JP2003258372A - Light emitting module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting module capable of performing a very accurate wavelength control by suppressing a shift in locked wavelength due to a change in temperature of an optical device. <P>SOLUTION: When the power is turned on, a switching means SW which comprises a CPU 61 selects a first set value Vref<SB>1</SB>until a wavelength of light emitted from a semiconductor light emitting device 31 becomes close to a target wavelength, and controls a temperature monitoring voltage (the output of F(T)) corresponding to the target wavelength so that it becomes the first set value Vref<SB>1</SB>, by means of a single feedback circuit. When the wavelength of light emitted from the semiconductor light emitting device 31 becomes close to the target wavelength, the switching means SW is switched to control a wavelength monitoring voltage (the output of G(T)) corresponding to the target wavelength so that it becomes a second set value Vref<SB>2</SB>, by means of a double feedback circuit. The CPU 61 corrects the second set value Vref<SB>2</SB>so as to compensate for a temperature characteristic of an etalon 34, based on temperature information obtained by a thermistor 39. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting module used in an optical communication system or the like.

[0002]

Light emitting modules are used, for example, in wavelength division multiplexing (WDM) transmission systems that use a plurality of wavelength components. In a 1.55 μm band WDM system, the wavelength spacing between adjacent grids is approximately 0.8 nm (100 GHz).
It is said that In order to realize this wavelength interval, the emission wavelength of the light from the light emitting module is ± the grid wavelength.
It is necessary to control the range within 0.03 nm.

Most of the light emitting modules currently used have a semiconductor light emitting element, a photodetector, and a temperature controller. The wavelength of the laser light slightly emitted from the light reflecting surface of the semiconductor light emitting element is monitored by the photodetector, the temperature of the semiconductor light emitting element is adjusted based on the monitoring result, and the wavelength of the laser light is controlled. Here, in order to detect wavelength fluctuations with high accuracy, an optical element having wavelength dependence (for example, an etalon) is provided between the semiconductor light emitting element and the photodetector, and the laser light component having a specific wavelength is monitored. To be done.

[0004]

As a result of the research conducted by the present inventors, it was found that the light emitting module having the above-mentioned structure has the following problems.

In the light emitting module using the etalon, the wavelength of the light emitted from the light emitting module is controlled as follows. FIGS. 6A and 6B are schematic diagrams showing the relationship between the wavelength of light output from the semiconductor light emitting element and the output current of the photodetector. As shown in FIG. 6A, the waveform W1 of the output current of the photodetector changes periodically as the wavelength λ increases. Here, the grid wavelength used in the WDM system is λ ₀ . Further, the current value of the output current output from the photodetector when the light of wavelength λ ₀ enters the photodetector is I ₀ . At this time, the output current is locked to the current value I ₀
By (controlling) the grid wavelength λ ₀ is also locked. However, when the temperature of the etalon rises from T ₀ to T ₁ due to the usage environment or the like during use of the light emitting module, the waveform W1 of the output current becomes long W2 as shown in FIG. 6B. It shifts to the wavelength side.
This is because the etalon thermally expands when the temperature of the etalon rises, and the refractive index of the material forming the etalon changes. Due to such wavelength shift, the grid wavelength to be locked at the wavelength λ ₀ (hereinafter, lock wavelength) is shifted to the wavelength λ _{1 due} to the lock of the current value I ₀ . The lock wavelength shift amount Δλ = λ ₁ −λ ₀ has a temperature dependence of about 0.013 nm / ° C. when the etalon is composed of a commonly used general optical glass.

On the other hand, since the light output decreases due to the deterioration of the semiconductor light emitting element, the driving current of the semiconductor light emitting element is corrected (increase correction) by an APC (Auto Power Control) circuit so that the light output of the semiconductor light emitting element becomes constant. is doing. In this case, since the wavelength of the light output from the semiconductor light emitting element shifts to the long wavelength side, the temperature of the semiconductor light emitting element is lowered by the temperature controller to prevent the wavelength shift.
However, when the temperature of the semiconductor light emitting element is lowered by the temperature regulator, the temperature of the etalon arranged in the vicinity of the semiconductor light emitting element may also drop, and the lock wavelength, that is, the output of the photodetector shifts, and the wavelength The control accuracy will decrease.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a light emitting module capable of controlling a wavelength shift with high accuracy by suppressing a lock wavelength shift due to a temperature change of an optical element. And

[0008]

