Laser diode device

Abstract

Provided is a laser diode device capable of turning off energization of a laser diode when an amount of light exceeds a specific value while adjusting the amount of light. The laser diode device comprises: the laser diode; a supply unit that supplies a specific amount of electric power to the laser diode; an energization stopping unit that stops the energization of the laser diode when a current flowing through or a voltage applied to the laser diode exceeds a threshold value; and a first adjustment unit that adjusts a current flowing through or a voltage applied to the energization stopping unit.

Description

Laser Diode Device

[0001] The present disclosure relates to laser diode devices.

[0002] Patent Document 1 discloses a laser driver circuit that prevents excessive output from a semiconductor laser and maintains stable optical output even when the power supply voltage rises due to an abnormal voltage. This laser driver circuit includes a semiconductor laser, a light-receiving element that receives light emitted from the semiconductor laser and outputs a monitor current based on the amount of received light, and multiple APC circuits connected in parallel, each including an operating current control element connected in series to the semiconductor laser and a light intensity control element that controls the operating current control element so that the monitor current value becomes a reference value for determining the optical output of the semiconductor laser. Each of the multiple APC circuits is provided with multiple power supplies for generating the reference value.

[0003] Japanese Patent Application Publication No. 2005-123536

[0004] The present disclosure has been devised in consideration of the above-mentioned conventional circumstances, and aims to provide a laser diode device that can adjust the light intensity and turn off power to the laser diode if the light intensity exceeds a certain level due to a malfunction or other reason.

[0005] The present disclosure provides a laser diode device comprising an adjustment unit that adjusts the current flowing through or the voltage applied to a laser diode in accordance with the amount of laser light, and a current stop unit that stops the flow of current to the laser diode when the current flowing through or the voltage applied to the laser diode exceeds a threshold value.

[0006] According to the present disclosure, while adjusting the light intensity, if the light intensity exceeds a certain level due to a malfunction or the like, power to the laser diode can be turned off.

[0007] Schematic diagram showing an example of the configuration of a laser diode device according to this embodiment. FIG. 1 shows an example of the configuration of an LD current limiting circuit according to this embodiment. FIG. 2 shows another example of the configuration of an LD current limiting circuit according to this embodiment. FIG. 3 shows an example of the configuration of a laser diode device according to this embodiment.

[0008] (Background to the present disclosure) The laser drive circuit of Patent Document 1 prevents excessive output from the semiconductor laser and maintains stable optical output even when the power supply voltage rises due to an abnormal voltage. For example, Patent Document 1 describes that by providing multiple APC circuits, even if one of them fails, stable optical output can be maintained by driving the other APC circuits. In other words, by providing multiple APC circuits, a constant output can be ensured even if an APC circuit fails. However, in this case, there was a problem in that a constant output could not be ensured if the laser diode itself failed.

[0009] Hereinafter, with reference to the drawings as appropriate, detailed descriptions of specific embodiments of a laser diode device according to the present disclosure will be provided. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0010] (First Embodiment) 1. Regarding the Laser Diode Device First, an example of a laser diode device according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an example of the configuration of a laser diode device 1 according to the present embodiment. The laser diode device 1 includes at least an LD driver circuit 10, a laser diode 11, a light intensity adjustment semi-fixed resistor 12, an LD current limiting circuit 20 having an LD shutdown current adjustment semi-fixed resistor 13 and a thermistor 14, and a control microcomputer 30.

[0011] The LD driver circuit 10 includes an APC (Auto Power Control) circuit that has the function of driving the laser diode 11, and a switch (transistor) that is controlled by the APC circuit.

