JP3540237B2 - Semiconductor laser module - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser module, and more particularly, to a semiconductor laser module that enables precise temperature control of a semiconductor laser mounted on the semiconductor laser module.
[0002]
[Prior art]
The optical communication market, with respect to a rapid increase in demand for communication bandwidth associated with the proliferation of the Internet and the like, time-division transmission in the conventional optical communication system (TDM: Time Division Multiplex) for have Do you to correspond Kuna' in method, The communication line capacity per optical fiber has been greatly increased by adopting a D-WDM (Dense-Wavelength Division Multiplex) system. In the D-WDM system, different signals are transmitted by transmission light sources of respective wavelengths, and the wavelengths of transmission light sources and their intervals are determined by ITU-T (International Telecommunication Union Telecommunication Standardization Sector). At the beginning of the D-WDM system, communication capacity was secured by wavelength multiplexing of 16 wavelengths, but recently, the multiplicity of wavelengths has been increased to 64, 80, 96, and 128 wavelengths and each wavelength has been increased. The interval is reduced to increase the communication capacity. Also, an optical communication system in which the transmission distance is dramatically improved by using an optical fiber amplifier in synchronization with the spread of the D-WDM system is becoming mainstream.
[0003]
Under these circumstances, the characteristics and stability required for the transmission light source and the excitation light source of the optical fiber amplifier are becoming more severe in the D-WDM transmission system as compared with the conventional optical communication system. Specifically, in the conventional transmission light source, the stability of the oscillation wavelength is rarely required. However, in a D-WDM system in which the wavelength multiplicity is increased and the wavelength interval is narrow, one of the important parameters is one. Has become one. In the case of pumping light sources for optical fiber amplifiers as well, it is strongly desired to improve the light output per light source in order to further increase the transmission distance, and it is important how to secure the heat radiation of the semiconductor laser that is the heat source. Is coming. That is, the temperature control method of the semiconductor laser influences the stability of the oscillation wavelength of the transmission light source, or has the effect of lowering the operating temperature of the pump light source, and is a key point for the semiconductor laser module required for the D-WDM system. Is coming.
[0004]
FIGS. 1A and 1B are a plan view and a cross-sectional view showing a state in which an upper lid of a metal case is removed for explaining a configuration of a semiconductor laser module.
As shown in FIG. 1, in a conventional semiconductor module, a Peltier element 103 for temperature control is mounted in a metal case 101, a metal base 105 is fixed on the Peltier element 103, and a photodiode 106 is mounted thereon. Thermistor substrate 114, heat sink 113 and first lens 107 are fixed. The thermistor 104 and the semiconductor laser 102 are respectively fixed on the thermistor substrate 114 and the heat sink 113 by using solder or the like. Further, the thermistor substrate 114 and the heat sink 113 are also fixed to the metal base 105 by solder or the like. A second lens 108 optically coupled to a first lens 107 and an optical fiber 109 is attached to a side surface of the metal case 101.
Further, the side surface portion of the metal case 101, the power of the external device of the semiconductor laser module (not shown), the outer lead 110 is attached, et al is for exchanging signals. Within the module, Ru wire 111 is provided to connect the power line 112 and each portion for performing power supply to the Peltier element 103.
[0005]
The light emitted from the semiconductor laser 102 enters the optical fiber 109 via the first lens 107 and the second lens 108. The output of the semiconductor laser 102 is monitored by a photodiode 106 at the rear thereof, and feedback is applied so that the output of the semiconductor laser always remains at a predetermined level.
[0006]
In the conventional semiconductor laser module, in order to stabilize the operating temperature of the semiconductor laser 102, a temperature that changes due to the amount of heat (radiation heat and conduction heat via the wire 111 and the power line 112) and the like flowing from the metal case is supplied to the thermistor 104. The Peltier element 103 is operated so that the temperature of the thermistor is always constant (usually 25 ° C.). The thermistor 104 indicates a resistance value corresponding to the ambient temperature, and the temperature is detected based on the resistance value. Then, the magnitude and direction of the current supplied to the Peltier element are determined by a drive circuit (not shown) based on the detected temperature, and the current is supplied via the external lead 110 and the power line 112. Accordingly, the Peltier element can control both cooling and overheating depending on the direction of the supplied current, and thus can control the semiconductor laser in the semiconductor laser module to a constant temperature.
