WO2020157886A1

WO2020157886A1 - Optical transmitter and method for controlling same

Info

Publication number: WO2020157886A1
Application number: PCT/JP2019/003301
Authority: WO
Inventors: 優輔三井; 聡志石飛
Original assignee: 三菱電機株式会社
Priority date: 2019-01-31
Filing date: 2019-01-31
Publication date: 2020-08-06

Abstract

An optical transmitter (1) comprises: a semiconductor laser (11); a holding unit (15) for optical fibers (90); a temperature monitor unit (51); a laser drive unit (30); a target voltage control unit (52); a thermoelectric element (12); a thermoelectric element drive unit (60); a target temperature control unit (53); and a memory (40) that pre-stores drive conditions information (D1) on the basis of a measured value. If a monitored temperature (Ta) is within a temperature range (TR1), operation of the thermoelectric element (12) is stopped and a target voltage (Vr) is determined on the basis of information corresponding to the present monitored temperature (Ta) in the drive conditions information (D1). If the monitored temperature (Ta) is within temperature ranges (TR2, TR3), a target temperature (Tld) is determined on the basis of information corresponding to the present monitored temperature (Ta) in the drive conditions information (D1), and the target voltage (Vr) is determined on the basis of information corresponding to the present monitored temperature (Ta) in the drive conditions information (D1).

Description

Optical transmitter and control method thereof

The present invention relates to an optical transmitter and its control method.

APC (Automatic Power Control) is known as a control method for maintaining a constant output power of laser light output from a semiconductor laser of an optical transmitter. In APC, a part of laser light output from a semiconductor laser is detected by a photodiode (PD), and a laser drive current is controlled so that a value of a monitor current output from the PD is constant (for example, Patent Document 1). 1).

Further, there has been proposed a method of suppressing fluctuations in output power of laser light output from a semiconductor laser by cooling or heating the semiconductor laser and adjusting the temperature of the semiconductor laser (for example, Patent Documents 1 and 2). reference).

International Publication No. 2015/162964 Japanese Patent Laid-Open No. 11-126939

However, due to thermal expansion caused by temperature changes in the environment where the optical transmitter is installed, changes in the relative position between the semiconductor laser and the optical module housing holding the optical fiber (that is, the optical system). (Change), the value of the output power loss L [dB] caused by the tracking error changes. Therefore, when the temperature changes, the output power of the laser light transmitted through the optical fiber fluctuates even if the output power of the laser light output from the semiconductor laser is maintained constant by the above-mentioned conventional technique. There is.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to maintain a constant output power of laser light transmitted through an optical fiber even when a temperature change occurs. An object is to provide a transmitter and a control method thereof.

An optical transmitter according to an aspect of the present invention is an optical transmitter that outputs laser light, and outputs the laser light having a first output power corresponding to a laser drive current and at the same time outputs the first output power. A semiconductor laser that outputs a monitor current corresponding to, a holding unit that holds the optical fiber so that the laser light output from the semiconductor laser enters the optical fiber, and a monitor temperature that corresponds to the temperature of the holding unit. A temperature monitor unit for measuring, a laser drive unit for supplying the laser drive current to the semiconductor laser, and a target voltage for the laser drive unit so that the monitor voltage corresponding to the monitor current approaches the target voltage. A target voltage control section, a first thermoelectric element for cooling or heating the semiconductor laser, a first thermoelectric element driving section for driving the first thermoelectric element, and a temperature of the first thermoelectric element as a target temperature. A target temperature control unit that gives a first drive control signal that approaches the first thermoelectric element drive unit to the first thermoelectric element drive unit, and an actual measurement of the relationship between the target voltage at each monitor temperature, the target temperature, and the power consumption of the optical transmitter. When the monitor temperature is within a first temperature range, the target temperature control unit includes a storage unit that stores drive condition information determined based on a value in advance. The driving of the first thermoelectric element by the element driving unit is stopped, and the target voltage control unit is based on the information corresponding to the current monitored temperature output from the temperature monitoring unit in the driving condition information. When the target voltage is determined and the monitor temperature is within the second temperature range higher than the first temperature range, the target temperature control unit determines the current monitor temperature in the drive condition information. Determines the target temperature based on the information corresponding to, the target voltage control unit determines the target voltage based on the information corresponding to the current monitor temperature of the drive condition information, the monitor temperature. Is within a third temperature range lower than the first temperature range, the target temperature control unit determines the target temperature based on the information corresponding to the current monitor temperature in the drive condition information. And the target voltage control unit determines the target voltage based on information corresponding to the current monitor temperature in the drive condition information.

A method for controlling an optical transmitter according to another aspect of the present invention is a semiconductor that outputs laser light having a first output power corresponding to a laser drive current and outputs a monitor current corresponding to the first output power. A laser, a holding unit that holds the optical fiber so that the laser light output from the semiconductor laser is incident on the optical fiber, a temperature monitor unit that measures a monitor temperature corresponding to the temperature of the holding unit, and A laser drive unit that supplies the laser drive current to the semiconductor laser, a target voltage control unit that supplies the target voltage to the laser drive unit, and a semiconductor laser so that the monitor voltage corresponding to the monitor current approaches the target voltage. A first thermoelectric element that cools or heats the first thermoelectric element, a first thermoelectric element drive unit that drives the first thermoelectric element, and a first drive control signal that brings the temperature of the first thermoelectric element close to the target temperature. Target temperature control unit given to the first thermoelectric element drive unit, drive conditions determined based on measured values of the target voltage at each monitor temperature, the target temperature, and the power consumption of the optical transmitter A method of controlling an optical transmitter including a storage unit that stores information in advance, wherein when the monitor temperature is within a first temperature range, the first thermoelectric element driving unit performs the The driving of the first thermoelectric element is stopped, the target voltage is determined based on the information corresponding to the current monitor temperature output from the temperature monitor unit in the drive condition information, and the monitor temperature is When in the second temperature range higher than the first temperature range, the target temperature is determined based on the information corresponding to the current monitor temperature in the driving condition information, If the target voltage is determined based on the information corresponding to the current monitor temperature, and the monitor temperature is within the third temperature range lower than the first temperature range, the drive condition information Characterized in that the target temperature is determined based on the information corresponding to the current monitor temperature, and the target voltage is determined based on the information corresponding to the current monitor temperature in the drive condition information. To do.

According to the present invention, there is an effect that the output power of the laser light transmitted through the optical fiber can be maintained constant even when the temperature changes.

1 is a block diagram schematically showing a configuration of an optical transmitter according to a first embodiment of the present invention. (A) to (F) are graphs showing the operation of the optical transmitter according to the first embodiment. 4 is a flowchart showing the operation of the optical transmitter according to the first embodiment. It is a block diagram which shows roughly the structure of the optical transmitter which concerns on Embodiment 2 of this invention. (A) to (F) are graphs showing the operation of the optical transmitter according to the second embodiment. 4 is a flowchart showing the operation of the optical transmitter according to the first embodiment. FIG. 11 is a diagram showing an example of a hardware configuration of an optical transmitter according to a modification of the first and second embodiments.

An optical transmitter and a control method thereof according to the embodiment of the present invention will be described below with reference to the drawings. The following embodiments are merely examples, and various modifications can be made within the scope of the present invention.

<<1>> Embodiment 1.
<<1-1>> Configuration FIG. 1 is a block diagram schematically showing a configuration of the optical transmitter 1 according to the first embodiment of the present invention. The optical transmitter 1 is, for example, a device that transmits an optical signal to an optical communication system. As shown in FIG. 1, the optical transmitter 1 includes an optical module 10, a monitor current detection unit 20, a laser drive unit 30, a memory 40, a control unit 50, and a thermoelectric element drive unit 60. There is. The optical transmitter 1 also includes a device housing 1a that houses the optical module 10, the monitor current detection unit 20, the laser drive unit 30, the memory 40, the control unit 50, and the thermoelectric element drive unit 60. The monitor current detector 20 may be a part of the laser driver 30. The monitor current detection unit 20, the laser drive unit 30, the control unit 50, and the thermoelectric element drive unit 60 can be configured by an electric circuit.

