JP2004015018A - Laser diode controller, control system, and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser diode controller, a control system, and a control method which can improve the precision of control even when the amount of data which should be stored is decreased. <P>SOLUTION: Parameters specifying a function showing the relation between a bias current and a modulating current to be supplied to a laser diode 12 are stored in a storage part 26; and the bias current and modulating current are supplied through a laser driving circuit 18 to make a laser diode emit light and a monitor means 20 monitors the quantity of light of the laser diode emitting the light. Further, an arithmetic processing part 28 computes a bias current and a modulating current to be supplied to the laser diode according to the function specified by the amount of light from the monitored laser diode and the parameters stored in the storage part. Then the bias current and modulating currents computed by the arithmetic processing part 28 are supplied to the laser diode through the laser driving circuit to control the laser diode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser diode control device, a control system, and a control method.
[0002]
[Prior art]
Since the optical output power and extinction ratio of the laser diode vary depending on the temperature, control is required to keep the optical output power and extinction ratio constant. Normally, a laser diode emits light when a bias current and a modulation current are supplied via a laser driving circuit. The bias current and modulation current determine the optical output power and extinction ratio of the laser diode. Therefore, in order to make the optical output power and the extinction ratio constant, the bias current and the modulation current may be controlled. Such control is known as Auto Power Control (hereinafter “APC control”).
[0003]
The combination of the bias current and modulation current that make the optical output power and extinction ratio of the laser diode constant is inherent to the laser diode. Therefore, in APC control, first, bias current and modulation current that make the optical output power and extinction ratio of a laser diode to be used constant are measured at various temperatures, and a combination thereof is stored in a nonvolatile memory as a table. . Then, the light quantity of the laser diode is monitored by the light receiving element, and when the monitored light quantity of the laser diode is deviated from the target value, the value of the table stored in the nonvolatile memory is reduced so that the deviation is reduced. Control is performed by appropriately reading and supplying the laser diode.
[0004]
[Problems to be solved by the invention]
However, in the above control method, since the combination of the bias current and the modulation current that make the optical output power and extinction ratio of the laser diode constant is stored in the nonvolatile memory as a table, it depends on the size of the table. Requires a large amount of memory. Further, in order to improve the control accuracy for keeping the optical output power and extinction ratio of the laser diode constant, the number of combinations of the bias current and the modulation current is increased, and the table may be enlarged. However, as described above, the larger the table, the larger the memory capacity. That is, in order to improve the control accuracy of the laser diode, there is a problem that a larger memory capacity is required as the combination of the bias current and the modulation current is increased.
[0005]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a laser diode control device, a control system, and a control system capable of improving the control accuracy even if the amount of data to be stored is reduced. It is to provide a control method.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a laser diode control device according to the present invention is a laser diode control device that controls light emission of a laser diode, and is a function indicating a relationship between a bias current to be supplied to the laser diode and a modulation current. And a bias to be supplied to the laser diode based on the monitoring result and a function specified by the parameter stored in the storage unit. An arithmetic processing unit for calculating a current and a modulation current.
[0007]
In this case, what is stored in the storage unit is a parameter that specifies a function indicating the relationship between the bias current to be supplied to the laser diode and the modulation current. Therefore, the storage unit only needs to have a memory capacity for storing the parameters.
[0008]
Further, the bias current and the modulation current to be supplied to the laser diode are calculated based on the monitoring result of the light amount of the laser diode and the function specified by the parameter stored in the storage unit. In this way, in order to calculate the bias current and the modulation current to be supplied to the laser diode by using the function, by finely adjusting one of the bias current and the modulation current and calculating the other, the light emission of the laser diode can be calculated. The accuracy of control can be improved. Also in this case, since it is the parameter that specifies the function that is stored in the storage unit, it is not necessary to increase the memory capacity of the storage unit in order to improve the accuracy of control of light emission of the laser diode.
