JPH0964447A - Variable wavelength light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a variable wavelength light source which enhances the degree of freedom of a range in which the oscillation wavelength of an LD element is made variable irrespective of an ambient temperature by a method wherein the electrifying amount of a second thermionic cooling element is controlled in such a way that the temperature of a case becomes a desired set value. SOLUTION: A second thermionic cooling element 7 which is used to cool and heat a case 1a is attached to the outside of an LD module 1, and a second temperature sensor 8 is attached to the thermionic cooling element 7 in order to measure the temperature of the thermionic cooling element 7. In addition, a second automatic temperature control circuit 9 is used to control the second thermionic cooling element 7 in such a way that the temperature of the LD module 1 becomes a prescribed temperature on the basis of the detection output of the second temperature sensor 8. Then, the detection output of the second temperature sensor 8 is compared with a reference value obtained by a setter 9a which sets the temperature of the second thermionic coiling element 7, and the cooling and heating action of the second thermionic cooling element 7 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable light source in which the temperature of a laser diode element is changed to change the laser light oscillation wavelength of the laser diode element.

[0002]

2. Description of the Related Art There is a wavelength tunable light source adapted to change the wavelength of laser light oscillated by a semiconductor laser element (laser diode element, hereinafter referred to as LD element) by changing the element temperature. .

A conventional device of this type is constructed as shown in FIG. That is, in the figure, 1 is an LD (laser diode) module, and this LD module 1 includes an LD element 2 serving as a laser light source, and a monitor PD (photodiode) 3 for monitoring the output laser light of this LD element 2. , LD to change the temperature of the LD element 2
Thermionic cooling element 4 for cooling / heating the module 1
And a temperature sensor 5 for detecting the temperature inside the LD module 1 are housed in a hermetically sealed case 1a.

Here, the thermoelectric cooling element 4 is an element having a function of exhibiting a cooling / heating action by energization, and is, for example, a Peltier element or the like. Further, in FIG. 3, reference numeral 6 denotes an automatic temperature control circuit, which controls the energization of the thermoelectric cooling element 4 so that the temperature inside the LD module 1 becomes a required temperature based on the detection output of the temperature sensor 5. The temperature of the element 2 is adjusted to control the wavelength of the oscillated laser light to be a desired wavelength.

The automatic temperature control circuit 6 has a setting device capable of setting the oscillation wavelength of the output laser light. When a desired wavelength is set by this setting device, a temperature reference value corresponding to the setting is obtained. By comparing the detection output of the temperature sensor 5 with the reference value, the thermoelectric cooling element 4 is supplied with an energization amount such that the current temperature inside the LD module 1 becomes a required temperature, It has a function of controlling the temperature in the LD module 1 to a temperature at which a target wavelength is obtained by the cooling / heating effect.

Since the LD element has a characteristic that the oscillation wavelength thereof, that is, the wavelength of the oscillation laser light increases in proportion to the temperature of the LD element, the LD having the configuration shown in FIG.
The oscillation wavelength can be changed by changing the temperature of the element.

That is, in order to change the oscillation wavelength of the LD, the temperature of the LD element 2 is detected by the temperature sensor 5, and the detected temperature is compared with the set value corresponding to the target wavelength.
The automatic temperature control circuit 6 drives the thermoelectric cooling element 4 so as to reach the target temperature. As a result, the temperature of the LD element 2 is controlled so as to obtain a desired wavelength.

[0008]

Since the LD element has a characteristic that the oscillation wavelength thereof, that is, the wavelength of the oscillated laser light increases in proportion to the temperature of the LD element, the LD having the cooling device built in as shown in FIG. As a module, the oscillation wavelength can be changed by changing the temperature of the LD element in the module.

In this conventional device, in order to change the oscillation wavelength of the LD, the temperature of the LD element 2 is detected by the temperature sensor 5, and the detected temperature is compared with the set value corresponding to the target wavelength to automatically control the temperature. The circuit 6 drives the thermoelectric cooling element 4 to reach the target temperature.

However, the above-mentioned conventional device is an LD
The element and the thermoelectric cooling element are hermetically sealed in the same package to form a module, and are therefore easily affected by the temperature of the external atmosphere. Therefore, when the ambient temperature is high, the LD element cannot be sufficiently cooled, and the LD element temperature can be used only in the limited variable region of the higher temperature. Further, when the ambient temperature is low, the LD element easily cools, The element temperature can be used only in the lower variable region.

