JP6321461B2 - Semiconductor optical device and control method - Google Patents

Description

  The present invention relates to a semiconductor optical device and a control method.

  Conventionally, a semiconductor optical device that transmits an optical signal in optical communication may generate a modulated optical signal by applying a current modulated at a high frequency to a semiconductor laser element. In some cases, laser light is generated by a semiconductor laser element, and the intensity of the laser light is modulated by a modulator to generate an optical signal.

  Here, the extinction ratio of the optical signal (ratio between the light intensity representing 1 and the light intensity representing 0 in the optical signal) is determined by customer specifications and international standards (allowable value, allowable range). The average output of the optical signal is preferably controlled according to the transmission distance of the optical signal.

  Patent Document 1 listed below discloses a light emitting element driving circuit that controls a driving current of a light emitting element in accordance with a peak value of a voltage between terminals of the light emitting element.

  Patent Document 2 describes a semiconductor laser stabilization device that calculates the temperature of a semiconductor laser element from a current injected into the semiconductor laser element and its forward voltage drop, and controls the temperature of the semiconductor laser element at a constant value. Yes.

JP-A-10-190118 JP 62-22494 A

A semiconductor laser element included in a semiconductor optical device has a PI characteristic (relationship between optical output and drive current) that varies depending on the drive temperature. Therefore, if the drive current is not controlled according to the temperature change, the extinction ratio and Average output fluctuates. FIG. 12 is a diagram showing PI characteristics of the semiconductor laser element. The vertical axis represents the magnitude of the average output of the semiconductor laser element, and the horizontal axis represents the magnitude of the bias current supplied to the semiconductor laser element. A curve J is a PI characteristic curve when the temperature of the semiconductor laser element is the reference value temperature T _adj , and a curve K is P when the temperature of the semiconductor laser element is a temperature T higher than the reference value temperature T _adj. -I characteristic curve.

When attention is paid to the curve J, it can be seen that in the case of the reference value temperature T _adj , the magnitude of the bias current should be I _adj in order to match the average output of the semiconductor laser element to P _adj . Further, in the optical signal, when the desired optical extinction ratio is realized by setting the optical output representing 0 as P1 and the optical output representing 1 as P2, the magnitude of the modulation current to be applied to the semiconductor laser element is I _{mod, adj} I understand. On the other hand, paying attention to the curve K, when the temperature T> T _adj , in order to realize an average output and extinction ratio that is not different from the case of the reference value temperature T _adj , the magnitude of the bias current is I1> I _adj. It can be seen that the magnitude of the modulation current should be adjusted as I _mod > I _{mod, adj} . That is, in order to realize a constant average output and extinction ratio, it is necessary to adjust so that the bias current and the modulation current increase as the temperature of the semiconductor laser element increases.

FIG. 13 is a diagram illustrating the VI characteristics of the semiconductor laser element. The vertical axis represents the magnitude of the bias voltage, which is the direct current component of the voltage applied between the terminals of the semiconductor laser element, and the horizontal axis represents the magnitude of the bias current supplied to the semiconductor laser element. A curve L is a VI characteristic curve when the temperature of the semiconductor laser element is the reference value temperature T _adj , and a curve M is V V when the temperature of the semiconductor laser element is higher than the reference value temperature T _adj. -I characteristic curve.

As shown in FIG. 12, in order to obtain P _adj as the average output in the case of the reference value temperature T _adj , the magnitude of the bias current must be I _adj . When attention is paid to the curve L, it can be seen that the voltage between the terminals in this case is V _adj . On the other hand, in order to obtain P _adj as an average output when temperature T> T _adj , the bias current must be I1, and when attention is paid to the curve M, the terminal voltage in that case may be V1. Recognize. That is, in order to obtain a constant average output, it is necessary to adjust the driving conditions of the semiconductor laser element so that the inter-terminal voltage decreases as the temperature of the semiconductor laser element increases.

  Here, a part of the light emitted from the semiconductor laser element is received by the light receiving element, and the extinction ratio and the average output of the optical signal are directly monitored to feedback control the bias current and the like.

  However, since an optical signal used in optical communication is a high-frequency signal of several GHz or more, it is suitable for receiving a high-frequency signal by receiving the optical signal with a light receiving element or the like and monitoring the extinction ratio and average output. A light receiving element and a receiving circuit are required. For this reason, it is necessary to incorporate dedicated parts into the semiconductor optical device, which is disadvantageous in terms of cost and the like.

  Therefore, the present invention provides a semiconductor optical device and a control method capable of controlling the average output of an optical signal to be constant without using a light receiving element, and controlling the extinction ratio of the optical signal to be constant. Objective.

  (1) In order to solve the above-described problem, a semiconductor optical device according to the present invention includes a semiconductor optical element that outputs an optical signal, a bias current supply unit that supplies a bias current to the semiconductor optical element, and the semiconductor optical element. A voltage measuring means for measuring a bias voltage applied between the terminals of the semiconductor device, a current measuring means for measuring the bias current, a temperature measuring means for measuring the temperature of the semiconductor optical device directly or indirectly, and a reference value Storage means for storing a bias voltage, a reference value bias current, a reference value temperature, and a reference value α, and a bias voltage measured by the voltage measuring means, which is established when an average output of the optical signal is constant, Bias current measured by current measuring means, temperature measured by temperature measuring means, reference value bias voltage, reference value bias current, reference value temperature, Based on the first information defining a relationship between the fine the reference value alpha, characterized in that it comprises a bias current control means for controlling the bias current supply means.

  (2) In the semiconductor optical device according to (1), the first information includes a first function having the measured temperature as a variable, the measured bias voltage, and the measured An equality relationship with a first value that is a ratio value with respect to the bias current is defined, and the bias current control unit is configured to satisfy the equality relationship defined in the first information. The supply unit may be controlled.

  (3) In the semiconductor optical device according to (2), the first function may be a monotonically decreasing function with respect to the measured temperature that is a variable.

(4) In the semiconductor optical device according to (3), the reference value bias voltage is V _adj , the reference value bias current is I _adj , the reference value bias voltage V _adj and the reference value bias current I _adj The first function f ₁ (T) is expressed as y = V _adj / I _adj , the reference value temperature is T _adj , the first value is x, and the measured temperature is T F ₁ (T) = y (α (T−T _adj ) +1) ^1/2 , and the bias current control means controls the bias current supply means so that x = f ₁ (T). You may be characterized by doing.

  (5) A semiconductor optical device according to the present invention includes a semiconductor optical element that outputs an optical signal, bias current supply means that supplies a bias current to the semiconductor optical element, and a modulation current that supplies a modulation current to the semiconductor optical element. A supply means; a voltage measuring means for measuring a bias voltage applied between the terminals of the semiconductor optical element; a current measuring means for measuring the bias current; and a temperature of the semiconductor optical element is measured directly or indirectly. This is established when the temperature measurement means for storing, the storage means for storing the reference value modulation current, the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value α, and the extinction ratio of the optical signal are constant. , The bias voltage measured by the voltage measuring means, the bias current measured by the current measuring means, the temperature measured by the temperature measuring means, the reference value modulation current, Modulation current control means for controlling the modulation current supply means based on second information defining the relationship between the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value α, It is characterized by providing.

  (6) In the semiconductor optical device according to (5), the second information is a first value that is a value of a ratio between the measured bias voltage and the measured bias current, and An equality relationship between the second function having the measured temperature as a variable and the modulation current supplied by the modulation current supply unit is defined, and the modulation current control unit is defined by the second information. The modulation current supply means may be controlled so that the equality relationship is satisfied.

  (7) In the semiconductor optical device according to (6), the second function may be a monotonically increasing function with respect to the measured temperature that is a variable.