A light emitting module according to the present invention includes a semiconductor light emitting element, an optical element having wavelength dependence, which transmits light from the semiconductor light emitting element, and an optical element which receives light transmitted through the optical element. Photodetector for monitoring the wavelength of the light of the semiconductor light emitting element, a temperature detector for detecting the temperature of the optical element, and a temperature adjusting means arranged to adjust the temperature of the semiconductor light emitting element and the optical element And temperature control means for controlling the temperature adjusting means based on the output of the temperature detector so as to match the output of the temperature detector with the first predetermined value, the output of the photodetector and the second predetermined value. A predetermined value determining means for determining the first predetermined value based on the above, and a predetermined value for correcting the second predetermined value so as to compensate the temperature characteristic in the wavelength dependence of the optical element based on the output of the temperature detector With value correction means, It is characterized in that.

In the light emitting module according to the present invention, when the temperature control means controls the temperature adjusting means so as to match the output of the temperature detector with the first predetermined value based on the output of the temperature detector, The second predetermined value for determining the first predetermined value is corrected by the predetermined value correction means so as to compensate the temperature characteristic in the wavelength dependence of the optical element based on the output of the temperature detector. As a result, the drive current is increased and corrected with the deterioration of the semiconductor light emitting element, and the fluctuation of the lock wavelength is suppressed even when the temperature of the optical element changes. Therefore, highly accurate wavelength control can be performed.

Further, the predetermined value correction means includes a storage means for storing the correction value, the correction value corresponding to the output of the temperature detector is read from the storage means, and the correction value is set to the second predetermined value. Is preferred. With this configuration, the second predetermined value can be easily set by reading the correction value from the storage unit, and a CPU having a slow processing capacity can be used as the predetermined value correction unit.

Further, it is preferable that the predetermined value correction means calculates a correction value based on the output of the temperature detector and sets the correction value to the second predetermined value. With such a configuration, it is possible to easily set the second predetermined value even when the predetermined value correction means and the like have a system configuration with a small storage capacity.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a light emitting module according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a light emitting module 1 of this embodiment. Referring to FIG. 1, the light emitting module 1 includes a light emitting module main part 10 and a housing 11.
With. The housing 11 includes a main body portion 11a that houses the light emitting module main portion 10, a tubular portion 11b that guides the optical fiber 12 to the light emitting module main portion 10, and a plurality of lead pins 11c.

The main part 10 of the light emitting module has a thermoelectric cooler 21 as a temperature adjusting means. As the thermoelectric cooler 21, for example, a temperature control element using the Peltier effect can be used. A semiconductor light emitting element 31, a collimator lens 32, and a photodetector 33 are provided on the thermoelectric cooler 21.
a, 33b, and the etalon 34 as an optical element having wavelength dependence are directly or indirectly mounted.

The semiconductor light emitting device 31 has a light emitting surface 31a and a light reflecting surface 31b. The light emitting surface 31a is formed by the optical portion 13 including a lens so that the cylindrical portion 1 of the housing 11
It is optically coupled to the optical fiber 12 guided to 1b. Therefore, the light emitted from the light emitting surface 31a is introduced into the optical fiber 12 through the optical unit 13. on the other hand,
The light reflecting surface 31b is optically coupled to the collimator lens 32, and the light enters the collimator lens 32 from the light reflecting surface 31b. As the semiconductor light emitting element 31, for example, a distributed feedback (DFB) or Fabry-Perot type semiconductor laser element can be used. In the following description, the semiconductor light emitting element 31 is a semiconductor laser element that emits laser light.

The collimator lens 32 is optically coupled to the light reflecting surface 31b of the semiconductor light emitting element 31. The light emitted from the light reflecting surface 31b is divergent light, and becomes parallel light by passing through the collimator lens 32. The parallel light transmitted through the collimator lens 32 is output to the corresponding photodetectors 33a and 33b.

The photodetector 33a includes a collimator lens 32.
It is arranged so that the parallel light transmitted through can be received. The photodetector 33a outputs a signal according to the intensity of the received parallel light.

The etalon 34 is optically coupled to the light reflecting surface 31b of the semiconductor light emitting element 31 via the collimator lens 32. In the etalon 34, the light incident surface 34
The a and the light emitting surface 34b form a minute angle and are relatively inclined. Here, the angle is set to a range in which the light incident on the etalon 34 can cause multiple interference between the light incident surface 34a and the light emitting surface 34b. Specifically, the angle is preferably 0.01 degrees or more and 0.1 degrees or less. Since the light incident surface 34a and the light emitting surface 34b are inclined with respect to each other, the distance between these surfaces 34a and 34b changes along the inclination direction. Therefore, the transmission wavelength of the etalon changes along the tilt direction. Also, the etalon 34
May have a multilayer reflective film on its light incident surface 34a and light emitting surface 34b. With this multilayer reflection film, the light incident surface 34a
Also, the reflectance of the light emitting surface 34b is adjusted.

