JP4779747B2 - Light emitting module - Google Patents

Description

  The present invention relates to a light emitting module.

One package of a light emitting module having a semiconductor laser element is a coaxial package. Examples of the coaxial package are disclosed in Patent Document 1 and Patent Document 2 below. In these coaxial packages, it is necessary to measure the ambient temperature of the LD in order to control the temperature of the laser diode (hereinafter referred to as “LD”), and a thermistor is installed in the immediate vicinity of the LD for the measurement. .
JP 2004-2537779 A JP 2003-142766 A

  However, in the coaxial package, since the linear distance between the LD and the case wall surface is only about 0.2 mm, if the thermistor is installed in the immediate vicinity of the LD, the thermistor inevitably approaches the case wall surface. Therefore, the thermistor is affected by the temperature outside the package (radiant heat from the case wall surface), and an error occurs in the temperature measurement of the LD. Since the thermoelectric conversion element equipped with the LD cools or heats the LD based on the temperature measured by the thermistor, an error in temperature measurement leads to overcooling or overheating of the LD. As a result, wavelength drift occurs in the laser light emitted from the LD.

  This invention is made | formed in view of the above, and makes it a subject to provide the light emitting module by which the wavelength drift was suppressed.

The present invention relates to a light emitting module. The light emitting module includes a stem, a cap fixed to the upper surface of the stem and having an upper wall facing the upper surface, a thermoelectric conversion element installed on the upper surface of the stem and covered by the cap, and the thermoelectric conversion element A base having a flat lower surface, a first side surface extending from the lower surface toward the upper wall of the cap, and a second side surface inclined so as to form an obtuse angle with respect to the lower surface, A semiconductor laser element fixed to the side surface and a temperature measuring element fixed to the second side surface are provided. The second side surface forms an overhang portion, and the temperature measuring element is shielded from the upper wall of the cap by the overhang portion.

  With the arrangement of the temperature measuring element as described above, the temperature measuring element and the base are at least partially shielded from the upper wall of the cap. Thereby, since transmission of the radiant heat from the upper wall of the cap to the temperature measuring element is suppressed, the temperature measuring element can accurately measure the ambient temperature of the LD. As a result, the accuracy of temperature control of the LD is improved, and the wavelength drift of the LD is reduced.

  According to the present invention, it is possible to provide a light emitting module in which wavelength drift is suppressed.

  Hereinafter, an embodiment of a light emitting module according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a partially broken perspective view of a light emitting module 10a according to the first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of the light emitting module 10a shown in FIG. The light emitting module 10a is of a coaxial type and includes a CAN case 30 that houses electronic components such as a semiconductor laser element.

  The CAN case 30 includes a stem 31 and a cap 32. The stem 31 has a disk shape, and its main surface 31 a is orthogonal to the central axis X of the CAN case 30. Electronic components such as a semiconductor laser element are mounted on the main surface 31a. A plurality of lead terminals 33 are connected to the stem 31. These lead terminals 33 penetrate the stem 31 in parallel with the central axis X.

  The cap 32 has a cylindrical shape with a lid, and a lens 32c that condenses laser light from the semiconductor laser element is fitted into an opening 32b provided in the upper wall 32a. The cap 32 is fixed on the main surface 31a of the stem 31 and covers an electronic component mounted on the main surface 31a. Specifically, a plurality of thermoelectric conversion elements 21, a lower plate 22a, an upper plate 22b, a photodiode (hereinafter referred to as “PD”) 23, a PD carrier 24, a laser diode (hereinafter referred to as LD) 25, a base 26, a thermistor 27, The LD carrier 28 is installed on the main surface 31 a and covered with the cap 32.

  The thermoelectric conversion element 21 is also called a Peltier element and is sandwiched between the lower plate 22a and the upper plate 22b. Both the lower plate 22a and the upper plate 22b are insulative and have excellent thermal conductivity. The lower plate 22 a is fixed to the upper surface 31 a of the stem 31. The upper plate 22 b is fixed to the upper surface of the thermoelectric conversion element 21. Each thermoelectric conversion element 21 is connected to two lead terminals 33 via bonding wires or the like. When a control current is supplied to each thermoelectric conversion element 21 via the lead terminal 33, heat can be taken from the object mounted on the thermoelectric conversion element 21, or heat can be given to the object. Depending on the direction of the control current, the lower surface of the thermoelectric conversion element 21 is one of the heat absorption surface or the heat dissipation surface, and the upper surface is the other of the heat absorption surface or the heat dissipation surface.