(8) The semiconductor optical device according to (7), wherein the reference value bias voltage is V _adj , the reference value bias current is I _adj , the reference value bias voltage V _adj and the reference value bias current I _{adj Is} the ratio y = V _adj / I _adj , the reference value temperature is T _adj , the reference value modulation current is I _{mod, adj} , the first value is x, the measured temperature is T, and the modulation current When the modulation current supplied by the supply means is expressed as I _mod , the second function f ₂ (x, T) is f ₂ (x, T) = (α (T−T _adj ) +1) ^{−1. / 2} (log (x ² ) / x ² ) ((y ² (α (T−T _adj ) +1) / log (y ² (α (T−T _adj ) +1))), and the modulation current control _{means, I mod = I mod, adj} f 2 (x, T) and It may be characterized in that for controlling the modulation current supply means so that.

  (9) The semiconductor optical device according to any one of (1) to (8), wherein the storage unit further stores a reference value average output, the measured bias voltage, and the measured Based on third information defining the relationship among the measured bias current, the measured temperature, the reference value bias voltage, the reference value bias current, the reference value temperature, the reference value α, and the reference value average output. Further, an average output calculating means for calculating an average output of the optical signal may be further provided.

  (10) In the semiconductor optical device according to (9), the third information includes a first value that is a value of a ratio between the measured bias voltage and the measured bias current, and An equality relationship between a third function having the measured temperature as a variable and an average output of the optical signal is defined, and the average output calculation means is based on an equality relationship defined in the third information. The average output of the optical signal may be calculated.

  (11) In the semiconductor optical device according to the above (10), the equality relationship defined in the third information indicates that the value of the measured bias current increases as the measured bias current increases. It may be characterized by approaching -I characteristics.

(12) The semiconductor optical device according to (10) or (11), wherein the reference value bias voltage is V _adj , the reference value bias current is I _adj , the reference value temperature is T _adj , and the reference value The average output is P _adj , the ratio of the reference value bias voltage to the reference value bias current is y = V _adj / I _adj , the first value is x, the measured temperature is T, and the average of the optical signal When the output is expressed as P, the third function f ₃ (x, T) is f ₃ (x, T) = (log (x ² ) / x ² ) ((y ² (α (T−T _adj ) +1) / log (y ² (α (T−T _adj ) +1))), and the average output calculation means calculates the average output of the optical signal by P = P _adj f ₃ (x, T). It is good also as calculating.

  (13) A semiconductor optical device according to the present invention includes a semiconductor optical element that outputs an optical signal, bias current supply means that supplies a bias current to the semiconductor optical element, and a modulation current that supplies a modulation current to the semiconductor optical element. A supply means; a voltage measuring means for measuring a bias voltage applied between the terminals of the semiconductor optical element; a current measuring means for measuring the bias current; and a temperature of the semiconductor optical element is measured directly or indirectly. This is established when the temperature measurement means for storing, the storage means for storing the reference value bias voltage, the reference value bias current, the reference value temperature, the reference value α, and the reference value modulation current, and the average output of the optical signal are constant. The bias voltage measured by the voltage measuring means, the bias current measured by the current measuring means, the temperature measured by the temperature measuring means, the reference value via Bias current control means for controlling the bias current supply means based on the first information defining the relationship between the voltage, the reference value bias current, the reference value temperature, and the reference value α; and quenching of the optical signal The bias voltage measured by the voltage measuring unit, the bias current measured by the current measuring unit, the temperature measured by the temperature measuring unit, the reference value modulation current, and the reference, which are established when the ratio is constant Modulation current control means for controlling the modulation current supply means based on second information defining the relationship between the value bias voltage, the reference value bias current, the reference value temperature, and the reference value α. It is characterized by.

  (14) A control method according to the present invention includes a voltage measuring step for measuring a bias voltage applied between terminals of a semiconductor optical device that outputs an optical signal, and a current for measuring a bias current supplied to the semiconductor optical device. A measurement step, a modulation current supply step for supplying a modulation current to the semiconductor optical device, a temperature measurement step for measuring the temperature of the semiconductor optical device directly or indirectly, and an average output of the optical signal is constant The first information that defines the relationship between the measured bias voltage, the measured bias current, the measured temperature, the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value α, And a bias current control step for controlling the bias current, and the measured bias voltage and the measured bias that are established when the extinction ratio of the optical signal is constant. The modulation based on the second information defining the relationship of the current, the measured temperature, the reference value modulation current, the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value α And a modulation current control step for controlling the current.

  According to the present invention, there is provided a semiconductor optical device and a control method capable of controlling the average output of an optical signal to be constant and also controlling the extinction ratio of the optical signal to be constant without using a light receiving element.

1 is a configuration diagram of a semiconductor optical device according to a first embodiment of the present invention. It is a flowchart which shows the control process performed at the time of the drive of the semiconductor optical device concerning the 1st Embodiment of this invention. It is a 1st flowchart which shows the reference value determination process performed at the time of manufacture of the semiconductor optical device concerning the 1st Embodiment of this invention. It is a 2nd flowchart which shows the reference value determination process performed at the time of manufacture of the semiconductor optical device concerning the 1st Embodiment of this invention. It is a 3rd flowchart which shows the reference value determination process performed at the time of manufacture of the semiconductor optical device concerning the 1st Embodiment of this invention. It is a figure which shows the relationship prescribed | regulated by 2nd information. It is a figure which shows the relationship prescribed | regulated by 2nd information in the case of a different average output. It is a figure which shows the relationship prescribed | regulated by 3rd information. It is a figure which shows the range where numerical formula (1) which is the relationship prescribed | regulated by 3rd information is materialized. It is a figure which shows the relationship prescribed | regulated by 1st information. It is a block diagram of the semiconductor optical device concerning the 2nd Embodiment of this invention. It is a figure which shows the PI characteristic of a semiconductor laser element. It is a figure which shows the VI characteristic of a semiconductor laser element.

  Hereinafter, embodiments of the present invention will be described specifically and in detail based on the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.

[First Embodiment]
FIG. 1 is a configuration diagram of a semiconductor optical device 1 according to the first embodiment of the present invention. The semiconductor optical device 1 according to this embodiment includes a driver circuit 2, an optical transmission module 3, a microcomputer 4, a bias current source 5, a voltage measurement unit 6, and a current measurement unit 7. With.

  The drive circuit 2 includes a modulation current source 20 and two transistors connected to the modulation current source 20 in parallel. Signals P and N are input to the gate electrodes of the two transistors from the outside, respectively, and the drive circuit 2 outputs a modulation signal to the optical transmission module 3.

  The optical transmission module 3 is an optical transmission sub-assembly (TOSA) including the semiconductor optical element 30. In the present embodiment, the semiconductor optical device 30 is a semiconductor laser device, and may be a DFB laser that emits laser light having a specific wavelength. The semiconductor optical device 30 is supplied with a current modulated in accordance with the modulation signal input from the drive circuit 2, and the semiconductor optical device 30 outputs an optical signal. Here, the difference between the maximum output and the minimum output of the light emitted from the semiconductor optical device 30 is determined according to the magnitude of the current supplied from the modulation current source 20. That is, by controlling the modulation current source 20, the extinction ratio of the optical signal output from the semiconductor optical device 30 is controlled.

  The microcomputer 4 includes a storage unit 40, a thermometer 42, and a control unit 44. The controller 44 includes an average output calculator 440, a modulation current controller 442, and a bias current controller 444.

  The storage unit 40 includes, for example, a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 40 stores a program executed by the control unit 44 and also functions as a work memory for the control unit 44. Note that the program executed by the control unit 44 stored in the storage unit 40 may be provided via an electric communication line or stored in a computer-readable information storage medium such as a semiconductor storage element. And may be provided. Information stored in the storage unit 40 will be described in detail later.