[0012] The light intensity adjustment semi-fixed resistor 12 is a resistor whose resistance value can be finely adjusted by the APC circuit, and by finely adjusting the resistance value, it is possible to finely adjust the power value (e.g., the current flowing through the laser diode 11 or the voltage applied to the laser diode 11) as a reference value to be supplied to the laser diode 11, thereby finely adjusting the light intensity of the laser diode 11 to a constant level. In other words, the light intensity adjustment semi-fixed resistor 12 functions as an adjustment unit that adjusts the current flowing through the LD, which is a light-emitting element of the laser diode 11, or the voltage applied to the LD of the laser diode 11 in accordance with the light intensity of the laser diode 11. Furthermore, because the light intensity adjustment semi-fixed resistor 12 is a semi-fixed resistor, it is possible to adjust the current flowing through the laser diode 11 or the voltage applied to the laser diode 11.

[0013] The laser diode 11 includes a laser diode (LD) as a light-emitting element and a photodiode (PD) as a light-receiving element. The APC circuit of the LD driver circuit 10 receives the light intensity of the LD, which is the light-emitting element constituting the laser diode 11, via the PD and adjusts the resistance value of the light intensity adjustment semi-fixed resistor 12 so that the received light intensity of the LD is constant. Laser diodes 11 are generally subject to safety standards to prevent injury to users. For example, laser diodes 11 classified as Class 1 are required to be used within a light intensity range deemed safe even for extended periods of direct intrabeam observation, even when using optical observation tools (such as a magnifying glass or binoculars). For example, the maximum light intensity power is 7 mW or less. While it is desirable for the laser diode 11 to output the maximum light intensity within the Class 1 range, individual differences exist among the LDs constituting the laser diode 11, and the current value corresponding to the maximum light intensity within the Class 1 range also varies from one individual to another.

[0014] The LD current limiting circuit 20 can turn off (stop or limit) the power supply to the laser diode 11 so that the output does not exceed a certain level when the light intensity of the LD, which is a light-emitting element constituting the laser diode 11, exceeds a threshold, i.e., when the current flowing through the laser diode 11 exceeds a threshold. Note that this threshold light intensity and current threshold are threshold light intensity and current thresholds that increase due to, for example, a failure of the PD, which is a light-receiving element constituting the laser diode 11, or a failure of the APC circuit of the LD driver circuit 10.

[0015] The LD current limiting circuit 20 may also have a reset function that turns on the laser diode 11 again (i.e., unlatches) after turning off the power to the laser diode 11 based on an instruction from the control microcomputer 30 at an appropriate timing selected by the user. However, if there are no individual differences in the LD of the laser diode 11, the LD shutdown current adjustment semi-fixed resistor 13 does not need to be driven to a fixed value and adjusted, and therefore the LD current limiting circuit 20 does not need to have the reset function. The LD shutdown current adjustment semi-fixed resistor 13 included in the LD current limiting circuit 20 will be described in detail later. The LD shutdown current adjustment semi-fixed resistor 13 is a resistor whose resistance value can be finely adjusted, and by finely adjusting the resistance value, the current or voltage threshold at which power to the laser diode 11 is stopped can be adjusted. In other words, because the LD shutdown current adjustment semi-fixed resistor 13 is a semi-fixed resistor, it is possible to adjust the current flowing through the LD current limiting circuit 20 or the voltage applied to the LD current limiting circuit 20. That is, the LD shutdown current adjusting semi-fixed resistor 13 adjusts the current flowing through the LD current limiting circuit 20 or the voltage applied to the LD current limiting circuit 20. This adjustment determines at what current value or voltage value the LD current limiting circuit 20 will shut off the power supply to the laser diode 11. When the temperature of the laser diode 11 rises due to light emission, the current flowing through it increases, but the thermistor 14 included in the LD current limiting circuit 20 decreases in resistance as the temperature rises, so that the voltage applied to the LD, which is the light emitting element constituting the laser diode 11, can be kept relatively constant even when the temperature changes.

[0016] The control microcomputer 30 controls the laser diode 11 and includes an interface, a processor, and a memory. The processor may be configured using, for example, a central processing unit (CPU), a digital signal processor (DSP), or a field programmable gate array (FPGA). The memory includes a read-only memory (ROM) and a random access memory (RAM). The ROM stores programs that define the processing (operations) of the processor of the control microcomputer 30 and data referenced when the programs are executed. The RAM is a working memory used when the processor processes (operations) and temporarily stores data or information generated or acquired during each process.