The photodetector 33b is arranged so as to be able to receive the light emitted from the light emitting surface 34b of the etalon 34. The relative positional relationship between the photodetector 33b and the etalon 34 is determined such that the light with a predetermined grid wavelength λ ₀ from the etalon 34 is detected by the photodetector 33b at a predetermined current value. By locking at this current value, the wavelength of the laser light emitted from the semiconductor light emitting device 31 is locked at the grid wavelength λ ₀ . Specifically, by adjusting the temperature of the thermoelectric cooler 21 based on these signals, the temperature of the semiconductor light emitting element 31 is adjusted and the wavelength of the laser light is made constant.

The photodetectors 33a and 33b may be, for example, InGaAs-pin type photodiodes having an InGaAs semiconductor layer formed on an InP substrate as a light receiving window.

A thermistor 39 is provided on the thermoelectric cooler 21.
Are mounted directly or indirectly. The thermistor 39
It functions as a temperature detector that detects the temperatures of the semiconductor light emitting element 31 and the etalon 34.

Further, the main part 10 of the light emitting module uses the semiconductor light emitting element 3 based on the output signal from the photodetector 33a.
1, a driver IC 41 constituting a semiconductor light emitting element drive circuit 42 for driving 1 and a thermionic cooler drive circuit 52 for driving the thermoelectric cooler 21 based on the output signal from the thermistor 39. Custom IC51
And CP for controlling the operation of the entire light emitting module 1.
U61 and. The light emitting module main part 10, the driver IC 41, the custom IC 51, and the CPU 61 are mounted on a board 71.

FIG. 2 is a block diagram showing the light emitting module 1 of this embodiment.

The custom IC 51 includes the current-voltage conversion circuit 5
3, 54, an automatic temperature control circuit (ATC) 55, a thermoelectric cooler drive circuit (TEC Drv) 52, an automatic output control circuit (APC / ACC) 56, and the like.

The current-voltage conversion circuit 53 includes a photodetector 33a.
The output current of is converted into voltage. Current-voltage conversion circuit 54
Converts the output current of the photodetector 33b into a voltage. The automatic temperature control circuit 55 generates and outputs a control signal for controlling the temperature of the thermoelectric cooler 21 based on the output signal from the thermistor 39. The thermoelectric cooler drive circuit 52 adjusts the current supplied to the thermoelectric cooler 21 based on the control signal from the automatic temperature control circuit 55. The automatic output control circuit 56 generates and outputs a control signal for controlling the intensity of light output from the semiconductor light emitting element 31 based on the output of the photodetector 33a input via the current-voltage conversion circuit 53. To do. Based on the control signal from the automatic output control circuit 56, the semiconductor light emitting element drive circuit 42 adjusts the current supplied to the semiconductor light emitting element 31.

The automatic temperature control circuit 55 and the automatic output control circuit 56 are connected to the CP via the digital-analog conversion circuit 57.
It is connected to U61. The CPU 61 has a ROM 62,
It includes the RAM 63 and performs processing based on the program stored in the ROM 62. Further, the output signal from the thermistor 39 and the output signal from the current-voltage conversion circuit 54 are connected to the CPU 61 via an analog-digital conversion circuit 58. The CPU 61 has a ROM 62 and an R
It does not have to include AM63, but it is ROM by bus etc.
Also, it may be connected to the RAM.

Next, the control program executed by the CPU 61 will be described with reference to FIG.

Firstly, the power-on or wavelength switching is performed ( "YES" at S101), CPU 61 outputs the first set value Vref ₁ to the digital-analog converter circuit 57 (S103). At this time, the first set value Vref ₁ output to the digital-analog conversion circuit 57 is converted into a current signal and sent to the automatic temperature control circuit 55, and the automatic temperature control circuit 55 receives the output signal from the thermistor 39 as the first signal. Feedback control is performed so as to match the set value Vref ₁ . As a result, the CPU 61 and the automatic temperature control circuit 55
Will constitute the temperature control means.