  The thermometer 42 is a thermometer built in the microcomputer 4 and is, for example, a thermistor. In the present embodiment, the temperature of the microcomputer 4 is measured by the thermometer 42, the measured value is transmitted to the control unit 44, and the temperature of the semiconductor optical element 30 is indirectly measured. When the optical transmission module 3 and the microcomputer 4 are installed physically apart from each other, the temperature detected by the thermometer 42 is not necessarily the temperature of the semiconductor optical element 30, but the temperature detected by the thermometer 42 and the semiconductor light Since there is a correlation with the temperature of the element 30, the temperature of the semiconductor optical element 30 can be indirectly measured based on the temperature detected by the thermometer 42. Alternatively, a value obtained by replacing the temperature detected by the thermometer 42 with the control unit 44 by a predetermined method may be used. However, the temperature of the semiconductor optical device 30 may be directly measured by providing the thermometer 42 separately from the microcomputer 4. Hereinafter, unless otherwise specified, in this specification, “the temperature of the semiconductor optical device 30 measured by the thermometer 42” is defined as the temperature of the semiconductor optical device 30 detected by the thermometer 42 itself. When the temperature detected by the thermometer 42 is changed to a read value, or when the temperature of the semiconductor optical device 30 is directly measured, the case is shown.

  The control unit 44 includes, for example, a CPU (Central Processing Unit), and by executing a program stored in the storage unit 40, the average output of the optical signal output from the semiconductor optical device 30 by the average output calculation unit 440 , The modulation current control unit 442 controls the modulation current source 20, and the bias current control unit 444 controls the bias current source 5. The control performed by the control unit 44 will be described in detail later. The value calculated by the average output calculation unit 440 is output to the outside as a signal Out. The value indicated by the signal Out may be output to a display unit such as a liquid crystal display device.

  The bias current source 5 supplies a direct-current bias current to the optical transmission module 3. The bias current supplied by the bias current source 5 determines the average output of the optical signal output from the semiconductor optical device 30. The bias current source 5 is controlled by the bias current control unit 444.

The voltage measurement unit 6 includes an operational amplifier 60, a resistor R ₂ , a capacitor C ₂ , and a first voltmeter 62. The operational amplifier 60 receives the voltage between the electrodes of the semiconductor optical device 30, and is amplified and output with a specified amplification factor. In the present embodiment, the voltage amplification factor by the operational amplifier 60 is n, and the amplification factor is stored in the storage unit 40. Resistor _{R 2} and capacitor _{C 2} functions as a low-pass filter. Since the semiconductor optical device 30 is supplied with a current modulated at a high frequency by the drive circuit 2, the interelectrode voltage of the semiconductor optical device 30 has a high frequency component. Such a high frequency component is removed by the resistor R ₂ and the capacitor C ₂ , and in the first voltmeter 62, a direct current component (hereinafter referred to as a bias voltage) among voltages applied between the terminals of the semiconductor optical device 30. Is measured. The measured voltage value is transmitted to the control unit 44 of the microcomputer 4. The control unit 44 calculates the bias voltage applied between the terminals of the semiconductor optical device 30 by dividing the value received from the first voltmeter 62 by n.

The current measurement unit 7 includes a resistor R _i , a resistor R ₁ , a capacitor C ₁ , and a second voltmeter 70. The resistor R _i is a resistor provided between the bias current source 5 and the ground. When the DC current I is supplied from the bias current source 5, the voltage between the terminals of the resistor R _i is R _i I. . Here, it is assumed that the resistance value of the resistor R _i is stored in the storage unit 40. The low pass filter formed by the resistor R ₁ and the capacitor C ₁ removes the high frequency component of the voltage. The second voltmeter 70 measures the voltage that has passed through the low-pass filter formed by the resistor R ₁ and the capacitor C ₁ and transmits it to the control unit 44. The control unit 44, the value received from the second voltmeter 70 by dividing by R _i, and calculates the value of the bias current I is supplied to the semiconductor optical device 30. In some cases, the bias current source 5 and the current measurement unit 7 are built in, for example, the drive circuit 2 (the drive circuit 2 has functions as a bias current source and a current measurement unit). In that case, the current measurement unit provided in the drive circuit 2 measures the value of the bias current output from the bias current source provided in the drive circuit 2, and measures the bias current value output from the drive circuit 2 to the microcomputer 4. It may be used as a value.

  In the present embodiment, a forward current is supplied to the semiconductor optical device 30 of the optical transmission module 3. The semiconductor optical element 30 is supplied with a current modulated at a high frequency by the bias current source 5 and the drive circuit 2 but is not supplied with a reverse current. As for the voltage applied between the terminals of the semiconductor optical device 30, a forward voltage is applied and no reverse voltage is applied.

  FIG. 2 is a flowchart showing a control process performed when the semiconductor optical device 1 according to the first embodiment of the present invention is driven. Prior to driving the semiconductor optical device 1, a bias applied between the terminals of the semiconductor optical device 30 is established in the storage unit 40 when the average output of the optical signal output from the semiconductor optical device 30 is constant. It is assumed that first information that defines the relationship among the voltage, the bias current supplied to the semiconductor optical device 30, the temperature of the semiconductor optical device 30 measured by the thermometer 42, and the reference value is stored. Further, the storage unit 40 applies the modulation current supplied from the modulation current source 20 between the terminals of the semiconductor optical element 30 that is established when the extinction ratio of the optical signal output from the semiconductor optical element 30 is constant. The second information defining the relationship between the bias voltage to be applied, the bias current supplied to the semiconductor optical device 30, the temperature of the semiconductor optical device 30 measured by the thermometer 42, and the reference value is stored. . Further, the storage unit 40 includes an average output of the optical signal output from the semiconductor optical element 30, a bias voltage applied between the terminals of the semiconductor optical element 30, a bias current supplied to the semiconductor optical element 30, and a thermometer 42. It is assumed that the third information defining the relationship between the temperature of the semiconductor optical device 30 measured by the above and the reference value is stored.

  A control process performed when the semiconductor optical device 1 is driven starts with measurement of a bias current, a bias voltage, and a temperature (S10). Here, the bias current is a current supplied to the semiconductor optical device 30 from the bias current source 5 and is measured by the current measuring unit 7 and the control unit 44. The bias voltage is a direct current component of the voltage applied between the terminals of the semiconductor optical device 30 and is measured by the voltage measurement unit 6 and the control unit 44. The temperature is the temperature of the semiconductor optical device 30 and is measured by the thermometer 42 and the control unit 44.

  Next, the modulation current control unit 442 of the control unit 44 controls the modulation current based on the second information (S11). More specifically, the modulation current control unit 442 defines the relationship between the measured bias voltage, the measured bias current, the measured temperature, and the reference value that is established when the extinction ratio of the optical signal is constant. The modulation current source 20 is controlled based on the second information. The modulation current control unit 442 receives the measured bias voltage, the measured bias current, and the measured temperature as inputs, based on the second information that is established when the extinction ratio of the optical signal is constant. The source 20 is controlled.

  Moreover, the average output calculation part 440 of the control part 44 calculates an average output based on 3rd information (S12). More specifically, the average output calculation unit 440 calculates the average output of the optical signal based on the measured bias voltage, the measured bias current, the measured temperature, and the third information. The average output calculation unit 440 outputs the calculated value to the outside as a signal Out.

  The bias current control unit 444 of the control unit 44 determines whether or not the measured bias voltage, bias current, and temperature satisfy the relationship defined by the first information (S13). The bias current control unit 444 receives the measured bias voltage, the measured bias current, and the measured temperature as inputs, and these values are first information that is established when the average output of the optical signal is constant. It is determined whether or not the relationship specified in the above is satisfied.

  When the bias current control unit 444 determines that the measured bias voltage, the measured bias current, and the measured temperature do not satisfy the relationship defined in the first information (in the case of NO in S13) The bias current control unit 444 corrects the bias current (S14). That is, the bias current control unit 444 controls the bias current source 5 so that the average output of the optical signal output from the semiconductor optical device 30 is constant.

