JP2008153467A - Light emitting module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce temperature drift in a laser diode at low costs to a coaxial optical module. <P>SOLUTION: There are provided: a stem 11; a cap 12 provided on the stem 11; an LD 25; a thermoelectric conversion element 21 that is provided on the stem 11 and controls the temperature of the LD 25; a base 23 provided between the thermoelectric conversion element 21 and an upper wall 12a of the cap 12; and a thermistor 26 that is provided on the base 23 and monitors the temperature of the LD 25. In the base 23, there is recess 23e near the center of a side 232a of the base 23 extended in a direction toward the upper wall 12a from the thermoelectric conversion element 21. The thermistor 26 is arranged in the recess 23e and shielded from the upper wall 12a thermally by the inner wall of the recess 23e. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting module.

An example of a temperature control technique for a laser diode of a light emitting module is disclosed in Patent Document 1 and Patent Document 2. A laser module (light emitting module) described in Patent Document 1 includes a butterfly-type package, a plurality of elements to be cooled including laser diodes accommodated in the package, and covers the elements to be cooled and spatially And a heat shielding member provided in such a manner that it does not come into direct contact. Further, the laser module (light emitting module) described in Patent Document 2 detects the wavelength fluctuation of the laser light from the semiconductor laser using an etalon and two pin diodes.
JP 2003-142767 A Japanese Patent Laid-Open No. 11-238946

  The technique of Patent Document 1 is suitable for a butterfly type package and is difficult to apply to a narrow coaxial type package. Further, the technique of Patent Document 2 has a complicated apparatus configuration and high cost. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce temperature drift in a laser diode at a low cost with respect to a coaxial optical module.

  The present invention provides a stem, a thermoelectric conversion element provided on the stem, a base provided on the thermoelectric conversion element, a laser diode provided on the base, and provided on the base. A thermistor for monitoring the temperature of the laser diode; and a cap provided on the stem and having an upper wall covering the laser diode, the thermoelectric conversion element, the base and the thermistor, and a side surface of the base Is formed with a recess extending in a direction from the thermoelectric conversion element toward the upper wall, and the thermistor is disposed in the recess and is thermally shielded from the upper wall by the inner wall of the recess. The base is provided with a groove extending from the recess to an edge of the side surface, and the thermistor includes the recess and the It may be thermally shielded from the upper wall by the inner wall of.

  According to the present invention, since the thermistor is disposed in the recess of the base and is thermally shielded from the upper wall of the cap, the upper side of the thermistor even in the narrow package of the coaxial light emitting module consisting of the stem and the cap. The influence of radiant heat from the wall can be reduced. As a result, since the thermistor can measure the ambient temperature of the laser diode relatively accurately, the temperature control accuracy of the laser diode is improved, and the temperature drift in the laser diode can be reduced. Further, according to the present invention, it is relatively easy to provide the recess in the base. For this reason, the influence of the radiant heat from the upper wall on the thermistor can be reduced easily and at low cost.

  ADVANTAGE OF THE INVENTION According to this invention, the temperature drift in a laser diode can be reduced at low cost with respect to a coaxial type optical module.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a perspective view of a light emitting module 1 according to an embodiment, with a part thereof broken. FIG. 2 is a cross-sectional view of the light emitting module 1 taken along the line II-II shown in FIG. FIG. 3 is an exploded perspective view showing the base 23 according to the embodiment. The light emitting module 1 includes a CAN case 10, a lower plate 20, a plurality of thermoelectric conversion elements 21, an upper plate 22, a base 23, an LD carrier 24, an LD 25 (LD: Laser Diode), a thermistor 26, a PD carrier 27, and a PD 28 (PD: This is a so-called coaxial light emitting module including a Photo Diode.