[0017] The optical power meter 100 can measure the amount of light (optical power) of the laser diode 11. The optical power meter 100 determines whether each laser diode 11 is emitting a value close to the threshold value of the amount of light of Class 1.

[0018] 2. Light Intensity Adjustment Next, the light intensity adjustment of the laser diode 11 will be described. As mentioned above, there is a demand for the laser diode 11 to output the maximum light intensity within the range classified as Class 1. However, there are individual differences in the LDs, which are the light-emitting elements that make up the laser diode 11, and the current value corresponding to the maximum light intensity within the range classified as Class 1 also differs from one laser diode to another. As a result, it is ideal to adjust the current value for each laser diode 11 so that it corresponds to the maximum light intensity within the range classified as Class 1.

[0019] First, the control microcomputer 30 issues an instruction to the LD driver circuit 10 to turn on the LD, which is the light-emitting element constituting the laser diode 11. Then, based on the instruction from the control microcomputer 30, the APC circuit of the LD driver circuit 10 sets the light intensity to limit the current flowing through the LD, which is the light-emitting element constituting the laser diode 11. Furthermore, the control microcomputer 30 causes the LD current limiting circuit 20 to adjust the resistance value of the LD shutdown current adjusting semi-fixed resistor 13. Specifically, the resistance value of the LD shutdown current adjusting semi-fixed resistor 13 is set to the maximum adjustable value. This prevents the LD current limiting circuit 20 from turning on when adjusting the output of the laser diode 11. Then, the resistance value of the light intensity adjusting semi-fixed resistor 12 is adjusted to adjust the power value so that the output of the laser diode 11 is constant (i.e., so that individual differences between laser diodes 11 are eliminated). The output of the laser diode 11 is adjusted so as not to exceed a threshold value. For example, this is 7 mW for Class 1. The resistance value of the LD shutdown current adjustment semi-fixed resistor 13 is then gradually decreased until the laser diode 11 is turned off (i.e., the LD current limiting circuit 20 is ON), at which point the adjustment is stopped. The resistance value of the light intensity adjustment semi-fixed resistor 12 is then set to its maximum value, and the LD current limiting circuit 20 is turned OFF. The resistance value of the light intensity adjustment semi-fixed resistor 12 is then gradually decreased until it is set to a desired value within a range in which the output of the laser diode 11 does not exceed a threshold value (e.g., 7 mW for Class 1), thereby enabling adjustment of the light intensity of the laser diode 11.

[0020] 3. When an Abnormality Occurs Next, we will explain what happens when an abnormality occurs in the PD, which is the light-receiving element of the laser diode 11, or in the APC circuit of the LD driver circuit 10. First, the control microcomputer 30 issues an instruction to the LD driver circuit 10 to turn on the LD, which is the light-emitting element of the laser diode 11, thereby turning on the LD. If an abnormality occurs in the PD, which is the light-emitting element of the laser diode 11, or in the APC circuit of the LD driver circuit 10 (for example, if a current or voltage is detected that causes the light intensity of the laser diode 11 to exceed a threshold), the LD current limiting circuit 20 sends an alert to the control microcomputer 30 indicating that an abnormality has been detected. Then, based on the alert detection, the control microcomputer 30 issues an instruction to the LD driver circuit 10 to turn off the LD, which is the light-emitting element of the laser diode 11.

[0021] 4. Abnormality Detection and Response Next, detection and response when an abnormality occurs in the PD, which is the light receiving element provided in the laser diode 11, or the LD driver circuit 10 will be described. Fig. 2 is a diagram showing an example of the configuration of the LD current limiting circuit according to this embodiment. Fig. 3 is a diagram showing another example of the configuration of the LD current limiting circuit according to this embodiment. Fig. 4 is a diagram showing an example of the configuration of the laser diode device according to this embodiment.

