JP2008153529A - Optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmitter that has a coaxial package structure and can measure the temperature of a semiconductor laser element precisely. <P>SOLUTION: The optical transmitter 1 has: a carrier 29 mounting a laser diode 11 and a thermistor 27; a pedestal section 23 mounting the carrier 29; a thermoelectric conversion element 15 mounting the pedestal section 23; a stem 7 mounting the thermoelectric conversion element 15; and a lens cap 9a fixed to the stem 7. The laser diode 11 and the thermistor 27 are packaged onto opposite surfaces 29a, 29b of the carrier 29. The carrier 29 is fixed to the pedestal section 23 so that the thermistor 27 packaged to the carrier 29 and a bonding wire 27a for electric connection of the thermistor 27 are stored in a recess 23b at the pedestal section 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmitter.

  An optical transmitter package having a semiconductor laser element has the following two shapes. One is a so-called butterfly type package as disclosed in Patent Document 1. The other one is a so-called coaxial package as disclosed in Patent Document 2.

  The laser module described in Patent Document 1 includes a butterfly-type package, a base accommodated in the package, a cooling thermo module disposed between the package and the base, and a substrate mounted on the base. A cooling element (laser diode, lens, photodiode, etc.). And the invention which concerns on patent document 1 reduces the heat | fever transmitted from a package to a to-be-cooled element in this laser module by covering each to-be-cooled element mounted on the base with a heat shielding member, and is a thermostat module for cooling. Is intended to reduce power consumption by reducing the amount of heat to be cooled.

  Moreover, the laser package described in Patent Document 2 includes a thermoelectric element, a laser emitter, and a thermistor. The laser emitter and the thermistor are mounted on the thermoelectric element through one member. The invention according to Patent Document 2 is intended to enable control of the temperature of a laser emitter using a thermoelectric element in a small-sized laser package such as a coaxial type.

JP 2003-142767 A JP 2003-142766 A JP 2004-2537779 A Japanese Patent Laid-Open No. 11-238946 Japanese Patent Laid-Open No. 2959678 Japanese Patent No. 3035852

  One advantage of the optical transmitter having the coaxial package described in Patent Document 2 is that it can be configured smaller than the butterfly package because of its structure. However, this optical transmitter has the following problems due to its small size. That is, the distance between the temperature measuring element such as a thermistor and the wall surface of the case is reduced, and the temperature signal from the temperature measuring element is easily affected by the temperature of the case (that is, the ambient temperature of the optical transmitter).

  Specifically, if the temperature of the semiconductor laser element is set to T [° C.], the temperature signal from the temperature measuring element is added with a temperature increase (or decrease) Δ [° C.] due to radiant heat from the case. The semiconductor laser element is overcooled (or overheated) to T-Δ [° C.] by the thermoelectric element. Therefore, it is difficult to accurately control the temperature of the semiconductor laser element to a desired temperature.

In particular, the optical transmitter is a dense wavelength division multiplexing (DWDM).
This problem becomes important when it is used for optical communication of ion multiplexing. That is, the emission wavelength of the semiconductor laser element varies depending on the temperature. However, in the DWDM optical communication, the wavelength interval of the signal light is set to be narrow, and therefore, the fluctuation range of the emission wavelength needs to be extremely small. In the conventional optical transmitter, for example, a circuit for controlling the emission wavelength of the semiconductor laser element to be constant is provided outside the optical transmitter, so that the fluctuation range of the emission wavelength is kept small. However, this method increases the peripheral circuit scale of the optical transmitter.

  Further, the heat shielding member described in Patent Document 1 covers the semiconductor laser element and other elements to be cooled together, but it is difficult to provide such a member inside the coaxial package. That is, since the coaxial package has a structure in which the case holds the lens, the distance between the semiconductor laser element and the case is extremely narrow, and it is difficult to provide a heat shielding member as described in Patent Document 1.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical transmitter having a coaxial package structure and capable of accurately measuring the temperature of a semiconductor laser element.

  An optical transmitter according to the present invention includes a carrier on which a semiconductor laser element and a thermistor are mounted, a pedestal portion on which the carrier is mounted, a thermoelectric conversion element on which the pedestal portion is mounted, a stem on which the thermoelectric conversion element is mounted, and a fixing to the stem The semiconductor laser element and the thermistor are mounted on opposite mounting surfaces of the carrier, and the carrier mounting surface is electrically connected to the thermistor. A wiring pattern is formed, the base is provided with a recess, and the carrier is fixed to the base so that the thermistor and the wire connecting the thermistor to the wiring pattern are accommodated in the recess. It is characterized by that.