As described above, since the conventional device has a structure that is easily affected by the outside air temperature, a sufficient temperature difference cannot be obtained between the temperature of the LD element and the ambient temperature, and the variable range of the oscillation wavelength of the LD element and There is a problem that the usable ambient temperature is limited.

Therefore, the object of the present invention is to
The temperature of the LD element can be varied in a wide range regardless of the ambient temperature, the degree of freedom of the variable range of the oscillation wavelength of the LD element can be improved, and the usable ambient temperature is not limited. It is to provide such a wavelength tunable light source.

[0013]

In order to achieve the above object, the present invention is configured as follows. That is, by changing the temperature of the semiconductor laser element, in the wavelength tunable light source capable of changing the wavelength of the oscillation laser light,
The temperature of the semiconductor laser element and the case for accommodating the semiconductor laser element, the first thermoelectric cooling element for controlling the temperature of the semiconductor laser element, which has a cooling / heating action according to the energization amount, A first temperature control means for controlling the energization amount of the first thermoelectric cooling element so as to obtain a desired set value, and a cooling / heating action according to the energization amount for controlling the temperature of the case. The thermoelectric cooling element No. 2 and the second temperature control means for controlling the energization amount of the second thermoelectric cooling element so that the temperature of the case becomes a desired set value.

The second temperature control means may be added with a function of controlling the minimum temperature of the case to be equal to or higher than the dew point in the humidity condition of the external atmosphere.
In the present device having such a configuration, the temperature of the semiconductor laser element housed in the case is controlled by the first thermoelectric cooling element to change the semiconductor laser element temperature and change the wavelength of the oscillated laser light. However, the temperature of the case housing the semiconductor laser device can be controlled to a desired value by the second thermoelectric cooling device and the second automatic temperature control means.

As described above, in the present apparatus, the entire case constituting the LD module can be controlled to the desired set temperature by the second thermoelectric cooling element, and the LD element (semiconductor laser element) temperature is further inside the case. Since the temperature is controlled to the desired temperature by the provided first thermoelectric cooling element, the temperature difference between the LD element temperature and the ambient temperature can be made sufficiently large, and a wide temperature variable range can be secured, which is sufficient. A wide wavelength range and usable temperature range can be obtained. In addition, since the temperature of the case that constitutes the LD module is controlled to be equal to or higher than the dew point under the ambient temperature conditions in which it is used, there is no fear of degrading the second thermoelectric cooling element and sufficient wavelength tunability. You can get a range.

Therefore, according to the present invention, the temperature of the LD element can be varied over a wide range regardless of the ambient temperature, the degree of freedom of the variable range of the oscillation wavelength of the LD element can be improved, and the LD element can be used. It is possible to provide a wavelength tunable light source that is not restricted by possible ambient temperature.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (Device Configuration) FIG. 1 is a block diagram showing an example of the configuration of the present invention. In FIG. 1, reference numeral 1 is an LD (laser diode) module. The LD module 1 includes an LD (laser diode) element 2 that serves as a laser light source, a monitor PD (photodiode) 3 that monitors the output laser light of the LD element 2, and a temperature that the LD element 2 can change. A thermoelectric cooling element 4 for cooling and heating the LD element 2 and a temperature sensor 5 for detecting the temperature inside the LD element 2 are housed in a hermetically sealed case 1a.

The thermionic cooling element 4 is an element which exhibits a cooling / heating action when energized, and may be the same as a conventional one. Further, 6 is an automatic temperature control circuit, which energizes the thermoelectric cooling element 4 so that the temperature inside the LD element 2 (the temperature inside the case 1a) becomes a required temperature based on the detection output of the temperature sensor 5. However, the wavelength of the oscillated laser light is controlled to be a desired wavelength.

The automatic temperature control circuit 6 has a setting device 6a capable of setting the oscillation wavelength of the output laser light. When a desired wavelength is set by this setting device 6a, a temperature reference value corresponding to it is set. Then, by comparing the detection output of the temperature sensor 5 with the reference value, the energization amount that brings the temperature of the LD element 2 to the required temperature can be obtained.
And has a function of controlling the temperature of the LD element 2 to a temperature at which a target wavelength is obtained by the cooling effect of the thermoelectric cooling element 4.