[0009]
The arithmetic processing unit adjusts one of the bias current and the modulation current in accordance with the difference between the monitoring result and the target value described above, and based on the function specified by the parameter stored in the storage unit It is also desirable to calculate by In this case, since one of the bias current and the modulation current is adjusted according to the difference between the monitor result and the target value, the target value is set earlier than when the adjustment is performed with a constant value regardless of the difference with the target value. It is possible to approach.
[0010]
The invention also relates to a laser diode control system. A laser diode control system according to the present invention shows a relationship between a laser diode, a laser driving circuit for supplying a bias current and a modulation current to drive the laser diode, and a bias current and a modulation current to be supplied to the laser diode. Based on a storage unit for storing a parameter for specifying a function, a monitoring unit for monitoring the light amount of the laser diode, a light amount of the laser diode monitored by the monitoring unit, and a function specified by the parameter stored in the storage unit An arithmetic processing unit that calculates a bias current and a modulation current to be supplied to the laser diode.
[0011]
In this laser diode control system, the bias current and modulation current calculated by the arithmetic processing unit described above are supplied to the laser diode via the laser drive circuit to control the light emission of the laser diode.
[0012]
Further, according to the present invention, a parameter for specifying a function indicating the relationship between the bias current to be supplied to the laser diode and the modulation current is stored in the storage unit, the monitor result of the light amount of the laser diode is received, the monitor result and The present invention also relates to a laser diode control method that calculates a bias current and a modulation current to be supplied to the laser diode based on a function specified by parameters stored in a storage unit.
[0013]
In this method, the bias current to be supplied to the laser diode is not extracted from the combination of the bias current and the modulation current stored in the storage unit in advance, but the bias current and the modulation current to be supplied are modulated with the bias current and the modulation current. Since the calculation is performed using a function indicating the relationship with the current, the memory capacity required for the storage unit only needs to have a capacity required for storing a parameter specifying the function.
[0014]
In the laser diode control method, when calculating the bias current and the modulation current to be supplied to the laser diode, one of the bias current and the modulation current is adjusted according to the difference between the monitor result and the target value, It is desirable to calculate the other based on a function specified by parameters stored in the storage unit. Since adjustment is performed according to the difference between the monitor result and the target value, convergence to the target value can be achieved in a short time.
[0015]
The present invention also relates to a laser diode control method having the following characteristics.
[0016]
That is, in the laser diode control method according to the present invention, a parameter for specifying a function indicating the relationship between the bias current to be supplied to the laser diode and the modulation current is stored in the storage unit, and the bias current is supplied via the laser drive circuit. And a modulation current to cause the laser diode to emit light, monitor the light quantity of the laser diode that emits light, and the function specified by the light quantity of the monitored laser diode and the parameters stored in the storage unit, Based on the above, a bias current and a modulation current to be supplied to the laser diode are calculated, and the calculated bias current and modulation current are supplied to the laser diode via a laser driving circuit.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 is a schematic configuration diagram of a laser diode control system 10 according to the present embodiment. The laser diode control system 10 includes a laser module 12 and a laser control device 14.
[0019]
The laser module 12 includes a laser diode (hereinafter referred to as “LD”) 16, a laser drive circuit 18 that drives the LD 16, and a monitor unit 20 that monitors the light quantity of the LD 16.
[0020]
The LD 16 emits light when supplied with the supply current I via the laser drive circuit 18. Then, the light intensity is monitored by the monitor unit 20, the monitoring results are outputted as the photocurrent I _PD corresponding to the light amount of LD 16. As the monitoring means 20, for example, a photodiode or the like can be considered.
[0021]
FIG. 2 shows the IL characteristic, which is the relationship between the supply current I to the LD 16 and the optical output power P of the LD 16, and the temperature dependency. In FIG. 2, the horizontal axis indicates the current I, and the vertical axis indicates the optical output power P of the LD 16. As the I-L characteristics, LD 16 is made to emit light when the supply current I exceeds the threshold current I _TH. LD16 is, a case where light and optical output power of light output power is P ₁ outputs one of the light which is P _2. The optical output power P ₁ as shown in FIG. 2 is made larger than P _2. Current supplied optical output power in the LD16 in the case of _{P 2} of LD16 is the bias current _{I B} plus a margin to the threshold current _{I TH.} The current supplied to the LD 16 when the optical output power of the LD 16 is P ₁ is a current obtained by adding the modulation current I _M to the bias current I _B. If the difference between P ₁ and P ₂ is ΔP, the extinction ratio is 10 × log ₁₀ (ΔP / P ₂ ). Incidentally, I-L characteristic curve of the curve T _M room temperature in Fig. 2, the curve T _L I-L characteristic curve at low temperature, the curve T _H illustrates respectively the I-L characteristic curve at high temperature.