  When the bias current is corrected by the bias current control unit 444, the bias current and the bias voltage applied between the terminals of the semiconductor optical device 30 change, so that the modulation current source 20 of the modulation current source 20 performed by the modulation current control unit 442 changes. The premise of the control (S11) and the calculation (S12) of the average output of the optical signal performed by the average output calculation unit 440 changes. Therefore, after the bias current correction (S14), the process returns to the step (S10) of measuring the bias current, bias voltage, and temperature, and the steps S10 to S13 are performed again. Until the bias current control unit 444 determines that the measured bias voltage, the measured bias current, and the measured temperature satisfy the relationship defined in the first information (determined as YES in S13). Steps S10 to S14 are repeated.

  When the bias current control unit 444 determines that the measured bias voltage, the measured bias current, and the measured temperature satisfy the relationship defined in the first information (in the case of YES in S13), The control process ends.

As described above, in this embodiment, the bias voltage applied between the terminals of the semiconductor optical device 30, the bias current supplied to the semiconductor optical device 30, and the temperature of the semiconductor optical device 30 are measured and stored in the storage unit 40. Based on the obtained information, the bias current source 5 is controlled so that the average output of the optical signal output from the semiconductor optical element 30 is constant, and the extinction ratio of the optical signal output from the semiconductor optical element 30 is constant. Such control of the modulation current source 20 and monitoring of the average output of the optical signal output from the semiconductor optical device 30 can be performed. Therefore, the semiconductor optical device 1 according to the present embodiment can control the average output of the optical signal to be constant and can also control the extinction ratio of the optical signal to be constant without using a light receiving element. Further, the average output of the optical signal can be monitored without using a light receiving element. Conventionally, the control of the average output and the extinction ratio has been controlled using the monitor value using the light receiving element, but the inventors etc. have intensively studied to control the bias voltage, the bias current, and the temperature. Three parameters were measured, and it was found that the average output and the extinction ratio can be controlled to be constant (desired values) using these three measured values. More specific control will be described later.

  Note that the control process of the semiconductor optical device 1 may be performed periodically, for example, every few seconds, when the semiconductor optical device 1 is driven. Further, the bias current correction (S14) may be performed by a specified increase / decrease amount, for example, every 0.01 mA. But it is good also as being able to correct | amend freely, without adding a restriction | limiting to the increase / decrease amount.

  FIG. 3 is a first flowchart showing a reference value determining step performed at the time of manufacturing the semiconductor optical device 1 according to the first embodiment of the present invention. The reference value determination step is a step performed after the semiconductor optical device 1 is assembled in a drivable state, and is a step performed to determine various reference values stored in the storage unit 40 of the semiconductor optical device 1. It is. In particular, the process shown in the first flowchart is performed to determine the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value average output.

In the reference value determination step, first, the fixed resistance value R _i and the operational amplifier gain n are stored in the storage unit 40 (S20). These values are known at the time of designing the semiconductor optical device 1.

  Next, the ambient temperature in which the semiconductor optical device 1 is placed is set (S21). The set ambient temperature may be set freely as long as it is sufficiently stable within a range that does not place an excessive burden on the semiconductor optical device 1, but the ambient temperature when the semiconductor optical device 1 is actually used. It is desirable that the temperature be close to, for example, 25 ° C. Here, not the ambient temperature, but the temperature of the semiconductor optical device 30 may be set. In that case, the temperature of the semiconductor optical device 30 may be kept constant by a Peltier device or the like.

  Next, the initial value of the bias current is set (S22). The initial value of the bias current is set by connecting an input unit to the microcomputer 4 and operating the bias current control unit 444 from the outside or storing it in the storage unit 40 in advance as an initial set value. This is done by operating the current control unit 444. The initial value of the bias current may be set freely, but is within a range in which the semiconductor optical device 30 outputs sufficient average output light and does not place an excessive burden on the semiconductor optical device 30.

  After the state in which the semiconductor optical device 30 outputs light is obtained, it is determined whether or not the average output is within a specified range (S23). Here, the output of the light output from the semiconductor optical device 30 is measured by a light output measuring instrument prepared in the reference value determining step. Also, whether or not the average output is within the specified range means whether or not the average output is a desired value with a specified accuracy. For example, if an output within ± 5% of a desired value is achieved, it may be determined that the average output is within a specified range. If the optical average output is not within the specified range (NO in S23), the bias current source 5 is controlled via the bias current control unit 444 to correct the bias current (S24).

  If it is determined that the average output is within the specified range (YES in S23), the average output, bias current, bias voltage, and temperature are measured (S25). These values are measured using the light output measuring instrument prepared in the reference value determining step, the voltage measuring unit 6, the current measuring unit 7, the thermometer 42, and the control unit 44 provided in the semiconductor optical device 1.

The measured bias voltage, bias current, temperature, and average output are respectively stored in the storage unit 40 as a reference value bias voltage V _adj , a reference value bias current I _adj , a reference value temperature T _adj , and a reference value average output P _adj. Store (S26). These values are referred to in the relationship defined by the first information, the second information, and the third information. In the control process of the semiconductor optical device 1, the bias current control unit 444, the modulation current control unit 442, The average output calculation unit 440 executes the process.

  FIG. 4 is a second flowchart showing a reference value determining step performed at the time of manufacturing the semiconductor optical device 1 according to the first embodiment of the present invention. The process shown in the second flowchart is performed after the process shown in the first flowchart is performed, and is performed to determine the reference value α.

First, the ambient temperature in which the semiconductor optical device 1 is placed is changed (S30). That is, the semiconductor optical device 1 is placed at an atmospheric temperature different from that in the step of determining the reference values V _adj , I _adj , T _adj , and P _adj shown in the first flowchart. For example, the ambient temperature is 85 ° C. Also in this case, the temperature of the semiconductor optical device 30 may be directly controlled by a Peltier device or the like.

  Then, using the optical output measuring instrument prepared in the reference value determining step, the voltage measuring unit 6 provided in the semiconductor optical device 1, the current measuring unit 7, the thermometer 42, and the control unit 44, the average output, the bias current Then, the bias voltage and the temperature are measured (S31). The measured average output, bias current, bias voltage, and temperature values are denoted as P, V, I, and T, respectively.

The measured values of P, V, I, and T, the reference values P _adj , V _adj , I _adj , and T _adj already stored in the storage unit 40, and the relationship defined in the third information The reference value α is calculated based on and stored in the storage unit 40 (S32). The relationship defined in the third information includes the measured bias voltage V, the measured bias current I, the measured temperature T, the reference value bias voltage V _adj , the reference value bias current I _adj , and the reference value temperature T. The relationship between _adj and the reference value α, specifically, the relationship defined by the following formula (1). In the present embodiment, the reference value α is a negative value of about −0.01. However, the value of the reference value α varies depending on the configuration and material of the semiconductor optical device 1 and the semiconductor optical element 30.

Here, log represents a logarithm having a base of 10, and P, V, and I represent values of average output, bias voltage, and bias current normalized in units of mW, mV, and mA. The same applies to P _adj , V _adj and I _adj . T and T _adj are temperatures expressed in K units, and the unit of the reference value α is [K ⁻¹ ]. The relationship defined by Equation (1) has a condition for establishing it. Therefore, it is necessary to determine the reference value α using a bias current value that satisfies such a condition. This condition will be described in detail later.

Equation (1) is an equation representing the relationship between bias voltage, bias current, temperature, and average output under two different conditions. That is, an average output at a bias voltage V _adj , a bias current I _adj , and a temperature T _adj which are first conditions (conditions determined in the reference value determining step) is P _adj , and a second condition (measurement at a certain time) When the average light output at the bias voltage V, the bias current I, and the temperature T is P, these parameters have the relationship of the formula (1) including the reference value α. α is a so-called coefficient. This numerical formula (1) is obtained by the inventors, etc., by diligently examining the relationship between the average output, the bias voltage, the bias current, and the temperature under various conditions of many semiconductor optical devices. This is an empirical formula that was first discovered by the inventors. The same applies to formulas (2), (3), and (4) described later.

