Drive circuit and control method for the drive circuit

Abstract

To provide a technology to realize a drive circuit that can suppress fluctuations in optical output due to temperature with a simple configuration.SOLUTION: A drive circuit has a first terminal and a second terminal to which a semiconductor laser diode can be connected, a current monitoring circuit that generates a first voltage that decreases monotonically with an increase in the drive current flowing through the semiconductor laser diode connected between the first and second terminals, a reference voltage generation circuit that generates the second voltage that monotonically decreases with an increase in the ambient temperature, and a control circuit that controls the drive current to reduce the difference between the first and second voltages.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a drive circuit and the like.

Background Art

[0002] With the increase in data traffic, the capacity of optical transmission systems has been increasing. In order to support high-capacity optical transmission systems, higher functionality and lower cost are required for terrestrial stations and submarine repeaters in terrestrial optical transmission systems and submarine optical transmission systems. For example, a drive circuit for driving a semiconductor laser diode is used as a light source for optical signals and an excitation light source for optical fiber amplifiers. Drive circuits are required to achieve the function of stabilizing optical output with a simple configuration. Hereinafter, a semiconductor laser diode is simply referred to as "LD".

[0003] Figure 7 is a diagram showing a general circuit of a drive circuit 900 for driving an LD. The drive circuit 900 includes resistors R1, R4, and R5, an LD 910, and a control circuit 920. Voltage V1 represents the voltage of the power supply voltage Vcc after the voltage drop across the resistor R1. By keeping the voltage V1 constant, the drive current of the LD 910 can be controlled to a constant value. Voltage V2 is a constant voltage obtained by dividing the power supply voltage Vcc by the resistor R4 and the resistor R5, and is constant regardless of temperature. The control circuit 920 controls the drive current of the LD 910 so that the voltage V1 approaches the voltage V2. Since the voltage V2 is constant, the control circuit 920 can drive the LD 910 with a constant current by setting the voltage V2 such that the current flowing through the LD 910 reaches a desired value.

[0004] In relation to the present invention, Patent Document 1 describes a constant current drive circuit for an LD.

Prior Art Literature

Patent Literature

[0005]

Patent Literature 1

Summary of the Invention

[0006] In general, the threshold current of a laser diode (LD) increases at high temperatures, while the slope efficiency (SE) decreases at high temperatures. Here, the threshold current is the current at which the LD begins to oscillate. Slope efficiency is the change in optical output with respect to the change in the drive current of the LD, and is measured in watts (W / A). Slope efficiency can also be expressed as the slope of the current-optical output characteristic of the LD. Due to these characteristics of the LD, when the LD is driven with a constant current, fluctuations in temperature cause large fluctuations in the optical output of the LD. Such fluctuations in optical output are particularly noticeable when the LD is driven with a current close to the threshold current.

[0007] Figure 8 illustrates the relationship between the drive current and optical output of the LD910 shown in Figure 7. The horizontal axis (Id) represents the drive current of the LD910, and the vertical axis (P) represents the optical output of the LD910. Figure 8 shows examples of the current-optical output characteristics (hereinafter referred to as "IL characteristics") of the LD910 when the ambient temperature is low and when it is higher. Here, "low temperature" refers to room temperature, for example, around 25°C, and "high temperature" refers to a temperature higher than "low temperature" (for example, around 40°C). Id1 is the drive current when the optical output of the LD910 is low (i.e., when the drive current is close to the threshold current), and Id2 is the drive current when the optical output is greater than Id1. In Figure 8, when the drive current Id of the LD910 is less than the threshold current, the optical output P of the LD910 is considered to be 0, and when it is above the threshold current, the optical output P is considered to increase linearly with respect to the drive current.

[0008] As the ambient temperature of the LD910 increases, the slope of the IL characteristic (i.e., the slope efficiency) decreases. Also, the threshold current Ith2 at a high ambient temperature is greater than the threshold current Ith1 at a lower ambient temperature. Therefore, even when the LD910 is driven with the same current (Id1 or Id2), as the ambient temperature of the LD910 changes from low to high, the optical output of the LD910 changes downward in Figure 8. That is, the optical output decreases as shown by the difference between "P1 (low temperature)" and "P1 (high temperature)" or the difference between "P2 (low temperature)" and "P2 (high temperature)". Furthermore, the rate of decrease in optical output is greater as the driving current Id decreases.