[0022]
As understood from FIG. 2, to constant irrespective of the optical output power and extinction ratio of the temperature, it is necessary to control the bias current I _B and the modulation current I _M in response to temperature changes.
[0023]
Thus by controlling the bias current _{I B} and the modulation current _{I M,} control to maintain a constant optical output power and extinction ratio of even if the temperature changes LD16 is Auto Power Control (hereinafter, referred to as "the APC") in is there.
[0024]
Next, the laser diode controller 14 will be described with reference to FIG.
[0025]
The laser diode control device 14 performs the above-described APC control, and includes an A / D converter 22, a variable storage unit 24, a storage unit 26, an arithmetic processing unit 28, and a D / A converter 30.
[0026]
A / D converter 22, a photocurrent _{I PD} corresponding to the amount of LD16 output from the monitor unit 20 is intended for converting A / D.
[0027]
The variable storage unit 24 temporarily stores the photocurrent value _IPD output from the A / D converter 22.
[0028]
Storage unit 26 is for storing the parameters specifying the function f indicating the relationship between the bias current I _B and the modulation current I _M. When the function f is an n-order function, the parameters are n + 1 parameters X _{1 to} X _{n + 1} , but in the following description, for the sake of simplicity, the parameter is _{denoted by} the symbol X. In the present embodiment, the function f indicates the relationship between the bias current I _B and the modulation current I _M that make the optical output power and extinction ratio of the LD 16 constant, and the modulation current I _M is a function of the bias current I _B. That is, I _M = f (I _B ). The storage unit 26 may be a non-volatile memory, for example.
[0029]
Processing unit 28, based on the function f which is specified by the parameter X which is stored a quantity of LD16 which is monitored by the monitor unit 20 in the storage unit 26, the bias current I _B and the modulation current to be supplied to the LD16 I _M is calculated.
[0030]
D / A converter 30, a bias current I _B calculated by the arithmetic processing unit 28 and the modulation current I _M is intended for converting D / A. D / A converter 30 and the bias current _{I B} which is outputted from the modulation current _{I M} is supplied to the LD16 via the laser drive circuit 18.
[0031]
Hereinafter, a procedure for controlling the light emission of the LD 16 and a method for controlling the light emission of the LD 16 will be described with reference to FIG. In the following description, it is assumed that the flag indicating the APC control state is set to 0 when the LD 16 is caused to emit light for the first time.
[0032]
First, to emit LD16 by supplying a certain bias current _{I B} through the laser drive circuit 18 and the modulation current _{I M} to the LD16 (S100). Next, the monitor unit 20 monitors the light amount of the LD 16 and outputs a photocurrent value _IPD corresponding to the light amount (S102). Photocurrent _{I PD} output from the monitor unit 20 is stored is A / D converted by the A / D converter 22 to the variable storage unit 24 (S104).
[0033]
Next, the arithmetic processing unit 28 reads the photocurrent value _IPD stored in the variable storage unit 24 (S106). Then, the arithmetic processing unit 28, the bias current _{I B} and the modulation current _{I M} to be supplied to the LD16 based on the function f specified by the photocurrent _{I PD} and the parameter X corresponding to the amount of LD16 read in S106 And calculate. Hereinafter, the calculation procedure of the arithmetic processing unit 28 will be described.
[0034]
First, the target value _{I PD0} a photocurrent value corresponding to the amount of LD16 to be achieved by the APC control, and calculates the absolute value _{D IPD} of the difference between the photocurrent _{I PD} (S108). Then, it is determined whether or not the absolute value D _IPD is larger than an upper threshold TH _u that is a reference value for starting APC control (S110).
