JP2002335042A - Method of expanding wavelength locked optical output range of laser diode module with external resonator and laser diode module for executing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of expanding the wavelength-locked optical output range of a laser diode module with an external resonator. SOLUTION: The temperature of a laser diode is controlled, based on the magnitude of optical output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for extending the optical output range of the wavelength lock of a laser diode module with an external resonator, and a laser diode module capable of implementing the method.

[0002]

2. Description of the Related Art An EDFA pump module is an EDF.
To fix the gain of A, the light output and wavelength of the pump light module must be stabilized. Therefore, the laser diode drive is stabilized while monitoring the optical output by incorporating a photodiode, and the wavelength deviation is stabilized to 0.5 nm or less using an external resonator such as a fiber grating (hereinafter referred to as FBG). This method is mainly employed. However, in order for the laser diode to follow the FBG wavelength of the external resonator (to lock the wavelength), it is required that the difference between the oscillation wavelength specific to the laser diode and the FBG wavelength is close to some extent, depending on the reflectance of the FBG. . This wavelength difference is, for example, an FBG reflectance of 3%.
In this case, the oscillation wavelength is about ± 3 nm, which is a condition in which the oscillation wavelength specific to the laser diode is locked in the range of 3 nm from the FBG wavelength. This is called a wavelength lock range. The wavelength lock range becomes narrower as the FBG reflectance becomes smaller.

On the other hand, the oscillation wavelength inherent in a laser diode becomes longer as the light output becomes larger. Although it depends on the type of laser diode and the usage environment, it is generally 0.03 to 0.0
The oscillation wavelength changes at 4 nm / mW. Therefore, when it is desired to use a laser diode while changing the optical output in a wide range, the oscillation wavelength specific to the laser diode changes according to the change in the optical output, and the wavelength is not locked. However, there is a problem that the amount of fluctuation of the data becomes large.

[0004] On the other hand, in recent years, it has become increasingly necessary for laser diode modules to have stable wavelengths from low output to high output. For example, F
It is assumed that the ratio of the light emission of the laser diode including the BG reflectance to the fiber out is 70%. Assuming that the width of the wavelength lock range is 6 nm, the wavelength lock range at the optical output of the laser diode is in the range of 200 mW, and the fiber out width is in the range of 140 mW. With this, 10mW to 200mW, which is expected to be the next-generation main product
Can not make a wavelength locked module.

Therefore, it is conceivable to increase the FBG reflectance to widen the wavelength lock range. However, in the future 35
Considering a module down to 0 mW, it is difficult to make a module that locks the wavelength in the entire region. For this reason, it is required to provide a laser diode module whose wavelength is stable over a wide range from low output to high output.

[0006]

SUMMARY OF THE INVENTION In view of these problems of the prior art, an object of the present invention is to provide a method for widening the optical output range of the wavelength lock of a laser diode module with an external resonator. did. That is, an object of the present invention is to provide a method capable of locking the wavelength up to an optical output range in which the conventional method does not lock the wavelength. Another object of the present invention is to provide a laser diode module suitable for performing this method.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that if the property that the oscillation wavelength of a laser diode becomes shorter as the temperature rises is used, the optical output range of the wavelength lock of the laser diode module can be improved. The present invention was thought to be able to be broadened, and the present invention was provided.

That is, the present invention is a method for expanding the wavelength locked optical output range of a laser diode module with an external resonator, wherein the temperature of the laser diode is controlled based on the magnitude of the optical output. Provide a way.

In a preferred embodiment of the method of the present invention, the temperature of the laser diode is controlled to be low when the light output is increased, and the temperature of the laser diode is controlled to be high when the light output is reduced; Examples include a mode in which the temperature of the laser diode is controlled at a fixed rate with respect to the amount of output fluctuation; a mode in which an FBG is used as an external resonator; and a mode in which temperature control is performed using a Peltier.

The present invention also provides a laser diode module comprising a laser diode temperature control means for performing the above method. It is preferable that the laser diode module of the present invention includes means for measuring the light output, and means for controlling the temperature of the laser diode based on the light output measured by the means.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention for widening the wavelength lock optical output range of a laser diode module with an external resonator and its application will be described in detail below. In this specification, “to” means a range including the numerical values described before and after it as a minimum value and a maximum value, respectively.

The method according to the invention is characterized in that the temperature of the laser diode is controlled. The temperature of the laser diode as referred to in this specification means a temperature felt by the laser diode. That is, it means not the temperature outside the module but the temperature felt by the laser diode inside the module.

