JP2009070879A - Laser diode drive circuit and drive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain desired optical output and extinction ratio, without having to implement regulation of the optical output and extinction ratio at each temperature. <P>SOLUTION: A laser diode drive circuit comprises a temperature sensor 14, a first storage section 20 for storing the threshold and the slope efficiency of an LD1a at each ambient temperature and outputting the threshold and slope efficiency corresponding to the ambient temperature; a first current control section 21 for determining the bias current and the modulation current of the LD1a by using the threshold and the slope efficiency, and the values of a set optical output and a set extinction ratio; a second storage section 22 for storing a first reference value and a second reference value, respectively representating the average value and the maximum value of the output from a monitor PD at an initial set time; a second current control section 23 for compensating the bias current to minimize the difference between the average value of the output from a monitor PD1b and a first reference value, and compensating the modulation current so as to minimize the difference between the maximum value of the output from a monitor PD1b and a second reference value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical transmission circuit used for optical communication, and more particularly to a laser diode driving circuit and a driving method for driving a laser diode for optical signal transmission.

  In an optical transmission circuit that transmits an optical signal using an LD (laser diode), an LD driving circuit that stabilizes the optical output without being affected by the ambient temperature by controlling the driving current of the LD is used. .

A related LD driving circuit will be described with reference to FIG. The LD 101a emits light upon receiving a drive current as will be described later.
The temperature sensor 108 is connected to the memory 109, senses the ambient temperature, and outputs the sensed ambient temperature as an address of the memory 109.

  The memory 109 holds information on control signals to the bias current control circuit 103 and the modulation current control circuit 102 at the temperature at an address corresponding to the temperature. Then, the memory 109 outputs the control signal recorded at the address designated by the temperature sensor 108 to the bias current control circuit 103 and the modulation current control circuit 102.

The bias current control circuit 103 supplies a bias current corresponding to the control signal from the memory 109 to the LD 101a. The modulation current control circuit 102 supplies a modulation current corresponding to the control signal from the memory 109 to the LD 101a.
The monitor PD (photodiode) 101b outputs a monitor current corresponding to the optical output power of the LD 101a. The I / V conversion circuit 104 converts the monitor current into a voltage and outputs the voltage, and the average value detection circuit 105 detects the average voltage of the output of the I / V conversion circuit 104.

  Then, the comparison amplifier 106 compares the average voltage detected by the average value detection circuit 105 with the reference voltage of the reference voltage source 107, and calculates the bias current through the bias current control circuit 103 so that the average voltage matches the reference voltage. Control. In this way, it is possible to control the light output of the LD 101a to be constant. The LD driving circuit as described above is disclosed in Patent Document 1, for example.

However, the related LD driving circuit shown in FIG. 6 has the following problems.
The first problem is that it is necessary to measure in advance the bias current and modulation current so that the light output becomes constant at each temperature within the temperature range used as the transmitter, and record the control signal information in the memory 109. Therefore, it is not easy to adjust the transmitter.
The second problem is that only the bias current is compensated for the degradation of the LD 101a, that is, only the degradation of the optical output is compensated, so that the extinction ratio cannot be compensated.

  As an LD drive circuit that can compensate not only for optical output degradation but also extinction ratio degradation, the one disclosed in Patent Document 2 is known. FIG. 7 is a block diagram showing a configuration of the LD driving circuit disclosed in Patent Document 2. In FIG.

  The LD driving circuit includes a temperature sensor 200, A / D converters 201 and 202, D / A converters 203 to 205, current control circuits 206 to 208, a memory 209, a preamplifier 210, and a peak detector. 211, an inverting amplifier 212, a low-pass filter 213, a switch 214, an LD module 217 including an LD 215 and a monitor PD 216, and transistors 218 and 219.

  The temperature sensor 200 generates a voltage corresponding to the ambient temperature and outputs the voltage to the A / D converter 201 as a temperature signal. The A / D converter 201 performs analog-digital conversion on this temperature signal and outputs it to the memory 209 as an address.

