JP3806464B2 - Semiconductor laser drive device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser driving device.
[0002]
[Prior art]
FIG. 7 shows current-light characteristics (IL characteristics) of a semiconductor laser composed of a laser diode. When the current flowing through the semiconductor laser is less than or equal to the threshold Ith, the semiconductor laser does not emit light, and when the current flowing through the semiconductor laser is greater than or equal to Ith, the semiconductor laser emits light with a light amount corresponding to the current.
FIG. 10 shows an example of a conventional semiconductor laser driving device, and FIG. 11 shows the operating characteristics of the semiconductor laser driving device.
[0003]
The lighting control of the semiconductor laser 1 composed of a laser diode is performed by supplying a current to the semiconductor laser 1 such that a predetermined amount of light is obtained from the semiconductor laser 1. When high-speed switching of light emission of the semiconductor laser 1 is necessary, a bias current is supplied from the bias current source 13 to the semiconductor laser 1 in advance, and when the switch circuit 5 is turned on by the switching signal, the bias current and a predetermined light amount are changed. A switching current different from the current obtained from the semiconductor laser 1 is applied from the switching current source 14 to the semiconductor laser 1. If the amount of switching current from the switching current source 14 is small, the switching of the light emission of the semiconductor laser 1 is faster.
[0004]
Thus, when switching the light emission of the semiconductor laser 1 at high speed, conventionally, a controlled bias current is applied to the semiconductor laser 1. In order to supply a controlled bias current to the semiconductor laser 1, an expensive circuit for supplying a controlled bias current to the semiconductor laser as described in Japanese Patent Application Laid-Open No. 62-237786 is added. Is a complicated process.
[0005]
[Problems to be solved by the invention]
As described above, when the emission of the semiconductor laser 1 is switched at high speed, conventionally, a controlled bias current is applied to the semiconductor laser, as described in Japanese Patent Application Laid-Open No. 62-237786. Since an expensive circuit for supplying a controlled bias current to the semiconductor laser is added and complicated processing is performed in this circuit, the cost is high.
SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser driving device that can switch light emission of a semiconductor laser at high speed and can be made inexpensively without requiring complicated processing.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is directed to a current source connected in series to a semiconductor laser and supplying a current to the semiconductor laser to emit the semiconductor laser with a predetermined amount of light, and in parallel with the semiconductor laser. A voltage source connected in series to a resistor connected to the power source, and a switch circuit connected in series to the voltage source to turn on / off the semiconductor laser, and the current according to on / off of the switch circuit The current flowing from the source to the resistor and the voltage source is turned on / off, the light emission of the semiconductor laser can be switched at high speed, and the cost can be reduced without requiring complicated processing.
[0007]
According to a second aspect of the present invention, in the semiconductor laser driving device according to the first aspect, the voltage source is a Zener diode, and the Zener voltage of the Zener diode is the voltage of the voltage source. Switching can be made inexpensively without requiring complicated processing .
[0008]
According to a third aspect of the present invention, in the semiconductor laser driving device according to the first aspect, the voltage source is composed of one or a plurality of diodes, and the forward voltage drop of the diode is used as the voltage of the voltage source. In addition, it is possible to switch the emission of the semiconductor laser at high speed, and it is possible to reduce the cost without requiring complicated processing .
[0009]
According to a fourth aspect of the present invention, in the semiconductor laser driving device according to the first, second, or third aspect, a forward voltage is applied to the semiconductor laser when a current from the current source is supplied to the resistor and the voltage source. Therefore, it is possible to switch the light emission of the semiconductor laser at high speed, and to reduce the cost without requiring complicated processing.
[0010]
According to a fifth aspect of the present invention, in the semiconductor laser driving device according to the fourth aspect, the forward voltage applied to the semiconductor laser when a current from the current source flows through the resistor and the voltage source is the semiconductor laser. Is a voltage that does not emit light, the light emission of the semiconductor laser can be switched at high speed, and can be made inexpensive without requiring complicated processing.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 8 shows voltage-current characteristics (V-I characteristics) of a semiconductor laser (hereinafter referred to as LD) made of a laser diode, and FIG. 9 shows voltage-light characteristics (VL characteristics) of the LD. When controlling the amount of light emitted from the LD, the amount of current supplied to the LD is controlled according to the IL characteristic as shown in FIG. If the current supplied to the LD is equal to or less than Ith, the LD does not emit light. If the current supplied to the LD is equal to or greater than Ith, the LD emits light, and the amount of emitted light increases rapidly according to the amount of current.
