JP2010123775A - Thermoelectric module for optical transmission module and optical transmission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a CAN-type thermoelectric module for an optical transmission module capable of efficiently radiating heat from a light emitting element and adapted to high-speed transmission, and to provide the optical transmission module. <P>SOLUTION: The thermoelectric module 25 has a structure in which a heat discharge side ceramic substrate 27 is formed to be wider than a heat absorption side ceramic substrate 26 and having power feeding wiring posts 29 at both sides, the heat absorption side ceramic substrate 26 has a pillar 30 protruding from one end of the heat discharge side ceramic substrate 27 and extending in the heat discharge ceramic substrate side, and a light emitting element 24 is mounted. The thermoelectric module is disposed so as to contact with one surface of a pedestal 23 protruding from the datum of a stem 21 where a lead terminal 22 is disposed to an optical axis direction, a wiring carrier 32 of a light emitting element is disposed on the other surface of the pedestal 23, and the thermoelectric module 25 is sealed by a CAN case 40 having a lens 41. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a thermoelectric module that controls the temperature of a light emitting element of an optical transmission module, and an optical transmission module using the thermoelectric module.

  The transmission speed of optical communication networks has been increased from 2.5 Gbps to 10 Gbps, and further to 100 Gbps. The transmission rate of 100 Gbps can be realized by, for example, combining 25 Gbps signals four times, but in this case, the wavelength interval of the four waves to be combined is small, so it is necessary to suppress wavelength fluctuation due to temperature changes. . Furthermore, when directly modulating a transmission rate of about 25 Gbps, it is necessary to stabilize the output characteristics of a light emitting element such as a laser diode (hereinafter referred to as LD). For this purpose, it is necessary to adjust the temperature of the light-emitting element even in the case of short-distance use.

  Conventionally, in order to make the characteristics of a light emitting element such as an LD constant, for example, an optical transmitter as disclosed in Patent Document 1 is known. As shown in FIG. 5, in this optical transmitter, a thermoelectric module 7 is mounted on a circular stem 2 in which lead terminals 3 are arranged, and an LD carrier 8 having good thermal conductivity is placed on the thermoelectric module. The LD 4 is mounted and sealed with a coaxial case (also called a CAN case). The signal light transmitted from the LD 4 is collected by the lens 5 attached to the CAN case 6 and is incident on an optical fiber (not shown).

  The thermoelectric module 7 is configured by arranging a first plate-like body 10 on the heat absorption side of the thermoelectric conversion element 9 and arranging a second plate-like body 11 on the exhaust heat side. An opening 10a through which the monitor light of the LD 4 passes is formed in a partial region of the first plate-like body 10, and the second plate-like body 11 has a region 11a coinciding with the opening 10a on the back side of the LD 4 A photodiode 12 (hereinafter referred to as PD) for monitoring the light output from the is mounted. Further, a thermistor 13 for detecting the temperature of the LD is mounted in a portion close to the LD 4.

  By using the thermoelectric module having the above configuration, the PD 12 that is also an element that stores heat in a steady state is mounted on the second plate-like body 11 on the exhaust heat side, and is mounted on the first plate-like body 10 on the heat absorption side. Only the LD 4 and the thermistor 13 are mounted. Thereby, the elements and components mounted on the first plate-like body 10 can be reduced, and the power consumption of the thermoelectric module 7 can be reduced.

Further, Patent Document 2 discloses a technology that eliminates parasitic reactance and enables impedance-matched high-speed modulation drive in a circuit from the input to the semiconductor laser in a coaxial semiconductor laser module. . Specifically, a coplanar line including a signal line and a ground line is formed on the heat sink plate, and the heat sink plate is disposed and fixed on a support base fixed to the stem. The lead terminal is directly connected to the line on the heat sink plate so as to eliminate parasitic reactance.
JP 2004-2537779 A JP 2004-356217 A

  In the optical transmitter shown in FIG. 5 (Patent Document 1), the LD 4 and the lead terminal 3 are normally electrically connected in the order of lead terminal → wire → LD carrier → wire → LD terminal. For this reason, there is no problem at a transmission rate of about 2.5 Gbps, but when the transmission rate is increased, the parasitic inductance due to the bonding wire cannot be ignored. For example, as shown in FIG. 6, the deterioration of the output waveform becomes more remarkable as the transmission speed becomes higher.