The oscillation wavelength of a laser diode becomes shorter as the temperature rises. Further, the oscillation wavelength of the laser diode becomes longer as the optical output is increased. With these trends in mind,
In the present invention, it is preferable to control so as to lower the temperature of the laser diode when increasing the optical output, and to increase the temperature of the laser diode when decreasing the optical output.

The relationship between the light output and the temperature to be controlled is not particularly limited as long as the object of the present invention can be achieved. Therefore, the temperature may be controlled at a fixed rate according to the amount of change in the optical output, or the temperature may be controlled stepwise. Further, a constant temperature control may be performed when a specific light output is reached. For example, only when the light output exceeds a specific value, the temperature of the laser diode may be controlled to be intentionally lowered. These control methods may be used in appropriate combination. For example, the temperature control method may be changed depending on the range of the light output.

From the viewpoint of easy temperature control, it is preferable to adopt a method of controlling the temperature at a constant rate in accordance with the fluctuation amount of the light output. The upper and lower limits of the ratio are not particularly limited. For example, -0.03
The temperature of the laser diode can be controlled at a rate of ° C / mW to -0.2 ° C / mW.

The laser diode module according to the present invention comprises:
It has at least a laser diode, an external resonator and temperature control means for the laser diode operative to carry out the method of the invention. The laser diode and the external resonator used in the present invention can be appropriately combined and selected from those that can constitute a normal laser diode module. For example, FBG can be preferably used as the external resonator. However, the laser diode and the external resonator used in the present invention need to be wavelength-locked at a certain temperature in at least a part of the light output range required for the module of the present invention. The optical output range of the wavelength lock preferably includes the median of the optical output range required for the module. For example, when it is desired to create a module whose wavelength is locked in the range of 10 mW to 280 mW according to the present invention, it is preferable to previously select a system whose wavelength is locked in a range including 145 mW which is the central value of the optical output range. .
However, the present invention can be applied to a system in which the wavelength is locked in a range that does not include such a median.

The details of the laser diode temperature control means operating to carry out the method of the present invention are not particularly limited as long as they can control the temperature of the laser diode in accordance with the light output. Therefore, the temperature control means of the present invention can be used by appropriately combining the temperature control means usually used for the package containing the laser diode. For example, a Peltier or thermistor can be used. Normally, it is necessary to raise and lower the temperature of the laser diode in accordance with the level of light output, and therefore it is required to provide both a heating unit and a cooling unit. However, depending on the mode of use, it may be sufficient to provide only the cooling means.

The laser diode module according to the present invention comprises:
Preferably, the apparatus further comprises means for measuring the light output, and controls the temperature of the laser diode based on the light output measured by the means. The method for measuring the light output is not particularly limited. For example, the light output of the laser diode can be measured by a semiconductor light receiving element that receives a laser beam emitted from the rear end face of the laser diode as detection light. A photodiode or the like is used as such a semiconductor light receiving element. Alternatively, the output (optical output of the module) of the output end of the optical fiber that receives the laser beam emitted from the front end face of the laser diode may be measured. In some cases, both may be used in combination for the temperature control of the present invention.

The result of measuring the light output of the laser diode by these means is used for controlling the temperature of the laser diode according to the present invention. Specifically, the heating circuit of the constant voltage source always supplies a constant amount of heat to the inside of the package containing the laser diode, for example, by functioning a means for lowering the temperature inside the package according to the amount of light detected by the semiconductor light receiving element. The temperature of the laser diode can be controlled. The combination of the laser diode light output measuring means and the laser diode temperature control means can be appropriately determined according to the purpose of use of the laser diode, the use environment, and the like.

The method of controlling the temperature according to the light output is preferably determined as appropriate in consideration of the minimum output and the maximum output required of the module, the operating environment of the module, the means for adjusting the temperature of the laser diode, and the like. For example, the minimum output required for the module is 10 mW, and the maximum output is 28 mW.
If it is 0 mW, temperature control is performed to lock the wavelength within the range of 10 mW to 280 mW. When controlling the temperature of the laser diode at a constant rate with respect to the variation of the optical output, the test is performed by changing the rate variously,
The ratio of wavelength locking within the range of mW to 280 mW is found.

The ratio of wavelength locking within the range of 10 mW to 280 mW has a range, but among them, 10 mW
It is most desirable to select a wavelength variation within the range of 範 囲 280 mW. However, the absolute value of the ratio at which the wavelength variation is minimized is relatively large, and the required temperature control is wide. There is no problem if the function of the Peltier that constitutes the module is extremely advanced and can effectively exert the function over a wide temperature range. If temperature control is performed at this ratio, a heavy load is imposed on Peltier, and efficiency and ease of temperature control may be sacrificed in some cases.