In the present apparatus, the second thermoelectric cooling element 7 that is large enough to cool and heat the case 1a is provided outside the LD module 1, that is, outside the case 1a.
Is attached to the second thermoelectric cooling element 7
A second temperature sensor 8 is attached to the thermoelectric cooling element 7 in order to measure the temperature. Further, 9 is a second automatic temperature control circuit, which is a circuit for controlling cooling / heating of the second thermoelectric cooling element 7.

The second automatic temperature control circuit 9 controls the energization of the second thermoelectric cooling element 7 so that the temperature of the LD module 1 becomes a required temperature based on the detection output of the second temperature sensor 8. It is for doing.

The second automatic temperature control circuit 9 has a setting device 9a for setting the temperature of the second thermoelectric cooling element 7. When the desired temperature setting is made by the setting device 9a. By obtaining a temperature reference value corresponding thereto and comparing the detection output of the second temperature sensor 8 with this reference value, the temperature of the second thermoelectric cooling element 7 becomes the set temperature by the setter 7a. Such a power supply amount is applied to the second thermoelectric cooling element 7 to control the cooling / heating action of the thermoelectric cooling element 7.

The second thermoelectric cooling element 7 is composed of the same element as the first thermoelectric cooling element 4, for example, a Peltier element or the like. (Operation of the present device) In the present device having such a configuration, the desired wavelength of the laser beam to be oscillated is set by the setting device 6a of the first automatic temperature control circuit 6 as in the conventional case. Then, a drive input is supplied to the LD element 2 to oscillate laser light. The output of the LD element 2 is detected and monitored by the monitor PD element 3.

On the other hand, the temperature of the LD element 2 is detected by the first temperature sensor 5, and the detection output is supplied to the first automatic temperature control circuit 6. The first automatic temperature control circuit 6 is provided with a reference value corresponding to the set value of the setter 6a. Therefore, the first automatic temperature control circuit 6 detects the first temperature sensor 5 with respect to this reference value. A control output corresponding to the output difference is generated to control the energization amount of the first thermoelectric cooling element 4. As a result, the first thermoelectric cooling element 4 cools
When the heating operation is performed, the temperature of the LD element 2 is cooled / heated to a temperature at which the wavelength is set by the setting device 6a.

In this way, the first temperature sensor 5 causes L
The temperature of the D element 2 is detected, and the temperature detected by driving the first thermoelectric cooling element 4 via the first automatic temperature control circuit 6 becomes the temperature corresponding to the oscillation wavelength to be set. Then, the temperature of the LD element 2 is controlled.

Since the oscillation wavelength of the LD element 2 changes in proportion to the temperature, the oscillation wavelength of the LD element 2 can be changed by changing the set temperature of the first automatic temperature control circuit 6. By the first automatic temperature control circuit 6,
The temperature of the LD element 2 is controlled to a temperature at which a desired wavelength is obtained, and laser light having a target wavelength is oscillated.

If the case temperature of the LD module 1 is set by the setter 9a, the temperature of the case of the LD module 1 can be controlled. That is, the second temperature sensor 8
Detects the temperature of the case of the LD module 1 and supplies the detected output to the second automatic temperature control circuit 9. Since the second automatic temperature control circuit 9 is provided with the reference value corresponding to the set value of the setter 9a, the second automatic temperature control circuit 9 detects the second temperature sensor 8 with respect to this reference value. A control output corresponding to the output difference is generated to control the energization amount of the second thermoelectric cooling element 7. As a result, the second thermoelectric cooling element 7 performs a cooling / heating operation corresponding to the energization amount thereof to cool / heat the case of the LD module 1 and maintain it at the set temperature.

According to this structure, the temperature difference between the LD element temperature and the ambient temperature can be reached by the first thermoelectric cooling element 4 and that by the second thermoelectric cooling element 7. Therefore, in the present invention, the range can be widened by the temperature difference that can be reached by the second thermoelectric cooling element 7, as compared with the conventional variable temperature difference.

Further, if the temperature of the case 1a of the LD module 1 is controlled to be constant, the stability of the LD element temperature can be improved. Therefore, it becomes possible to expand the tunable wavelength range or usable ambient temperature range to provide a wavelength tunable light source with a high degree of freedom.