The optical module 10 includes a semiconductor laser 11, a thermoelectric element 12, a thermistor 13, and a module housing 15 that houses these. The thermoelectric element 12 is a temperature adjusting element that cools or heats the semiconductor laser 11. The thermoelectric element 12 is, for example, a Peltier element. The thermoelectric element 12 is arranged near the semiconductor laser 11. The vicinity of the semiconductor laser 11 includes the state of being in contact with the semiconductor laser 11, the state of being in contact with the semiconductor laser 11 via another member, and the information slightly separated from the semiconductor laser 11. The thermoelectric element 12 is also referred to as a "first thermoelectric element". The thermoelectric element 12 and the thermistor 13 constitute a thermoelectric element section 14 as a temperature adjusting section. The thermoelectric element drive unit 60 supplies the thermoelectric element drive current to the thermoelectric element 12 so as to change the temperature of the thermoelectric element 12 to the target temperature Tld [°C] according to the drive control signal C1 provided from the control unit 50. Change Ite. The thermoelectric element driving unit 60 is also referred to as a “first thermoelectric element driving unit”. The thermoelectric element drive unit 60 reads the detected temperature Tt of the thermistor 13 and supplies the thermoelectric element drive current Ite to the thermoelectric element 12 based on the difference between the detected temperature Tt and the target temperature Tld [° C.] targeted by the semiconductor laser 11. Thus, the temperature of the semiconductor laser 11 is controlled. The thermistor 13 is arranged near the thermoelectric element 12 and the semiconductor laser 11. Therefore, the detected temperature Tt of the thermistor 13 can be regarded as indicating the temperature of the thermoelectric element 12 and the temperature of the semiconductor laser 11.

For example, the thermoelectric element drive unit 60 reads the detected temperature Tt of the thermistor 13, and the larger the difference between the detected temperature Tt and the target temperature Tld [° C.] of the thermoelectric element 12, the larger the thermoelectric element drive current Ite can flow. .. However, the drive control method of the thermoelectric element 12 is not limited to the above control method as long as it is a control method that brings the temperature of the thermoelectric element 12 and the temperature of the semiconductor laser 11 close to the target temperature Tld [° C.].

The module housing 15 has a function as a holding unit that holds the optical fiber 90. By holding the optical fiber 90 in the module housing 15, the laser light L1 output from the light emitting surface of the semiconductor laser 11 advances toward the end of the optical fiber 90 as the light incident end. In this way, the light emitting surface of the semiconductor laser 11 and the end of the optical fiber 90 are optically coupled by having a predetermined positional relationship.

The semiconductor laser 11 outputs a monitor current Im corresponding to the output power P1 [dB] of the laser light L1 by detecting a part of the laser light (LD) as a laser light emitting element that generates a laser light. It has PD as a photodetector. The output power of the laser light L1 is the output power P1 [dB] of the laser light L1 output from the semiconductor laser 11. The output power P1 [dB] of the laser beam L1 output from the semiconductor laser 11 is also referred to as “first output power”. In the semiconductor laser 11, the conversion efficiency of light output changes depending on the temperature. The conversion efficiency of the semiconductor laser 11 decreases as the temperature of the semiconductor laser 11 increases, and improves as the temperature decreases. The optical transmitter 1 may include an optical modulator that modulates the laser light L1 output from the semiconductor laser 11 according to the transmission information.

The laser light L1 output from the semiconductor laser 11 is transmitted to the optical network forming the optical communication system through the optical fiber 90. The output power P1a [dBm] of the laser light transmitted from the semiconductor laser 11 through the optical fiber 90 is the output power P1 [dB] of the laser light L1 output from the semiconductor laser 11 due to the output power loss L [dB] caused by the tracking error. ] Is lower than. The output power P1a [dBm] is also referred to as “second output power”. In the optical transmitter 1 according to the first embodiment, even when the output power loss L [dB] caused by a tracking error varies, the actual measurement data (that is, the product) specific to each optical transmitter that is acquired in advance by actual measurement. The output power P1a [dBm] of the laser light transmitted through the optical fiber 90 can be kept constant by the control using the drive condition information D1 based on the actual measurement data). The driving condition information D1 is used for compensation of the output power loss L [dB], and is also referred to as “compensation profile”.

Generally, the power consumed by supplying the laser driving current Id [mA] is smaller than the power consumed by supplying the thermoelectric element driving current Ite by the thermoelectric element driving unit 60. Therefore, the optical transmitter 1 according to the first embodiment controls the laser drive current Id [mA] by the APC in the temperature range in which the output power P1a [dBm] of the laser light can be kept constant by the APC. Then, the output power P1a [dBm] of the laser light cannot be maintained constant only by APC, or in the temperature range in which the central wavelength λ [nm] of the laser light deviates from the desired wavelength range, the laser drive current Id by APC It is configured to perform [mA] control and temperature control using the thermoelectric element 12.

The monitor current detection unit 20 is an electric circuit that receives the monitor current Im output from the PD of the semiconductor laser 11 and outputs the monitor voltage Vm corresponding to the monitor current Im. The monitor voltage Vm is proportional to the monitor current Im.

The laser drive unit 30 is an electric circuit having an APC unit 31 that performs feedback control. The APC unit 31 has a target voltage comparison unit 32. The target voltage comparison unit 32 compares the monitor voltage Vm [V] corresponding to the monitor current Im with the target voltage Vr [V] that is the reference voltage. The APC unit 31 controls the laser drive current Id [mA] so that the monitor voltage Vm approaches the target voltage Vr [V]. The target voltage Vr [V] is provided by the control unit 50. In the first embodiment, the target voltage Vr [V] is the driving condition information D1 based on the actual measurement data unique to each optical transmitter acquired in advance by measurement, and the monitor temperature Ta measured by the temperature monitor unit 51 described later. [° C.] and determined. The target voltage Vr [V] is changed based on the driving condition information D1 and the monitor temperature Ta [°C] measured by the temperature monitor 51.

In the first embodiment, the APC performed using the target voltage Vr [V] changed by the control unit 50 and the thermoelectric element 12 performed using the target temperature Tld [° C.] changed by the control unit 50. The drive control compensates for a tracking error that changes according to changes in the temperature of the outside air. Further, in the first embodiment, the control unit 50 compensates for the tracking error by different methods in each of the plurality of temperature ranges.

The memory 40 is a non-volatile storage unit that stores information. The memory 40 is, for example, a semiconductor memory device. The memory 40 stores in advance measurement data for each optical transmitter, which is used by the control unit 50, that is, various information based on the measurement data for each product. The memory 40 shows the relationship among the target temperature Tld [°C], the target voltage Vr [V], and the power consumption [W] of the optical transmitter 1 at each of the monitor temperatures Ta [°C] measured by the temperature monitor unit 51. The drive condition information D1 shown is stored in advance. The memory 40 may store in advance information about the center wavelength λ [nm] of the laser light L1 at each of the monitor temperatures Ta [° C.] measured by the temperature monitor unit 51.

The information on the central wavelength λ [nm] of the laser light L1 at each of the plurality of monitor temperatures Ta [° C.] is acquired, for example, by the following procedures (1) to (5).
(1) A wavelength measuring device is connected to the optical fiber 90 shown in FIG.
(2) The optical transmitter 1 outputs the laser beam L1.
(3) By changing the temperature of the optical transmitter 1, the monitor temperature Ta [°C] measured by the temperature monitor unit 51 is changed.
(4) The wavelength detected by the wavelength measuring device is detected at each of the plurality of monitor temperatures Ta [° C.].
(5) The optical transmitter 1 is stopped, the wavelength measuring device is removed, and information indicating the relationship between the monitor temperature Ta [°C] and the wavelength of the laser light is recorded in the memory 40 as the driving condition information D1.