[0007]
[Problems to be solved by the invention]
However, the conventional semiconductor laser temperature control has the following problems.
The thickness of the heat sink on which the semiconductor laser is mounted is t, the area is S, the thermal conductivity is k, the thickness of the thermistor substrate on which the thermistor is mounted is t ', the area is S', and the thermal conductivity is k '. The heat flowing into the semiconductor laser and the thermistor due to the temperature fluctuation of the metal case 101 is W, W ′, the amount of heat generated by the operation of the semiconductor laser is w, the temperature of the metal base 105 is TL, and the temperature of the semiconductor laser and the thermistor are respectively Assuming Th and Th ', the following equations (1) and (2) are established in a thermal equilibrium state.
k · S (Th−TL) / t = W + w (1)
k ′ · S ′ (Th′−TL) / t ′ = W ′ (2)
Here, since W and W 'are in a proportional relationship, equation (2) can be expressed as follows using a as a proportionality constant.
k ′ · S ′ (Th′−TL) / t ′ = aW (3)
[0008]
As described above, in the conventional semiconductor laser module, as a method of controlling the operating temperature of the semiconductor laser, the resistance value of the thermistor is simply detected, and the Peltier element is operated so that the resistance value becomes equivalent to 25 ° C. . Therefore, when there is a difference in the thermal resistance between the thermistor and the metal base and the thermal resistance between the semiconductor laser and the metal base described in the above equations (1) and (3), the resistance value (that is, the temperature) of the thermistor is changed. Even if the temperature is controlled to 25 ° C., the operating temperature of the semiconductor laser is different from 25 ° C. For example, a case where AlN (thermal conductivity 140 W / mK) having a size of 800 μm × 1000 μm and a thickness of 220 μm is used as a heat sink and alumina (a thermal conductivity of 17 W / mK) having a thickness of 1000 μm × 1400 μm and a thickness of 250 μm is used as a thermistor substrate Assuming that, the term k · S / t (k ′ · S ′ / t ′ in the case of a thermistor substrate) in the above equation is about 5.3 times better in heat conduction in an AlN heat sink than in alumina. You can see that.
[0009]
When the semiconductor laser is actually operated in a low output region (corresponding to the case where w = 0 is assumed) and temperature control is performed so that the case temperature Tc is 70 ° C. and the thermistor temperature (Th ′) is 25 ° C. In the semiconductor laser, the oscillation wavelength of the semiconductor laser is observed to be about 0.05 nm shorter, and the oscillation wavelength variation of the used distributed feedback semiconductor laser with respect to the temperature is about 0.1 nm / ° C., so that the semiconductor laser is about 24.5. It turns out that it is controlled to ° C. The fluctuation range of the case temperature generally required for the D-WDM system is about 0 to 70 ° C., and the fluctuation of the oscillation wavelength of the semiconductor laser with respect to the case temperature fluctuation is expected to be about 1 pm / ° C. Considering the entire temperature range of 70 ° C., a wavelength fluctuation of 0.07 nm occurs. Since the wavelength interval in the recent 96-wavelength D-WDM system is 0.4 nm, the fluctuation of the oscillation wavelength due to the case temperature fluctuation is small even if the fluctuation of the wavelength of the semiconductor laser over time is considered. is not.
[0010]
As described above, a conventional temperature control method for a semiconductor laser module is to detect the temperature of the thermistor itself and control the temperature of the thermistor itself.The thermal resistance from the upper surface of the Peltier element to the thermistor and the Peltier element Since the difference in thermal resistance between the top surface and the semiconductor laser is not taken into account, the temperature of the semiconductor laser fluctuates with the case temperature, causing a problem that the oscillation wavelength fluctuates and the semiconductor laser tends to operate erratically. Had.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problem, and to adjust the thermal resistance between the thermistor-Peltier element and the semiconductor laser-Peltier element of the semiconductor laser module in consideration of the load of the semiconductor laser. Another object of the present invention is to provide a semiconductor laser module capable of performing a stable operation by suppressing a change in an operating temperature of a semiconductor laser due to a change in a case temperature.