[0022] Normally, the light intensity of the laser diode 11 can be adjusted by finely adjusting the resistance value of the light intensity adjustment semi-fixed resistor 12. However, if an abnormality occurs in the PD, which is the light receiving element provided in the laser diode 11, or in the APC circuit of the LD driver circuit 10, it may become impossible to maintain a constant light intensity of the laser diode 11. In such a case, the light intensity of the laser diode 11 may increase and exceed Class 1. Therefore, an LD current limiting circuit 20 is provided to turn off the power supply to the laser diode 11 in such a case.

[0023] First, the light intensity of the laser diode 11 is normally determined by the resistance value of the light intensity adjustment semi-fixed resistor 12. If an abnormality occurs in the PD, which is the light receiving element of the laser diode 11, or in the APC circuit of the LD driver circuit 10, the current flowing through or voltage applied to the laser diode 11 may exceed a threshold, which may result in the light intensity of the laser diode 11 exceeding the threshold. Therefore, when the light intensity of the laser diode 11 reaches the threshold, it is necessary to turn off the current supply to the laser diode 11.

[0024] 2 and 3, the LD current limiting circuit 20 includes a current amplifier circuit 21, a voltage detection circuit 22, a latch circuit 23, and an LD shutdown circuit 24. In the current amplifier circuit 21, the following equation (1) holds true.

[0025] Vout=(Rout(R3+R4) / Rin(R2))×LD current×R1...(1)

[0026] 2, R4 is a semi-fixed resistor, so Vout can be adjusted by adjusting R4, which is the resistance value of the semi-fixed resistor 13 for adjusting the LD shutdown current.

[0027] The voltage detection circuit 22 includes IC2. IC2 is a voltage comparator, and when the reference voltage Vout is smaller than Vout, the voltage at the OUT terminal of IC2 changes from 0V to 5V.

[0028] Latch circuit 23 is a circuit that, once switched on, maintains the on state even when the switch is turned off. Specifically, when Vout of IC2 reaches 5V, current flows through the base (B) of transistor Q3. The current flowing through the base (B) of transistor Q3 turns on transistor Q3, and current flows from the emitter (E) of transistor Q4 to transistor Q3. The current flowing through the base (B) of transistor Q4 turns on transistor Q4, and current flows from the emitter (E) of transistor Q4 to the base (B) of transistor Q3. As a result, a voltage is applied to the base (B) of transistor Q3, so the gate voltage of Q2 remains at 5V even when Vout of IC2 reaches 0V. In other words, latch circuit 23 can maintain a state in which power is not supplied to the laser diode (LD).

[0029] The LD shutdown circuit 24 has an FET Q2 that turns on and off the voltage supply to the laser diode 11. By controlling the voltage applied to the gate, the laser diode 11 can be turned on and off. For example, when Vout of IC2 becomes 5 V, the gate voltage of Q2 becomes 5 V, so Q2 is turned off. As a result, power supply to LD1 is cut off, and LD1 is turned off.

[0030] In the example shown in Figure 2, the resistance value of R4 is adjusted to adjust Vout so that the reference voltage < Vout is met only at the current value (LD current) corresponding to the maximum light output within the Class 1 range for the corresponding laser diode 11. When the LD current exceeds the threshold, the reference voltage < Vout occurs, and the OUT voltage of IC2 changes from 0V to 5V. When the OUT voltage of IC2 changes from 0V to 5V, the gate voltage of Q2 becomes 5V, turning Q2 OFF. As a result, power is no longer supplied to LD1, and LD1 turns off. When Vout of IC2 reaches 5V, the latch circuit 23 functions, maintaining the gate voltage of Q2 at 5V even when Vout of IC2 drops to 0V. In other words, Q2 remains OFF. While Q2 is OFF, any necessary repairs can be performed.