Information indicating the relationship between the target temperature Tld [°C], the target voltage Vr [V], and the power consumption [W] of the optical transmitter 1 at each of the plurality of monitor temperatures Ta [°C] is, for example, the following procedure. It is acquired in (15) from (11).
(11) A power meter, which is a measuring instrument capable of measuring optical power, is connected to the optical fiber 90 shown in FIG.
(12) The optical transmitter 1 outputs the laser beam L1.
(13) By changing the temperature of the optical transmitter 1, the monitor temperature Ta [°C] measured by the temperature monitor unit 51 is changed.
(14) At each of the plurality of monitor temperatures Ta [°C], the target temperature Tld [°C] and the target voltage Vr [V] are set so that the optical power measured by the power meter is maintained constant. The power consumption [W] for each combination of Tld [° C.] and target voltage Vr [V] is measured.
(15) Stop the optical transmitter 1, remove the power meter, and combine the monitor temperature Ta [°C] with the target temperature Tld [°C] and the target voltage Vr [V] that minimize the power consumption [W], The information indicating the relationship is recorded in the memory 40 as the driving condition information D1.

The control unit 50 has a temperature monitor unit 51, a target voltage control unit 52, a target temperature control unit 53, and an optical output monitor unit 54. The temperature monitor unit 51 outputs the monitor temperature Ta [° C.] by measuring the temperature corresponding to the temperature of the optical module 10. The temperature monitor unit 51 may be arranged outside the control unit 50. In FIG. 1, the temperature monitor 51 and the optical module 10 are arranged separately, but they may be arranged in contact with each other. The temperature monitor unit 51 can measure the temperature inside the device housing 1a to measure the temperature corresponding to the temperature of the optical module 10. The target voltage control unit 52 determines the target voltage Vr [V] used when compensating for the tracking error by APC. The target temperature control unit 53 determines the target temperature Tld [° C.] used for driving control of the thermoelectric element 12 by the thermoelectric element driving unit 60.

The control unit 50 executes control for compensating for tracking errors. The tracking error is an optical coupling state determined by the relative position between the light emitting surface of the semiconductor laser 11 arranged in the optical module 10 and the end of the optical fiber 90 held in the module housing 15. It is caused by the change of 10 due to the thermal expansion accompanying the temperature change. In other words, the tracking error is a phenomenon caused by the displacement of the relative position between the components of the optical system due to the temperature change. That is, the tracking error occurs due to the positional deviation between the optical axis of the light emitting end of the semiconductor laser 11 and the optical axis of the end of the optical fiber 90. When the tracking error is not compensated when the tracking error occurs, the output power loss L [dB] increases, and the output power P1a [dBm] of the laser light output from the semiconductor laser 11 and transmitted through the optical fiber 90 decreases. ..

The target voltage control unit 52 repeatedly performs control to change the target voltage Vr[V] used in the target voltage comparison unit 32 using the driving condition information D1 stored in the memory 40 in advance. The target temperature control unit 53 repeatedly performs control to change the target temperature Tld [° C.] used for drive control of the thermoelectric element 12 using the drive condition information D1 stored in the memory 40 in advance. The drive condition information D1 is stored in the memory 40 as a calculation formula or a look-up table (LUT), for example. That is, the target voltage control unit 52 changes the target voltage Vr [V] to an appropriate value based on the monitor temperature Ta [° C.] measured by the temperature monitoring unit 51, and then the target voltage comparison unit 32 sets the target voltage Vr [V]. V] is provided. Further, the target temperature control unit 53 drives the thermoelectric element by driving the drive control signal C1 instructing to change the target temperature Tld [°C] to an appropriate value based on the monitor temperature Ta [°C] measured by the temperature monitor 51. It is provided to the part 60. That is, the control unit 50 executes variable control for changing the target voltage Vr [V] and the target temperature Tld [°C] in synchronization with the output of the monitor temperature Ta [°C] by the temperature monitoring unit 51.

When adopting a control method that changes the target voltage Vr [V] used for APC and the target temperature Tld [°C] used for drive control of the thermoelectric element 12, a general method represented by DDM (Digital Diagnostic Monitoring) The optical output monitor unit cannot output a signal that accurately indicates the output power of the laser light output through the optical fiber. This is because the general optical output monitor unit calculates the output power based on the monitor current detected by the monitor PD of the semiconductor laser, but this output power is a value that does not take the influence of the tracking error into consideration. Because. Therefore, the optical output monitor unit 54 in the optical transmitter 1 according to the first embodiment uses the drive condition information D1 stored in the memory 40 in advance to obtain the output power in consideration of the influence of the tracking error. There is. Therefore, the optical output monitor unit 54 in the first embodiment can provide the host device with a signal indicating an output power close to the output power P1a [dBm] of the laser light output through the optical fiber 90.

<<1-2>> Operation FIGS. 2A to 2F are graphs showing the operation of the optical transmitter 1 according to the first embodiment. The graphs of FIGS. 2A to 2F are graphs based on actual measurement values. 2A to 2F, the graph drawn by a solid line shows the operation of the optical transmitter 1 according to the first embodiment, and the graph drawn by a broken line shows the operation of the optical transmitter of the comparative example. Is shown. In the optical transmitter of the comparative example, the laser drive current is controlled by the laser drive unit and the temperature of the semiconductor laser is controlled by the thermoelectric element in the entire range of the monitor temperature Ta [° C.], and the dashed line is shown in FIG. Thus, the output power of the laser light output from the semiconductor laser is constant.

The graph of FIG. 2A shows the power consumption [W] of the optical transmitter 1 according to the first embodiment and the power consumption [W] of the optical transmitter of the comparative example at each monitor temperature Ta [° C.]. ing. The graph of FIG. 2B shows the output power P1a [dBm] of the laser light transmitted from the optical transmitter 1 according to the first embodiment through the optical fiber 90 and the light of the comparative example at each monitor temperature Ta [° C.]. The output power [dBm] of the laser light transmitted from the transmitter through the optical fiber 90 is shown. The graph of FIG. 2C shows the output power P1 [dB] of the laser light output from the semiconductor laser 11 of the optical transmitter 1 according to the first embodiment and the light of the comparative example at each monitor temperature Ta [° C.]. The output power [dB] of the laser light output from the semiconductor laser of the transmitter is shown. The graph of FIG. 2D shows the laser drive current Id [mA] output from the laser drive unit 30 of the optical transmitter 1 according to the first embodiment at each monitor temperature Ta [° C.]. The graph in FIG. 2E shows the target temperature Tld [°C] determined by the controller 50 of the optical transmitter 1 according to the first embodiment at each monitor temperature Ta [°C]. The graph of FIG. 2F shows the output power loss L [dB] caused by the tracking error of the optical transmitter 1 according to the first embodiment at each monitor temperature Ta [° C.].

In the comparative example, the target voltage Vr [V] is fixed and APC is performed, and the target temperature Tld [°C] is fixed and the thermoelectric element is controlled. In the optical transmitter 1 according to the first embodiment, different control is performed in each of the temperature range TR1, the temperature range TR2 higher than the temperature range TR1, and the temperature range TR3 lower than the temperature range TR1. In the first embodiment, temperature range TR1 is also referred to as “first temperature range”. The temperature range TR2 is also referred to as a "second temperature range". The temperature range TR3 is also referred to as a "third temperature range".