  In order to determine the reference value α based on the third information (formula (1)), it is necessary to measure the average output, the bias voltage, the bias current, and the temperature under at least two different conditions. However, the average output, the bias voltage, the bias current, and the temperature are measured under three or more different conditions, α is calculated using Formula (1) for a combination of a plurality of conditions, and the reference value α is calculated as the average value thereof. It may be determined.

  The reference value α is a value determined by the configuration of the semiconductor optical device 1 and the individual difference is small. Therefore, the reference value α may be determined using at least one semiconductor optical device 1. The processing shown in the flowchart may not be performed. However, the processing shown in the second flowchart may be performed for a plurality of semiconductor optical devices 1, and the average value of the obtained values may be stored in the storage unit 40 of all the semiconductor optical devices 1 as a reference value α. The reference value α may be determined for all the semiconductor optical devices 1.

  FIG. 5 is a third flowchart showing a reference value determining step performed at the time of manufacturing the semiconductor optical device 1 according to the first embodiment of the present invention. The process shown in the third flowchart is performed after the process shown in the second flowchart, and is performed to determine the reference value modulation current.

First, the initial value of the modulation current is set (S40). The modulation current initial value is set by connecting an input unit to the microcomputer 4 and operating the modulation current control unit 442 from the outside, or storing the initial setting value in the storage unit 40 in advance, and modulating the initial value by this initial setting value. This is done by operating the current control unit 442. The initial value of the modulation current may be set freely, but is preferably set so that the extinction ratio of the semiconductor optical element 30 is close to a specified value, and does not place an excessive burden on the semiconductor optical element 30. It shall be within. The ambient temperature is T _adj stored in the storage unit 40 in the second flowchart, and the bias current is also I _adj . The initial value is not limited to this, and an arbitrary value may be set.

  After the state in which the semiconductor optical device 30 outputs light is obtained, it is determined whether or not the extinction ratio is within a specified range (S41). Here, the extinction ratio of the light output from the semiconductor optical device 30 is measured by an optical waveform measuring instrument such as an optical oscilloscope prepared in the reference value determining step. Whether or not the extinction ratio is within a specified range refers to whether or not the extinction ratio is a desired value with a specified accuracy. For example, if an extinction ratio within ± 5% of a desired value is achieved, it may be determined that the extinction ratio is within a specified range. When the extinction ratio is not within the specified range (NO in S41), the modulation current source 20 is controlled via the modulation current control unit 442 to correct the modulation current (S42).

If it is determined that the extinction ratio is within the specified range (YES in S41), the modulation current value in that case is stored in the storage unit 40 as the reference value modulation current I _{mod, adj} (S43). Here, it is assumed that the relationship between the signal supplied from the modulation current control unit 442 to the modulation current source 20 and the current supplied by the modulation current source 20 is known, and the modulation current source is determined based on the control status of the modulation current control unit 442. It is assumed that the modulation current value supplied by 20 can be read.

The reference value determination process is thus completed, and the fixed resistance value R _i , the operational amplifier amplification factor n, the reference values α, V _adj , I _adj , T _adj , P _adj , and I are stored in the storage unit 40 of the semiconductor optical device 1. _{“mod” and “adj”} are stored. Thereafter, the storage unit 40 stores first to third information referring to these reference values, and is shipped. When the semiconductor optical device 1 is driven, the control process shown in FIG. 2 controls the average output and extinction ratio of the optical signal to be constant, calculates the average output of the optical signal, and outputs the calculated value to the outside. Output as Out.

FIG. 6 is a diagram illustrating a relationship defined by the second information. The second information is a measured modulation current, a measured bias voltage V, a measured bias current I, a measured temperature T, a reference value modulation current, which is established when the extinction ratio of the optical signal is constant. I _{mod, adj} , reference value bias voltage V _adj , reference value bias current I _adj , reference value temperature T _adj , and reference value α. The second information includes a first value V / I that is a value of a ratio of V and I, a second function f ₂ (V / I, T) having the measured temperature T as a variable, and modulation. The following equation (2) that is an equality relationship with the modulation current I _mod supplied by the current source 20 is defined.

Here, log represents a logarithm having a base of 10, and I _mod , V, and I represent values of modulation current, bias voltage, and bias current normalized in units of mA, mV, and mA, respectively. The same applies to I _{mod, adj} , V _adj and I _adj . T and T _adj are temperatures expressed in K units, and the unit of the reference value α is [K ⁻¹ ].

The relationship of I _mod / I _{mod, adj} = f ₂ (V / I, T) defined in the second information is a relationship that is established when the extinction ratio is constant at a specified value. Further, the relationship defined by the second information can be expressed as the following mathematical formula (3) when transformed using the mathematical formula (1) (third information).

In FIG. 6, the average output of the optical signal is particularly shown in the relationship of I _mod / I _{mod, adj} = f ₂ (V / I, T), where I _mod / I _{mod, adj is} the vertical axis and T is the horizontal axis. A curve A representing the case where P is equal to P _adj is shown. That is, the curve A is a curve representing the relationship between I _mod and T so that the extinction ratio of the optical signal is constant when P = P _adj . That is, the curve A is a relationship curve of I _mod / I _{mod, adj} and T based on the equation (3) when P = P _adj and the extinction ratio are constant.

When the temperature T of the semiconductor optical element 30 measured by the thermometer 42 is T = T _adj which is the origin, the same condition as that when the extinction ratio is adjusted in the reference value determination step is used, and _therefore I _mod / When I _{mod, adj} = 1, the extinction ratio becomes a specified value. Therefore, the curve A intersects the vertical axis with I _mod / I _{mod, adj} = 1. In this case, the modulation current control unit 442 can adjust the extinction ratio of the optical signal to the specified value by controlling the modulation current source 20 to be I _mod = I _{mod, adj} .

The temperature T to be measured, if a value represented by the point Z, the modulation current control unit 442, a modulation current source _{20, I mod /} I _mod, the _{I mod} so that adj = Z1 By controlling, the extinction ratio of the optical signal can be adjusted to the specified value. On the other hand, when the measured temperature T is a value represented by the point Q, the modulation current control unit 442 sets the modulation current source 20 to I _mod / I _{mod, adj} = Q1 so that I _mod / I _{mod, adj} = Q1. By controlling, the extinction ratio of the optical signal can be adjusted to the specified value.

The second function f ₂ (V / I, T) is a monotonically increasing function with respect to the measured temperature T. For this reason, the curve A is an upward curve, and in order to keep the extinction ratio of the optical signal constant, when the measured temperature T is higher than the reference value temperature T _adj , I _mod > I _{mod, adj} When the measured temperature T is smaller than the reference value temperature T _adj, it is necessary to control so that I _mod <I _{mod, adj} . This can be qualitatively read from the PI characteristics of the semiconductor laser element shown in FIG. The mathematical expression (2) or (3) representing the relationship defined in the second information in the present embodiment quantitatively represents the content that can be qualitatively read from the PI characteristic of the semiconductor laser element. That is, at the time of driving, in order to keep the extinction ratio of the semiconductor optical device 1 constant, for example, after performing the average output constant control described later, the extinction ratio can be set by controlling I _mod so that Equation (3) is satisfied. Constant control is possible. More specifically, when the average output constant control is performed, P / P _adj = 1 in Expression (3). As a result, Expression (3) becomes an expression expressed only by the modulation current and the temperature. Then, if I _mod is controlled so as to satisfy the relationship of Equation (3), the extinction ratio is controlled to be constant. Further, depending on customer specifications, there is a case where the optical output is not an extinction ratio but is based on OMA (Optical Modulation Amplitude) which is a difference between light intensity representing 1 and light intensity representing 0 in the optical signal. If the constant and extinction ratio constant control is performed, the OMA is inevitably controlled to satisfy the customer specifications defined by the OMA. Moreover, if the relationship of Formula (2) is used, the extinction ratio can be controlled independently of the average output constant control. For example, in the reference value determining step, each reference value used in the average output constant control uses the value obtained in the first flowchart, and each reference value used in the extinction ratio constant control is a value obtained individually in the second flowchart. You may control using. Thereafter, if the average output constant control described later is performed, the average output and the extinction ratio can be controlled constant, and the above-described OMA is also in a state where the constant control is performed.