[0031] 3, the resistance value of R5 is a fixed value. On the other hand, R8 of the voltage detection circuit 22 is a semi-fixed resistor. In this case, the Vout value is a fixed value, but the value of the reference voltage can be adjusted by R8 as shown in the following equation (2).

[0032] Reference voltage = 5V × (R9 / (R8+R9)) (2)

[0033] Therefore, in the case of Figure 3, the resistance value of R8 is adjusted to adjust the reference voltage so that the reference voltage < Vout is met only at the current value (LD current) corresponding to the maximum light intensity within the Class 1 range for the corresponding laser diode 11. When the LD current exceeds the threshold, the reference voltage < Vout occurs, and the OUT voltage of IC2 changes from 0V to 5V. When the OUT voltage of IC2 changes from 0V to 5V, the gate voltage of Q2 becomes 5V, turning Q2 OFF. As a result, power is no longer supplied to LD1, and LD1 turns off. Furthermore, when Vout of IC2 reaches 5V, the latch circuit 23 functions, maintaining the gate voltage of Q2 at 5V even when Vout of IC2 drops to 0V. In other words, Q2 remains OFF. While Q2 is OFF, any necessary repairs can be performed.

[0034] As shown in FIG. 4, the laser diode device 1 may have a configuration in which part of the LD current limiting circuit 20 is realized by an integrated circuit, an IC chip, or the like.

[0035] 5. Thermistor: The light intensity of the laser diode 11 changes significantly with temperature. That is, as the temperature of the laser diode 11 rises, the current increases even if the light intensity remains the same. Therefore, it is recommended to provide a thermistor 14 in series or parallel to the semi-fixed resistor 13 for adjusting the LD shutdown current.

[0036] In the case of Figure 2, the resistance value of the thermistor 14 (R3) decreases as the temperature rises. If the temperature of the laser diode 11 rises without the thermistor 14 (R3), the LD current increases, causing Vout to increase, and the laser diode 11 turns off even if the light intensity does not reach the threshold. However, if the thermistor 14 (R3) is present, the resistance value of Rout decreases, and Vout decreases. As a result, even if the temperature rises, Vout can be kept relatively constant, and the light intensity of the laser diode 11 can be maintained at a desired level.

[0037] In addition, in the case of FIG. 3, a thermistor 14 (R9) is provided. If the temperature rises without the thermistor 14 (R9), the LD current increases, causing Vout to increase, and the laser diode 11 turns off even if the light intensity has not reached the threshold. However, if the thermistor 14 (R9) is present, the resistance of the thermistor 14 (R9) decreases even when the temperature rises, causing the reference voltage to increase. As a result, even if Vout increases, the reference voltage also increases, making it possible to adjust the relationship so that the reference voltage is less than Vout when the light intensity of the laser diode 11 reaches the threshold. As a result, the light intensity of the laser diode 11 can be maintained at a desired level even when the temperature rises.

[0038] In this way, by providing the thermistor 14 connected in series or parallel to the semi-fixed resistor 13 for adjusting the LD shutdown current, which adjusts the threshold of the current flowing through the laser diode (LD) or the voltage applied thereto, the light intensity of the laser diode 11 can be maintained at a desired level.

[0039] (Additional Notes) The above description of each embodiment discloses the following techniques.

[0040] (Item 1) A laser diode device (1) comprising: a laser diode (LD, which is a light-emitting element provided in the laser diode); a supply unit (APC circuit) that supplies a constant power to the laser diode; a current-supply stopping unit (LD current limiting circuit 20) that stops power supply to the laser diode when a current flowing through or a voltage applied to the laser diode exceeds a threshold; and a first adjusting unit (LD shutdown current adjusting semi-fixed resistor 13) that adjusts the current flowing through or the voltage applied to the current-supply stopping unit. As a result, the laser diode device can adjust the light intensity while turning off power supply to the laser diode when the light intensity exceeds a certain level.