In the first embodiment, the temperature range TR1 is a temperature range above the temperature T2 [°C] and below the temperature T3 [°C]. The temperature range TR2 is a range higher than the temperature T3 [°C] and lower than the temperature T4 [°C]. The temperature range TR3 is a temperature range equal to or higher than the temperature T1 [° C.] and lower than the temperature T2 [° C.]. Further, the temperature T1 [° C.] and the temperature T4 [° C.] are temperatures specified by the specifications of the optical transmitter 1. The temperature T1 [° C.] indicates the minimum value of the specified temperature, and the temperature T4 [° C.] indicates the maximum value of the specified temperature. The performance of the optical transmitter 1 is guaranteed within the range from the minimum specification temperature to the maximum specification temperature. The central wavelength λ [nm] of the laser light output from the semiconductor laser 11 shifts depending on the temperature. The minimum specification temperature and the maximum specification temperature are determined, for example, based on the central wavelength λ [nm] of the laser light. That is, when the optical transmitter 1 is used in a temperature environment within the range from the minimum value of the specified temperature to the maximum value of the specified temperature, the center wavelength λ [nm] within the wavelength range determined by the specification, that is, the desired center Laser light having a wavelength λ [nm] can be output.

<Temperature range TR1>
The boundary temperature between the temperature range TR1 and the temperature range TR2 (that is, the temperature T3 [° C.]) is the upper limit temperature of the temperature range TR1. The upper limit temperature of the temperature range TR1 is based on the center wavelength λ [nm] of the laser beam L1 output from the semiconductor laser 11 at this upper limit temperature or the upper limit value of the laser drive current Id [mA] at the upper limit temperature of the temperature range TR1. It is the determined temperature. As shown in FIG. 2D, in the first embodiment, the upper limit temperature of temperature range TR1 is determined based on the upper limit value of laser drive current Id [mA] at this upper limit temperature.

The boundary temperature between the temperature range TR1 and the temperature range TR3 is the lower limit temperature of the temperature range TR1 (that is, the temperature T2 [° C.]). The lower limit temperature of the temperature range TR1 is based on the center wavelength λ [nm] of the laser beam L1 output from the semiconductor laser 11 at this lower limit temperature or the upper limit value of the laser drive current Id [mA] at the lower limit temperature of the temperature range TR1. It is the determined temperature. In the first embodiment, the lower limit temperature of temperature range TR1 is determined based on the center wavelength λ [nm] of laser light L1 output from semiconductor laser 11 at this lower limit temperature.

When the current monitor temperature Ta [° C.] output from the temperature monitor unit 51 is within the temperature range TR1, the target temperature control unit 53 stops the driving of the thermoelectric element 12 by the thermoelectric element driving unit 60, The target voltage control unit 52 determines the target voltage Vr [V] based on the information corresponding to the current monitor temperature Ta [°C] in the drive condition information D1. Within the temperature range TR1, the output power P1 [dB] of the laser beam L1 output from the semiconductor laser 11 is low as shown in FIG. 2C, but as shown in FIG. L[dB] is also low. Therefore, as shown in FIG. 2B, the optical output power P1a [dBm] of the laser light transmitted through the optical fiber 90 can be kept constant. Further, within the temperature range TR1, as shown in FIG. 2(E), the thermoelectric element 12 requiring relatively large driving power is not driven, so as shown in FIG. 2(A), the optical transmitter The power consumption [W] of 1 is lower than the power consumption [W] of the optical transmitter of the comparative example.

In the temperature range TR1, the driving of the thermoelectric element 12 by the thermoelectric element driving unit 60 is stopped, so the temperature of the semiconductor laser 11 changes. Generally, the oscillation wavelength of the modulated laser light output from the semiconductor laser 11 changes at about 0.1 nm/°C. Therefore, when the oscillation wavelength of the semiconductor laser 11, that is, the center wavelength λ [nm] is within a certain wavelength range, the temperature range TR1 can be controlled. The fixed wavelength range is, for example, a range of 1575 nm to 1580 nm.

<Temperature range TR2>
When the current monitor temperature Ta [°C] output from the temperature monitor 51 is within the temperature range TR2, the target temperature controller 53 causes the target monitor temperature Ta [°C] of the drive condition information D1. The target temperature Tld [°C] is determined based on the information corresponding to the target voltage Vr[, and the target voltage control unit 52 determines the target voltage Vr[ based on the information corresponding to the current monitor temperature Ta [°C] in the driving condition information D1. V] is determined. At this time, the target temperature control unit 53 and the target voltage control unit 52 of the control unit 50 combine the target temperature Tld [° C.] and the target voltage Vr [V] that minimize the power consumption [W] of the optical transmitter 1. It is desirable to select.

In the temperature range TR2, as shown in FIG. 2(E), the higher the monitor temperature Ta[° C.] is, the lower the target temperature Tld[° C.] is set to drive the thermoelectric element 12, and the target voltage By adjusting Vr [V], the laser drive current Id [mA] is controlled to its upper limit value as shown in FIG. Therefore, as shown in FIG. 2B, the optical output power P1a [dBm] of the laser light transmitted through the optical fiber 90 can be kept constant. Further, within the temperature range TR2, as shown in FIG. 2(E), the thermoelectric element 12 is driven, but since the laser drive current Id [mA] is set as the upper limit value, it is shown in FIG. 2(A). As described above, the power consumption [W] of the optical transmitter 1 is lower than the power consumption [W] of the optical transmitter of the comparative example.

For example, as shown in FIG. 2D, when the laser drive current Id [mA] is the upper limit value, the compensation of the output power loss L [dB] caused by the tracking error is shown in FIG. 2E. As described above, it is performed by driving the thermoelectric element 12 by the thermoelectric element driving unit 60. The output power P1 [dB] of the laser light output from the semiconductor laser 11 increases as the temperature of the semiconductor laser 11 decreases. Therefore, the target temperature control unit 53 controls the target temperature Tld [°C] to decrease as the monitor temperature Ta [°C] increases in the temperature range TR2 higher than the temperature range TR1. The target temperature control unit 53 can control the target temperature Tld [° C.] shown in the temperature range TR2 of FIG. 2(E) based on the driving condition information D1 which is the actually measured data. Further, the target temperature control unit 53 can control the target temperature Tld [° C.] shown in the temperature range TR2 of FIG. 2(E) based on the driving condition information D1 which is the actually measured data. .. The actual measurement data is obtained by measuring the output power P1a [dBm] of the laser light transmitted through the optical fiber 90 with the measuring device while the target temperature control unit 53 outputs the output power loss L [dB] shown in FIG. Can be obtained by changing the target temperature Tld [° C.] so as to compensate the output power of

When the target temperature control unit 53 outputs the drive control signal C1 instructing to set the target temperature Tld [°C], the thermoelectric element driving unit 60 causes the thermoelectric element 12 to reach the target temperature Tld [°C]. The drive current Ite is supplied to 12. The target temperature control unit 53 uses the drive condition information D1 stored in the memory 40, that is, the compensation profile, according to the monitor temperature Ta [° C.] measured by the temperature monitor unit 51, and the required target temperature Tld. Determine [°C].

When the monitor temperature Ta [°C] is higher than the target temperature Tld [°C] in the temperature range TR2, the higher the target temperature Tld [°C], the smaller the thermoelectric element drive current Ite and the smaller the power consumption [W]. Therefore, in the temperature range TR2, near the boundary temperature between the temperature range TR1 and the temperature range TR2 where the output power loss L[dB] caused by the tracking error is relatively small, that is, near the temperature T3[°C], the target temperature Tld[°C]. Is set to a predetermined maximum value. In this way, as shown in FIG. 2E, by setting the target temperature Tld [°C] to the maximum in the vicinity of the temperature T3 [°C], that is, the target temperature Tld [°C] is set to the monitor temperature Ta [. By setting the temperature close to [° C.], the power consumption [W] of the optical transmitter 1 can be reduced.

Further, as shown in FIG. 2E, in the temperature range TR2, the output power loss L[dB] caused by the tracking error increases as the temperature becomes higher than the temperature T3[° C.], and thus the output power loss L[dB]. By lowering the target temperature Tld [° C.] by the amount, compensation is performed.