The OMA constant control can be performed regardless of the average output. For this purpose, the modulation current source 20 may be controlled so as to satisfy the relationship of I _mod / I _{mod, adj} = (α (T−T _adj ) +1) ^−1/2 . Here, when the average output is P, the output representing 1 in the optical signal is represented as P + P0, and the output representing 0 in the optical signal is represented as P-P0, OMA is (P + P0)-(P-P0) = 2P0, It does not depend on the average output. The magnitude of P0 is controlled by the magnitude of the modulation current I _mod . Therefore, OMA can be controlled to be constant by the relationship not depending on the average output as described above. On the other hand, the extinction ratio is (P + P0) / (P-P0) and depends on the average output. Therefore, constant extinction ratio control is performed according to the relationship depending on the average output as shown in Equation (3).

  FIG. 7 is a diagram illustrating a relationship defined by the second information in the case of different average outputs. In FIG. 7, the curve A shown in FIG. 6 is represented by a broken line, and the curves B and C are represented by a solid line.

Curve B shows the relationship that is established when the optical signal extinction ratio is constant when the average output of the optical signal is twice the reference value average output P _adj . Curve B intersects the vertical axis with I _mod / I _{mod, adj} = 2. From the curve B, in the case of P = 2P _adj , when the measured temperature T is a value represented by the point Z, the modulation current control unit 442 changes the modulation current source 20 to I _mod / I _{mod, adj} = It can be seen that the extinction ratio of the optical signal can be adjusted to the specified value by controlling I _mod so as to be Z3. Further, when the value of the temperature T to be measured is represented by point Q, modulation current control unit 442, a modulation current source _20, to control the _{I mod} so that _{I mod / I mod, adj =} Q3 Thus, the extinction ratio of the optical signal can be adjusted to the specified value. The difference between Z3 and Q3 is larger than the difference between Z1 and Q1, and is twice the difference between Z1 and Q1.

Since the semiconductor optical device 1 is normally driven at a predetermined average output P _adj , the reference value average output P _adj is stored in the storage unit 40 as a desired average output value at the time of manufacture, and modulated according to the curve A at the time of driving. By controlling the current source 20, the extinction ratio of the optical signal can be controlled to be constant. However, for example, when there is a change in the specifications of the optical signal, the optical signal is output at an average output different from the average output of the optical signal originally planned, and the same extinction ratio as originally planned is obtained. The case where it wants to realize is also assumed. Curve B or C is the relationship used when one wants to achieve the same extinction ratio as originally planned with a different average power than originally planned. Although not shown, the same applies to the extinction ratio, and when it is desired to operate constantly at a value different from the originally planned extinction ratio, modulation is performed so as to obtain a desired extinction ratio from the formulas (1) to (3). The current can also be calculated.

Curve C shows the relationship that is established when the optical signal extinction ratio is constant when the average output of the optical signal is half of the reference value average output P _adj . Curve C intersects the vertical axis at I _mod / I _{mod, adj} = 0.5. From the curve C, in the case of P = 0.5P _adj , when the measured temperature T is a value represented by the point Z, the modulation current control unit 442 changes the modulation current source 20 to I _mod / I _mod, It can be seen that the extinction ratio of the optical signal can be adjusted to the specified value by controlling so that _adj = Z2. When the measured temperature T is a value represented by the point Q, the modulation current control unit 442 controls the modulation current source 20 so that I _mod = Q 2, thereby reducing the extinction ratio of the optical signal. Can be adjusted to the specified value. The difference between Z2 and Q2 is smaller than the difference between Z1 and Q1, and is half of the difference between Z1 and Q1.

FIG. 8 is a diagram illustrating a relationship defined in the third information. The relationship defined by the third information is a relationship defined by Equation (1). In FIG. 8, the vertical axis is P / P _adj and the horizontal axis is V / I (first value x), and the relationship defined by Equation (1) is shown. The right side of Equation (1) is the third function f ₃ (V / I, T), and the average output calculation unit 440 uses the measured bias current, the measured bias voltage, and the measured temperature as the third function. By substituting into the function f ₃ (V / I, T), the average output P of the optical signal is calculated according to the equality relationship of P = P _adj f ₃ (V / I, T).

Curve D shows the relationship defined in the third information when the measured temperature T is equal to the reference value temperature T _adj . That is, the relationship of P / P _adj = f ₃ (V / I, T = T _adj ) is shown. For example, when the first value x = V / I, which is the value of the ratio of the measured bias voltage and bias current, is a value represented by a point R, it is calculated that P = P _adj . The third function is a monotonically decreasing function with respect to the first value x in the range shown in FIG. That is, as the first value x increases, the average output of the optical signal decreases.

On the other hand, the curve E shows the relationship defined in the third information when the measured temperature T is higher than the reference value temperature _Tadj . That is, an example of a relationship of P / P _adj = f ₃ (V / I, T> T _adj ) is shown. The curve E has a smaller slope and a smaller value than the curve D. Therefore, in the state of T> T _adj , P <P _adj is satisfied when the first value x = V / I is a value represented by the point R. When the first value x is a value represented by the point S, P = P _adj . On the other hand, when the measured temperature T is smaller than the reference value temperature T _adj , P> P _adj when the first value x is a value represented by the point R, and the first value x is the point R When the value is larger than the value represented by P = P _adj .

FIG. 9 is a diagram illustrating a range in which the mathematical formula (1) that is the relationship defined by the third information is established. In FIG. 9, the vertical axis represents the average output P of the optical signal, the horizontal axis represents the measured bias current value I, and the relationship defined by Equation (1) is shown by a solid line as a curve F. The PI characteristic of the element 30 is indicated by a broken line. A curve F is a relationship defined by Equation (1) when the measured temperature T is equal to the reference value temperature T _adj .

In the present embodiment, the semiconductor optical device 30 is a semiconductor laser element, having the value of the bias current I exceeds the threshold current I _th, the property that the average output P increases roughly as proportional to the bias current I. Here, the curve F approaches a broken line representing the PI characteristic of the semiconductor optical device 30 as the measured bias current value I increases, and substantially coincides with I = I1 or more. I1, in the P-I characteristic curve of the semiconductor optical device 30, the value of the bias current corresponding to only in advanced on P-I characteristic curve minute size of the more I _th from the bent point at the threshold current I _th is there. I1 is the threshold current _{I th} is greater than value.

  The magnitude of the bias current that can be applied to the semiconductor optical device 30 has an upper limit from the viewpoint of preventing breakage, and if it is expressed as I2, Equation (1) can be expressed as P− of the semiconductor optical device 30. It can be seen that the range in which the I characteristic is reproduced (the range in which Formula (1) can be used) is I1 ≦ I ≦ I2. Here, the average output of the optical signal when the bias current is I1 is P1, and the average output when the bias current is I2 is P2.

The reference value bias current I _adj is selected so as to satisfy I1 ≦ I _adj ≦ I2. Since the magnitude of the bias current I supplied when driving the semiconductor optical device 1 is adjusted before and after I _adj , it falls within the range of I1 ≦ I ≦ I2, and the optical signal is based on the third information. The average output can be calculated. In other words, in the semiconductor optical device 1 according to the present embodiment, when the temperature is T _adj , the average output of the optical signal is based on the third information if the average output of the optical signal is P1 or more and P2 or less. Can be calculated.