For example, if the cooling capacities of the first thermionic cooling element 4 and the second thermionic cooling element 7 are both 30 degrees Celsius, the wavelength tunable light source having the structure described in the conventional example has an ambient temperature. When the temperature is 60 degrees Celsius, the LD element temperature is 3 degrees Celsius.
Although it could be cooled only to 0 degrees, according to the configuration example of the present invention described above, it becomes possible to cool to 0 degrees.

In the present invention, in addition to cooling the inside of the LD element 2, the case itself of the LD module 1 is also cooled, so that the influence of the outside temperature on the case 1a is suppressed. This is because you can do it. As a result, the variable wavelength range can be doubled.

Further, when it is desired to set the LD element temperature to 0 degrees Celsius, in the conventional method, this light source can be used only when the ambient temperature is 30 degrees Celsius, but according to the present invention,
The range of use and temperature can be expanded up to 60 degrees Celsius. Therefore, a sufficient wavelength tunable range can be obtained even when this tunable light source is installed in a high-temperature device, and a sufficient tunable range is always ensured even when used in summer or high temperature areas. You can do it.

FIG. 2 is a graph showing the relationship between ambient temperature and saturated vapor pressure. In the wavelength tunable light source having the structure described in the example of FIG. 1, the case of the LD module 1 by the second thermoelectric cooling element 7 is used. When controlling 1a to a constant temperature, the second
FIG. 7 is a diagram for obtaining a set temperature that does not deteriorate the characteristics of the thermoelectric cooling element 7.

In FIG. 2, the horizontal axis represents the ambient temperature and the vertical axis represents the saturated vapor pressure at that temperature. A shaded area EXA in the drawing is an example of an environment of ambient temperature and humidity in which the present wavelength tunable light source is used. A in the figure indicates a saturated vapor pressure curve, and Ts indicates the maximum temperature of the dew point under this environment.

In the case 1a of the LD module 1 and the second
When the temperature of the cooling surface of the thermionic cooling element 7 becomes a temperature below the dew point Ts, dew condensation occurs, and if the second thermionic cooling element 7 is not hermetically sealed, the second thermionic cooling element The cooling element 7 will deteriorate due to dew condensation.

Therefore, in such a case, for example, the area E
If the second thermoelectric cooling element 7 is controlled so as to be in a temperature range equal to or higher than the dew point Ts like XA, the case temperature of the LD module 1 is controlled to be constant without causing deterioration of the thermoelectric cooling element due to dew condensation. It becomes possible.

On the other hand, if the control temperature by the second thermoelectric cooling element 7 is shifted to the higher side, the case temperature of the LD module 1 will rise and it will be accommodated in the case 1a of the LD module 1. The cooling range of the first thermoelectric cooling element 4 is narrowed, and the variable wavelength range of the LD element 2 is narrowed.

Therefore, by controlling the minimum value of the cooling temperature of the second thermoelectric cooling element 7 to be a temperature higher than the dew point Ts by the control deviation of the second automatic temperature control circuit 9, It is possible to provide a wavelength tunable light source that can ensure a sufficient wavelength tunable range without causing deterioration of the second thermoelectric cooling element 7 due to dew condensation.

As described above, this apparatus accommodates the first thermoelectric cooling element and the semiconductor laser element in the sealed case, and controls the energization of the first thermoelectric cooling element to keep the semiconductor laser element in the case. In the wavelength tunable light source capable of varying the wavelength of the oscillation laser light of the semiconductor laser element by cooling and controlling the temperature of the semiconductor laser element, the second heat for cooling and heating the case The thermoelectric cooling element and a control circuit for controlling the second thermoelectric cooling element are provided, and the second thermoelectric cooling element can cool and heat the case. At the same time, the inside of the case can be cooled and heated by the first thermionic cooling element to suppress the influence of the temperature of the external atmosphere on the semiconductor laser element (LD element), The temperature of the internal semiconductor laser element can be easily lowered and raised, and the variable range of the temperature can be widened. As a result, the variable wavelength range of the laser light can be achieved regardless of the external environment. Will be able to widen.

As described above, not only can the oscillation wavelength variable range of the LD element and the usable ambient temperature be expanded, but also a sufficient wavelength variable range can be secured while maintaining reliability. There are advantages.

The present invention is not limited to the examples described above and shown in the drawings, but can be appropriately modified and carried out within the scope not changing the gist of the present invention. Although the temperature sensor is attached to the second thermoelectric cooling element, the temperature sensor may be attached to the outer surface of the LD module to detect the temperature.