Then, the CPU 61 reads the output signal from the thermistor 39 through the analog-digital conversion circuit 58 (S105), compares it with the first set value Vref ₁ and outputs the output signal from the thermistor 39 and the first set value Vref.
It is determined whether the difference from ₁ is within a predetermined range (S10).
7). The output signal from the thermistor 39 and the first set value Vr
If the difference from ef ₁ is within the predetermined range (“YES” in S107), the CPU 61 determines that the wavelength of the light output from the semiconductor light emitting element 31 is stable, and determines the wavelength dependence of the etalon 34. The second set value Vref ₂ is calculated so as to compensate the temperature characteristic in the characteristic (S109). As a result, the CPU 61 functions as a predetermined value correction means, and the second set value Vref ₂ corresponds to the second predetermined value.

Second set value Vref _{2 in} CPU 61
Can be calculated as follows.

The ROM 62 has a correction table 62a in which a correction value for compensating the temperature characteristic in the wavelength dependence of the etalon 34 is stored in correspondence with the output signal from the thermistor 39, and the CPU 61 has a correction table. 6
2a, the correction value corresponding to the output signal from the thermistor 39 is read, and the correction value is set to the second set value Vre.
Set to f ₂ . The correction table 62a, for example, as shown in FIG. 4, is configured to store correction values corresponding to the values of the output signal from the thermistor 39. Here, the ROM 62 functions as a storage unit.

The CPU 61 limits the area to be corrected,
By considering that the characteristic in the region is linear, the calculation based on the correction calculation formula represented by the following formula (1) is performed, and the wavelength dependence of the etalon 34 is determined based on the output signal from the thermistor 39. A correction value for compensating for the temperature characteristic at is obtained, and the correction value is set to the second set value Vref ₂ . V = α (S−S ₀ ) + V ₀ (1) where V: correction value α: temperature coefficient of etalon 34 S: output signal from thermistor 39 S ₀ : output from thermistor 39 during wavelength adjustment Signal V ₀ : second set value Vref ₂ at the time of wavelength adjustment

When the second set value Vref ₂ is calculated, CP
U61 reads the output signal of the current-voltage conversion circuit 54, that is, the output signal of the photodetector 33b through the analog-digital conversion circuit 58 (S111). And CPU6
1, the output value is determined by calculating the difference between the second set value Vref ₂ and the output signal of the current-voltage conversion circuit 54 (the output signal of the photodetector 33b) (S113), and the determined output value is digital-analog. The data is output to the conversion circuit 57 (S115). Thereby, the CPU 61 functions as a predetermined value determining means, and the output value corresponds to the first predetermined value. The output value output to the digital-analog conversion circuit 57 is converted into a current signal and sent to the automatic temperature control circuit 55, and the automatic temperature control circuit 55 performs feedback control so that the output signal from the thermistor 39 matches the output value. To do.

On the other hand, when the difference between the output signal from the thermistor 39 and the first set value Vref ₁ is not within the predetermined range (S
When “NO” in 107), the CPU 61 determines that the wavelength of the light output from the semiconductor light emitting element 31 is unstable, and returns to S105. As a result, the automatic temperature control circuit 5
In 5, the feedback control based on the first set value Vref ₁ is continued.

Next, the operation of the light emitting module 1 will be described with reference to FIG.

In FIG. 5, C (t) is composed of an electric circuit including a gain (thermoelectron cooler drive circuit 52 and the like) and the thermoelectron cooler 21, and converts an input signal into heat ΔT. F
(T) is a thermistor 39 near the semiconductor light emitting element 31.
And detects the sum of the environmental temperature Ta and the heat ΔT and outputs it as a temperature monitor voltage. m is environmental temperature Ta and heat ΔT
It means that the temperature of the semiconductor light emitting device 31 is determined by and the arbitrary wavelength λ is output. Finally, G (T) is composed of an etalon 34 having a wavelength dependence, a photodetector 33b, and a current-voltage conversion circuit 54 for converting the current of the photodetector 33b into a voltage, and a wavelength monitor corresponding to the wavelength λ. The voltage is output.

When the power is turned on, the CPU 6 waits until the wavelength of the light output from the semiconductor light emitting device 31 is close to the target wavelength.
The switching means SW composed of 1 has a first set value Vref ₁
Is selected and the temperature monitor voltage (F
The output of (T)) so becomes the first set value Vref ₁ 1
It is controlled by a heavy feedback circuit.