Curves D and E shown in FIG. 8 are in a range satisfying the condition I1 ≦ I ≦ I2, and the third function f ₃ (V / I, T) is in a range satisfying the condition I1 ≦ I ≦ I2. , A monotonically decreasing function with respect to the first value x.

FIG. 10 is a diagram illustrating a relationship defined by the first information. In FIG. 10, the vertical axis is the first value V / I, and the horizontal axis is the measured temperature T, and a curve G that is a relationship defined by the first information is shown. The first information is established when the average output of the optical signal is constant, and is measured bias voltage V, measured bias current I, measured temperature T, reference value bias voltage V _adj , reference value bias current. The relationship between I _adj , reference value temperature T _adj , and reference value α is expressed by the following equation (4).

Here, V and I represent bias voltage and bias current values normalized in units of mV and mA. The same applies to V _adj and I _adj . T and T _adj are temperatures expressed in K units, and the unit of the reference value α is [K ⁻¹ ]. The right side of Equation (4) will be referred to as the first function f ₁ (T).

In the present embodiment, since the value of α is negative, the first function f ₁ (T) is a monotonically decreasing function with respect to the temperature T. For this reason, the curve G is downwardly inclined. For T _{= T adj,} the average output of the optical signal is _{P adj is} the case of the _{V / I = V adj / I} adj, the curve G and the vertical axis intersect at _{V adj / I} adj.

In the case of T = T1> T _adj , in order to match P = P _adj , it is necessary to control the bias current source 5 by the bias current control unit 444 so that V / I = V1 / I1 <V _adj / I _adj. is there. When T = T2 <T _adj , the bias current source 5 is controlled by the bias current control unit 444 in order to match P = P _adj so that V / I = V2 / I2> V _adj / I _adj . There is a need.

This can be qualitatively read from FIGS. According to the PI characteristics of the semiconductor laser shown in FIG. 12, it can be seen that in order to keep the average output of the optical signal constant, it is necessary to increase the value of the bias current as the temperature rises. Further, according to the VI characteristic of the semiconductor laser shown in FIG. 13, it can be seen that the bias voltage when the value of the bias current is increased decreases as the temperature rises. That is, in order to make the average output of the optical signal constant, it can be seen that control is required to decrease the first value x = V / I as the temperature rises. Formula (4) representing the relationship defined in the first information is a quantitative representation of the contents that can be qualitatively read from the PI characteristics and the VI characteristics of the semiconductor laser element. Considering the relationship defined by Equation (1) as well, when the temperature T of the semiconductor optical device 1 becomes higher than T _adj during driving (in the case of the curve E in FIG. 8), the average output is calculated. In order to perform constant control, it is indicated that the first value x should be controlled to be the value of the point S. More specifically, since the first value x = V / I is controlled to be smaller than the point R, it can be seen that the bias current I should be increased. When the bias current I is changed, the bias voltage V is also changed. Therefore, by observing both the values of the bias current I and the bias voltage V, and the temperature T at that time, and changing the bias current so that Equation (4) is satisfied, the average output can be controlled to be constant.

As described above, according to the present invention, a desired average output P _adj , a bias current I _adj , a bias voltage V _adj , a modulation current I _{mod, adj} , a temperature T _adj , and α that have a desired extinction ratio are set in advance. If stored in the storage unit, during driving, if the bias current I, bias voltage V, and temperature T at a certain point in time are measured, the average output and extinction ratio can be calculated using equations (1)-(4). Can be controlled constantly. Thereby, compared with the control using the conventional light receiving element, it can contribute to the cost reduction by the reduction of components, and the miniaturization of the semiconductor optical device.

[Second Embodiment]
FIG. 11 is a configuration diagram of a semiconductor optical device 1 according to the second embodiment of the present invention. The semiconductor optical device 1 according to the present embodiment includes a drive circuit 2, an optical transmission module 3, a microcomputer 4, a bias current source 5, a voltage measurement unit 6, a current measurement unit 7, and a thermometer. 8 and. The semiconductor optical device 1 according to the second embodiment is different from the semiconductor optical device 1 according to the first embodiment in that a thermometer 8 is provided separately from the microcomputer 4. Further, the voltage measuring unit 6 and the current measuring unit 7 in the semiconductor optical device 1 according to the second embodiment are different from those in the semiconductor optical device 1 according to the first embodiment. Other configurations are the same as the configuration of the semiconductor optical device 1 according to the second embodiment and the configuration of the semiconductor optical device 1 according to the first embodiment.

  The thermometer 8 according to the present embodiment is a thermistor or the like and directly measures the temperature of the optical transmission module 3. The point that the measured data is transmitted to the control unit 44 of the microcomputer 4 is the same as that of the semiconductor optical device 1 according to the first embodiment.

  The voltage measurement unit 6 according to the present embodiment includes digital filters 64 and 66 as low-pass filters. The digital filters 64 and 66 are connected to both electrodes of the semiconductor optical device 30 through appropriate resistors. The value of the voltage that has passed through the digital filters 64 and 66 is measured by the first voltmeter 62 and transmitted to the control unit 44. Here, similarly to the semiconductor optical device 1 according to the first embodiment, the voltage between the terminals of the semiconductor optical device 30 may be amplified by an operational amplifier and then passed through a low-pass filter. In that case, the amplification factor is stored in the storage unit 40.

The current measurement unit 7 according to the present embodiment includes a digital filter 72 as a low-pass filter, measures the value of R _i I with the second voltmeter 70, and removes the fixed resistance value R _i in the control unit 44, and the bias current The value I of the bias current supplied by the source 5 is measured.

  The control process performed at the time of driving the semiconductor optical device 1 according to the present embodiment and the reference value determination process performed at the time of manufacturing are the same as those in the semiconductor optical device 1 according to the first embodiment. Even in the configuration shown in the present embodiment, the average output of the optical signal can be controlled to be constant and the extinction ratio of the optical signal can be controlled to be constant without using a light receiving element. In addition, the average output of the optical signal can be monitored without using a light receiving element.

In the first or second embodiment, the reference value α is calculated based on the third information in the reference value determining step (S32). However, the reference value α is calculated based on the first information. It may be calculated. In that case, the optical output measuring device confirms that the average output is the same under different conditions (when the ambient temperature is T _adj and when T ≠ T _adj ), and the reference value α is calculated by Equation (4). To do.

  In addition, the structure shown in the 1st or 2nd embodiment was shown as an example, and it is not intending limiting the technical scope of this invention to this. The technical scope of the invention disclosed in this specification includes a range obtained by a person skilled in the art appropriately modifying the semiconductor optical device 1 according to the embodiment.

  In the first or second embodiment, an example in which both the average output and the extinction ratio are controlled constant has been described. However, it goes without saying that the present invention can also be applied to a semiconductor optical device having only one control function. Specifically, the average output constant control of the present invention may be used in a light source that does not have an optical signal modulation function and outputs continuous light. The constant average output control may be performed using a light receiving element, and the constant extinction ratio control may be performed using the configuration of the present invention. If it is only for constant average output control, it is not necessary to use a light-receiving element corresponding to high-speed modulated light, and a lower-priced light-receiving element can be used, and the overall cost can be reduced.

In the first or second embodiment, the reference value is determined by using the optical output measuring device or the optical waveform measuring device in the reference value determining step, but it can also be determined by the following method. For example, the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference in the state of the semiconductor optical element before being mounted on the semiconductor optical device or the state of the optical transmission module (TOSA etc.) incorporating the semiconductor optical element. The value average output is determined, and the value of the reference value α determined by a similar semiconductor optical device is stored in the storage unit 40, and the semiconductor optical device may not perform the reference value determining step. Further, each reference value determined in the state of the conductor optical element or the state of the optical transmission module is temporarily stored in the storage unit 40, and the bias current I at a certain temperature T is expressed by the formula (1) so that the desired average output P is obtained. ) And the obtained bias current I may be stored in the storage unit 40 as I _adj , the bias voltage at that time as V _adj , and the temperature as T _adj . Similarly, the modulation current is determined so that Formula (2) is established. If it does in this way, in a reference value determination process of a semiconductor optical device, a reference value can be determined without using an optical output measuring instrument and an optical waveform measuring instrument.