[0035]
Here, a case where the absolute value D _IPD is larger than the upper threshold TH _u (“Y” in S110) will be described.
[0036]
In this case, the flag is changed to 1 (S112). It is determined photocurrent _{I PD} is the greater or not than the target value _{I PD0} (S114). If the photocurrent value _{I PD} is larger than the target value _{I PD0} ( "Y" in S114) reduces the bias current _{I B} by ΔI _B (S116). On the other hand, if the photocurrent _{I PD} is smaller than the target value _{I PD0} ( "N" in S114) increases the bias current _{I B} by ΔI _B (S118). Here, [Delta] I _B is a fixed value, and is a positive value. Then, based on the function f which is specified by the parameter X which is stored in the bias current _{I B} and the storage unit 26 calculated in S116 or S118, to calculate the modulation current _{I M} to be supplied to the LD 16 (S120) .
[0037]
Bias current _{I B} and the modulation current _{I M} calculated by the arithmetic processing unit 28 in this way is D / A converted by a D / A converter 30, is supplied to the LD16 via the laser drive circuit 18 (S122) .
[0038]
Next, the case where the absolute value D _IPD is not larger than the upper threshold TH _u , that is, the absolute value D _IPD is equal to or smaller than the upper threshold TH _u will be described (“N” in S110).
[0039]
In this case, first, it is determined whether or not the flag is 1 (S124). Flag is ( "Y" in S124) if one is, determines whether the absolute value _{D IPD} is greater than the lower threshold value TH _l which is a reference value for ending the APC control (S126). When the absolute value D _IPD is larger than the lower threshold TH ₁ (“Y” in S126), the process proceeds to S114. If the absolute value D _IPD is less than or equal to the lower threshold TH ₁ (“N” in S126), the flag is changed to 0 (S128), and the process proceeds to S122. In this case, the bias current I _B and the modulation current I _M intact value without being adjusted is supplied to the LD 16.
[0040]
As shown in the above procedure, the light emission control of the LD 16 by adjusting the bias current I _B and the modulation current I _M is started when the absolute value D _IPD exceeds the upper threshold value TH _u . Then, the absolute value _{D IPD} is below the lower threshold TH _l, following the steps described above until the bias current _{I B} and the modulation current _{I M} is supplied to the LD16 is maintained. That is, the absolute value _{D IPD} is below the lower threshold TH _l, if it becomes the bias current _{I B} and the modulation current _{I M} is supplied to the LD16 is maintained, APC control ends.
[0041]
In the present embodiment, as described above, the storage unit 26 stores the parameter X that specifies the function f indicating the relationship between the bias current I _B and the modulation current I _M that makes the optical output power and extinction ratio of the LD 16 constant. Is done. Then, the arithmetic processing unit 28, using the function f that is identified by the parameter X from the storage unit 26 reads the parameters X, calculates the bias current I _B to be supplied to the LD16 and the modulation current I _M. Therefore, the storage unit 26 only needs to have a capacity required to store the parameter X for specifying the function f.
[0042]
Furthermore, in order to improve the accuracy of control of the light emission of the LD16, for example, the combination of the bias current I _B and the modulation current I _M to the optical output power and extinction ratio of LD16 in the storage unit 26 as in the conventional constant as a table If stored, the combination of the bias current I _B and the modulation current I _M to be stored must be increased. However, in the case of the present embodiment can improve the accuracy by reducing the [Delta] I _B when the operation processing unit 28 calculates the bias current I _B to be supplied to the LD 16. That is, in this embodiment, it is possible to improve the control accuracy of the LD 16 without increasing the amount of data to be stored in the storage unit 26.
[0043]
In the above embodiment, the fixed value [Delta] I _B for calculating the bias current I _B to be supplied to the LD 16, for example, may be a variable which varies according to the magnitude of the absolute value D _IPD. In this case, a larger [Delta] I _B when the absolute value D _IPD is large, by reducing the [Delta] I _B when the absolute value D _IPD is small, to converge earlier target value the optical output power and extinction ratio of LD16 It is possible.