  The address corresponding to the ambient temperature of the memory 209 stores data corresponding to the modulation current, the bias current, and the monitor PD current before deterioration. The values of the modulation current and the bias current are determined so that the light output and the extinction ratio are constant with respect to fluctuations in the ambient temperature. The memory 209 outputs the digital data stored at the corresponding address to the D / A converter 203 and the D / A converter 204.

  Data output to the D / A converter 203 and the D / A converter 204 are data of modulation current and bias current, respectively. The D / A converter 203 and the D / A converter 204 convert the data from digital to analog and output the data to the current control circuit 206 and the current control circuit 207, respectively.

The current control circuit 206 adjusts the constant current Iac common to the transistors 218 and 219 using the analog signal from the D / A converter 203, and the current control circuit 207 receives the analog signal from the D / A converter 204. To adjust the constant current Idc.
The light receiving current of the monitor PD 216 is converted into a voltage signal by the preamplifier 210. The peak detector 211 detects the peak voltage of the voltage signal output from the preamplifier 210 and outputs the detected voltage to the A / D converter 202 and the inverting input terminal of the inverting amplifier 212.

  The A / D converter 202 performs analog-digital conversion on the output voltage of the peak detector 211 and outputs it to the memory 209 via the switch 214 as data. The memory 209 stores this data at an address corresponding to the temperature detected by the temperature sensor 200. This data serves as a reference voltage for compensating the optical output due to degradation of the laser diode.

  The memory 209 outputs the reference voltage data to the D / A converter 205 via the switch 214, and the D / A converter 205 performs digital-analog conversion on this data and outputs it to the non-inverting input of the inverting amplifier 212. .

  The inverting amplifier 212 uses the voltage output from the D / A converter 205 to the non-inverting input terminal as a reference voltage, the voltage output from the D / A converter 205 as the reference voltage, and the inverting input terminal from the peak detector 211. Is inverted and amplified and output to the LPF 213.

  The LPF 213 smoothes the inverted and amplified voltage value and outputs it to the current control circuit 208. The current control circuit 208 adjusts the constant currents Iapc1 and Iapc2 corresponding to the decrease in the monitor PD current caused by deterioration with time for each ambient temperature. The constant current Iapc1 is a bias current that flows directly to the LD 215, and the constant current Iapc2 is a modulation current controlled by an input signal.

JP-A-2005-32340 JP-A-11-135871

According to the LD drive circuit disclosed in Patent Document 2, not only the deterioration of the optical output but also the deterioration of the extinction ratio can be compensated.
However, also in the LD driving circuit disclosed in Patent Document 2, as in Patent Document 1, a bias current and a modulation current are set in advance so that the light output and the extinction ratio are constant at each temperature within the ambient temperature range to be used. It was necessary to measure and record the bias current and modulation current data at each temperature in the memory, and there was a problem that adjustment of the LD drive circuit was difficult.

  The present invention has been made in order to solve the above-mentioned problems, and without adjusting the actual light output and extinction ratio at each ambient temperature, the desired light output and extinction ratio can be obtained even if the ambient temperature changes. It is an object to provide a laser diode driving circuit and a driving method that can be easily maintained.

  The present invention provides a temperature sensor for detecting an ambient temperature in a laser diode driving circuit that drives the laser diode with a current in which a bias current and a modulation current that causes the laser diode to emit light according to a transmission signal pattern are superimposed, and each ambient temperature First storage means for preliminarily storing threshold value and slope efficiency data of the laser diode and outputting a threshold value and slope efficiency value corresponding to the ambient temperature detected by the temperature sensor; and from the first storage means A bias current and a modulation current of the laser diode are determined using the output threshold value and the slope efficiency value, the set light output value and the set extinction ratio value, and a first driving the laser diode is performed. Current control means.

  Further, one configuration example of the laser diode driving circuit according to the present invention further includes a monitor photodiode for detecting a light output of the laser diode, and the monitor photodiode at an initial setting time when a desired light output and extinction ratio are set. A first reference value that is an average value of the outputs of the first and a second reference value that is a maximum value of the output of the monitor photodiode at the time of the initial setting are stored in advance, and a second reference value is output. The bias current is compensated so as to minimize the difference between the storage means, the first reference value, and the average value of the current output of the monitor photodiode, and the second reference value and the monitor photodiode And a second current control means for compensating the modulation current so that a difference from the maximum value of the current output is minimized.