[0041] (Item 2) The laser diode device according to Item 1, further comprising a second adjustment unit (light intensity adjustment semi-fixed resistor 12) that adjusts the current flowing through or voltage applied to the laser diode. This makes it possible for the laser diode device to effectively adjust the light intensity while turning off power to the laser diode if the light intensity exceeds a certain level due to a malfunction or the like.

[0042] (Item 3) The laser diode device according to Item 1 or 2, wherein the power supply stopping unit further includes a power supply restarting unit (LD current limiting circuit 20) that restarts power supply to the laser diode. As a result, the laser diode device can adjust the output of the laser diode by current limiting, and then restart power supply to the laser diode by canceling the current limiting.

[0043] (Item 4) The laser diode device according to Item 1, further comprising a thermistor (14) provided in series or parallel to the second adjustment unit (light intensity adjustment semi-fixed resistor 12). As a result, even if a temperature change occurs in the laser diode, the laser diode device can adjust the light intensity and turn off power to the laser diode when the light intensity exceeds a certain level.

[0044] (Item 5) The laser diode device according to Item 1 or 2, wherein the first adjustment unit (semi-fixed resistor 13 for adjusting the LD shutdown current) adjusts the current flowing through or the voltage applied to the laser diode (LD) using a semi-fixed resistor. This allows the laser diode device to effectively adjust the light intensity and turn off the power to the laser diode when the light intensity exceeds a certain level.

[0045] (Item 6) The laser diode device according to Item 2, wherein the second adjustment unit (light intensity adjustment semi-fixed resistor 12) adjusts a threshold value of a current flowing through or a voltage applied to the laser diode (LD) using a semi-fixed resistor. As a result, the laser diode device can adjust the light intensity and effectively turn off the power to the laser diode when the light intensity exceeds a certain level.

[0046] (Item 7) The laser diode device according to Item 1 or 2, wherein the power supply stopping unit (LD current limiting circuit 20) includes a latch circuit (latch circuit 23) that maintains the power supply limit to the laser diode. As a result, the laser diode device can adjust the light intensity while turning off the power supply to the laser diode when the light intensity exceeds a certain level, and can effectively maintain the off state.

[0047] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0048] This application is based on a Japanese patent application (Patent Application No. 2024-146472) filed on August 28, 2024, the contents of which are incorporated herein by reference.

[0049] INDUSTRIAL APPLICABILITY The present disclosure is useful as a laser diode device that can adjust the light intensity and turn off power to the laser diode when the light intensity exceeds a certain level.

[0050] REFERENCE SIGNS LIST 1 Laser diode device 10 LD driver circuit 11 Laser diode 12 Light intensity adjustment semi-fixed resistor 13 Semi-fixed resistor for adjusting LD shutdown current 14 Thermistor 20 LD current limiting circuit 21 Current amplifier circuit 22 Voltage detection circuit 23 Latch circuit 24 LD shutdown circuit 30 Control microcomputer 100 Optical power meter

Claims

1. A laser diode device comprising: a laser diode; a supply unit that supplies a constant power to the laser diode; a current stop unit that stops the supply of power to the laser diode when the current flowing through or the voltage applied to the laser diode exceeds a threshold; and a first adjustment unit that adjusts the current flowing through or the voltage applied to the current stop unit.

2. The laser diode device according to claim 1, further comprising a second adjustment section that adjusts the current flowing through or the voltage applied to the laser diode.

3. The laser diode device according to claim 1, wherein the power supply stopping unit further comprises a power supply restarting unit that restarts power supply to the laser diode.

4. The laser diode device according to claim 2, further comprising a thermistor provided in series or parallel to the second adjustment section.

5. The laser diode device according to claim 1 or 2, wherein the first adjustment section adjusts the current flowing through or the voltage applied to the laser diode using a semi-fixed resistor.

6. The laser diode device according to claim 2, wherein the second adjustment section adjusts the threshold of the current flowing through or the voltage applied to the laser diode using a semi-fixed resistor.

7. The laser diode device according to claim 1 or 2, wherein the power supply stopping section includes a latch circuit that maintains the power supply restriction to the laser diode.

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