  A base 26 is mounted on the upper plate 22b. The base 26 is a columnar body having a trapezoidal cross section, and is made of a material having excellent thermal conductivity, for example, a metal such as CuW, or ceramics. The first side surface 26a, the second side surface 26b, the lower surface 26c, and the upper surface 26d of the base 26 are all flat. As shown in FIG. 2, the LD carrier 28 is fixed to the first side surface 26a, and the thermistor 27 is fixed to the second side surface 26b. The lower surface 26c is parallel to the upper surface 31a of the stem 31, and is joined to the upper plate 22b. The upper surface 26d is parallel to the upper wall 32a of the cap 32.

  The two side surfaces 26a and 26b both extend from the lower surface 26c toward the upper wall 32a of the cap 32. However, the first side surface 26a is perpendicular to the lower surface 26c, whereas the second side surface 26b is on the lower surface 26c. It is inclined to form an obtuse angle. For this reason, the base 26 has an overhang portion 26 e protruding above the thermistor 27.

  The LD carrier 28 is equipped with an LD 25 as a semiconductor laser element and is made of an insulating material such as ceramics (for example, AlN). The LD 25 is fixed on the first side surface 26 a of the base 26 via the LD carrier 28. The LD 25 is arranged so that its light emitting end face 25a and light reflecting end face 25b are orthogonal to the central axis X.

  The anode of the LD 25 is connected to the wiring pattern on the LD carrier 28 via a bonding wire (not shown). Similarly, the cathode electrode of the LD 25 is directly bonded to the wiring pattern on the LD carrier 28 by soldering or the like. Further, these wiring patterns are connected to a plurality of lead terminals 33 via bonding wires (not shown). When a current is supplied to the LD 25 via the lead terminal 33, laser light is emitted from the light emitting end face 25a of the LD 25.

  The PD 23 is a light receiving element that measures the light output of the LD 25. The PD 23 has a light receiving surface 23 a that faces the light reflecting end surface 25 b of the LD 25. One of the anode and cathode of the PD 23 is directly joined to the PD carrier 24 by soldering or the like. The PD carrier 24 is fixed on the lower plate 22a and connected to one of the lead terminals 33 via a bonding wire (not shown). The other electrode of the PD 23 is connected to another lead terminal 33 via a bonding wire (not shown). The PD 23 detects the laser light leaking from the light reflection end face 25 b of the LD 25, and outputs a current corresponding to the intensity to the outside of the light emitting module 10 a via the lead terminal 33.

  The thermistor 27 is a temperature measuring element that measures the ambient temperature of the LD 25. The overhang portion 26 e of the base 26 at least partially shields the thermistor 27 from the upper wall 32 a of the cap 32. In the present embodiment, the thermistor 27 is arranged so that the thermistor 27 is completely shielded by the overhang portion 26e when the base 26 is viewed from the upper wall 32a of the cap 32 in parallel with the central axis X.

  The two electrodes of the thermistor 27 are connected to a plurality of lead terminals 33 via bonding wires (not shown). The thermistor 27 changes its electric resistance value according to the ambient temperature of the LD 25, generates an electric signal according to the temperature of the LD 25, and outputs it to the outside of the light emitting module 10 a via the lead terminal 33.

  Hereinafter, advantages of the light emitting module 10a will be described with reference to FIG. FIG. 3A is a graph showing the correlation between the temperature of the CAN case 30 and the wavelength drift of the LD 25 with respect to the light emitting module 10a. FIG. 3B is a graph showing the correlation between the temperature of the CAN case and the wavelength drift of the LD for the light emitting module prepared for comparison with the present embodiment. The comparative light-emitting module has a rectangular parallelepiped base, and the side surface of the base on which the thermistor is fixed is perpendicular to the lower surface and the upper surface of the base. For this reason, in this comparative example, the thermistor is completely exposed to the upper wall of the cap. In obtaining the graphs of FIGS. 3A and 3B, the LD drive current was controlled to 40 mA, and the LD temperature was controlled to 40 ° C.

  As shown in FIG. 3B, in the comparative example, the wavelength drift width reaches about 200 pm while the case temperature varies between −40 ° C. and 80 ° C. On the other hand, in the light emitting module 10a of this embodiment, as shown in FIG. 3A, the wavelength drift width is suppressed to 20 pm or less while the temperature of the CAN case 30 varies between −10 ° C. and 80 ° C. It has been.

  The reason why the wavelength drift width is reduced is as follows. In the light emitting module 10 a, the thermistor 27 is shielded from the upper wall 32 a of the cap 32 by the overhang portion 26 e of the base 26, so that the radiant heat from the upper wall 32 a is blocked and absorbed by the base 26. The absorbed radiant heat is cooled by the thermoelectric conversion element 21 thermally connected to the base 26. Thereby, since it can suppress that radiant heat is transmitted to the thermistor 27, the thermistor 27 becomes possible [measuring the ambient temperature of LD25 correctly]. As a result, the accuracy of temperature control of the LD 25 is improved, so that the wavelength drift of the LD 25 can be reduced as shown in FIG.