  In one configuration example of the laser diode driving circuit according to the present invention, the first current control unit calculates a bias current and a modulation current of the laser diode, and sets the first bias current to the calculated bias current value. A calculation means for outputting a control signal and outputting a second control signal so as to have a calculated modulation current value, and a first current for supplying a bias current corresponding to the first control signal to the laser diode It comprises a current source and a second current source for supplying a modulation current corresponding to the second control signal to the laser diode.

  In one configuration example of the laser diode driving circuit according to the present invention, the second current control means includes an average value detecting means for detecting an average value of the output of the monitor photodiode, and a maximum output of the monitor photodiode. Maximum value detecting means for detecting a value, and first comparative amplification for outputting a third control signal so that a difference between the first reference value and an average value of the current output of the monitor photodiode is minimized. Means, a second comparison amplification means for outputting a fourth control signal so that a difference between the second reference value and a maximum value of the current output of the monitor photodiode is minimized, and the third comparison amplification means A third current source for supplying a bias current corresponding to the control signal to the laser diode; and a fourth current source for supplying a modulation current corresponding to the fourth control signal to the laser diode. Than is.

  Further, the present invention provides a temperature detection procedure for detecting an ambient temperature in a laser diode driving method for driving the laser diode with a current superimposed with a bias current and a modulation current for causing the laser diode to emit light according to a transmission signal pattern, The threshold value and the slope efficiency value corresponding to the ambient temperature detected in the temperature detection procedure are obtained from the first storage means for preliminarily storing the threshold value and slope efficiency data of the laser diode at each ambient temperature. A first current control procedure for determining a bias current and a modulation current of the laser diode using the value, a set light output and a set extinction ratio value, and driving the laser diode It is.

  In addition, one configuration example of the laser diode driving method of the present invention further includes a light output detection procedure for detecting the light output of the laser diode with a monitor photodiode, and an initial setting time point when a desired light output and extinction ratio are set. A first reference value that is an average value of the output of the monitor photodiode and a second reference value that is a maximum value of the output of the monitor photodiode at the time of the initial setting; , Obtaining these reference values, compensating the bias current so that the difference between the first reference value and the average value of the current output of the monitor photodiode is minimized, and the second reference value And a second current control procedure for compensating the modulation current so that the difference between the current value of the monitor photodiode and the maximum value of the current output of the monitor photodiode is minimized.

  According to the present invention, the threshold value and slope efficiency data of the laser diode at each ambient temperature are stored in the first storage means in advance, thereby adjusting the actual light output and extinction ratio at each ambient temperature. Without giving a desired set light output and set extinction ratio, the laser diode bias current and modulation current can be easily determined with respect to changes in ambient temperature, and the light output and extinction ratio are feedforward controlled. The light output and extinction ratio of the laser diode can be set constant. Therefore, according to the present invention, as in the conventional laser diode driving circuit, it is necessary to measure in advance the bias current and the modulation current so that the light output and the extinction ratio are constant at each temperature within the ambient temperature range to be used. Disappear.

  In the present invention, the first reference value that is the average value of the output of the monitor photodiode at the time of initial setting and the second reference value that is the maximum value of the output of the monitor photodiode at the time of initial setting are the first reference value. By storing these values in advance in the second storage means and using these values as reference values for feedback control, it is possible to compensate for deterioration from the initial setting of the light output and extinction ratio due to deterioration of the laser diode. In the present invention, the average value of the output of the monitor photodiode is used for feedback control of the light output, and the maximum value of the output of the monitor photodiode is used for feedback control of the extinction ratio. Thus, it is possible to realize driving of the laser diode with higher accuracy.

  Further, in the present invention, the first current control means includes the calculation means, the first current source, and the second current source, so that the feedforward control of the light output and the extinction ratio according to the ambient temperature is performed. Can be realized.

  In the present invention, the second current control means includes an average value detection means, a maximum value detection means, a first comparison amplification means, a second comparison amplification means, a third current source, and a fourth current source. Thus, feedback control of the light output and the extinction ratio according to the deterioration of the laser diode can be realized.