[0012]
Since LD is a diode, its VI characteristic is the same as that of a general silicon diode. When the voltage is gradually increased as shown in FIG. 8, the amount of current suddenly (exponentially) from a certain voltage. Will increase. As shown in FIG. 7, the LD emits light when a current of Ith or more flows. Therefore, as shown in FIG. 9, since the LD has a VL characteristic that light is emitted when the voltage is equal to or higher than the threshold value Vfld, the on / off of the LD can be controlled by the voltage applied to the LD. By alternately applying two voltages sandwiching Vfld to the LD at high speed, the LD is turned on and off at high speed (the current flowing through the LD is switched at high speed).
[0013]
However, switching of the LD emission by the LD voltage has a large change in the LD current with respect to the change in the LD voltage, so that the desired LD emission light quantity control accuracy cannot be obtained.
Therefore, in the embodiment of the present invention, the on / off control of LD light emission is performed by the voltage applied to the terminal of the LD, and the amount of light emitted from the LD is controlled by the current source. By doing so, it is possible to perform high-speed LD emission switching in which the amount of light is controlled.
When the voltage applied to the LD when the LD is extinguished is close to Vfld, the light emission of the LD is switched at a higher speed. Therefore, in the embodiment of the present invention, a bias voltage close to Vfld is given to the LD by the voltage source when the LD is extinguished.
[0014]
By the way, it is known that the luminous efficiency of the LD changes with time, and the IL characteristic of the LD shifts from the solid line shown in FIG. 7 to the direction of the arrow and changes as indicated by the broken line (the LD deteriorates). . Due to this change, the VL characteristic of the LD also changes in the direction of the arrow as shown in FIG. 9, and Vfld shifts in the (+) direction. For this reason, if the bias voltage applied from the voltage source to the LD remains constant, the switching characteristics of the light emission of the LD will change.
[0015]
Since the bias voltage does not change when the LD is turned off, if the current supplied from the current source to the LD increases in order to obtain a predetermined amount of light from the LD when the light emission efficiency of the LD decreases, the current increases. The minute flows into a voltage source that applies a bias voltage to the LD. If a resistor is connected in series with this voltage source, as the current flowing into the voltage source increases, the voltage drop of the resistor increases, thereby increasing the terminal voltage of the LD. This is because the bias voltage applied to the LD from the voltage source increases as the light emission efficiency of the LD decreases, and the deterioration of the switching characteristics caused by the decrease of the light emission efficiency of the LD is alleviated.
[0016]
FIG. 1 shows a first embodiment of the present invention. The first embodiment is an embodiment of the invention according to claim 1, and includes a current source 2 connected in series with LD 1 to control the amount of light emitted from LD 1, a resistor 3 connected in parallel to LD 1, and this resistor 3 and a switch circuit 5 connected in series to the voltage source 4 and turned on / off by a switching signal. The voltage drop Vr of the resistor 3 and the voltage E of the voltage source 4 The combined voltage is a voltage smaller than the voltage Vfld as shown in FIG.
[0017]
FIG. 2 shows the LD1 on state of the first embodiment, and FIG. 3 shows the LD1 off state of the first embodiment. In the first embodiment, the state in which the LD 1 is lit is a state in which the switch circuit 5 is open (turned off). At this time, the LD 1 is supplied with a current so as to obtain a predetermined amount of light from the current source 2 as shown in FIG. Further, the state where the LD 1 is turned off is a state where the switch circuit 5 is closed (turned on) as shown in FIG. At this time, the terminal voltage Vop of the LD 1 is equal to the combined voltage of the voltage drop Vr of the resistor 3 and the voltage E of the voltage source 4. Therefore, the terminal voltage Vop of LD1 is smaller than the voltage Vfld as shown in FIG.
[0018]
When the terminal voltage Vop of LD1 is smaller than Vfld, a current sufficient for LD1 to emit light does not flow to LD1, and LD1 does not emit light. As for the current supplied from the current source 2, a current amount according to the VI characteristic of the LD 1 as shown in FIG. 8 flows through the LD 1, and a current that does not flow through the LD 1 flows through the resistor 3 and the voltage source 4.
[0019]
When the light emission efficiency of the LD 1 decreases, the current supplied from the current source 2 increases in order to obtain a predetermined amount of light from the LD 1. This increase in current flows to the resistor 3 and the voltage source 4, and the voltage drop Vr of the resistor 3 increases. This increases the bias voltage applied to the terminal of LD1.
[0020]
Due to the decrease in the luminous efficiency of LD1, Vfld of LD1 changes in the (+) direction, but the amount of change in the difference between Vfld and the bias voltage is greater than the amount of change in Vfld due to an increase in the bias voltage applied to the terminal of LD1. Compared with the case where the resistance 3 is not provided, the deterioration of the switching characteristics of LD1 emission is reduced.