  The CAN case 10 accommodates the lower plate 20 to the PD 28 described above. The CAN case 10 includes a stem 11 and a cap 12. The stem 11 has a disk shape, and the main surface 11 a of the stem 11 is orthogonal to the axis X of the CAN case 10. The stem 11 is made of a conductive material such as metal and has a ground potential. On the main surface 11a of the stem 11, the lower plates 20 to PD28 are provided. A plurality of rod-like lead terminals 13 are attached to the stem 11, and each lead terminal 13 is parallel to the axis X. The plurality of lead terminals 13 penetrate the stem 11, but are electrically insulated from the stem 11.

  The cap 12 has a cylindrical shape with a lid, and has an opening 12b provided in the upper wall 12a of the cap 12 and a lens 12c fitted in the upper wall 12a. The cap 12 is fixed on the main surface 11a of the stem 11 and covers the lower plate 20 to the PD 28 described above. The upper wall 12 a of the cap 12 is perpendicular to the axis X and is parallel to the main surface 11 a of the stem 11. The lens 12c condenses the laser light emitted from the laser diode 25. The cap 12, particularly the upper wall 12 a of the cap 12 covers the lower plate 20 to PD 28 described above.

  The lower plate 20 has a plate shape and is made of a material such as insulating ceramics (for example, AlN ceramics) having excellent thermal conductivity. The lower plate 20 is fixed on the main surface 11 a of the stem 11. A plurality of thermoelectric conversion elements 21 are fixed on the surface 20 a of the lower plate 20. The surface 20 a of the lower plate 20 is parallel to the main surface 11 a of the stem 11 and is perpendicular to the axis X.

  The thermoelectric conversion element 21 is a TEC (Thermo Electric Cooler) such as a Peltier element for controlling the temperature of the LD 25. The thermoelectric conversion element 21 is provided on the stem 11 and is erected on the surface 20 a of the lower plate 20. The thermoelectric conversion element 21 is electrically connected to the two lead terminals 13 via a current introduction pattern (not shown) provided on the surface 20 a of the lower plate 20. When a control current is supplied to the thermoelectric conversion element 21 through the current introduction pattern, the thermoelectric conversion element 21 causes the upper plates 22 to LD25 provided on the thermoelectric conversion element 21 to be connected in accordance with the direction of the control current. Cool or heat the upper plates 22 to LD25. When the lower plate 20 receives heat generated from the thermoelectric conversion element 21, this heat is transferred to the stem 11 in contact with the lower plate 20 and is exhausted to the outside.

  The base 23 is provided between the main surface 11 a of the stem 11 and the upper wall 12 a of the cap 12, and is fixed on the upper surface 22 b of the upper plate 22. A plurality of thermoelectric conversion elements 21 are provided on the lower surface 22 a of the upper plate 22. The base 23 has a lower surface 23a joined to the upper surface 22b of the upper plate 22 and an upper surface 23d on the opposite side of the lower surface 23a. The lower surface 23 a and the upper surface 23 d are parallel to each other, and are parallel to the surface 20 a of the lower plate 20, the lower surface 22 a of the upper plate 22, and the main surface 11 a of the stem 11. The base 23 has a side surface 23 b and a side surface 23 c that extend in a direction from the thermoelectric conversion element 21 toward the upper wall 12 a of the cap 12. An LD carrier 24 is fixed on the side surface 23b, and the side surface 23b and the side surface 24b of the LD carrier 24 are joined. The side surface 23c is on the opposite side of the side surface 23b.

  Further, the base 23 is a columnar body made of a material such as insulating ceramics (for example, AlN ceramics) excellent in thermal conductivity or conductive CuW, and includes a first region 231 and a second region 232. have. The first region 231 has a side surface 231 a and a side surface 231 b extending in the direction from the thermoelectric conversion element 21 toward the upper wall 12 a, and the side surface 231 b is also the side surface 23 b of the base 23. The second region 232 has a side surface 232 a and a side surface 232 b extending in the direction from the thermoelectric conversion element 21 toward the upper wall 12 a, and the side surface 232 a is also the side surface 23 c of the base 23. The side surface 231a of the first region 231 and the side surface 232b of the second region 232 are joined.