  In this optical transmitter, by controlling the thermoelectric conversion element based on the temperature of the semiconductor laser element measured by the thermistor, the temperature of the semiconductor laser element is made constant, and the emission wavelength shift (wavelength drift) of the semiconductor laser element is suppressed. Can do. In this optical transmitter, the semiconductor laser and the thermistor are mounted on the mounting surfaces opposite to each other in the carrier, and the thermistor is housed in the recess of the pedestal, so that the thermistor is surrounded by the pedestal and the ambient temperature It is hard to be influenced by. Furthermore, by arranging the thermistor and the semiconductor laser element at positions close to each other with the carrier interposed therebetween, the temperature of the semiconductor laser element can be accurately reflected on the thermistor, so that the temperature of the semiconductor laser element can be accurately measured. Can do.

  The carrier is preferably provided with a via electrode that connects the mounting surface of the semiconductor laser element and the mounting surface of the thermistor. According to this configuration, the thermistor can be electrically connected via the via electrode and the mounting surface of the semiconductor laser element even in the recess of the pedestal.

  The light emitting module according to the present invention has a coaxial package structure and can accurately measure the temperature of the semiconductor laser device.

  Hereinafter, preferred embodiments of an optical transmitter according to the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the optical transmitter 1 has a configuration of a so-called coaxial package including an element mounting portion 3 and a CAN case 5. The CAN case 5 has a stem 7 and a cap 9. The stem 7 includes a plurality of lead terminals 7a and a base portion 7b that supports the plurality of lead terminals 7a. The plurality of lead terminals 7a are rod-like metal members extending in a direction along the predetermined axis X, and are disposed through the base portion 7b. The base portion 7b has a main surface 7c along a plane that intersects the predetermined axis X. On the main surface 7c of the base portion 7b, an element mounting portion 3 to be described later is placed.

  The cap 9 has a lens cap 9a and a lens 9c fitted into the opening 9b of the lens cap 9a. Among these, the lens cap 9a has a cylindrical shape extending in the direction of the predetermined axis X. The lens cap 9 a is attached on the main surface 7 c of the base portion 7 b and covers the element mounting portion 3. Specifically, the lens cap 9a is fixed to the base portion 7b by joining one end of the lens cap 9a to the main surface 7c by resistance welding.

  The opening 9b is formed at the other end of the lens cap 9a. An inner peripheral surface that defines the opening 9b is a lens holding portion for holding the lens 9c. The opening 9b is an opening for allowing laser light output from a semiconductor laser diode 11 (described later) to pass therethrough. The lens cap 9 a is disposed so that the opening 9 b is positioned on the optical axis of the laser light from the laser diode 11. That is, the lens 9c is optically coupled to the laser diode 11 and condenses the laser light from the laser diode 11. The light collected by the lens 9c is guided to one end of an optical transmission medium (not shown) such as an optical fiber.

  The element mounting portion 3 includes a plurality of thermoelectric conversion elements 15, a support plate 17, a photodiode 19, a photodiode (PD) carrier 21, a laser diode 11, a pedestal portion 23, and a thermistor 27.

  The support plate 17 is provided on the base portion 7 b of the stem 7 along a plane that intersects the predetermined axis X. The support plate 17 is made of an insulating material. The plurality of thermoelectric conversion elements 15 are so-called Peltier elements, and are arranged between the support plate 17 and the pedestal portion 23. Each of the plurality of thermoelectric conversion elements 15 is electrically connected to at least two of the plurality of lead terminals 7a of the CAN case 5 via bonding wires or the like. The plurality of thermoelectric conversion elements 15 can take (or give) heat from members mounted on the thermoelectric conversion elements 15 according to the amount of control current supplied via the lead terminals 7a. In the thermoelectric conversion element 15, the lower surface becomes one of the heat absorption surface or the heat dissipation surface, and the upper surface becomes the other of the heat absorption surface or the heat dissipation surface, depending on the direction of the control current.