Therefore, when practicing the present invention using a Peltier having a low capacity, it may be preferable to perform the temperature control at a rate whose absolute value is smaller than the rate at which the wavelength variation is minimized. By choosing these percentages,
The efficiency and easiness of the temperature control can be increased, the load on the Peltier can be reduced, and the original function of the Peltier, that is, the influence of the external temperature change can be cut off, can be sufficiently exhibited. Further, it is possible to reduce the cost because a relatively low-capacity Peltier having relatively low capacity can be employed.

If the absolute value of the temperature control ratio is reduced, the wavelength fluctuation range of the module light within the wavelength lock range becomes large. For this reason, it is necessary to determine the temperature control ratio in consideration of the allowable range of the wavelength variation width. The specific method of determining the rate of temperature control can be understood from the examples and the like in this specification.

[0024]

The features of the present invention will be described more specifically with reference to the following examples. Components, ratios, processing contents, processing procedures, and the like shown in the following embodiments can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples described below.

The test was performed using a module equipped with a laser diode, FBG and Peltier. The oscillation wavelength of the laser diode and the wavelength of the FBG are both 980 nm. Temperature of the laser diode of the module (T:
Tests 1 to 4 were performed under the following four conditions in accordance with the optical output (P: unit mW) of the module.

[0026]

(Equation 1)

The optical output (P) of the module is changed from 0 mW to 2
The center wavelength of light from the module was measured while varying between 80 mW. The results are shown in FIG. Also, controlled temperature range, wavelength locked light output range, and 0-280 m
Table 1 summarizes the fluctuation of the center wavelength in W.

[0028]

[Table 1]

In Test 1, the laser diode was maintained at a constant temperature according to the conventional method. in this way,
Since the practical use range of the module is 60 mW to 200 mW, the optical communication system is less than 60 mW (for example, 1 mW).
When control of 0 mW to 60 mW is required, it is necessary to separately prepare a dedicated laser diode module. Therefore, the method of Test 1 is uneconomical and not preferable.

On the other hand, in Test 2 in which the temperature was controlled,
Wavelength locked over the entire 280 mW output range,
Moreover, there was no change in the center wavelength. In Test 3,
The wavelength was locked in the entire output range of 0 to 280 mW, and the change width of the center wavelength was 0.2 nm, which was negligible. However, in Test 4, the wavelength lock range was 60 m.
W to 220 mW, which was not much different from Test 1. Therefore, if the temperature control in Test 2 or Test 3 is performed on the module used here, the optical output range of the wavelength lock can be widened, and a wide range of control such as 10 mW to 200 mW is required. In such a case, it is possible to cope with one module.

In Test 2 and Test 3, the load on Peltier is smaller because Test 3 has a narrower temperature range to control.
For this reason, it is possible to construct a module in which the original function of the Peltier is more effectively exerted, and there is less variation with respect to an external temperature change. Those skilled in the art can determine the temperature range to be controlled based on the results in Table 1 after determining the performance of the Peltier to be used, and can determine a more practical temperature control method.

[0032]

According to the present invention, the optical output range of the wavelength lock of the laser diode module with an external resonator can be easily widened. Therefore, it is possible to lock the wavelength up to the optical output range where the wavelength lock does not occur in the conventional method. Therefore, the method of the present invention can be widely applied in a situation where the wavelength is required to be stable from low output to high output.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a light output of a module and a center wavelength of light from the module.

Claims (7)

[Claims] 1. A method for widening an optical output range of a wavelength lock of a laser diode module with an external resonator, wherein the temperature of the laser diode is controlled based on the magnitude of the optical output. 2. The method according to claim 1, wherein the temperature of the laser diode is controlled to decrease when increasing the light output, and the temperature of the laser diode is controlled to increase when decreasing the light output. A method for widening the optical output range of the wavelength lock described. 3. The method according to claim 2, wherein the temperature of the laser diode is controlled at a constant rate with respect to the fluctuation amount of the light output. 4. A fiber grating is used as said external resonator.
A method for widening the optical output range of the wavelength lock according to any one of the above. 5. The method according to claim 1, wherein the temperature control is performed using a Peltier. 6. A laser diode module with an external resonator, comprising a temperature control means of a laser diode for performing the method according to claim 1. 7. The laser with an external resonator according to claim 6, further comprising: means for measuring an optical output, and means for controlling a temperature of the laser diode based on the optical output measured by the means. Diode module.