[0009] As shown in Figure 8, the temperature-dependent fluctuations in the optical output of the LD910 can cause fluctuations in the transmission level of the optical signal and fluctuations in the gain of the optical amplifier. In other words, fluctuations in the ambient temperature of the LD910 may adversely affect the transmission quality of the optical transmission system. Therefore, the LD driver circuit used in optical transmission systems is required to have a simple configuration that can suppress fluctuations in optical output in response to temperature changes.

[0010] (Purpose of the invention) The present invention aims to provide a technology for realizing a drive circuit with a simple configuration that can suppress fluctuations in optical output due to temperature. [Means for solving the problem]

[0011] The drive circuit of the present invention is A first terminal and a second terminal to which a semiconductor laser can be connected, A current monitoring means that generates a first voltage that decreases monotonically with respect to the drive current flowing through the semiconductor laser connected between the first terminal and the second terminal, A reference voltage generating means that generates a second voltage that decreases monotonically with respect to ambient temperature, Control means for controlling the drive current to reduce the difference between the first voltage and the second voltage, It is equipped with.

[0012] The control method for the drive circuit of the present invention is: generating a first voltage that decreases monotonically with respect to a driving current, generating a second voltage that decreases monotonically with respect to an ambient temperature, controlling the driving current so as to reduce a difference between the first voltage and the second voltage. Effects of the Invention

[0013] The present invention enables provision of a driving circuit that can suppress fluctuation of light output due to temperature with a simple configuration. Brief Description of Drawings

[0014] [Figure 1] It is a diagram showing a configuration example of a driving circuit according to a first embodiment. [Figure 2] It is a diagram showing a configuration example of a driving circuit according to a second embodiment. [Figure 3] It is a diagram showing a configuration example of a diode group. [Figure 4] It is a diagram showing a configuration example of a diode group. [Figure 5] It is a diagram for explaining an example of a relationship between an LD driving current and light output in the second embodiment. [Figure 6] It is a flowchart showing an example of a control method for a driving circuit. [Figure 7] It is a diagram showing a general circuit of a driving circuit. [Figure 8] It is a diagram explaining a relationship between an LD driving current and light output. Mode for Carrying Out the Invention

[0015] Embodiments of the present invention will be described below with reference to the drawings. In the embodiments and the drawings, already described elements are denoted by the same reference numerals, and overlapping descriptions may be omitted.

[0016] First Embodiment FIG. 1 is a diagram showing a configuration example of the drive circuit 100 according to the first embodiment of the present invention. The drive circuit 100 includes a first terminal 111, a second terminal 112, a current monitoring circuit 120, a reference voltage generation circuit 130, and a control circuit 140. The first terminal 111 and the second terminal 112 are electrical interfaces that allow connection of a general semiconductor laser diode (LD) 180 inside or outside the drive circuit 100. Note that the LD 180 does not need to be included in the drive circuit 100.

[0017] The LD 180 is connected between the first terminal 111 and the second terminal 112. The current monitoring circuit 120 outputs a first voltage V1. The first voltage V1 decreases monotonically with an increase in the current flowing through the LD 180 (drive current). Further, the first voltage V1 rises monotonically with a decrease in the drive current. The reference voltage generation circuit 130 outputs a second voltage V2. The second voltage V2 decreases monotonically with an increase in the ambient temperature of the drive circuit 100. Further, the second voltage V2 rises monotonically with a decrease in the ambient temperature of the drive circuit 100. The first voltage V1 and the second voltage V2 are input to the control circuit 140. The control circuit 140 controls the drive current so as to reduce a difference between the first voltage V1 and the second voltage V2. Note that the current monitoring circuit 120 is one form of current monitoring means, the reference voltage generation circuit 130 is one form of reference voltage generation means, and the control circuit 140 is one form of control means.

[0018] The drive circuit 100 having such a configuration can suppress fluctuations in the optical output of the LD 180 due to temperature changes with a simple structure. The reason is as follows.