  The pedestal portion 23 is made of a metal material such as CuW, and is mounted on the plurality of thermoelectric conversion elements 15 on the base portion 7b. A concave portion 23b having a rectangular parallelepiped shape is formed on a side surface 23a of the base portion 23 having a rectangular parallelepiped shape. As shown in FIG. 3, a plate-like carrier 29 on which the laser diode 11 and the thermistor 27 are mounted is mounted on the side surface 23 a of the pedestal portion 23. The material of the carrier 29 is an electrically insulating material and a material having high thermal conductivity. For example, a material such as aluminum nitride is preferably used. The thickness of the carrier 29 is about 0.2 mm.

  The laser diode 11 is mounted on the first mounting surface 29 a on the opposite side of the carrier 29 from the bonding surface with the pedestal 23. At this time, the laser diode 11 has its light emitting end face 11a and light reflecting end face 11b intersecting the predetermined axis X (that is, the optical axis of the laser light from the laser diode 11 is parallel to the predetermined axis X). ), Arranged coaxially with the lens 9c. The anode electrode of the laser diode 11 is electrically connected to a wiring pattern provided on the carrier 29 by a bonding wire. Similarly, the cathode electrode of the laser diode 11 is electrically connected to another wiring pattern provided on the LD carrier 29 by a bonding wire. Further, these wiring patterns are electrically connected to the lead terminals 7a of the CAN case 5 through bonding wires. The laser diode 11 can emit laser light having a light amount corresponding to the amount of drive current supplied via the lead terminal 7a from the light emitting end face 11a.

  On the other hand, the thermistor 27 is mounted on a second mounting surface 29b located on the opposite side of the first mounting surface 29a. One of the two electrodes of the thermistor 27 is electrically connected to the back surface wiring pattern 29d on the second mounting surface 29b by a bonding wire (electric connection wire) 27a. The back surface wiring pattern 29d is connected to the wiring pattern 29e on the first mounting surface 29a through a via electrode 29c penetrating the carrier 29 in the thickness direction. Further, the wiring pattern 29e is electrically connected to the lead terminal 7a of the CAN case 5 through a bonding wire (not shown). The other electrode of the two electrodes of the thermistor 27 is directly bonded to another back surface wiring pattern on the second mounting surface 29b, and although not shown in the drawing, the first electrode is connected via another via electrode. It is electrically connected to the wiring pattern 29f on the mounting surface 29a. Then, the wiring pattern 29f is electrically connected to the lead terminal 7a of the CAN case 5 via a bonding wire (not shown).

  The thermistor 27 generates an electric signal (temperature signal) according to the temperature of the laser diode 11 by changing its electric resistance value according to the temperature of the laser diode 11 transmitted through the carrier 29, and the lead terminal 7a is connected to the thermistor 27. The temperature signal can be output to the outside of the optical transmitter 1. An external control device (not shown) can control the temperature of the laser diode 11 to be constant by controlling the amount of control current to the thermoelectric conversion element 15 based on this temperature signal. it can.

  Since the carrier 29 as described above is fixed to the side surface 23a of the pedestal 23 with the second mounting surface 29b as a joining surface, the thermistor 27 and the bonding wire 27a are accommodated in the recess 23b of the pedestal 23. That is, it is located in a space surrounded by the pedestal 23 and the carrier 29. As described above, since the via electrode 29c is provided in the carrier 29, the thermistor 27 is connected to the lead terminal 7a via the via electrode 29c even in the closed space inside the pedestal portion 23. The electrical connection can be achieved.

  The photodiode 19 is a light receiving element for monitoring the light emission intensity of the laser diode 11. The photodiode 19 has a light receiving surface 19 a that faces the light reflecting end surface 11 b of the laser diode 11. One of the anode electrode and the cathode electrode of the photodiode 19 is directly joined to the PD carrier 21 by soldering or the like. The PD carrier 21 is electrically connected to the lead terminal 7a via a bonding wire. The other electrode of the photodiode 19 is electrically connected to another lead terminal 7a via a bonding wire. The photodiode 19 can output a current corresponding to the intensity of light (back light) from the light reflection end face 11b of the laser diode 11 to the outside of the optical transmitter 1 via the lead terminal 7a.