Further, when the wavelength of the light output from the semiconductor light emitting element 31 is near the target wavelength, the switching means SW is switched, and the wavelength monitor voltage (output of G (T)) corresponding to the target wavelength is set to the second setting. It is controlled by a double feedback circuit so that the value becomes Vref ₂ . However, in this case, since the wavelength dependency of the etalon 34 has temperature characteristics, the wavelength monitor voltage also has temperature characteristics, and as a result, the wavelength shifts. Therefore, the CPU 61 corrects the value of the second set value Vref ₂ so as to compensate the temperature characteristic of the etalon 34 based on the temperature information obtained by the thermistor 39. Accordingly, even if the set temperature of the semiconductor light emitting element 31 is largely changed when the supply current to the semiconductor light emitting element 31 is increased in order to obtain a constant light output due to the deterioration of the semiconductor light emitting element 31, the wavelength with high accuracy is obtained. It becomes possible to control.

From the above, in the light emitting module 1 according to this embodiment, the CPU 61 and the automatic temperature control circuit 55.
The thermoelectric cooler 2 so that the output of the thermistor 39 matches the output value based on the output of the thermistor 39.
When 1 is controlled, the second set value Vref ₂ for determining the output value is corrected by the CPU 61 based on the output of the thermistor 39 so as to compensate the temperature characteristic in the wavelength dependence of the etalon 34. This makes etalon 3
Even when the temperature of 4 changes, the fluctuation of the lock wavelength is suppressed. Therefore, highly accurate wavelength control can be performed.

Also, the CPU 61 stores the correction value in R
The correction value corresponding to the output of the thermistor 39 is read from the ROM 62 including the OM 62 (correction table 62a), and the correction value is set to the second set value Vref ₂ . In such a configuration, the ROM 62 can be easily set by reading the correction value from the ROM 62, and a CPU having a slow processing capacity can be used as the CPU 61.

Further, the CPU 61 calculates a correction value based on the output of the thermistor 39 and sets the correction value to the second set value Vref ₂ . With this configuration, the second set value Vref ₂ can be easily set even when the CPU 61 has a system configuration with a small storage capacity.

[0042]

As described above in detail, according to the present invention, the driving current increases due to the deterioration of the semiconductor light emitting element and the set temperature is different, but the lock wavelength shift due to the temperature change of the optical element is suppressed. As a result, it is possible to provide a light emitting module that can perform wavelength control with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a light emitting module according to the present embodiment.

FIG. 2 is a block diagram showing a light emitting module according to the present embodiment.

FIG. 3 is a diagram showing a C included in the light emitting module according to the present embodiment.
6 is a flowchart for explaining a control program executed by PU.

FIG. 4 is a diagram showing a configuration of a correction table.

FIG. 5 is a functional block diagram for explaining a light emitting module according to the present embodiment.

6A and 6B are schematic diagrams showing the relationship between the wavelength of light from a semiconductor light emitting element and the output current of a photodetector.

[Explanation of symbols]

1 ... Light emitting module, 10 ... Main part of light emitting module, 1
2 ... Optical fiber, 21 ... Thermoelectron cooler, 31 ... Semiconductor light emitting element, 33a, 33b ... Photodetector, 34 ... Etalon,
39 ... Thermistor, 42 ... Semiconductor light emitting element drive circuit, 5
2 ... Thermoelectric cooler drive circuit, 55 ... Automatic temperature control circuit,
56 ... Automatic output control circuit, 62a ... Correction table.

Claims (3)

[Claims] 1. A semiconductor light emitting element, an optical element having wavelength dependence, which transmits light from the semiconductor light emitting element, and a wavelength of light of the semiconductor light emitting element which receives light transmitted through the optical element. A photodetector for monitoring, a temperature detector for detecting the temperature of the optical element, a temperature adjusting means arranged to adjust the temperature of the semiconductor light emitting element and the optical element, and the temperature detector Based on the output of the photodetector and the second predetermined value, the temperature control means for controlling the temperature adjusting means to match the output of the temperature detector with the first predetermined value. The first
Predetermined value determining means for determining a predetermined value, and a predetermined value correction for correcting the second predetermined value so as to compensate the temperature characteristic in the wavelength dependence of the optical element based on the output of the temperature detector. A light emitting module comprising: 2. The predetermined value correction means includes a storage means for storing the correction value, and reads out the correction value corresponding to the output of the temperature detector from the storage means and sets the correction value as the second predetermined value. The light emitting module according to claim 1, wherein 3. The predetermined value correcting means calculates a correction value based on the output of the temperature detector, and sets the correction value to the second predetermined value. Light emitting module.