 2b to the circuit board 2a, a semiconductor laser driving pulse is generated, which is transmitted to the coaxial cable 10. The signal is transmitted to drive the semiconductor laser in the semiconductor laser 1b.

[0022] Here, the semiconductor laser module 1b is:
As shown in FIG. 2, a semiconductor laser chip 11 is mounted on a die provided with leads, and a cap is placed on the die. In this embodiment, in particular, this semiconductor laser module 1
A thermistor 12 is installed in the vicinity of the laser chip 11 in the inside. This provides a configuration in which temperature changes in the laser chip 11 can be directly and accurately measured.

A temperature controller 8 is connected to the Peltier element 4b, and the temperature information from the thermistor 12 built in the module 1b is guided to the temperature controller 8, thereby controlling the current flowing through the Peltier element 4b, thereby controlling the semiconductor laser. The temperature of module 1b is controlled.

By the way, in order to transmit the high frequency generated by the circuit board 2a to the semiconductor laser module 1b without causing distortion of the pulse waveform, the coaxial cable 10 is used.
The characteristic impedance of the semiconductor laser module 1b is
must be equal to the impedance of The impedance of the semiconductor laser module 1b is usually several ohms. If the coaxial cable 10 having the same impedance cannot be easily and inexpensively obtained, the following modifications or substitutes may be used.

The characteristic impedance of commonly available coaxial cables is several tens of times larger than that of semiconductor lasers, but the impedance can be reduced by connecting a plurality of coaxial cables in parallel as shown in the following equation.

Z0
'=Z0 /n However, Z0
;Characteristic impedance of one coaxial cable
n; Number of parallel connections Z0'; Characteristic impedance of parallel connected coaxial cables The characteristic impedance of common coaxial cables is 50 or 75Ω. Therefore, for example, if a coaxial flat cable with Z0 = 50Ω, which is often used for computer equipment, is used, if 10 coaxial cables are used in parallel, Z0' = 5Ω, and impedance matching can be easily achieved.

As described above, in this embodiment, the semiconductor laser module and the semiconductor laser drive circuit board are spatially separated and electrically connected using a coaxial cable having a characteristic impedance equivalent to the impedance of the semiconductor laser. Therefore, the temperature of the semiconductor laser can be controlled independently. Therefore, since only the semiconductor laser module that originally needs to be controlled can be controlled, there is no need for a heat sink heat dissipation fan, and the control device can be downsized. In addition, there is no need to mold the semiconductor laser module and circuit board with resin, and the area for temperature control is only the semiconductor laser module, which is very narrow, making delicate temperature control possible, and fluctuations in the oscillation wavelength, output, etc. of the optical output. It becomes easier to effectively suppress Furthermore, since the thermistor 12 is built into the semiconductor laser module 1b and can more accurately measure temperature changes in the laser chip, it is possible to detect instantaneous temperature changes in the semiconductor laser whose temperature is to be controlled. Therefore, highly accurate temperature control of the high-power semiconductor laser becomes possible. It goes without saying that the present invention can also be applied to low-power semiconductor lasers.

[0028] In addition, if coaxial cables cannot be matched in parallel, in series, or by a combination of these,
As shown in FIG. 3, an impedance element of several Ω, such as a resistor 13, is connected in series with the impedance of the semiconductor laser. The connection points of the resistor 13 are as shown in the figure.
It is connected to the output end of the coaxial cable 10 opposite to the input end connected to the drive circuit board 2a. By doing this, it is also possible to achieve consistency. In particular, by performing such matching correction, there are two advantages as follows. (1)
Normally, it is not easy to create a coaxial cable line with low characteristic impedance, partly because it is non-standard. However, if the input impedance of the semiconductor laser is increased through matching correction as described above, the characteristic impedance of the coaxial cable line (one or more parallel connections) can be made larger than the characteristic impedance of the semiconductor laser. Therefore, a coaxial cable line with desired characteristics can be easily obtained.

(2) Even if the impedance of the semiconductor laser varies from element to element, if the characteristic impedance of the coaxial cable line is higher than the upper limit of the variation of the inherent impedance of the semiconductor laser, the impedance of the semiconductor laser can be adjusted. The impedance mismatch between the coaxial cable and the coaxial cable line due to variations in the values can be absorbed by appropriately selecting the impedance of the elements inserted in series. In this case, in particular, the method of connecting the semiconductor laser and the impedance element is not limited to series connection, but may be parallel connection or a combination of both.

[0030]

[Effects of the Invention] As described above, the present invention provides the following effects.

(1) Since the semiconductor laser and the semiconductor laser drive circuit that drives it are spatially separated, it is possible to efficiently control the temperature of only the semiconductor laser.

(2) Since the only part that controls the temperature is the semiconductor laser, the device can be made smaller and the cost can be reduced.

(3) In particular, the semiconductor laser can be driven without waveform distortion by connecting the semiconductor laser drive circuit, which is a heating element, with a coaxial cable having a characteristic impedance equal to the impedance of the semiconductor laser.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of a semiconductor laser driving device of the present invention.

FIG. 2 is a cross-sectional view of an embodiment of a semiconductor laser module.

FIG. 3 is a configuration diagram according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional semiconductor laser driving device.

[Explanation of symbols]

1a Optical fiber 1b Semiconductor laser module 2a Semiconductor laser drive circuit board 2b Synchronous signal generator 4a, 4b Peltier elements 5a, 5b Heat sink 6 Heat sink heat dissipation fan 7 High voltage power supply 8 Temperature controller 9 Temperature sensor 10 Coaxial cable 11 Semiconductor laser chip 12 Thermistor 13 Impedance element

Claims (3)

[Claims] 1. A semiconductor laser and a semiconductor laser drive circuit for driving the same are spatially separated, and the semiconductor laser and the semiconductor laser drive circuit are electrically connected by a line having a characteristic impedance equivalent to the impedance of the semiconductor laser. A semiconductor laser driving device characterized in that the temperature of the semiconductor laser is independently controlled. 2. The semiconductor laser driving device according to claim 1, wherein the characteristic impedance line is a coaxial cable. 3. An impedance element is inserted into at least one input/output end of the characteristic impedance line to perform impedance matching at the end of the characteristic impedance line.
Or the semiconductor laser drive device according to 2.