  The PD carrier 21 is a member for mounting the photodiode 19. The PD carrier 21 is disposed on the support plate 17 in the direction of the predetermined axis X with respect to the laser diode 11. The PD carrier 21 has a surface inclined at a predetermined angle with respect to the predetermined axis X, and the photodiode 19 is mounted on the inclined surface. As a result, the light receiving surface 19a of the photodiode 19 is also inclined at a predetermined angle with respect to the predetermined axis X (that is, the optical axis of the laser diode 11), and the return light from the photodiode 19 to the laser diode 11 is transmitted. Reduced.

  As in the present embodiment, the photodiode 19 is preferably provided on the base portion 7b (on the PD carrier 21) without the thermoelectric conversion element 15 interposed therebetween. The photodiode 19 is less affected by temperature changes than the laser diode 11 in a room temperature environment of −40 ° C. to 85 ° C. Accordingly, the photodiode 19 can be provided on the base portion 7b without using the thermoelectric conversion element 15, and the load (power consumption) of the thermoelectric conversion element 15 can be reduced.

  Then, the effect by the optical transmitter 1 of the above structures is demonstrated. In general, when driving a laser diode, the amount of current and the direction of the current to the thermoelectric conversion element are controlled so that the temperature signal from the thermistor approaches a value corresponding to the set temperature. For example, when the set temperature is 40 ° C., a feedback loop is formed by sending a control current based on the difference between the reference signal corresponding to 40 ° C. and the temperature signal from the thermistor to the thermoelectric conversion element, and the temperature from the thermistor The signal value can be kept at a value indicating 40 ° C. (constant).

  Here, when the ambient temperature of the light emitting module rises to, for example, 75 ° C., the case temperature rises accordingly, and heat radiation from the case to the thermistor occurs. Therefore, the temperature actually sensed by the thermistor is 40 + α [° C.] by adding the temperature increase α [° C.] due to radiant heat. Therefore, when the amount of current and the direction of the current to the thermoelectric conversion element are controlled so that the temperature signal value from the thermistor is kept at 40 ° C., as a result, it is supercooled by α [° C.]. As a result, the emission wavelength of the laser diode is shorter than the wavelength that should be output by A × α [nm] (A: correlation coefficient between temperature change and wavelength variation). When the ambient temperature of the light emitting module decreases, the temperature actually sensed by the thermistor is 40-β [° C.] by subtracting the temperature decrease β [° C.] contrary to the above. Accordingly, the laser diode is overheated by β [° C.], and the emission wavelength of the laser diode becomes longer by A × β [nm] than the wavelength that should be output.

  The amount of radiant heat from the case to the thermistor depends greatly on the distance between the thermistor and the case. In the case of the butterfly type package described in Patent Document 1, the distance between the thermistor and the case is sufficiently secured to be about 3 mm. On the other hand, in the case of the coaxial package as in the present embodiment, it is often very small, about 0.2 mm to 0.5 mm. One of the factors is that the case size of the butterfly package is generally about 10 mm square, whereas the case size of the coaxial package (the outer diameter of the CAN case 5) is relatively small, about 3 to 5 mm. It is. In the case of a coaxial package, the lens cap that holds the lens forms part of the CAN case. However, it is necessary to bring the laser diode and the lens close to the focal length, and the laser diode and the cap are inevitably placed. Proximity.

  On the other hand, in the optical transmitter 1 according to the present embodiment, the thermistor 27 is in a space surrounded by the pedestal portion 23 and the carrier 29, and the pedestal portion 23 has a constant temperature by the thermoelectric conversion element 15. The thermistor 27 is not easily affected by the temperature around the element mounting portion 3 such as radiant heat from the cap 9. Further, since the thermistor 27 is disposed at a position close to the laser diode 11 with a thin carrier 29 (having a thickness of about 0.2 mm) having high thermal conductivity, the temperature of the laser diode 11 is accurately measured in the thermistor 27. It is easy to be reflected in. As a result, in the optical transmitter 1, the thermistor 27 can monitor the temperature of the laser diode 11 with high accuracy.

  FIG. 4A is a graph showing the correlation between the temperature of the CAN case 5 and the emission wavelength shift (wavelength drift) of the laser diode 11 in the optical transmitter 1 described above. FIG. 4B is a graph showing the correlation between the temperature of the CAN case and the wavelength drift in the conventional optical transmitter shown in FIG. 1 of Patent Document 3 listed above for comparison. When obtaining these graphs, the drive current value to the laser diode is set to 40 [mA], and the temperature signal value from the thermistor is maintained at a value indicating 40 ° C. The amount of current and the direction of current were controlled.