[First embodiment]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an LD driving circuit according to a first embodiment of the present invention.
The LD driving circuit of this embodiment includes an LD 1a, transistors 2a and 2b, a temperature sensor 14, a first storage unit 20, and a first current control unit 21.

  The first current control unit 21 supplies a common current Iac to the transistors 2a and 2b. Here, when the input signal DATA + is at a high level and the input signal DATA− complementary to DATA + is at a low level, the transistor 2a is turned on, the transistor 2b is turned off, the current Iac flows to the LD 1a, and the input signal DATA + is at a low level. When the input signal DATA- is at a high level, the transistor 2b is turned on, the transistor 2a is turned off, and the current Iac does not flow to the LD 1a. That is, the current Iac drives the LD 1a as a modulation current according to the transmission signal pattern.

  The first current control unit 21 supplies a bias current Idc that flows through the LD 1a. This bias current Idc is set to be in the vicinity of the threshold current of the LD 1a, for example.

The temperature sensor 14 detects the ambient temperature and outputs a voltage value corresponding to the detected temperature.
The first storage unit 20 stores in advance data on the threshold value Ith and slope efficiency η of the LD 1a at each ambient temperature. FIG. 2 is a diagram showing an example of current-light output characteristics of the LD 1a. As shown in FIG. 2, the threshold value Ith is a drive current value at which the LD 1a starts laser oscillation, and the slope efficiency η is an increase in light output per unit drive current of the LD 1a. The first storage unit 20 outputs threshold value Ith and slope efficiency η data corresponding to the ambient temperature detected by the temperature sensor 14.

  The first current control unit 21 uses the threshold Ith and slope efficiency η values output from the first storage unit 20 and the set light output and set extinction ratio values set from the outside. The bias current Idc and the modulation current Iac are calculated, and the bias current Idc and the modulation current Iac supplied to the LD 1a are controlled so as to have the calculated values.

Assuming that the target set average light output is Po, the set extinction ratio is Re, the L level of the modulated light output is P1, and the H level of the modulated light output is P2, the set average light output Po and the set extinction ratio Re are It can be expressed as
Po = (P1 + P2) / 2 (1)
Re = P2 / P1 (2)

At this time, the L level P1 and the H level P2 of the modulated light output are expressed as follows using the threshold Ith, the slope efficiency η, the bias current Idc, and the modulation current Iac.
P1 = η × (Idc−Ith) (3)
P2 = η × (Idc−Ith + Iac) (4)
From the equations (1) to (4), the following equation is obtained.
Po = η × (Idc−Ith + Iac / 2) (5)
Re = 1 + Iac / (Idc−Ith) (6)

  For the expressions (5) and (6), the values of the threshold value Ith and the slope efficiency η output from the first storage unit 20, and the values of the set light output Po and the set extinction ratio Re set from the outside are set. By substituting, the bias current Idc and the modulation current Iac can be calculated.

  As described above, in this embodiment, the data of the threshold value Ith and the slope efficiency η of the LD 1a at each ambient temperature are stored in the first storage unit 20 in advance, so that the actual light output and extinction ratio at each temperature. The bias current Idc and the modulation current Iac of the LD 1a can be easily determined with respect to the change in the ambient temperature, and the light output and the extinction can be easily determined by merely giving the desired set light output and set extinction ratio values without performing the above adjustment. The ratio can be feedforward controlled, and the light output and extinction ratio of the LD 1a can be set constant.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 3 is a block diagram showing the configuration of the LD driving circuit according to the second embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.
The LD driving circuit of this embodiment includes an LD module 1, transistors 2a and 2b, an I / V conversion circuit 7, a temperature sensor 14, a first storage unit 20, a first current control unit 21, A second storage unit 22 and a second current control unit 23 are provided.

In FIG. 3, the LD module 1 includes an LD 1a and a monitor PD 1b. The monitor PD1b outputs a monitor current corresponding to the optical output of the LD1a.
Since the temperature sensor 14, the first storage unit 20, and the first current control unit 21 are the same as those in the first embodiment, the description thereof is omitted.