[0019] For the LD 180, when the ambient temperature rises, the threshold current increases and the slope efficiency decreases. The ambient temperature is a temperature of a space including the LD 180 and the reference voltage generation circuit 130. Therefore, when the LD 180 is driven at a constant drive current, as described with reference to FIG. 8, the optical output of the LD 180 decreases due to the rise in the ambient temperature.

[0020] However, in the drive circuit 100 of this embodiment, when the ambient temperature of the drive circuit 100 rises, the second voltage V2 output by the reference voltage generation circuit 130 decreases. The control circuit 140 then controls the drive current of the LD180 so that the first voltage V1 approaches the second voltage V2. Here, since the first voltage V1 decreases monotonically with increasing drive current, the control circuit 140 increases the drive current to lower the first voltage V1. As a result, the optical output of the LD180 increases, and the decrease in the optical output of the LD180 caused by the rise in ambient temperature of the drive circuit 100 is suppressed. Thus, the control circuit 140 increases the drive current of the LD180 when the temperature rises.

[0021] Furthermore, when the ambient temperature decreases, the drive circuit 100 operates to suppress the increase in the optical output of the LD180 caused by the decrease in ambient temperature. That is, when the ambient temperature decreases, the second voltage V2 output by the reference voltage generation circuit 130 increases. On the other hand, the first voltage V1 increases monotonically with decreasing drive current, so the control circuit 140 reduces the drive current in order to increase the first voltage V1. As a result of the decrease in drive current, the increase in the optical output of the LD180 caused by the decrease in ambient temperature is suppressed.

[0022] In this way, the drive circuit 100 operates to suppress fluctuations in the optical output of the LD180 caused by changes in ambient temperature. As a result, the drive circuit can stabilize the optical output of the LD180. The LD180 is used, for example, as a light source for an optical transmitter used in an optical transmission system or as an excitation light source for an optical fiber amplifier.

[0023] (Second embodiment) Figure 2 shows an example configuration of the drive circuit 200 according to the second embodiment of the present invention. In the second embodiment, specific configuration examples of the current monitoring circuit 120 and the reference voltage generation circuit 130 described in the first embodiment will be explained.

[0024] The drive circuit 200 includes a first terminal 211, a second terminal 212, a current monitoring circuit 220, a reference voltage generation circuit 230, and a control circuit 240. The first terminal 211 and the second terminal 212 correspond to the first terminal 111 and the second terminal 112 of the first embodiment. The current monitoring circuit 220, the reference voltage generation circuit 230, and the control circuit 240 correspond to the current monitoring circuit 120, the reference voltage generation circuit 130, and the control circuit 140 of the first embodiment, respectively.

[0025] The anode of the LD180 is connected to the first terminal 211, and the cathode of the LD180 is connected to the second terminal 212. The current monitoring circuit 220 includes a resistor R1. The resistor R1 is placed between the first terminal 211 and the positive power supply (Vcc).

[0026] The current monitoring circuit 220 outputs the voltage between resistor R1 and the first terminal 211 as the first voltage V1. When LD180 is connected between the first terminal 211 and the second terminal 212, the voltage drop across resistor R1 (Id × R1) increases as the drive current of LD180 increases. Since the first voltage V1 is expressed as Vcc - (Id × R1), the first voltage V1 decreases monotonically with increasing drive current of LD180.

[0027] The reference voltage generation circuit 230 comprises resistors R2 and R3, and a diode group 231. One end of resistor R2 is connected to Vcc, and the other end of resistor R2 is connected to one end of resistor R3. The other end of resistor R3 is connected to one end of diode group 231, and the other end of diode group 231 is grounded (i.e., connected to GND). Resistors R2, R3, and diode group 231 are connected in series in this order. The reference voltage generation circuit 230 then outputs the voltage between resistors R2 and R3 as a second voltage V2.

[0028] Figures 3 and 4 both show examples of the configuration of diode group 231. Diode group 231 includes one or more semiconductor diodes. Figure 3 shows an example in which diode group 231 consists of one PN junction diode 232. Figure 4 shows an example in which diode group 231 consists of n PN junction diodes 232-1 to 232-n, where n is an integer of 2 or more. The PN junction diodes 232-1 to 232-n are connected in series. In both Figures 3 and 4, the PN junction diodes 232 are connected in the forward direction with respect to the power supply Vcc. That is, the anode of each PN junction diode 232 is on the side of resistor R3, and the cathode is on the side of GND.