  Near the center of the side surface 232a of the second region 232, a hole 232c penetrating the second region 232 is provided, and the side surface 231a of the first region 231 is formed by the hole 232c of the second region 232. Is exposed. A recess 23e is formed in the base 23 by the hole 232c. The thermistor 26 is disposed in the hollow 23e and substantially at the center of the exposed region 231c of the side surface 231a of the thermoelectric conversion element 21. The thermistor 26 is thermally shielded from the upper wall 12a of the cap 12 by the inner wall of the recess 23e (the thermistor 26 is shielded from radiant heat from the upper wall 12a). A wiring pattern that is electrically connected to the thermistor 26 is provided on the side surface 231a.

  The recess 23e of the base 23 is provided with a first region 231 and a second region 232 provided with a hole 232c separately in advance, and the first region 231 and the second region 232 provided separately. The side surface 23c of the base 23 that is integrated in advance without joining the first region 231 and the second region 232 may be formed. It may be formed by rolling using a technique such as etching.

  The LD carrier 24 is made of ceramic such as AlN and is fixed on the side surface 23 b of the base 23. The side surface 23b of the base 23 and the side surface 24b of the LD carrier 24 are joined. The LD 25 is fixed on the side surface 24 a of the LD carrier 24, and a wiring pattern that is electrically connected to the anode and cathode electrodes of the LD 25 is provided. This wiring pattern is electrically connected to the plurality of lead terminals 13 via bonding wires. The side surface 24 a of the LD carrier 24 is a surface exposed on the opposite side of the base 23. The side surface 24 a of the LD carrier 24 faces the side surface 24 b, and the side surface 24 b is joined to the side surface 23 b of the base 23.

  The LD 25 is provided on the stem 11 and is fixed on the side surface 24 a of the LD carrier 24. The LD carrier 24 is fixed on the side surface 23 b of the base 23. The LD 25 is disposed so that the end face 25a and the end face 25b of the LD 25 are orthogonal to the axis X. Thereby, the laser beam emitted from the end face 25a of the LD 25 enters the lens 12c along the axis X. The plurality of electrodes of the LD 25 are connected to a wiring pattern provided on the side surface 24 a of the LD carrier 24. When a drive current is supplied from the lead terminal 13 to the LD 25 via the wiring pattern on the side surface 24a, laser light is emitted from the end face 25a of the LD 25.

  The thermistor 26 is provided on the base 23 and monitors the temperature of the LD 25. The thermistor 26 changes the electric resistance value according to the ambient temperature. The thermistor 26 is fixed on the side surface 231 a of the first region 231 of the base 23. The thermistor 26 is disposed in the recess 23e of the base 23, and is thermally shielded from the upper wall 12a of the cap 12 by the inner wall of the recess 23e. The two electrodes of the thermistor 26 are electrically connected to the lead terminals 13 via bonding wires.

  The PD 28 is a light receiving element that monitors the light emission intensity of the LD 25. The PD 28 is fixed on the surface 27 a of the PD carrier 27. The PD 28 has a light receiving surface 28 a that faces the end surface 25 b of the LD 25. One of the anode and cathode of the PD 28 is directly joined to the PD carrier 27 by soldering or the like. The PD carrier 27 is made of a conductive material such as metal. The PD carrier 27 is fixed on the surface 20a of the lower plate 20, and is connected to one of the lead terminals 13 via a bonding wire. The other electrode of the PD 28 is connected to one of the lead terminals 13 through a bonding wire. When the PD carrier 27 receives laser light leaking from the end face 25 b of the LD 25, the PD carrier 27 outputs a current corresponding to the intensity of the laser light to the outside of the light emitting module 1 via the lead terminal 13.

  When the base 23 (particularly, the second region 232) is made of AlN, it is desirable to provide the pad 29 and the via 30 in the second region 232 as shown in FIG. FIG. 4A is a diagram showing the configuration of the base 23 provided with the pads 29 and vias 30, and FIG. 4B is taken along the line IV-IV shown in FIG. 4A. FIG. 6 is a diagram showing a cross section of a second region 232. The pad 29 and the via 30 are made of a conductive material such as metal. The second region 232 is provided with a through hole 232d penetrating from the side surface 232a to the side surface 232b of the second region 232, and the via 30 is filled in the through hole 232d. The pad 29 is provided on the side surface 232 a of the second region 232 of the base 23 so as to cover the through hole 232 d and the via 30. The pad 29 is joined to one end of the via 30 exposed at the side surface 232a of the second region 232, and the pad 29 and the via 30 are electrically connected.