[0011]
[Means for Solving the Problems]
The semiconductor laser module of the present invention has a temperature control element disposed in a case, a metal base disposed on the temperature control element, a heat sink mounted on the metal base, and mounted on the heat sink. a semiconductor laser, a thermistor board mounted on said metal base, in a semiconductor laser module comprising a temperature sensing element mounted on the thermistor on the substrate, wherein the thermistor substrate each thermal resistance at different thermistors substrate In this case, one of the thermistor substrates is selected according to the operating conditions, and the temperature detecting element is mounted thereon.
Further, another semiconductor laser of the present invention includes a temperature control element disposed in a case, a metal base disposed on the temperature control element, a heat sink mounted on the metal base, in the semiconductor laser module comprising a semiconductor laser is mounted, a pedestal mounted on the metal base, and a thermistor board mounted on said base, and a temperature sensing element mounted on the thermistor on the substrate, The pedestal is a plurality of pedestals each having a different thermal resistance, and one of the pedestals is selected according to operating conditions, and the thermistor substrate is mounted thereon.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings according to examples.
[First Embodiment]
FIG. 1 is a plan view and a cross-sectional view of a semiconductor laser module for explaining a first embodiment of the present invention. The basic configuration of the semiconductor laser module according to the present embodiment is the same as that of the conventional example, and a duplicate description will be omitted.
In the semiconductor laser module according to the first embodiment of the present invention, the thickness of the heat sink on which the semiconductor laser is mounted is t, the area is S, the thermal conductivity is k, and the thickness of the thermistor substrate on which the thermistor is mounted is t. ′, The area is S ′, and the thermal conductivity is k ′, the amounts of heat flowing into the semiconductor laser and the thermistor from the metal case 101 are W and aW, the amount of heat generated by the operation of the semiconductor laser is w, and the temperature of the metal base 105 is Assuming that the temperatures of the TL, the semiconductor laser, and the thermistor are Th and Th ', respectively, the following equation holds in a thermal equilibrium state.
k · S (Th−TL) / t = W + w (1)
k ′ · S ′ (Th′−TL) / t ′ = aW (3)
[0013]
Among these parameters, the heat sink on which the semiconductor laser is mounted is limited as a material because it is desired that the heat sink has a good thermal conductivity and a thermal expansion coefficient close to that of the semiconductor laser, but there is a margin in design in terms of area and thickness. And can be adjusted. Although the thermistor substrate may be limited by the coefficient of thermal expansion of the thermistor, there is a relatively large design margin for the material, area and thickness.
Specifically, under operating conditions (w to 0) where the heat value w (power consumption amount) of the semiconductor laser is small and can be almost ignored compared to the heat amount flowing into the semiconductor laser or the thermistor, the above equations (1) and (3) are used. Can be modified as follows with w = 0.
a ｛k · S (Th−TL) / t｝ = k ′ · S ′ (Th′−TL) / t ′ (4)
[0014]
Here, by using a sample semiconductor laser and a thermistor whose temperature, oscillation wavelength, and resistance value are known and changing the temperature of the metal case to measure Th and Th ', the same type of semiconductor laser and thermistor can be used. Can be experimentally determined when a is combined. Therefore, using this a, Th = Th ′, that is, a · k · S / t = k ′ · S ′ / t ′, without depending on the amounts of heat W and W ′ flowing into the semiconductor laser and the thermistor from the metal case. It is possible to select such a heat sink and the thermal conductivity (k, k '), area (S, S'), and thickness (t, t ') of the thermistor substrate. Actually, in the conventional example, AlN (thermal conductivity 140 W / mK) is used as a heat sink material, and alumina (thermal conductivity 17 W / mK) is used as a thermistor substrate material. By adjusting the area and thickness, the thermal resistance between the semiconductor laser and the metal base can be made a times the thermal resistance between the thermistor and the metal base. It is possible to keep the operating temperature of the semiconductor laser constant within the entire temperature fluctuation range.