In this way, by recording the compensation profile for changing the target temperature Tld [°C] according to the monitor temperature Ta [°C] in the memory 40, the target temperature according to the monitor temperature Ta [°C] is recorded. A process for changing Tld [°C] is possible. That is, the optical transmitter 1 gradually lowers the target temperature Tld [° C.] so as to compensate for the output power loss L [dB] caused by the tracking error, and transmits through the optical fiber 90 with the minimum power consumption [W]. The output power P1a [dBm] of the generated laser light can be maintained constant.

When the central wavelength λ [nm] reaches the limit value of the wavelength range specified in the specification, the control unit 50 turns on the thermoelectric element driving unit 60 to drive the thermoelectric element 12, and the optical fiber 90 While measuring the center wavelength λ [nm] of the output laser light with a wavelength measuring device, the target temperature Tld [°C] in the temperature range TR2 is gradually decreased from the maximum value, and the center wavelength λ [nm] is the wavelength. The thermoelectric element drive unit 60 is controlled so that the maximum target temperature Tld [° C.] that satisfies the range is reached. When the laser drive current Id [mA] does not reach the upper limit value, the control unit 50 confirms the output power P1a [dBm] and controls the target voltage Vr [V] of the APC so as to obtain a desired output power. To do. If the central wavelength λ [nm] reaches the limit value of the wavelength range defined in the specification before the laser drive current Id [mA] reaches the upper limit value, the control unit 50 causes the laser drive current The output power loss L [dB] is compensated by APC that changes Id [mA] and control of the target temperature Tld [°C].

That is, the output power loss L [dB] in the temperature range TR2 is compensated by increasing the target voltage Vr [V] of the APC first, and not by increasing the target voltage Vr [V] of the APC. When the output power loss L [dB] cannot be compensated, control for making the target temperature Tld [°C] follow the monitor temperature Ta [°C] by using the thermoelectric element driving unit 60 as shown in FIG. To do. Note that when the laser drive current Id [mA] reaches the upper limit and the central wavelength λ [nm] of the laser light reaches the limit value of the wavelength range specified in the specification, it is shown in FIG. As described above, the target temperature Tld [° C.] is controlled so that the output power P2a [dBm] becomes constant and the center wavelength λ [nm] falls within the wavelength range specified in the specifications.

<Temperature range TR3>
When the current monitor temperature Ta [°C] measured by the temperature monitor unit 51 is within the temperature range TR3, the target temperature control unit 53 sets the current monitor temperature Ta [°C] in the drive condition information D1. The target temperature Tld [°C] is determined based on the corresponding information, and the target voltage control unit 52 determines the target voltage Vr [V] based on the information corresponding to the current monitor temperature Ta [°C] in the driving condition information D1. ] Is decided. At this time, the target temperature control unit 53 and the target voltage control unit 52 of the control unit 50 select the combination of the target temperature Tld [° C.] and the target voltage Vr [V] that minimizes the power consumption [W].

Within the temperature range TR3, as shown in FIG. 2(E), the target temperature Tld [° C.] is lowered to drive the thermoelectric element 12, and the target voltage Vr [V] is adjusted. As shown in (D), since the laser drive current Id [mA] is controlled to the upper limit value or in the vicinity of the upper limit value, transmission is performed through the optical fiber 90 as shown in FIG. 2B. The optical output power P1a [dBm] of the generated laser light can be maintained constant. In the temperature range TR3, as shown in FIG. 2(E), the thermoelectric element 12 is driven, but the laser drive current Id [mA] is set to the upper limit value or in the vicinity of the upper limit value. As shown in FIG. 2A, the power consumption [W] of the optical transmitter 1 is lower than the power consumption [W] of the optical transmitter of the comparative example.

The influence of the output power loss L [dB] shown by the broken line in FIG. 2B can be confirmed from the output power of the laser light transmitted from the optical transmitter of the comparative example through the optical fiber. However, as indicated by the broken line in FIG. 2C, the effect of the output power loss L [dB] cannot be known from the output power of the laser light output from the semiconductor laser of the optical transmitter of the comparative example. ..

In the optical transmitter 1 according to the first embodiment, in order to compensate the output power loss L [dB] shown in FIG. 2(F), the output power loss L caused by the tracking error at each of the plurality of monitor temperatures Ta [° C.] Actual measurement data including the influence of [dB] is acquired in advance for each product. The actual measurement data is acquired for each product at the adjustment stage in the manufacturing process. For example, while measuring the output power P1a [dBm] of the laser light output through the optical fiber 90, the target voltage control unit 52 compensates the output power loss L [dB] shown in FIG. By changing the target voltage Vr [V] provided to the target voltage comparison unit 32, as shown by the solid line in FIG. 2B, the output power P1a [dBm] in which the tracking error is compensated, and The target voltage Vr [V] can be obtained.

For example, when the output power loss L [dB] caused by the tracking error occurs and the output power P1a [dBm] becomes lower than the desired output power, the target voltage control unit 52 uses the driving condition information D1 based on the actual measurement data. Then, the target voltage Vr [V] is increased and the laser drive current Id [mA] is increased so as to compensate the output power loss L [dB] caused by the tracking error caused by the temperature change. Specifically, the target voltage control unit 52 starts from the monitor temperature Ta [° C.] corresponding to the temperature of the optical module 10 based on the output power loss L [dB] caused by the tracking error caused by the temperature change, and outputs the target voltage Vr [ V] is determined and the target voltage Vr [V] is notified to the target voltage comparison unit 32. The APC unit 31 controls the laser drive current Id [mA] based on the target voltage Vr [V] received by the target voltage comparison unit 32. By such control, the optical transmitter 1 can output a laser beam having a desired output power P1a [dBm] through the optical fiber 90 as shown by the solid line in FIG.

When the monitor temperature Ta [°C] is lower than the target temperature Tld [°C] in the temperature range TR3, the lower the target temperature Tld [°C], the smaller the thermoelectric element drive current Ite and the smaller the power consumption [W]. Therefore, in the temperature range TR3, the thermoelectric element drive current Ite is kept at the minimum target temperature Tld [° C.] with the central wavelength λ [nm] within the desired wavelength range, and thus the optical transmitter 1 Power consumption [W] can be minimized. The recording of the compensation profile at each monitor temperature Ta [° C.] is preferably performed after the temperature becomes stable in consideration of the self-heating of the semiconductor laser 11 and the self-heating of the thermoelectric element 12. Further, it is desirable from the viewpoint of improving accuracy that the compensation profile is recorded at each monitor temperature Ta [° C.] a plurality of times after temperature stabilization.

In this way, the compensation profile including the optimum values of the target voltage Vr[V] of the APC and the target temperature Tld[°C] at each of the plurality of monitor temperatures Ta[°C] is stored in the memory 40 in the form of LUT or as a calculation formula. Held in. As the calculation formula, for example, a fitting function of the second order or lower in each of the temperature ranges TR1, TR2, TR3 can be used.

FIG. 3 is a flowchart showing the operation of the optical transmitter 1 according to the first embodiment. When the semiconductor laser 11 is outputting the laser beam L1, the control unit 50 controls the output power P1a [dBm] of the laser beam transmitted through the optical fiber 90 to be constant without depending on the monitor temperature Ta [° C.]. So that the target voltage Vr[V] is controlled, or the target voltage Vr[V] and the target temperature Tld[°C. ] Control is performed.

First, in step S1, the control unit 50 reads the monitor temperature Ta [° C.] of the temperature monitor unit 51.

In step S2, the control unit 50 determines whether the monitor temperature Ta [°C] is within the temperature range TR1. When the monitor temperature Ta [°C] is within the temperature range TR1 (that is, when the determination is YES), the process proceeds to step S4a, and when the monitor temperature Ta [°C] is not within the temperature range TR1 (that is, the determination is made). Is NO), the process proceeds to step S3.