  The other end of the via 30 is exposed to the side surface 232b of the second region 232 of the base 23 and is electrically connected to the wiring pattern provided on the side surface 231a of the first region 231. In this case, the pad 29 is electrically connected to the terminal of the thermistor 26 via the via 30 and the wiring pattern on the side surface 231 a of the first region 231. For this reason, by joining the wire to the via 30, it becomes easy to conduct the wire and the thermistor 26. If the second region 232 or the like is made of conductive CuW, the wire and the thermistor 26 can be directly bonded to the second region 232 without using the pad 29 and the via 30. Can be conducted.

  Next, the effect of the light emitting module 1 will be described with reference to FIG. FIG. 5A is a graph showing the correlation between the temperature of the cap 12 and the wavelength drift of the LD 25, and FIG. 5B is a light emitting module prepared for comparison with the light emitting module 1 according to the present embodiment. It is a graph which shows the correlation with the cap and the wavelength drift of LD in (it is hereafter called the light emitting module for a comparison). This comparative light emitting module has the same configuration except for the base 23 in the light emitting module 1. The base of the comparative light emitting module corresponding to the base 23 is configured to have only the first region 231 of the base 23. For this reason, when the base is viewed from the upper wall of the cap of the comparative light emitting module, the thermistor is exposed. In other words, the comparative light-emitting module is not provided with a member that thermally shields between the upper wall of the cap of the comparative light-emitting module and the thermistor.

  On the other hand, in the light emitting module 1 according to this embodiment, the thermistor 26 is disposed in the recess 23 e of the base 23. For this reason, when the base 23 is viewed from the upper wall 12a of the cap 12 of the light emitting module 1, the thermistor 26 is thermally shielded by the inner wall of the recess 23e. That is, the inner wall of the recess 23 e thermally shields between the upper wall 12 a of the cap 12 and the thermistor 26. The results shown in the graphs of FIGS. 5A and 5B are obtained by controlling the drive current of the LD 25 to 40 mA and controlling the temperature of the LD 25 to 40 degrees Celsius.

  As shown in FIG. 5B, in the comparative light emitting module, when the cap temperature fluctuated in the range of minus 40 degrees Celsius to 80 degrees Celsius, the wavelength drift width reached about 200 pm. On the other hand, as shown in FIG. 5A, in the light emitting module 1 according to this embodiment, when the temperature of the cap 12 varies in the range of minus 10 degrees Celsius to 80 degrees Celsius, the wavelength drift width A is It became 20 pm or less (A <20 pm).

  The reason why the results shown in FIGS. 5A and 5B are obtained will be described below. Since the thermistor 26 of the light emitting module 1 according to the present embodiment is thermally shielded from the upper wall 12a of the cap 12 by the second region 232 of the base 23, the radiant heat from the upper wall 12a is blocked by the base 23. And absorbed. The absorbed radiant heat is cooled by the thermoelectric conversion element 21 thermally connected to the base 23. Thereby, since it is possible to suppress the radiant heat from the upper wall 12a from being transmitted to the thermistor 26, the ambient temperature of the LD 25 can be accurately measured using the thermistor 26. 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.