[0029] The forward voltage drop across a single PN junction diode 232 is approximately 0.5V for a silicon diode, and it has a temperature characteristic of approximately -2mV / °C. That is, as the ambient temperature of the drive circuit 200 rises, the voltage drop across the PN junction diode 232 decreases. In Figure 2, the voltage drop across the diode group 231 is the voltage at the connection point between resistor R3 and the diode group 231 (i.e., the voltage on the GND side of resistor R3). Therefore, as the voltage drop across the diode group 231 decreases, the second voltage V2, which is divided by resistors R2 and R3, also decreases. On the other hand, the control circuit 240 controls the drive current of LD180 so that the first voltage V1 and the second voltage V2 are close together. For this reason, as the voltage drop across the diode group 231 decreases, the control circuit 240 increases the drive current of LD180 to lower the first voltage V1.

[0030] In this way, the control circuit 240 increases the drive current to the LD180 when the ambient temperature of the drive circuit 200 rises. Through this operation, the drive circuit 200 can suppress fluctuations in the optical output caused by the temperature characteristics of the optical output of the LD180. Furthermore, by appropriately selecting the number n of PN junction diodes 232 connected in series in the diode group 231, the amount of temperature-dependent change in the second voltage V2 generated by the reference voltage generation circuit 230 can be adjusted. For example, by connecting three PN junction diodes 232 in series in the diode group 231, the temperature characteristic of the voltage drop of the diode group 231 becomes approximately -6mV / °C. That is, in this case, the sensitivity of the second voltage V2 to temperature changes can be increased threefold compared to the case where only one PN junction diode 232 is used. The number n of PN junction diodes 232 in series may be selected in advance as a preferred number depending on individual differences in the LD180, etc.

[0031] Figure 5 illustrates an example of the relationship between the drive current and optical output of the LD180 when using the drive circuit 200 of this embodiment. In Figure 5, the specified value of the optical output of the LD180 is assumed to be P1. The specified value is, for example, the optical output power of the LD180 based on the specifications of the optical transmission system in which the LD180 is used. In Figure 5, at temperature T1 (low temperature), the threshold current of the LD180 is Ith1, and the drive current at which the optical output is P1 is Id1. At temperature T2 (high temperature), the threshold current of the LD180 is Ith2, and the drive current at which the optical output is P1 is Id2. Similar to Figure 8, "low temperature" in Figure 5 refers to, for example, room temperature of about 25°C, and "high temperature" refers to a temperature higher than "low temperature" (for example, about 40°C). When the ambient temperature of the LD180 is high, the slope of the IL characteristic (i.e., slope efficiency) is smaller compared to when the ambient temperature is low. In Figure 5, the optical output of LD180 is assumed to be 0 when the drive current of LD180 is less than the threshold current, and the optical output P is assumed to increase linearly with respect to the drive current when the drive current is greater than or equal to the threshold current.

[0032] If the drive current of the LD180 is not controlled even when the ambient temperature changes, the drive current Id remains at Id1. Therefore, when the ambient temperature rises from T1 to T2, the optical output of the LD180 decreases from P1 to P2.

[0033] However, in the drive circuit 200 shown in Figure 2 above, the control circuit 240 controls the drive current in accordance with the change in ambient temperature, thereby suppressing the change in drive current in response to the change in ambient temperature. In other words, in this embodiment, the drive circuit 200 controls the drive current of the LD180 in such a way that it suppresses the fluctuation in the optical output of the LD180 that accompanies fluctuations in ambient temperature. Figure 5 shows an example in which, when the ambient temperature of the LD180 fluctuates between T1 and T2, the control circuit 240 changes the drive current between Id1 and Id2, thereby maintaining the optical output P at P1 between T1 and T2.