The I / V conversion circuit 7 converts the monitor current from the monitor PD 1b into a voltage (monitor voltage) and outputs it.
The second storage unit 22 stores information on the average value (first reference value) of the monitor voltage at the initial setting time when the desired light output and extinction ratio are set, and the maximum value of the monitor voltage at the initial setting time ( Information on the second reference value) is stored in advance. The second storage unit 22 outputs these pieces of information to the second current control unit 23.

  The second current control unit 23 compensates the bias current Idc of the LD 1a so that the difference between the first reference value and the average value of the monitor voltage from the I / V conversion circuit 7 is minimized, and the second current control unit 23 The modulation current Iac of the LD 1a is compensated so that the difference between the reference value and the maximum value of the monitor voltage from the I / V conversion circuit 7 is minimized.

  Thus, in this embodiment, the same effect as that of the first embodiment can be obtained. In the present embodiment, information on the average value (first reference value) and the maximum value (second reference value) of the monitor voltage at the time of initial setting is stored in advance in the second storage unit 22. By using these values as reference values for feedback control, it is possible to compensate for deterioration from the initial setting of the light output and extinction ratio due to deterioration of the LD 1a. Further, in this embodiment, the average value of the monitor voltage is used for feedback control of the light output, and the maximum value of the monitor voltage is used for feedback control of the extinction ratio, so that it can be compared with the LD drive circuit disclosed in Patent Document 2. Therefore, it is possible to realize driving of the LD 1a with higher accuracy.

[Third embodiment]
Next, a third embodiment of the present invention will be described in detail. This embodiment will more specifically describe the second embodiment described above. FIG. 4 is a block diagram showing the configuration of the LD drive circuit according to the third embodiment of the present invention. The same components as those in FIG. 3 are denoted by the same reference numerals.

  The LD driving circuit of this embodiment includes an LD module 1, transistors 2a and 2b, current sources 3 to 6, an I / V conversion circuit 7, an average value detection circuit 8, a maximum value detection circuit 9, and an LPF. (Low Pass Filter) 10, 11, comparison amplifiers 12, 13, temperature sensor 14, A / D converter 15, memory 16, microprocessor 17, D / A converters 18a, 18b, 18c, 18d.

The current source 6, the average value detection circuit 8, the LPF 10, and the comparison amplifier 12 constitute an optical output deterioration compensation circuit.
The current source 5, the maximum value detection circuit 9, the LPF 11 and the comparison amplifier 13 constitute an extinction ratio deterioration compensation circuit.

The memory 16 constitutes the first storage unit 20 and the second storage unit 22 of the second embodiment.
The microprocessor 17, the D / A converters 18c and 18d, and the current sources 3 and 4 serving as calculation means constitute the first current control unit 21 of the first and second embodiments.
The D / A converters 18a and 18b, the average value detection circuit 8, the maximum value detection circuit 9, the LPFs 10 and 11, the comparison amplifiers 12 and 13, and the current sources 5 and 6 are the second current control unit of the second embodiment. 23.

The current source 3 supplies a common current Iac to the transistors 2a and 2b. Similar to the second embodiment, the current Iac drives the LD 1a as a modulation current according to the transmission signal pattern.
On the other hand, the current source 4 supplies a bias current Idc flowing through the LD 1a.

The temperature sensor 14 detects the ambient temperature and outputs a voltage value corresponding to the detected ambient temperature to the A / D converter 15.
The A / D converter 15 converts the voltage value output from the temperature sensor 14 into a digital value, and outputs the digital value to the memory 16 as an address.

  The memory 16 stores data of the threshold value Ith and slope efficiency η of the LD 1a at the ambient temperature at addresses corresponding to the ambient temperatures. The memory 16 outputs the threshold value Ith and the slope efficiency η data recorded at the address output from the A / D converter 15 to the microprocessor 17.

  The microprocessor 17 calculates the bias current Idc and the modulation current Iac of the LD 1a using the threshold value Ith and the slope efficiency η output from the memory 16, and the set light output and set extinction ratio values set from the outside. The control signal for calculating and controlling the modulation current Iac is output to the current source 3, and the control signal for controlling the bias current Idc is output to the current source 4 so that the current sources 3 and 4 are feedforward controlled with respect to the temperature. To do. The microprocessor 17 includes a CPU and a storage device (not shown), and the CPU executes processing according to a program stored in the storage device.