When the process proceeds from step S2 to step S4a, the control unit 50 controls the temperature range TR1. That is, the control unit 50 determines the target voltage Vr [V] used for APC to a value according to the monitor temperature Ta [°C], and executes APC. At this time, the control unit 50 does not instruct to drive the thermoelectric element 12.

In step S5a, the control unit 50 reads the monitor temperature Ta [°C] of the temperature monitor unit 51.

In step S6a, the control unit 50 determines whether the monitor temperature Ta [°C] is out of the temperature range TR1. That is, the control unit 50 determines whether or not the monitor temperature Ta [°C] changes across the temperature T2 [°C] that is the lower limit or the upper limit temperature T3 [°C] of the temperature range TR1. If the monitor temperature Ta [°C] is outside the temperature range TR1 (that is, if the determination is YES), the process returns to step S2, and if the monitor temperature Ta [°C] is within the temperature range TR1 (that is, the determination is made). Is NO), the process returns to step S4a.

When the process proceeds from step S2 to step S3, the control unit 50 determines whether the monitor temperature Ta [°C] is within the temperature range TR2. When the monitor temperature Ta [°C] is within the temperature range TR2 (that is, when the determination is YES), the process proceeds to step S4b, and when the monitor temperature Ta [°C] is not within the temperature range TR2 (that is, the determination is made). Is NO), the process proceeds to step S4c.

When the process proceeds from step S3 to step S4b, the control unit 50 controls the temperature range TR2. That is, the control unit 50 sets the target voltage Vr [V] used for APC and the target temperature Tld [° C.] used for driving the thermoelectric element 12 by the thermoelectric element driving unit 60 according to the monitor temperature Ta [° C.]. Is determined and the target voltage Vr [V] is applied to the laser drive unit 30, and the drive control signal C1 is applied to the thermoelectric element drive unit 60.

In step S5b, the control unit 50 reads the monitor temperature Ta [°C] of the temperature monitor unit 51.

In step S6b, the control unit 50 determines whether the monitor temperature Ta [°C] is out of the temperature range TR2. That is, the control unit 50 determines whether the monitor temperature Ta [°C] changes across the lower limit temperature T3 [°C] or the upper limit temperature T4 [°C] of the temperature range TR2. If the monitor temperature Ta [°C] is out of the temperature range TR2 (that is, if the determination is YES), the process returns to step S2, and if the monitor temperature Ta [°C] is within the temperature range TR2 (that is, the determination is made). Is NO), the process returns to step S4b.

When the process proceeds from step S3 to step S4c, the control unit 50 controls the temperature range TR3. That is, the control unit 50 sets the target voltage Vr [V] used for APC and the target temperature Tld [° C.] used for driving the thermoelectric element 12 by the thermoelectric element driving unit 60 according to the monitor temperature Ta [° C.]. Is determined and the target voltage Vr [V] is applied to the laser drive unit 30, and the drive control signal C1 is applied to the thermoelectric element drive unit 60.

In step S5c, the control unit 50 reads the monitor temperature Ta [°C] of the temperature monitor unit 51.

In step S6c, the control unit 50 determines whether the monitor temperature Ta [°C] is out of the temperature range TR3. That is, the control unit 50 determines whether the monitor temperature Ta [°C] changes across the lower limit temperature T1 [°C] or the upper limit temperature T2 [°C] of the temperature range TR3. If the monitor temperature Ta [°C] is outside the temperature range TR3 (that is, if the determination is YES), the process returns to step S2, and if the monitor temperature Ta [°C] is within the temperature range TR3 (that is, the determination is made). Is NO), the process returns to step S4c.

<<1-3>> Effect As described above, in the optical transmitter 1 according to the first embodiment, the drive condition information D1 based on the actual measurement data measured in advance for each product is stored in the memory 40. Further, when the optical transmitter 1 is used, the control unit 50 reads the monitor temperature Ta [° C.] and sets the drive condition according to the monitor temperature Ta [° C.] of the drive condition information D1 stored in the memory 40. , LUT or using a formula. Therefore, the optical transmitter 1 can drive the semiconductor laser 11 under the driving condition suitable for each of the temperature ranges TR1, TR2, and TR3, and the output power P1a [dBm] of the laser light transmitted through the optical fiber 90. Can be kept constant.

Further, in the temperature range TR1, since the thermoelectric element driving unit 60 is turned off and the thermoelectric element 12 is not driven, the power consumption [W] can be suppressed. Further, in the temperature ranges TR2 and TR3, the set value of the target temperature Tld [° C.] is set to a value considering the power consumption [W], so that the power consumption [W] can be suppressed.

<<2>> Embodiment 2.
<<2-1>> Configuration FIG. 4 is a block diagram schematically showing a configuration of the optical transmitter 2 according to the second embodiment of the present invention. 4, constituent elements that are the same as or correspond to the constituent elements shown in FIG. 1 are assigned the same reference numerals as those shown in FIG.

The optical transmitter 2 according to the second embodiment is provided with a thermoelectric element 80 that directly cools or heats the optical module 10 so that it can be used in a wider temperature range than the optical transmitter 1 according to the first embodiment. , And a thermoelectric element drive unit 70 for driving the same. The thermoelectric element 80 is also referred to as a "second thermoelectric element". The thermoelectric element driving unit 70 is also referred to as a “second thermoelectric element driving unit”. The thermoelectric element drive unit 70 is composed of an electric circuit. The thermoelectric element 80 has the same configuration as the thermoelectric element 12. Further, in the optical transmitter 2 according to the second embodiment, the control unit 50a provides the thermoelectric element drive unit 70 with the drive control signal C2. By using the thermoelectric element 80 and the thermoelectric element drive unit 70, the output power loss L [dB] caused by the tracking error caused by the temperature change can be suppressed in a wide temperature range. Except for this point, the optical transmitter 2 according to the second embodiment is the same as the optical transmitter 1 according to the first embodiment.

<<2-2>> operation

5A to 5F are graphs showing the operation of the optical transmitter 2 according to the second embodiment. 5A to 5F, the same or corresponding portions as those shown in FIGS. 2A to 2F have the same reference numerals as those shown in FIGS. 5A to 5F. It is attached. The graphs of FIGS. 5A to 5F are graphs based on actual measurement values. In FIGS. 5A to 5F, the graph drawn by the solid line shows the operation of the optical transmitter 2 according to the second embodiment, and the graph drawn by the broken line shows the operation of the optical transmitter of the comparative example. Is shown. In the optical transmitter of the comparative example, the laser drive current is controlled by the laser drive section and the temperature of the semiconductor laser is controlled by the thermoelectric element in the entire range of the monitor temperature Ta [° C.], and the dashed line is shown in FIG. 5C. Thus, the output power of the laser light output from the semiconductor laser is constant.

The graph of FIG. 5A shows the power consumption [W] of the optical transmitter 2 according to the second embodiment and the power consumption [W] of the optical transmitter of the comparative example at each monitor temperature Ta [° C.]. ing. The graph of FIG. 5B shows the output power P2a [dBm] of the laser light transmitted through the optical fiber 90 from the optical transmitter 2 according to the second embodiment and the light of the comparative example at each monitor temperature Ta [° C.]. The output power [dBm] of the laser light transmitted from the transmitter through the optical fiber 90 is shown. The graph of FIG. 5C shows the output power P2 [dB] of the laser light output from the semiconductor laser 11 of the optical transmitter 2 according to the second embodiment and the light of the comparative example at each monitor temperature Ta [° C.]. The output power [dB] of the laser light output from the semiconductor laser of the transmitter is shown. The graph of FIG. 5D shows the laser drive current Id [mA] output from the laser drive unit 30 of the optical transmitter 2 according to the second embodiment at each monitor temperature Ta [° C.]. The graph in FIG. 5E shows the target temperature Tld [°C] determined by the controller 50 of the optical transmitter 2 according to the second embodiment at each monitor temperature Ta [°C]. The graph of FIG. 5F shows the output power loss L [dB] caused by the tracking error of the optical transmitter 2 according to the second embodiment and the tracking error of the optical transmitter of the comparative example at each monitor temperature Ta [° C.]. The resulting output power loss [dB] is shown.