[0015]
[Second embodiment]
On the other hand, when the heat value w (power consumption) of the semiconductor laser cannot be ignored with respect to the heat amount W flowing into the semiconductor laser and the thermistor due to the temperature fluctuation of the metal case, the above equations (1) and (3) are modified. hand,
k · S (Th−TL) t ′ / k ′ · S ′ (Th′−TL) t = (W + w) / aW (5)
Therefore, the semiconductor laser temperature (Th) and the thermistor temperature (Th ′) cannot be uniquely determined. That is, since the right side of the equation (5) depends on the ratio of W flowing in due to the temperature variation of the metal case and the calorific value w of the semiconductor laser, the semiconductor laser temperature (Th) and the thermistor temperature (Th) over the entire operating temperature range of the semiconductor laser module. It becomes impossible to select k, S, and t such that Th ′) is the same.
[0016]
However, the value of a can be determined experimentally in the same manner as in the first embodiment, and the power (w) supplied to the semiconductor laser is almost determined by the application, so that w is constant (for example, rated current). When the semiconductor laser module is operated at the maximum operating temperature (Tcmax) which is the highest temperature in the entire operating temperature range, k is such that the semiconductor laser temperature (Th) and the thermistor temperature (Th ′) are the same. , S, t and k ', S', t 'can be selected. That is, if W on the right side of the equation (5) is specified as the amount of heat at Tcmax, a combination of k, S, t and k ', S', t 'for establishing the equation can be obtained. In this case, Th ≦ Th ′ in the entire operating temperature range, that is, the semiconductor laser tends to always operate at a temperature lower than the thermistor temperature (≦ 25 ° C.), and stable operation is ensured in the entire operating temperature range. It becomes possible.
[0017]
[Third embodiment]
In the second embodiment, when w ≠ 0, k, S, and t are set so that the semiconductor laser temperature (Th) and the thermistor temperature (Th ′) are the same at the maximum operating temperature (Tcmax) of the semiconductor laser module. Although the combination of k ', S', and t 'has been obtained, when the heat generation of the semiconductor laser is relatively small, the adjustment of the semiconductor laser temperature (Th) and the thermistor temperature (Th') is performed at the maximum operating temperature. It is not necessary to limit to the conditions. For example, the thermal conductivity (k, k ′) is set so that the difference Th′−Th between the thermistor temperature (Th ′) and the semiconductor laser temperature (Th) is minimized in the entire operating temperature range. ), Area (S, S ′), and thickness (t, t ′) can also be adjusted.
[0018]
That is, in this embodiment, a semiconductor laser having a known relationship between the temperature and the oscillation wavelength and a thermistor having a known relationship between the temperature and the resistance value are operated within the entire operating temperature range, and the thermistor temperature (Th ′) is used. ) And the absolute value of the difference between the semiconductor laser temperature (Th) and the thermal conductivity (k, k ') and area of the heat sink and the thermistor substrate so that the integrated value (integrated value) of | Th'-Th | (S, S ') and thickness (t, t') are obtained, and this combination is adopted.
According to this embodiment, the semiconductor laser can obtain a stable laser output without exceeding the upper limit of the operating current.
[0019]
[Fourth embodiment]
FIGS. 2A and 2B are a plan view and a schematic cross-sectional view showing a configuration of a semiconductor laser module according to a fourth embodiment of the present invention, with an upper lid removed. In FIG. 2, portions equivalent to those in FIG. 1 are denoted by the same reference numerals having the last two digits in common, and duplicate description will be omitted. In this embodiment, pedestals 215A and 215B having different thermal resistances are provided on a metal base 205, and a thermistor substrate 214 and a thermistor 204 are stacked and mounted on one of the pedestals 215B. As described above, the fourth embodiment is different from the other embodiments in that the thermistor substrate is fixed on an appropriate pedestal selected.
[0020]
3 (a) and 3 (b) are partially enlarged views of FIGS. 2 (a) and 2 (b). As shown in FIG. 3, in the fourth embodiment, the pedestal 215A is mounted on the metal base 205 alongside the pedestal 215B, but nothing is mounted thereon. That is, only the pedestal 215B is actually used. Although two pedestals are provided in the illustrated example, three or more pedestals having different thermal resistances may be provided, and one of them may be selected to provide a thermistor substrate and a thermistor thereon. . Here, a plurality of pedestals having different materials, areas, and thicknesses are provided, each having a thermal conductivity ki, an area Si, and a thickness ti (i = 1, 2, 3,...). Assuming that the pedestal ti is used, the equation (3) in the thermal equilibrium state is as follows:
(Th'-TL) / (ti / ki.Si + t '/ k'.S') = aW (3 ')
And can be transformed. Therefore, a semiconductor laser module is constructed using common members such as a metal base having a pedestal, a thermistor substrate, and a heat sink, and the semiconductor laser temperature (Th) and the thermistor temperature (Th ′) are the same at a specific operating temperature (Tc). By mounting the thermistor substrate on a pedestal selected in consideration of the heat value w of the semiconductor laser, the semiconductor laser module can be stably operated within the entire operating temperature range.