  The D / A converter 18 c converts the control signal for the current source 4 from the microprocessor 17 into an analog signal and outputs the analog signal to the current source 4. The current Idc of the current source 4 determined by the analog signal from the D / A converter 18c drives the LD 1a as a bias current.

  The D / A converter 18 d converts a control signal for the current source 3 from the microprocessor 17 into an analog signal and outputs the analog signal to the current source 3. The current Iac of the current source 3 determined by the analog signal from the D / A converter 18d drives the LD 1a as a modulation current according to the transmission signal pattern as described above.

The I / V conversion circuit 7 converts the monitor current from the monitor PD 1b into a voltage (monitor voltage) and outputs it.
The average value detection circuit 8 detects the average voltage of the monitor voltage output from the I / V conversion circuit 7 and outputs it to the comparison amplifier 12.

  The memory 16 stores in advance information on the average value of the monitor voltage at the initial setting time when the desired light output and extinction ratio are set. This average value information is converted into an analog signal by the D / A converter 18a and output to the comparison amplifier 12 as a reference voltage for feedback control of the optical output.

The comparison amplifier 12 amplifies the difference between the reference voltage output from the D / A converter 18 a and the average voltage output from the average value detection circuit 8, and outputs this difference voltage to an LPF (Low Pass Filter) 10. .
The LPF 10 smoothes the output voltage from the comparison amplifier 12 and outputs it to the current source 6 as a signal for optical output feedback control. The current of the current source 6 determined by the control signal from the LPF 10 compensates the bias current of the LD 1a so as to compensate for the variation from the initial value of the optical output.

The maximum value detection circuit 9 detects the maximum voltage of the monitor voltage output from the I / V conversion circuit 7 and outputs it to the comparison amplifier 13.
The memory 16 stores in advance information on the maximum value of the monitor voltage at the initial setting time when the desired light output and extinction ratio are set. This maximum value information is converted into an analog signal by the D / A converter 18b and output to the comparison amplifier 13 as a reference voltage for extinction ratio feedback control.

The comparison amplifier 13 amplifies the difference between the reference voltage output from the D / A converter 18b and the maximum voltage output from the maximum value detection circuit 9, and outputs the difference voltage to the LPF 11.
The LPF 11 smoothes the output voltage from the comparison amplifier 13 and outputs it to the current source 5 as a signal for extinction ratio feedback control. The current of the current source 5 determined by the control signal from the LPF 11 compensates the modulation current of the LD 1a so as to compensate for the variation from the initial value of the extinction ratio.

  Although the configuration of this embodiment has been described in detail above, the I / V conversion circuit 7, the average value detection circuit 8, the maximum value detection circuit 9, and the comparison amplifiers 12 and 13 in FIG. 4 are well known to those skilled in the art. Also, since it is not directly related to the present invention, the detailed description of the configuration is omitted.

Next, the operation of the LD drive circuit of this embodiment will be described. First, feedforward control of light output and extinction ratio with respect to ambient temperature will be described.
The temperature sensor 14 outputs a voltage value corresponding to the ambient temperature, and the A / D converter 15 converts this voltage value into a digital value and outputs it to the memory 16 as an address.

The memory 16 outputs data of the threshold value Ith and the slope efficiency η stored at the address specified by the A / D converter 15 to the microprocessor 17.
The microprocessor 17 calculates the bias current Idc and the modulation current Iac of the LD 1a using the threshold Ith and the slope efficiency η, the set light output and the set extinction ratio, and becomes the calculated modulation current Iac. In this manner, the control signal is output to the D / A converter 18d, and the control signal is output to the D / A converter 18c so that the calculated bias current Idc is obtained.

  The D / A converters 18d and 18c convert the control signals from the microprocessor 17 into analog signals and output the analog signals to the current sources 3 and 4, respectively. Thus, by driving the LD 1a with the modulation current Iac and the bias current Idc, a desired light output and extinction ratio can be obtained.