[0021]
As described above, the first embodiment is an embodiment of the invention according to claim 1, wherein the current source 2 is connected in series to the LD 1 and supplies current to the LD 1 to cause the LD 1 to emit light with a predetermined amount of light. A resistor 3 connected in parallel to the LD 1, a voltage source 4 connected in series to the resistor 3, and a switch circuit 5 connected in series to the voltage source 4 to turn on / off the LD 1. Since the current flowing from the current source 2 to the resistor 3 and the voltage source 4 is turned on / off according to the on / off of the switch circuit 5, it is possible to switch the light emission of the LD at a high speed, which is complicated. It is possible to reduce the cost without requiring treatment, and to alleviate the deterioration of the switching characteristics of LD light emission over time.
[0022]
FIG. 4 shows a second embodiment of the present invention. The second embodiment is an embodiment of the invention according to claim 2, and in the first embodiment, the voltage source 4 is replaced with the Zener diode 6 and the Zener voltage Vz of the Zener diode 6 is set smaller than Vfld. It is. When the switch circuit 5 is closed, the Zener diode 6 generates a Zener voltage Vz by the current flowing from the current source 2, and the combined voltage of the voltage drop Vr of the resistor 3 and the Zener voltage Vz of the Zener diode 6 is the terminal of LD1. It becomes equal to the voltage Vop. Therefore, the terminal voltage Vop of LD1 is smaller than the voltage Vfld as shown in FIG.
[0023]
As described above, the second embodiment is an embodiment of the invention according to claim 2, and in the semiconductor laser driving device according to claim 1, the voltage source 4 is used as a Zener diode 6 and the Zener voltage of the Zener diode 6 is changed. Since Vz is the voltage of the voltage source 4, it is possible to switch the light emission of the LD at high speed, to reduce the cost without requiring a complicated process, and to alleviate the deterioration of the switching characteristics of the LD light emission over time. Can do.
[0024]
FIG. 5 shows a third embodiment of the present invention. The third embodiment is an embodiment of the invention according to claim 3. In the first embodiment, the voltage source 4 is replaced with the diode 7, and the forward drop voltage Vf of the diode 7 is changed to that of the voltage source 4. It is a voltage. The forward voltage drop Vf of the diode 7 is set smaller than Vfld. When the switch circuit 5 is closed, a current flows from the current source 2 to the diode 7 to generate a forward drop voltage Vf, and a combined voltage of the voltage drop Vr of the resistor 3 and the forward drop voltage Vf of the diode 7 is LD1. Is equal to the terminal voltage Vop. Therefore, the terminal voltage Vop of LD1 is smaller than the voltage Vfld as shown in FIG.
[0025]
FIG. 6 shows a fourth embodiment of the present invention. The fourth embodiment is another embodiment of the invention according to claim 3. In the first embodiment, the switch circuit 5 is composed of the transistor 8, and the current source 2 is composed of the transistor 9 and the resistors 10 to 12. The current source is configured as follows. The current source 2 outputs a current corresponding to the current instruction signal, and the transistor 8 is turned on / off by the switching signal.
Incidentally, the third and fourth embodiments, although the diode 7 is one, which may be a plurality of diodes connected in series toward the same direction.
[0026]
Thus, the third embodiment and the fourth embodiment are embodiments of the invention according to claim 3, and in the semiconductor laser driving device according to claim 1, the voltage source 4 is replaced with one or a plurality of diodes. 7 and the forward voltage drop of the diode 7 is used as the voltage of the voltage source 4, so that the light emission of the LD can be switched at high speed and can be made inexpensive without requiring complicated processing. Degradation of switching characteristics of LD emission over time can be alleviated.
[0027]
The first to fourth embodiments are also embodiments of the invention according to claim 4, wherein the resistor 3 and the voltage source 4 in the semiconductor laser driving device according to claim 1, 2 or 3. , 6 and 7, forward current is applied to the LD 1 when the current from the current source 2 is supplied, and the light emission of the LD is switched at high speed as in the first to fourth embodiments. It is possible to reduce the switching characteristics of LD light emission over time, and it can be made inexpensive without requiring complicated processing.
[0028]
Further, the first to fourth embodiments are also embodiments of the invention according to claim 5, and in the semiconductor laser driving device according to claim 4, the resistor 3 and the voltage sources 4, 6, 7 are provided. The forward voltage applied to the LD 1 when the current from the current source 2 is supplied is a voltage at which the LD 1 does not emit light, and the LD emits light at high speed as in the first to fourth embodiments. It is possible to perform switching, the cost can be reduced without requiring complicated processing, and the deterioration of switching characteristics of LD light emission over time can be reduced.