[0034] However, the amount of control over the drive current of the LD180 in response to changes in ambient temperature is affected by the rate of change of the second voltage V2 in response to temperature changes, and the rate of change of the drive current in response to changes in the second voltage V2. For this reason, a value may be selected as the amount of change of the second voltage V2 in response to changes in ambient temperature that minimizes the fluctuation of the optical output P of the LD180 in response to changes in ambient temperature. The amount of change of the second voltage V2 in response to changes in ambient temperature may be set by selecting the type and number of PN junction diodes 232 in series based on prior evaluation. For example, the drive circuit 200 may first be operated using each of the diode groups 231 with different numbers of diodes in series n. Then, the diode group 231 with the number of diodes in series that provides the highest stability of the optical output of the LD180 in response to ambient temperature may be ultimately implemented in the drive circuit 200.

[0035] The temperature characteristics of the second voltage V2 output from the diode group 231 do not necessarily need to be such that the optical output of the LD180 can be kept strictly constant within the range of ambient temperature and drive current used by the drive circuit 200. Furthermore, the specifications and number of PN junction diodes 232 used in the diode group 231 may be selected differently depending on the specifications and individual differences of the LD180, as well as the power specifications of the optical signal required by the optical transmission system.

[0036] Figure 6 illustrates the control method of the drive circuit 200 described above as a flowchart. The drive circuit 200 generates a first voltage (V1) that decreases monotonically in response to an increase in drive current (step S1 in Figure 6). The drive circuit 200 also generates a second voltage (V2) that decreases monotonically in response to an increase in ambient temperature (step S2). Steps S1 and S2 may be performed in reverse order or simultaneously. The control circuit 240 then controls the drive current to reduce the difference between the first voltage and the second voltage.

[0037] Here, Second voltage V2 This may be generated by dividing the power supply voltage (Vcc) using a functional element (diode group 231) whose temperature characteristic of voltage drop is negative. The functional element consists, for example, of a single semiconductor diode or multiple semiconductor diodes connected in series. Second voltage V2 This may be generated by dividing the voltage (Vcc) supplied to the drive circuit 200 using resistors (R2 and R3) connected in series with the functional element. Then, following the procedure in Figure 6, the drive circuit 200 increases the drive current of the LD180 when the ambient temperature rises. As a result, the drive circuit 200 can suppress fluctuations in the optical output caused by the temperature characteristics of the optical output of the LD180.

[0038] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the embodiments described above. Various modifications to the configuration and details of the present invention can be made that will be understood by those skilled in the art within the scope of the present invention.

[0039] Furthermore, some or all of the functions and procedures described in each embodiment may be realized by a central processing unit (CPU) in the drive circuit 100 or 200 executing a control program.

[0040] For example, the control program causes the computer in the drive current control circuit to perform a procedure to acquire a first voltage that decreases monotonically with respect to the drive current. The control program also causes it to perform a procedure to acquire a second voltage that decreases monotonically with respect to the ambient temperature. Then, the control program causes it to perform a procedure to control the drive current. Here, the drive current is controlled to reduce the difference between the first voltage and the second voltage.

[0041] The control program is recorded on a fixed, non-temporary recording medium. Semiconductor memory is used as the recording medium, but is not limited to this. The computer is, for example, a CPU provided in the control circuit 140 or 240.

[0042] The embodiments of the present invention may also be described as follows, but are not limited thereto.

[0043] (Note 1) A first terminal and a second terminal to which a semiconductor laser diode can be connected, A current monitoring means that generates a first voltage that decreases monotonically with increasing drive current flowing through the semiconductor laser diode connected between the first terminal and the second terminal, A reference voltage generating means that generates a second voltage that decreases monotonically with increasing ambient temperature, Control means for controlling the drive current to reduce the difference between the first voltage and the second voltage, A drive circuit equipped with the following features.

[0044] (Note 2) The reference voltage generating means divides the power supply voltage using a functional element whose temperature characteristic of voltage drop is negative. Second voltage The drive circuit described in Appendix 1 generates the following.

[0045] (Note 3) The aforementioned functional element is a drive circuit as described in Appendix 2, comprising one semiconductor diode or multiple semiconductor diodes connected in series.

[0046] (Note 4) The aforementioned Second voltage The drive circuit described in Appendix 2 or 3 is generated by dividing the voltage supplied to the drive circuit by a resistor connected in series with the functional element.