Next, feedback control of the light output and the extinction ratio for the deterioration of the LD 1a will be described. The monitor PD1b outputs a monitor current corresponding to the optical output of the LD1a. The I / V conversion circuit 7 converts this monitor current into a monitor voltage and outputs it.
The average value detection circuit 8 detects the average voltage of the monitor voltage, and the maximum value detection circuit 9 detects the maximum voltage of the monitor voltage.

  The comparison amplifier 12 amplifies the difference between the reference voltage output from the memory 16 via the D / A converter 18a and the average voltage output from the average value detection circuit 8, and outputs the amplified difference to the LPF 10. The LPF 10 A control signal obtained by smoothing the output of the amplifier 12 is output to the current source 6. In this way, the current source 6 compensates for the shortage of the bias current Idc so that the difference between the reference value of the average voltage and the average voltage corresponding to the light output from the monitor PD1b is minimized, so that the light output due to the degradation of the LD1a. It is possible to compensate for deterioration from the initial setting.

  The comparison amplifier 13 amplifies the difference between the reference voltage output from the memory 16 via the D / A converter 18b and the maximum voltage output from the maximum value detection circuit 9, and outputs the amplified difference to the LPF 11. The LPF 11 Then, a control signal obtained by smoothing the output of the comparison amplifier 13 is output to the current source 5. In this way, the current source 5 compensates for the shortage of the modulation current Iac so that the difference between the reference value of the maximum voltage and the maximum voltage corresponding to the optical output from the monitor PD1b is minimized, so that the extinction ratio due to the deterioration of the LD1a is reduced. It is possible to compensate for deterioration from the initial setting.

  As described above, in this embodiment, the data of the threshold value Ith and slope efficiency η of the LD 1a at each ambient temperature is stored in the memory 16 in advance, thereby adjusting the actual light output and extinction ratio at each temperature. The bias current Idc and the modulation current Iac of the LD 1a can be easily determined with respect to changes in the ambient temperature, and the optical output and the extinction ratio can be fed forward simply by giving the desired set light output and set extinction ratio values. The light output and the extinction ratio of the LD 1a can be set constant.

Further, in this embodiment, information on the average value (first reference value) and the maximum value (second reference value) of the monitor voltage at the time of initial setting is stored in advance in the memory 16, and these values are stored. By using it as a reference value for feedback control, it is possible to compensate for deterioration from the initial setting of the light output and extinction ratio due to deterioration of the LD 1a.
As described above, also in this embodiment, the same effect as that of the second embodiment can be obtained.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described. FIG. 5 is a block diagram showing the configuration of an LD drive circuit according to the fourth embodiment of the present invention. The same components as those in FIG. 4 are denoted by the same reference numerals.

  In the second and third embodiments, information on the set light output and the set extinction ratio is given from the outside. However, in this embodiment, the information on the set light output and the set extinction ratio is stored in the memory 16a in advance. These pieces of information are passed from the memory 16a to the microprocessor 17.

The configuration and operation of the memory 16a are the same as those of the memory 16 of the third embodiment except that information on the set light output and the set extinction ratio is stored. Other configurations are the same as those of the third embodiment, and the description thereof is omitted.
Thus, also in this embodiment, the same effect as that of the second embodiment can be obtained.

  The present invention can be applied to a laser diode driving circuit used in an optical transmission circuit or the like.

1 is a block diagram showing a configuration of an LD drive circuit according to a first example of the present invention. FIG. It is a figure which shows one example of the current-light output characteristic of the laser diode in 1st Example of this invention. It is a block diagram which shows the structure of the LD drive circuit based on 2nd Example of this invention. It is a block diagram which shows the structure of the LD drive circuit based on 3rd Example of this invention. It is a block diagram which shows the structure of the LD drive circuit based on 4th Example of this invention. It is a block diagram which shows the structure of a related LD drive circuit. It is a block diagram which shows the structure of other related LD drive circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... LD module, 1a ... LD, 1b ... Monitor PD, 2a, 2b ... Transistor, 3-6 ... Current source, 7 ... I / V conversion circuit, 8 ... Average value detection circuit, 9 ... Maximum value detection circuit, 10 11 ... LPF, 12, 13 ... comparative amplifier, 14 ... temperature sensor, 15 ... A / D converter, 16, 16a ... memory, 17 ... microprocessor, 18a, 18b, 18c, 18d ... D / A converter, DESCRIPTION OF SYMBOLS 20 ... 1st memory | storage part, 21 ... 1st electric current control part, 22 ... 2nd memory | storage part, 23 ... 2nd electric current control part.