Further, although the second thermoelectric cooling element is constructed so as to be in direct contact with the external atmosphere in the above-mentioned example, it is also possible to adopt a hermetically sealed construction, in which case there is a risk of dew condensation. Therefore, it is not necessary to consider the dew point, and it can be used under a wider temperature condition. Further, since the monitor PD detects the light amount, it is sufficient that the monitor PD has a function of detecting the light amount, so that another light receiving element can be used.

[0043]

As described in detail above, according to the present invention, since the conventional device has the module structure in which the thermoelectric cooling element and the LD element are hermetically sealed in the same package, the package is affected by the outside air temperature. Therefore, a sufficient temperature difference cannot be given between the temperature of the LD element and the ambient temperature due to the limit of the cooling / heating ability of the thermoelectric cooling element, and the variable wavelength range of the oscillation laser light of the LD element or usable In order to eliminate the drawback that the ambient temperature is limited, a thermoelectric cooling element for cooling and heating the module from the outside of the package is provided outside the module in which the thermoelectric cooling element and the LD element are hermetically sealed in the same package. Is provided so that the temperature can be controlled also from the outside of the package, and a sufficient temperature difference is provided between the temperature of the LD element inside the package and the external ambient temperature. In which it was to be able to bet.

Therefore, according to the present invention, the temperature of the LD element can be varied in a wide range regardless of the ambient temperature, the degree of freedom of the variable range of the oscillation wavelength of the LD element can be improved, and the LD element can be used. It is possible to provide a wavelength tunable light source that is not restricted by possible ambient temperature.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration as an example of the present invention.

FIG. 2 is a view for explaining the operation of the device of the present invention, and in the variable wavelength light source of the present invention, when the case of the LD module is controlled to a constant temperature by the second thermoelectric cooling element, The figure for demonstrating the method of calculating | requiring the preset temperature which does not deteriorate the characteristic of a thermoelectric cooling element.

FIG. 3 is a block diagram showing a configuration of a conventional device.

[Explanation of symbols]

 1 ... LD (laser diode) module 1a ... Case of LD module 1 ... LD (laser diode) element 3 ... Monitor PD (photodiode) element 4 ... First thermoelectric cooling element 5 ... First temperature sensor 6 ... 1st automatic temperature control circuit 7 ... 2nd thermoelectric cooling element 8 ... 2nd temperature sensor 9 ... 2nd automatic temperature control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Jin Takahira, 2-3-2 Nishishinjuku, Shinjuku-ku, Tokyo Kokusai Telegraph and Telephone Corporation (72) Inventor, Shu Yamamoto 2--15, Ohara, Kamifukuoka City, Saitama Prefecture No. Kokusai Telegraph and Telephone Corporation Laboratory

Claims (3)

[Claims] 1. A wavelength tunable light source in which the wavelength of an oscillated laser beam is tunable by changing the temperature of a semiconductor laser element, a case for housing the semiconductor laser element, and cooling / heating according to the amount of energization. A first thermionic cooling element for controlling the temperature of the semiconductor laser element, and an energization amount of the first thermionic cooling element so that the temperature of the semiconductor laser element reaches a desired set value. And a second thermoelectric cooling element for controlling the temperature of the case, which has a cooling / heating action according to the amount of energization, and a temperature of the case to a desired set value. To be the second above
2. A variable temperature light source, comprising: a second temperature control means for controlling the amount of electricity supplied to the thermoelectric cooling element. 2. A first thermoelectric cooling element and a semiconductor laser element are housed in a hermetically sealed case, and the first thermoelectric cooling element is energized to cool the semiconductor laser element in the case. By controlling the temperature of the semiconductor laser device,
A wavelength tunable light source capable of varying the wavelength of oscillation laser light of a semiconductor laser device has a function of cooling / heating according to the amount of energization, and has a second heat for cooling / heating the outside of the case. A tunable light source, comprising: an electronic cooling element; and a control means for controlling the second thermoelectric cooling element so that the temperature of the case becomes a required temperature. 3. The minimum temperature condition of the second temperature control means is set such that the temperature of the case or the minimum temperature of the second thermoelectric cooling element is equal to or higher than the dew point in the humidity condition of the external atmosphere. Claim 1 or 2 characterized by the above-mentioned.
The tunable light source described.