  In addition, customer specifications such as average output and extinction ratio, and standard specifications in international standards are generally defined by a certain range (allowable range), upper limit value, and lower limit value instead of fixed values. For example, a range of −8.2 dB to +0.5 dB may be given as the average output specification, and a lower limit value of 3.5 dB or more may be given as the extinction ratio specification. Therefore, in the first and second embodiments, when the average output constant control or the extinction ratio constant control is used, the control is not limited to a constant value, but is controlled to be within a range that satisfies the specifications for the average output and extinction ratio. To be included. More specific control methods include, for example, the following methods. Customer specifications include optical mask regulations related to optical waveform quality. The optical waveform tends to deteriorate at a high temperature due to the characteristics of the semiconductor optical device. As a countermeasure, there is a method of using the high output state at a high temperature to easily maintain the optical waveform quality. On the contrary, at low temperatures, in order to obtain optical waveform quality equivalent to that at high temperatures, it may be desirable to reduce the output compared to high temperatures. That is, in order to satisfy the mask regulations, it is desirable to have a high output at high temperatures and a low output at low temperatures. Therefore, when the customer specifications for average output are specified in a certain range as described above, the average output is controlled by controlling the output to be high at high temperatures and to be low at low temperatures. Both output specifications and mask regulations can be satisfied. As a control method, for example, in Equation (4), a target average output value can be changed between a high temperature and a low temperature by applying a coefficient that varies with temperature to the left side. The same applies to the extinction ratio. When the target extinction ratio specification changes depending on the temperature, the extinction ratio specification and the mask specification can be satisfied by multiplying the equation by a coefficient that changes depending on the temperature.

  DESCRIPTION OF SYMBOLS 1 Semiconductor optical device, 2 Drive circuit, 3 Optical transmission module, 4 Microcomputer, 5 Bias current source, 6 Voltage measurement part, 7 Current measurement part, 8 Thermometer, 20 Modulation current source, 30 Semiconductor optical element, 40 Storage part , 42 thermometer, 44 control unit, 60 operational amplifier, 62 first voltmeter, 64 digital filter, 66 digital filter, 70 second voltmeter, 72 digital filter, 440 average output calculation unit, 442 modulation current control unit, 444 Bias current control unit.

Claims (8)

A semiconductor optical element that outputs an optical signal;
Bias current supply means for supplying a bias current to the semiconductor optical element;
Voltage measuring means for measuring a bias voltage applied between terminals of the semiconductor optical element;
Current measuring means for measuring the bias current;
Temperature measuring means for directly or indirectly measuring the temperature of the semiconductor optical element;
Storage means for storing a reference value bias voltage, a reference value bias current, a reference value temperature, and a reference value α;
The bias voltage measured by the voltage measurement unit, the bias current measured by the current measurement unit, the temperature measured by the temperature measurement unit, and the reference value, which are satisfied when the average output of the optical signal is constant. Bias current control means for controlling the bias current supply means based on first information defining a relationship between a bias voltage, the reference value bias current, the reference value temperature, and the reference value α;
With
The first information is an equal sign of a first function having the measured temperature as a variable and a first value that is a value of a ratio between the measured bias voltage and the measured bias current. Define the relationship,
The bias current control means includes
Controlling the bias current supply means so that the equality relationship defined in the first information is satisfied;
The first function is a monotonically decreasing function with respect to the measured temperature being a variable;
The bias current control means controls the bias current supply means so that the first value is equal to a value of the first function;
A semiconductor optical device. The semiconductor optical device according to claim 1 ,
The reference value bias voltage is V _adj , the reference value bias current is I _adj , the ratio of the reference value bias voltage V _adj to the reference value bias current I _adj is y = V _adj / I _adj , and the reference value temperature is T _adj , where the first value is x and the measured temperature is T,
Said first function _f 1 (T) _{is, f 1 (T) = y} (α (T-T adj) +1) Ru ^1/2 der,
A semiconductor optical device. A semiconductor optical element that outputs an optical signal;
Bias current supply means for supplying a bias current to the semiconductor optical element;
Modulation current supply means for supplying a modulation current to the semiconductor optical element;
Voltage measuring means for measuring a bias voltage applied between terminals of the semiconductor optical element;
Current measuring means for measuring the bias current;
Temperature measuring means for directly or indirectly measuring the temperature of the semiconductor optical element;
Storage means for storing a reference value modulation current, a reference value bias voltage, a reference value bias current, a reference value temperature, and a reference value α;
The bias voltage measured by the voltage measuring unit, the bias current measured by the current measuring unit, the temperature measured by the temperature measuring unit, and the reference value, which are satisfied when the extinction ratio of the optical signal is constant. Modulation current control means for controlling the modulation current supply means based on second information that defines the relationship among the modulation current, the reference value bias voltage, the reference value bias current, the reference value temperature, and the reference value α. And comprising
The second information includes a first value that is a value of a ratio between the measured bias voltage and the measured bias current, a second function having the measured temperature as a variable, and the modulation. Define the equality relationship with the modulation current supplied by the current supply means,
The modulation current control means includes
Controlling the modulation current supply means so that the equality relationship defined in the second information is satisfied;
The second function is a monotonically increasing function with respect to the measured temperature being a variable;
The modulation current control means controls the bias current supply means so that a ratio of the modulation current and the reference value modulation current is equal to a value of the second function;
A semiconductor optical device. The semiconductor optical device according to claim 3 ,
The reference value bias voltage is V _adj , the reference value bias current is I _adj , the ratio of the reference value bias voltage V _adj to the reference value bias current I _adj is y = V _adj / I _adj , and the reference value temperature is T _adj , the reference value modulation current is represented by I _{mod, adj} , the first value is represented by x, the measured temperature is represented by T, and the modulation current supplied by the modulation current supply unit is represented by I _mod ,
The second function f ₂ (x, T) is f ₂ (x, T) = (α (T−T _adj ) +1) ^−1/2 (log (x ² ) / x ² ) ((y ² _{(α (T-T adj)} +1) / log (y 2 (α (T-T adj) +1))) Ru der,
A semiconductor optical device. A semiconductor optical device according to any one of claims 1 to 4 ,
The storage means further stores a reference value average output,
Relationship between the measured bias voltage, the measured bias current, the measured temperature, the reference value bias voltage, the reference value bias current, the reference value temperature, the reference value α, and the reference value average output A semiconductor optical device, further comprising: an average output calculation unit that calculates an average output of the optical signal based on third information that defines The semiconductor optical device according to claim 5 ,
The third information includes a first value that is a value of a ratio between the measured bias voltage and the measured bias current, a third function having the measured temperature as a variable, the light Define the equality relationship with the average output of the signal,
The average output calculation means includes
The semiconductor optical device, wherein an average output of the optical signal is calculated according to an equality relationship defined in the third information. The semiconductor optical device according to claim 6 ,
The equality relationship defined in the third information approaches the PI characteristic of the semiconductor optical device as the value of the measured bias current increases. The semiconductor optical device according to claim 6 or 7 ,
The reference value bias voltage is V _adj , the reference value bias current is I _adj , the reference value temperature is T _adj , the reference value average output is P _adj , and the ratio between the reference value bias voltage and the reference value bias current is y = V _adj / I _adj , where the first value is x, the measured temperature is T, and the average output of the optical signal is P,
The third function f ₃ (x, T) is f ₃ (x, T) = (log (x ² ) / x ² ) ((y ² (α (T−T _adj ) +1) / log (y ² (α (T−T _adj ) +1))),
The average output calculating means calculates an average output of the optical signal by P = P _adj f ₃ (x, T).

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