In the comparative example, the target voltage Vr [V] is fixed and APC is performed, and the target temperature Tld [°C] is fixed and the thermoelectric element is controlled. In the optical transmitter 2 according to the second embodiment, the temperature range TR1, the temperature range TR2 higher than the temperature range TR1, the temperature range TR3 lower than the temperature range TR1, the temperature range TR4 higher than the temperature range TR2, and the temperature range lower than the temperature range TR3. Different control is performed in each of TR5. In the second embodiment, temperature range TR4 is also referred to as "fourth temperature range". The temperature range TR5 is also referred to as a "fifth temperature range".

The temperature ranges TR1, TR2, TR3 in the second embodiment are the same as the temperature ranges TR1, TR2, TR3 in the first embodiment. The temperature range TR4 in the second embodiment is a range higher than the temperature T4 [°C] and lower than the temperature T5 [°C]. The temperature range TR5 is lower than the temperature T1 [° C.] and is the temperature T0 [° C.] or higher.

In the temperature range TR4, which is higher than the temperature range TR2, or in the temperature range TR5, which is lower than the temperature range TR3, the thermoelectric element drive unit 70 is turned on to supply the thermoelectric element drive current to the thermoelectric element 80. By the operation of the thermoelectric element driving unit 70, the power consumption [W] in the temperature ranges TR4 and TR5 increases as shown in FIG. 5(A). However, in the temperature range TR4, cooling by the thermoelectric element 80 or cooling by the thermoelectric element 80 and the thermoelectric element 12 is performed so that the monitor temperature Ta [° C.] maintains the maximum monitor temperature within the temperature range TR2. Further, in the temperature range TR5, heating by the thermoelectric element 80 or heating by the

thermoelectric elements

80 and 12 is performed so that the monitor temperature Ta [° C.] maintains the minimum monitor temperature in the temperature range TR3.

In the optical transmitter 2 according to the second embodiment, the cooling or heating of the optical module 10 suppresses the influence of the output power loss L [dB] shown in FIG. 5(F) as shown in FIG. 5(B). Moreover, it can be realized in a wide temperature range. As a result, as shown in FIG. 5B, the output power P2a [dBm] of the laser light transmitted through the optical fiber 90 can be kept constant in a wide temperature range.

As shown in FIGS. 5D, 5E, and 5C, in the temperature range TR4, the laser drive current Id [mA] at the upper limit temperature T4 [° C.] in the temperature range TR2. , The target temperature Tld [° C.], and the output power P2 [dB] of the semiconductor laser 11 are maintained. Further, as shown in FIGS. 5D, 5E, and 5C, in the temperature range TR5, the laser drive current Id [mA] at the lower limit temperature T1 [° C.] in the temperature range TR3. , The target temperature Tld [° C.], and the output power P2 [dB] of the semiconductor laser 11 are maintained.

FIG. 6 is a flowchart showing the operation of the optical transmitter 2 according to the second embodiment. 6, steps that are the same as or correspond to the steps shown in FIG. 3 are given the same step numbers as the step numbers shown in FIG.

As shown in FIG. 6, in the operation of the optical transmitter 2 according to the second embodiment, the processing of steps S7, S8, S9, S4d, S4e, S5d, S5e, S6d, S6e, and S10 is added. The operation differs from that of the optical transmitter 1 according to the first embodiment.

When the process proceeds from step S7 to step S8 (that is, when the determination in step S7 is NO), the control unit 50 outputs the drive control signal C2 for starting the driving of the thermoelectric element 80. To provide.

In step S9, the control unit 50 determines whether the monitor temperature Ta [°C] is within the temperature range TR4. When the monitor temperature Ta [°C] is within the temperature range TR4 (that is, when the determination is YES), the process proceeds to step S4d, and when the monitor temperature Ta [°C] is not within the temperature range TR4 (that is, the determination is made). Is NO), the process proceeds to step S4e.

In step S4d, the control unit 50 controls the temperature range TR4. That is, the control unit 50 sets the target voltage Vr [V] used for APC and the target temperature Tld [° C.] used for driving the thermoelectric element 12 by the thermoelectric element driving unit 60 according to the monitor temperature Ta [° C.]. To supply the target voltage Vr [V] to the laser driving unit 30, provide the driving control signal C1 to the thermoelectric element driving unit 60, and supply the driving control signal C2 for executing the cooling by the thermoelectric element 80. It is given to the drive unit 70.

In step S5d, the control unit 50 reads the monitor temperature Ta [°C] of the temperature monitor unit 51.

In step S6d, the control unit 50 determines whether the monitor temperature Ta [°C] is out of the temperature range TR4. That is, the control unit 50 determines whether the monitor temperature Ta [°C] has changed across the lower limit temperature T4 [°C] or the upper limit temperature T5 [°C] of the temperature range TR4. When the monitor temperature Ta [°C] is out of the temperature range TR4 (that is, when the determination is YES), the driving of the thermoelectric element 80 is stopped in step S10, the process returns to step S2, and the monitor temperature Ta [°C]. Is within the temperature range TR4 (that is, the determination is NO), the process returns to step S4d.

When the process proceeds from step S9 to step S4e (that is, when the determination in step S9 is NO), the control unit 50 outputs the drive control signal C2 for starting the driving of the thermoelectric element 80. To provide.

In step S4e, the control unit 50 performs control in the temperature range TR5. That is, the control unit 50 sets the target voltage Vr [V] used for APC and the target temperature Tld [° C.] used for driving the thermoelectric element 12 by the thermoelectric element driving unit 60 according to the monitor temperature Ta [° C.]. To supply the target voltage Vr [V] to the laser driving unit 30, provide the driving control signal C1 to the thermoelectric element driving unit 60, and supply the driving control signal C2 for performing the heating by the thermoelectric element 80. It is given to the drive unit 70.

In step S5e, the control unit 50 reads the monitor temperature Ta [°C] of the temperature monitor unit 51.

In step S6e, the control unit 50 determines whether the monitor temperature Ta [°C] is out of the temperature range TR5. That is, the control unit 50 determines whether the monitor temperature Ta [°C] changes across the lower limit temperature T0 [°C] or the upper limit temperature T1 [°C] of the temperature range TR5. When the monitor temperature Ta [°C] is out of the temperature range TR5 (that is, when the determination is YES), the driving of the thermoelectric element 80 is stopped in step S10, the process returns to step S2, and the monitor temperature Ta [°C]. Is within the temperature range TR4 (that is, the determination is NO), the process returns to step S4e.

<<2-3>> Effects As described above, the optical transmitter 2 according to the second embodiment cools the optical module 10 at the upper limit temperature T4 [° C.] of the temperature range TR2 and lowers the lower limit of the temperature range TR3. The optical module 10 is configured to be heated at the temperature T1 [° C.]. Therefore, in the optical transmitter 2, the temperature range TR4 that is higher than the upper limit temperature T4 [°C] of the temperature range TR2 and the temperature range TR5 that is lower than the lower limit temperature T1 [°C] of the temperature range TR3. Also in, it is possible to suppress the tracking error. Therefore, by using the optical transmitter 2, the output power P2a [dBm] of the laser light transmitted through the optical fiber 90 can be kept constant in a wider temperature range TR5, TR3, TR1, TR2, TR4. ..

<<3>> Modification.
FIG. 7 is a diagram showing an example of the hardware configuration of the optical transmitter according to the modification of the first or second embodiment. The optical transmitter 1 according to the first embodiment uses a memory 101 that is a storage device that stores a program as software and a processor 102 that is an information processing unit that executes the program stored in the memory 101 (for example, , A computer, etc.). In this case, all or part of the control unit 50 and all or part of the laser driving unit 30 in FIG. 1 can be realized by the memory 101 storing the program and the processor 102.