[0044]
In the above embodiment, as a function indicating the relationship between the bias current I _B and the modulation current I _M, the modulation current although the I _M as a function of the bias current I _B, the bias current I _B function of the modulation current I _M That is, I _B = f (I _M ) may be set. In this case, the modulation current I _M may be adjusted by increasing / decreasing, and I _B may be calculated using the function f (I _M ).
[0045]
【The invention's effect】
As described above, according to the present invention, the parameter for specifying the function indicating the relationship between the bias current and the modulation current is stored in the storage unit. Therefore, the storage unit only needs to have a memory capacity for storing the parameter. . The bias current and modulation current supplied to the laser diode are calculated based on the monitoring result of the light amount of the laser diode and the function specified by the parameter stored in the storage unit. Therefore, the accuracy of laser diode control can be improved by reducing the amount of change for adjusting one of the bias current and the modulation current. In this case, the storage unit may have a memory capacity for storing parameters as described above. That is, the control accuracy can be improved even if the amount of data to be stored is reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a laser diode control system according to an embodiment.
FIG. 2 is a diagram showing IL characteristics and temperature dependence of a laser diode.
FIG. 3 is a flowchart illustrating a procedure related to control of light emission of a laser diode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Laser diode control system, 12 ... Laser module, 14 ... Laser diode control apparatus, 16 ... Laser diode, 18 ... Laser drive circuit, 20 ... Monitoring means, 22 ... A / D converter, 24 ... Variable storage part, 26 ... Storage unit, 28 ... arithmetic processing unit, 30 ... D / A converter

Claims (6)

A laser diode control device for controlling light emission of a laser diode,
A storage unit for storing a parameter for specifying a function indicating a relationship between a bias current to be supplied to the laser diode and a modulation current;
The monitoring result of the light amount of the laser diode is received, and a bias current and a modulation current to be supplied to the laser diode are calculated based on the monitoring result and a function specified by a parameter stored in the storage unit. A laser diode control device comprising: an arithmetic processing unit. The arithmetic processing unit is
Adjusting one of a bias current and a modulation current according to a difference between the monitoring result and a target value, and calculating the other based on a function specified by a parameter stored in the storage unit; The laser diode control device according to claim 1. A laser diode;
A laser driving circuit for supplying a bias current and a modulation current to drive the laser diode;
A storage unit for storing a parameter for specifying a function indicating a relationship between a bias current to be supplied to the laser diode and a modulation current;
Monitoring means for monitoring the light quantity of the laser diode;
Arithmetic processing for calculating a bias current and a modulation current to be supplied to the laser diode based on a light amount of the laser diode monitored by the monitoring means and a function specified by a parameter stored in the storage unit And
With
A laser diode control system for supplying a bias current and a modulation current calculated by the arithmetic processing unit to the laser diode via the laser driving circuit. A control method for controlling light emission of a laser diode,
A parameter for specifying a function indicating the relationship between the bias current to be supplied to the laser diode and the modulation current is stored in the storage unit, the monitor result of the light amount of the laser diode is received, and the monitor result and the storage unit are stored in the storage unit. A laser diode control method, comprising: calculating a bias current and a modulation current to be supplied to the laser diode based on a function specified by a stored parameter. When calculating the bias current and the modulation current to be supplied to the laser diode, one of the bias current and the modulation current is adjusted according to the difference between the monitoring result and the target value, and the other is stored in the storage unit. 5. The laser diode control method according to claim 4, wherein the calculation is performed based on a function specified by a stored parameter. A control method for controlling light emission of a laser diode,
A parameter for specifying a function indicating a relationship between a bias current to be supplied to the laser diode and a modulation current is stored in a storage unit, and the bias current and the modulation current are supplied via a laser driving circuit to supply the laser diode. The laser diode is monitored based on the monitored light quantity of the laser diode and a function specified by the parameter stored in the storage unit. A laser diode control method comprising: calculating a bias current and a modulation current to be supplied to the laser diode, and supplying the calculated bias current and modulation current to the laser diode via the laser driving circuit.

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