[0021]
Although the preferred embodiments have been described above, the present invention is not limited to these embodiments, and can be appropriately modified within the scope described in the claims. For example, in the fourth embodiment, a plurality of pedestals are provided in addition to the thermistor substrate as means for equalizing the semiconductor laser temperature and the thermistor temperature. However, the thermal resistance between the thermistor and the metal base is adjusted. As one of the options, the area and thickness can be adjusted using the thermistor substrate itself without using a specific pedestal. When a plurality of pedestals are used, it is not always necessary to make all the pedestals different in material, area, and thickness. For example, only the thickness may be made different. Further, the first to third embodiments and the fourth embodiment may be combined.
[0022]
【The invention's effect】
As described above, the semiconductor laser module according to the present invention adjusts the thermal resistance from the metal base to the thermistor and the thermal resistance from the metal base to the semiconductor laser so that the semiconductor laser operates almost at the thermistor temperature. Therefore, the oscillation wavelength of the semiconductor laser can be constantly maintained at a stable value. Therefore, by employing the semiconductor laser module of the present invention, it becomes possible to stably operate the D-WDM optical communication system having a narrow wavelength interval.
[Brief description of the drawings]
FIG. 1 is a plan view and a sectional view of a semiconductor laser module for explaining a conventional example and first to third embodiments of the present invention.
FIG. 2 is a plan view and a sectional view of a semiconductor laser module showing a fourth embodiment of the present invention.
FIG. 3 is a partially enlarged view of FIG. 2;
[Explanation of symbols]
101, 201 Metal case 102, 202 Semiconductor laser 103, 203 Peltier element 104, 204 Thermistor 105, 205 Metal base 106, 206 Photodiode 107, 207 First lens 108, 208 Second lens 109, 209 Optical fiber 110, 210 External Lead 111, 211 Wire 112, 212 Power line 113, 213 Heat sink 114, 214 Thermistor substrate 215A, 215B Base

Claims (6)

A temperature control element disposed in the case, a metal base disposed on the temperature control element, a heat sink mounted on the metal base, a semiconductor laser mounted on the heat sink, and a thermistor substrate mounted on a semiconductor laser module with a mounting temperature sensing element to the thermistor on the substrate, wherein the thermistor substrate is each thermal resistance at different thermistors substrates, that in accordance with the operating conditions A semiconductor laser module , wherein one of the thermistor substrates is selected and the temperature detecting element is mounted thereon . A temperature control element disposed in the case, a metal base disposed on the temperature control element, a heat sink mounted on the metal base, a semiconductor laser mounted on the heat sink, and a pedestal mounted on a thermistor board mounted on the pedestal, in the semiconductor laser module with a mounting temperature sensing element to the thermistor on the substrate, the pedestal each thermal resistance at different pedestals A semiconductor laser module , wherein one of the pedestals is selected according to operating conditions, and the thermistor substrate is mounted thereon . The ratio of the amount of heat flowing into the more the case with semiconductor lasers and said temperature detecting element is the reciprocal of the ratio of the thermal resistance of up to the metal base and the heat resistance from the semiconductor laser to the metal base from said temperature detecting element 3. The semiconductor laser module according to claim 1, wherein 3. The semiconductor laser module according to claim 1, wherein a maximum operating temperature of the semiconductor laser module is selected, and at that time, the temperature of the semiconductor laser and the temperature of the temperature detecting element substantially match. . When the semiconductor laser module is operated within a specified operating temperature range, the integrated value of the absolute value of the temperature difference between the semiconductor laser and the temperature detecting element is set to be minimum. The semiconductor laser module according to claim 1. 6. The semiconductor laser module according to claim 4, wherein said condition is satisfied under a condition of supplying a rated current to said semiconductor laser.

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