Similarly, the optical transmitter 2 according to the second embodiment can be realized by using a memory 101 that stores a program as software and a processor 102 that executes the program stored in the memory 101. In this case, the whole or part of the control unit 50a and the whole or part of the laser driving unit 30 in FIG. 4 can be realized by the memory 101 storing the program and the processor 102.

1, 2 optical transmitters, 1a, 2a device housings, 10 optical modules, 11 semiconductor lasers, 12 thermoelectric elements, 13 thermistors, 14 thermoelectric element parts, 15 module housings, 20 monitor current detection parts, 30 laser drive parts, 31 APC section, 40 memory, 50 control section, 51 temperature monitor section, 52 target voltage control section, 53 target temperature control section, 54 optical output monitor section, 60 thermoelectric element drive section, 70 thermoelectric element drive section, 80 thermoelectric element, 90 optical fiber.

Claims

An optical transmitter that outputs laser light,
A semiconductor laser that outputs the laser light having a first output power corresponding to a laser drive current and outputs a monitor current corresponding to the first output power;
A holding unit that holds the optical fiber so that the laser light output from the semiconductor laser is incident on the optical fiber,
A temperature monitor unit for measuring a monitor temperature corresponding to the temperature of the holding unit,
A laser drive unit that supplies the laser drive current to the semiconductor laser so that a monitor voltage corresponding to the monitor current approaches a target voltage,
A target voltage control unit for applying the target voltage to the laser drive unit;
A first thermoelectric element for cooling or heating the semiconductor laser;
A first thermoelectric element drive unit for driving the first thermoelectric element;
A target temperature control unit that gives a first drive control signal for bringing the temperature of the first thermoelectric element close to a target temperature to the first thermoelectric element driving unit;
Drive condition information determined based on an actual measurement value of the relationship between the target voltage at each monitor temperature, the target temperature, and the power consumption of the optical transmitter, a storage unit that stores in advance.
Equipped with
When the monitor temperature is within the first temperature range, the target temperature control unit stops the driving of the first thermoelectric element by the first thermoelectric element driving unit, and the target voltage control unit Determining the target voltage based on information corresponding to the current monitor temperature output from the temperature monitor unit in the drive condition information,
When the monitor temperature is in the second temperature range higher than the first temperature range, the target temperature control unit is based on the information corresponding to the current monitor temperature in the drive condition information. Determining the target temperature, the target voltage control unit determines the target voltage based on the information corresponding to the current monitor temperature of the driving condition information,
When the monitor temperature is in the third temperature range lower than the first temperature range, the target temperature control unit is based on the information corresponding to the current monitor temperature in the drive condition information. The optical transmitter, wherein the target voltage is determined, and the target voltage control unit determines the target voltage based on information corresponding to the current monitor temperature in the drive condition information.
A boundary temperature between the first temperature range and the second temperature range is an upper limit temperature of the first temperature range, and the semiconductor laser is output at the upper limit temperature of the first temperature range. A temperature determined based on the upper limit value of the laser drive current at the upper limit temperature of the central wavelength of the laser light or the first temperature range,
A boundary temperature between the first temperature range and the third temperature range is a lower limit temperature of the first temperature range, and the semiconductor laser is output at the lower limit temperature of the first temperature range. The optical transmitter according to claim 1, wherein the temperature is determined based on a center wavelength of laser light or an upper limit value of the laser drive current at the lower limit temperature of the first temperature range.
A second thermoelectric element for cooling or heating the holding part;
A second thermoelectric element drive unit for driving the second thermoelectric element;
Further equipped with,
When the monitor temperature is in the fourth temperature range higher than the second temperature range, the target temperature control unit is based on the information corresponding to the current monitor temperature in the drive condition information. The target temperature is determined, the target voltage control unit determines the target voltage based on information corresponding to the current monitor temperature in the driving condition information, and the target temperature control unit determines the second target temperature. Applying a second drive control signal for executing cooling by the thermoelectric element to the second thermoelectric element drive unit,
When the monitor temperature is in the fifth temperature range lower than the third temperature range, the target temperature control unit is based on the information corresponding to the current monitor temperature in the drive condition information. The target temperature is determined, the target voltage control unit determines the target voltage based on information corresponding to the current monitor temperature in the driving condition information, and the target temperature control unit determines the second target temperature. The optical transmitter according to claim 1 or 2, wherein a second drive control signal for executing heating by the thermoelectric element is given to the second thermoelectric element driving unit.
A boundary temperature between the second temperature range and the fourth temperature range is an upper limit temperature of the second temperature range, and the semiconductor laser is output at the upper limit temperature of the second temperature range. It is the temperature determined based on the central wavelength of the laser light,
A boundary temperature between the third temperature range and the fifth temperature range is a lower limit temperature of the third temperature range, and the semiconductor laser is output at the lower limit temperature of the third temperature range. The optical transmitter according to claim 3, wherein the temperature is determined based on the center wavelength of the laser light.
The optical transmitter according to any one of claims 1 to 4, wherein the storage unit stores a calculation formula or a lookup table as the driving condition information.
The storage unit stores, as the driving condition information, a combination of the target voltage and the target temperature that minimizes the power consumption of the optical transmitter at each monitor temperature. Item 6. The optical transmitter according to any one of items 1 to 5.
The target voltage control unit and the target temperature control unit obtain, from the driving condition information, a combination of the target voltage and the target temperature at which the power consumption of the optical transmitter is minimum at each monitor temperature. The optical transmitter according to any one of claims 1 to 5, wherein:
8. The target temperature obtained by the target temperature control unit from the drive condition information in the second temperature range decreases with an increase in the monitor temperature, according to any one of claims 1 to 7. The optical transmitter described in 1.
In the second temperature range, the target temperature acquired from the driving condition information by the target temperature control unit is such that a difference between the monitor temperature and the target temperature increases as the monitor temperature rises. The optical transmitter according to any one of claims 1 to 8.
The optical transmission according to any one of claims 1 to 9, wherein in the third temperature range, the target temperature that the target temperature control unit acquires from the drive condition information is a constant value. vessel.
A semiconductor laser which outputs a laser beam having a first output power corresponding to a laser drive current and outputs a monitor current corresponding to the first output power;
A holding unit that holds the optical fiber so that the laser light output from the semiconductor laser is incident on the optical fiber,
A temperature monitor unit for measuring a monitor temperature corresponding to the temperature of the holding unit,
A laser drive unit that supplies the laser drive current to the semiconductor laser so that a monitor voltage corresponding to the monitor current approaches a target voltage,
A target voltage control unit for applying the target voltage to the laser drive unit;
A first thermoelectric element for cooling or heating the semiconductor laser;
A first thermoelectric element drive unit for driving the first thermoelectric element;
A target temperature control unit that gives a first drive control signal for bringing the temperature of the first thermoelectric element close to a target temperature to the first thermoelectric element driving unit;
Drive condition information determined based on an actual measurement value of the relationship between the target voltage at each monitor temperature, the target temperature, and the power consumption of the optical transmitter, a storage unit that stores in advance.
A method of controlling an optical transmitter, comprising:
When the monitored temperature is within the first temperature range, the driving of the first thermoelectric element by the first thermoelectric element drive unit is stopped and the temperature monitor unit outputs the drive condition information from the temperature monitor unit. Determining the target voltage based on information corresponding to the current monitor temperature being
When the monitor temperature is in the second temperature range higher than the first temperature range, the target temperature is determined based on the information corresponding to the current monitor temperature in the driving condition information, Determining the target voltage based on the information corresponding to the current monitor temperature of the driving condition information,
When the monitor temperature is in the third temperature range lower than the first temperature range, the target temperature is determined based on the information corresponding to the current monitor temperature in the drive condition information, The control method of an optical transmitter, wherein the target voltage is determined based on information corresponding to the current monitor temperature in the drive condition information.