  As described above, in the light emitting module 1 according to this embodiment, the thermistor 26 is disposed in the recess 23e of the base 23 and is thermally shielded from the upper wall 12a of the cap 12, so that the stem 11 and the cap 12 Even within the coaxial narrow CAN case 10 (package), the influence of radiant heat from the upper wall 12a on the thermistor 26 can be reduced. As a result, the thermistor 26 can measure the ambient temperature of the LD 25 relatively accurately, so that the accuracy of temperature control of the LD 25 is improved and temperature drift in the LD 25 can be reduced. Further, it is relatively easy to provide the recess 23e in the base 23. For this reason, the influence of the radiant heat from the upper wall 12a with respect to the thermistor 26 can be reduced easily and at low cost. Therefore, even in the coaxial light emitting module 1, the temperature drift in the LD 25 can be reduced at a low cost.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  For example, instead of the base 23, a base 40 shown in FIG. The base 40 has a first region 231 and a third region 233. The base 40 is different from the base 23 in that the third region 233 is used in place of the second region 232. A side surface 233a (also referred to as a side surface 40a of the base 40) of the third region 233 is a surface exposed to the opposite side of the first region 231, and is directed from the thermoelectric conversion element 21 toward the upper wall 12a of the cap 12. Extend in the direction. The third region 233 is provided with a notch 233c extending from the edge 233b of the side surface 233a toward the center of the side surface 233a. A recess 40 b and a groove 40 c are formed in the base 40 by the notch 233 c of the third region 233.

  The recess 40 b is provided near the center of the side surface 233 a and corresponds to the recess 23 e of the base 23. The groove 40c extends from the recess 40b toward the edge 233b. The thermistor 26 is thermally shielded from the upper wall 12a of the cap 12 by the inner walls of the recess 40b and the groove 40c. The base 40 may be disposed so that the edge 233b is in contact with the upper plate 22 as shown in FIG. 6A, or the edge 233b is connected to the upper plate 22 as shown in FIG. 6B. The thermistor 26 only needs to be thermally shielded from the upper wall 12a of the cap 12 by the inner walls of the recess 40b and the groove 40c. The width of the groove 40c shown in FIG. 6 is drawn smaller than the width of the recess 40b, but may be the same as the width of the recess 40b, for example.

It is a figure which shows the structure of the light emitting module which concerns on embodiment. It is sectional drawing which shows the structure of the light emitting module which concerns on embodiment. It is a figure for demonstrating the structure of the base which concerns on embodiment. It is a figure which shows the other structural example of the base which concerns on embodiment. It is a figure for demonstrating the effect by the light emitting module which concerns on embodiment. It is a figure which shows the other structural example of the base which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting module, 10 ... CAN case, 11 ... Stem, 11a ... Main surface, 12 ... Cap, 12a ... Upper wall, 12b ... Opening, 12c ... Lens, 13 ... Lead terminal, 20 ... Lower plate, 20a, 27a ... Surface, 21 ... Thermoelectric conversion element, 22 ... Upper plate, 22a, 23a ... Lower surface, 22b ... Upper surface, 23, 40 ... Base, 23e, 40b ... Recess, 23c, 23b, 231a, 231b, 232a, 232b, 233a, 24a , 24b, 40a ... side surface, 23d ... upper surface, 231 ... first region, 231c ... exposed region, 232 ... second region, 232c ... hole, 232d ... through hole, 233 ... third region, 233c ... cut Notch, 233b ... Rim, 24 ... LD carrier, 25 ... LD, 25a, 25b, 30a, 30b ... End face, 26 ... Thermistor, 27 ... PD carrier, 28 ... PD, 8a ... light-receiving surface 29 ... pad, 30 ... via, 40c ... groove.

Claims (2)

Stem,
A thermoelectric conversion element provided on the stem;
A base provided on the thermoelectric conversion element;
A laser diode provided on the base;
A thermistor provided at the base for monitoring the temperature of the laser diode;
A cap that is provided on the stem and has an upper wall that covers the laser diode, the thermoelectric conversion element, the base, and the thermistor;
A depression extending in a direction from the thermoelectric conversion element toward the upper wall is formed on the side surface of the base,
The thermistor is disposed in the recess, and is thermally shielded from the upper wall by the inner wall of the recess. The base is provided with a groove extending from the recess to the edge of the side surface,
The light emitting module according to claim 1, wherein the thermistor is thermally shielded from the upper wall by the inner walls of the recess and the groove.

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