[0047] (Note 5) The drive circuit described in any one of the appendices 1 to 4, wherein the amount of change in the second voltage in response to the change in ambient temperature is selected to a value that suppresses fluctuations in the optical output of the semiconductor laser diode caused by the change in ambient temperature.

[0048] (Note 6) A first voltage is generated that decreases monotonically with increasing drive current of the semiconductor laser diode. A second voltage is generated that decreases monotonically with increasing ambient temperature. A control method for a drive circuit, which controls the drive current to reduce the difference between the first voltage and the second voltage.

[0049] (Note 7) By using a functional element whose temperature characteristic of voltage drop is negative, the power supply voltage is divided. Second voltage A control method for the drive circuit described in Appendix 6, which generates the following.

[0050] (Note 8) Using the functional element consisting of one semiconductor diode or multiple semiconductor diodes connected in series, Second voltage A control method for the drive circuit described in Appendix 7, which generates the following.

[0051] (Note 9) By using a resistor connected in series with the functional element, the voltage supplied to the drive circuit is divided. Second voltage A method for controlling the drive circuit described in Appendix 7 or 8, which generates the following.

[0052] (Note 10) A control method for a drive circuit as described in any one of the appendices 6 to 9, wherein the amount of change in the second voltage in response to the change in ambient temperature is selected to suppress fluctuations in the optical output of the semiconductor laser driven by the drive current caused by the change in ambient temperature.

[0053] (Note 11) The computer included in the drive current control circuit A procedure for obtaining a first voltage that decreases monotonically with respect to the drive current, A procedure for obtaining a second voltage that decreases monotonically with respect to ambient temperature. A procedure for controlling the drive current to reduce the difference between the first voltage and the second voltage, A control program to execute [the command / function]. [Explanation of symbols]

[0054] 100, 200 drive circuit 111, 211 First terminal 112, 212 Second terminal 120, 220 current monitoring circuit 130, 230 Reference Voltage Generation Circuit 140, 240 control circuits 180 Semiconductor laser diode (LD) 231 Diode Group 232, 232-1~232-n PN junction diodes 900 drive circuit 920 Control Circuit

Claims

1. A first terminal and a second terminal to which a semiconductor laser diode can be connected, A current monitoring means that generates a first voltage that decreases monotonically with increasing drive current flowing through the semiconductor laser diode connected between the first terminal and the second terminal, A reference voltage generating means that generates a second voltage that decreases monotonically with increasing ambient temperature, Control means for controlling the drive current to reduce the difference between the first voltage and the second voltage, A drive circuit equipped with the following features.

2. The drive circuit according to claim 1, wherein the reference voltage generating means generates the second voltage by dividing the power supply voltage using a functional element whose temperature characteristic of voltage drop is negative.

3. The drive circuit according to claim 2, wherein the functional element consists of one semiconductor diode or a plurality of semiconductor diodes connected in series.

4. The drive circuit according to claim 2, wherein the second voltage is generated by dividing the voltage supplied to the drive circuit by a resistor connected in series with the functional element.

5. The drive circuit according to any one of claims 1 to 4, wherein the amount of change in the second voltage in response to the change in ambient temperature is selected to a value that suppresses fluctuations in the optical output of the semiconductor laser diode caused by the change in ambient temperature.

6. A first voltage is generated that decreases monotonically with increasing drive current of the semiconductor laser diode. A second voltage is generated that decreases monotonically with increasing ambient temperature. A control method for a drive circuit, which controls the drive current to reduce the difference between the first voltage and the second voltage.

7. A control method for a drive circuit according to claim 6, wherein the second voltage is generated by dividing the power supply voltage using a functional element whose temperature characteristic of voltage drop is negative.

8. A control method for a drive circuit according to claim 7, wherein the second voltage is generated using the functional element consisting of one semiconductor diode or a plurality of semiconductor diodes connected in series.

9. A control method for a drive circuit according to claim 7, wherein the second voltage is generated by dividing the voltage supplied to the drive circuit using a resistor connected in series with the functional element.

10. A control method for a drive circuit according to any one of claims 6 to 9, wherein the amount of change in the second voltage in response to the change in ambient temperature is selected to suppress fluctuations in the optical output of the semiconductor laser diode driven by the drive current due to the change in ambient temperature.

Images