  As shown in FIG. 4A, in the optical transmitter 1, even when the temperature of the CAN case 5 varies between −10 [° C.] and 80 [° C.], the wavelength drift width is 20 [pm]. ] Was able to fit within. On the other hand, as shown in FIG. 4B, in the conventional optical transmitter, when the case temperature varies between −40 [° C.] and 80 [° C.], the wavelength drift width is 200 [pm]. It became close. As described above, if the optical transmitter 1 capable of measuring the temperature of the laser diode 11 with high accuracy is used, the temperature of the laser diode 11 can be accurately controlled near the set temperature, and the wavelength drift of the laser light can be effectively reduced. Can be reduced.

  In addition, in the light emitting module of the coaxial package such as the optical transmitter 1 as described above, the distance between the laser diode 11 and the case 5 is narrow. A configuration covering the cooling member is difficult to realize. On the other hand, since the optical transmitter 1 is configured to accommodate the thermistor 27 in the internal space of the pedestal portion 23 by providing the recess portion 23b in the pedestal portion 23, the element mounting portion 3 is reduced in size. The configuration is suitable for a coaxial package.

  The optical transmitter described in Patent Document 4 uses an etalon and two photodiodes to monitor the emission wavelength of the laser diode and control the thermoelectric cooler. However, the mounting is complicated and the cost is increased. It becomes a factor of. The optical transmitter 1 is superior to the optical transmitter described in Patent Document 4 in that the cost can be easily reduced.

  In order to reduce the radiant heat from the cap with respect to the thermistor, an optical transmitter 51 including a pedestal portion 53 having an L-shaped cross section as shown in FIG. Further, as shown in FIG. 5B, an optical transmitter 61 provided with a pedestal 63 having a recess 65 for installing the thermistor 27 on the opposite surface of the laser diode 11 is also conceivable. However, in these optical transmitters 51 and 61, the distance between the thermistor 27 and the laser diode 11 is large, and pedestals 53 and 63 having a certain thickness exist between them. It cannot be said that the thermistor 27 accurately reflects the temperature of the laser diode 11. Further, when the optical transmitter 51 is assembled, the pedestal portion 53 is pressed from above and mounted on the thermoelectric conversion element 15. According to the shape of the pedestal portion 53, the pedestal portion 53 pushed from above is provided. There is also a problem that it is difficult to mount, such as being unstable and falling down. On the other hand, the optical transmitter 1 is superior to the optical transmitters 51 and 61 in that such a problem can be solved.

It is a partially broken perspective view which shows one Embodiment of the optical transmitter which concerns on this invention. It is the II-II sectional view taken on the line of the optical transmitter 1 shown in FIG. It is a partially broken perspective view which shows the base part and carrier of the optical transmitter of FIG. (A) is a graph which shows the wavelength drift in the optical transmitter shown in FIG. 1, (b) is a graph which shows the wavelength drift in the conventional optical transmitter. (A), (b) is a side view which shows the other optical transmitter which concerns on the comparison of the optical transmitter of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical transmitter, 7 ... Stem, 9a ... Lens cap, 11 ... Laser diode (semiconductor laser element), 15 ... Thermoelectric conversion element, 23 ... Base part, 23b ... Recessed part, 27 ... Thermistor, 29 ... Carrier, 29a ... First mounting surface (mounting surface of the semiconductor laser element), 29b... Second mounting surface (mounting surface of the thermistor), 29c.

Claims (2)

A carrier equipped with a semiconductor laser element and a thermistor;
A pedestal portion on which the carrier is mounted;
A thermoelectric conversion element mounted with the pedestal, and
A stem on which the thermoelectric conversion element is mounted;
An optical transmitter comprising a lens cap fixed to the stem,
The semiconductor laser element and the thermistor are mounted on opposite mounting surfaces of the carrier, and a wiring pattern electrically connected to the thermistor is formed on the mounting surface of the carrier,
The pedestal is provided with a recess, and the carrier is fixed to the pedestal so that the thermistor and a wire connecting the thermistor to the wiring pattern are accommodated in the recess. An optical transmitter.   The optical transmitter according to claim 1, wherein the carrier is provided with a via electrode that connects a mounting surface of the semiconductor laser element and a mounting surface of the thermistor.

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