Claims (6)

In a laser diode driving circuit that drives the laser diode with a current superimposed with a bias current and a modulation current that causes the laser diode to emit light according to a transmission signal pattern,
A temperature sensor that detects the ambient temperature;
First storage means for preliminarily storing threshold values and slope efficiency data of the laser diode at each ambient temperature, and outputting threshold and slope efficiency values corresponding to the ambient temperature detected by the temperature sensor;
Using the threshold value and slope efficiency value output from the first storage means, the set light output and the set extinction ratio value, determine the bias current and modulation current of the laser diode, And a first current control means for driving the laser diode. The laser diode driving circuit according to claim 1, wherein
Furthermore, a monitor photodiode for detecting the light output of the laser diode;
A first reference value that is an average value of the output of the monitor photodiode at the initial setting time point when the desired light output and extinction ratio are set, and a second value that is the maximum value of the output of the monitor photodiode at the initial setting time point. Second reference means for storing the reference values in advance and outputting these reference values;
The bias current is compensated so that a difference between the first reference value and an average value of the current output of the monitor photodiode is minimized, and the second reference value and the current output of the monitor photodiode are compensated. And a second current control means for compensating the modulation current so that the difference from the maximum value of the laser current becomes minimum. The laser diode driving circuit according to claim 1, wherein
The first current control means includes
The bias current and modulation current of the laser diode are calculated, and a first control signal is output so that the calculated bias current value is obtained, and a second control signal is output so that the calculated modulation current value is obtained. Computing means for
A first current source for supplying a bias current corresponding to the first control signal to the laser diode;
A laser diode driving circuit comprising: a second current source for supplying a modulation current corresponding to the second control signal to the laser diode. The laser diode driving circuit according to claim 2, wherein
The second current control means includes
Average value detecting means for detecting an average value of the output of the monitor photodiode;
Maximum value detecting means for detecting the maximum value of the output of the monitor photodiode;
First comparison amplification means for outputting a third control signal so that a difference between the first reference value and an average value of the current output of the monitor photodiode is minimized;
Second comparison amplification means for outputting a fourth control signal so that a difference between the second reference value and the maximum value of the current output of the monitor photodiode is minimized;
A third current source for supplying a bias current corresponding to the third control signal to the laser diode;
A laser diode driving circuit comprising: a fourth current source for supplying a modulation current corresponding to the fourth control signal to the laser diode. In a laser diode driving method for driving the laser diode with a current superimposed with a bias current and a modulation current for causing the laser diode to emit light according to a transmission signal pattern,
A temperature detection procedure to detect the ambient temperature;
The threshold value and the slope efficiency value corresponding to the ambient temperature detected in the temperature detection procedure are obtained from the first storage means for preliminarily storing the threshold value and slope efficiency data of the laser diode at each ambient temperature. A first current control procedure for determining the bias current and the modulation current of the laser diode using the value, the set light output and the set extinction ratio value, and driving the laser diode; A method for driving a laser diode. The laser diode driving method according to claim 5, wherein
Furthermore, a light output detection procedure for detecting the light output of the laser diode with a monitor photodiode,
A first reference value that is an average value of the output of the monitor photodiode at the initial setting time point when the desired light output and extinction ratio are set, and a second value that is the maximum value of the output of the monitor photodiode at the initial setting time point. These reference values are acquired from the second storage means for storing the reference values in advance so that the difference between the first reference value and the average value of the current output of the monitor photodiode is minimized. And a second current control procedure for compensating the bias current and compensating the modulation current so that a difference between the second reference value and the maximum value of the current output of the monitor photodiode is minimized. And a laser diode driving method.

Images