  By using a metal or ceramic having excellent thermal conductivity as the material of the base 26, the radiant heat absorbed by the base 26 can be efficiently transmitted to the thermoelectric conversion element 21. Thereby, since transmission of the radiant heat to the thermistor 27 can be prevented satisfactorily, the temperature of the LD 25 can be controlled more accurately, and the wavelength drift of the LD 25 can be further reduced.

  Further, in manufacturing the light emitting module 10a, it is sufficient to change the shape of the base 26 from the conventional product, and there is no need to add additional components. Therefore, the light emitting module 10a is easy to assemble and can reduce the manufacturing cost.

(Second Embodiment)
FIG. 4 is a partially broken perspective view of the light emitting module 10b according to the second embodiment. FIG. 5 is a cross-sectional view taken along line VV of the light emitting module 10b shown in FIG. The light emitting module 10b includes an L-shaped base 36 instead of the trapezoidal base 26 in the first embodiment. Other configurations of the present embodiment are the same as those of the first embodiment.

  The base 36 is a columnar body having an L-shaped cross section. The first side surface 36a, the lower surface 36c, and the upper surface 36d of the base 36 are all flat, but the second side surface 36b is provided with a recess 36e adjacent to the lower surface 36c. The LD carrier 28 is fixed to the first side surface 36a. The thermistor 27 is installed in the recess 36e of the second side surface 36b. For this reason, the base 36 has an overhang portion 36 f protruding above the thermistor 27. The lower surface 36c is parallel to the upper surface 31a of the stem 31, and is joined to the upper plate 22b. The upper surface 36d is parallel to the upper wall 32a of the cap 32.

  The overhang portion 36 f of the base 36 at least partially shields the thermistor 27 from the upper wall 32 a of the cap 32. In the present embodiment, the thermistor 27 is arranged such that the thermistor 27 is completely shielded by the overhang portion 36f when the base 36 is viewed from the upper wall 32a of the cap 32 in parallel with the central axis X. Thereby, similarly to 1st Embodiment, the influence which the radiant heat from the upper wall 32a exerts on the thermistor 27 can be suppressed. As a result, temperature measurement by the thermistor 27 becomes accurate, so that the wavelength drift of the LD 25 can be reduced.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

  In the above embodiment, the thermistor 27 is completely shielded by the base 26 or 36 when viewed from the upper wall 32a of the cap 32 in parallel with the central axis X. However, even if the thermistor is only partially shielded by the base, the influence of thermal radiation from the upper wall 32a on the thermistor can be suppressed to some extent, so that the wavelength drift can be reduced. Of course, if the thermistor is completely shielded by the base, the influence of thermal radiation can be greatly suppressed, so that the wavelength drift can be further reduced.

  In the second embodiment, the recess 36e of the base 36 is provided at the end of the second side surface 36b adjacent to the lower surface 36c. However, the recess 36e may be provided in an intermediate portion of the second side surface 36b that is separated from the lower surface 36c and the upper surface 36d.

It is a partially broken perspective view of the light emitting module concerning a 1st embodiment of the present invention. It is sectional drawing along the II-II line of FIG. It is a graph which shows the correlation with the temperature of CAN case, and the wavelength drift of LD regarding 1st Embodiment and a comparative example. It is a partially broken perspective view of the light emitting module which concerns on 2nd Embodiment of this invention. It is sectional drawing along the VV line of FIG.

Explanation of symbols

10a and 10b ... light emitting module, 21 ... thermoelectric conversion element, 25 ... LD, 26 and 36 ... base, 27 ... thermistor, 28 ... LD carrier, 30 ... CAN case, 31 ... stem, 32 ... cap

Claims (1)

Stem,
A cap fixed to the upper surface of the stem and having an upper wall facing the upper surface;
A thermoelectric conversion element installed on the upper surface of the stem and covered by the cap;
A lower surface disposed on the thermoelectric conversion element and facing the thermoelectric conversion element; a first side surface extending from the lower surface toward the upper wall of the cap; and a first surface inclined at an obtuse angle with respect to the lower surface. A base having two sides;
A semiconductor laser element fixed to the first side surface;
A temperature measuring element fixed to the second side surface;
Equipped with a,
The light emitting module , wherein the second side surface forms an overhang portion, and the temperature measuring element is shielded from the upper wall of the cap by the overhang portion .

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