[0029]
【The invention's effect】
As described above, according to the first aspect of the present invention, the current source connected in series to the semiconductor laser to supply current to the semiconductor laser and emit the semiconductor laser with a predetermined amount of light, and in parallel with the semiconductor laser A voltage source connected in series to a connected resistor; and a switch circuit connected in series to the voltage source to turn on / off the semiconductor laser, and the current source according to on / off of the switch circuit wherein since the on / off the current flowing through the resistor and the voltage source from, can be switched to light-emitting semiconductor laser at a high speed, it can be inexpensively without requiring complicated processes, further switching of the LD light emission over time The deterioration of characteristics can be reduced.
[0030]
According to the invention of claim 2, in the semiconductor laser driving device of claim 1, since the voltage source is a Zener diode and the Zener voltage of the Zener diode is the voltage of the voltage source, the semiconductor laser emits light at high speed. It is possible to perform switching at a low cost without requiring complicated processing, and further, it is possible to alleviate the deterioration of switching characteristics of LD light emission over time.
[0031]
According to a third aspect of the present invention, in the semiconductor laser driving device according to the first aspect, the voltage source is constituted by one or a plurality of diodes, and the forward voltage drop of the diode is used as the voltage of the voltage source. Therefore, it is possible to switch the light emission of the semiconductor laser at high speed, to reduce the cost without requiring complicated processing, and to alleviate the deterioration of the switching characteristics of the LD light emission over time.
[0032]
According to a fourth aspect of the present invention, in the semiconductor laser driving device according to the first, second, or third aspect, when a current from the current source is supplied to the resistor and the voltage source, a forward voltage is applied to the semiconductor laser. Therefore, it is possible to switch the light emission of the semiconductor laser at high speed, to reduce the cost without requiring a complicated process, and to alleviate the deterioration of the switching characteristics of the LD light emission over time.
[0033]
According to a fifth aspect of the present invention, in the semiconductor laser driving device according to the fourth aspect, the forward voltage applied to the semiconductor laser when the current from the current source flows through the resistor and the voltage source is Since it is a voltage at which the semiconductor laser does not emit light, it is possible to switch the emission of the semiconductor laser at high speed, to reduce the cost without requiring complicated processing, and to alleviate the deterioration of the switching characteristics of the LD emission over time. it can.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram showing the semiconductor laser lighting state of the first embodiment.
FIG. 3 is an equivalent circuit diagram showing the semiconductor laser extinguishing state of the first embodiment;
FIG. 4 is a circuit diagram showing a second embodiment of the present invention.
FIG. 5 is a circuit diagram showing a third embodiment of the present invention.
FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention.
FIG. 7 is a characteristic diagram showing current-light characteristics of a semiconductor laser.
FIG. 8 is a characteristic diagram showing voltage-current characteristics of a semiconductor laser.
FIG. 9 is a characteristic diagram showing voltage-light characteristics of a semiconductor laser.
FIG. 10 is a circuit diagram showing an example of a conventional semiconductor laser driving device.
FIG. 11 is a characteristic diagram showing operating characteristics of the semiconductor laser driving device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Current source 3 Resistance 4 Voltage source 5 Switch circuit 6 Zener diode 7 Diode 8, 9 Transistors 10-12 Resistance 13 Bias current source 14 Switching current source

Claims (5)

A current source connected in series to the semiconductor laser to supply current to the semiconductor laser and emit the semiconductor laser at a predetermined light amount; a voltage source connected in series to a resistor connected in parallel with the semiconductor laser; A switch circuit connected in series to the voltage source to turn on / off the semiconductor laser, and the current flowing from the current source to the resistor and the voltage source is turned on / off according to on / off of the switch circuit. A semiconductor laser driving device.   2. The semiconductor laser driving device according to claim 1, wherein the voltage source is a Zener diode, and a Zener voltage of the Zener diode is a voltage of the voltage source.   2. The semiconductor laser driving device according to claim 1, wherein the voltage source is composed of one or a plurality of diodes, and a forward drop voltage of the diode is used as the voltage of the voltage source. 4. The semiconductor laser driving device according to claim 1, wherein a forward voltage is applied to the semiconductor laser when a current from the current source is supplied to the resistor and the voltage source. Drive device. 5. The semiconductor laser driving device according to claim 4, wherein a forward voltage applied to the semiconductor laser when a current from the current source is supplied to the resistor and the voltage source is a voltage at which the semiconductor laser does not emit light. A semiconductor laser driving device.

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