  The main cause of the output waveform deterioration is the structure of the thermoelectric module 7 and its supporting form. As shown in FIG. 5, the thermoelectric module 7 is usually structured such that the stem 2 that holds the lead terminals 3 and the exhaust heat side of the thermoelectric module 7 are adjacent to each other. For this reason, the LD 4 is vertically stacked on the thermoelectric module 7 mounted on the reference surface of the stem 2, and the lead terminal 3 extends from the stem side to the position of the LD 4 and is wire-connected. Since the surroundings of the lead terminal 3 connected to the LD 4 are air, even if impedance matching is achieved at the stem penetrating portion, impedance mismatch occurs inside the CAN case. Note that the length of the lead terminal 3 is also a cause of the waveform deterioration shown in FIG.

  As a form for eliminating adverse effects such as impedance mismatch due to parasitic inductance, it is effective to shorten the wire length and the length of the lead terminal as disclosed in Patent Document 2. However, Patent Document 2 does not disclose the relationship with the heat radiation of the LD, and it is not easy to apply the technique related to impedance matching to the optical transmitter (optical transmission module) shown in FIG. For example, even if the width of the LD carrier 8 in FIG. 5 is increased and the lead terminals 3 are directly connected, the length of the lead terminals 3 cannot be shortened, and it is difficult to increase the transmission speed.

  The present invention has been made in view of the above-described circumstances, and provides a thermoelectric module for an optical transmission module and an optical transmission module that are CAN-type, can effectively dissipate heat generated by a light emitting element, and can support high-speed transmission. With the goal.

  A thermoelectric module for an optical transmission module according to the present invention is a thermoelectric module having a light emitting element mounting portion and including a thermoelectric conversion element, an exhaust heat side ceramic substrate, and an endothermic side ceramic substrate. The heat exhaust side ceramic substrate is wider than the heat absorption side ceramic substrate, and has power supply wiring posts on both sides. The heat absorption side ceramic substrate has a columnar portion on which a light emitting element that protrudes from one end portion of the heat exhaust side ceramic substrate and extends toward the heat exhaust side ceramic substrate is mounted.

In addition, the optical transmission module according to the present invention includes a light emitting element or a carrier having a light emitting element mounted on the thermoelectric module, and one surface of a pedestal protruding in the optical axis direction from a reference surface of a stem on which a lead terminal is disposed Further, the exhaust heat-side ceramic substrate of the thermoelectric module is disposed so as to be in contact therewith, and the wiring carrier of the light emitting element is disposed on the other surface of the pedestal, and is sealed by a CAN case having a lens.
A light receiving element for monitoring the light emitting element is mounted on the wiring carrier. The wiring conductor of the wiring carrier is connected to the light emitting element by a plurality of wires parallel to each other, and is directly connected to the lead terminal for impedance matching. A thermistor is mounted on the heat absorption side ceramic substrate of the thermoelectric module.

  According to the present invention, in a coaxial optical transmission module capable of adjusting the temperature, only the light emitting element is cooled on the heat absorption side ceramic substrate of the thermoelectric module to reduce power consumption and to shorten the wiring path length. It can reduce parasitic impedance and achieve impedance matching and enable high-speed transmission.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an assembled state of components in the optical transmission module, FIG. 2 shows a state seen from the opposite direction of FIG. 1, and FIG. 3 shows an outline of the thermoelectric module. In the figure, 20 is an optical transmission module, 21 is a stem, 21a is a reference plane, 22, 22a to 22g are lead terminals, 22 'is a ground post, 23 is a base, 24 is a light emitting element, 25 is a thermoelectric module (TEC), 26 is a heat absorption side ceramic substrate, 27 is an exhaust heat side ceramic substrate, 28 is a thermoelectric conversion element, 29 is a wiring post, 30 is a columnar portion, 30a is a top portion, 30b is a back surface, 31 is an LD carrier, 32 is a wiring carrier, 33a 33b is a wiring conductor, 33c is a solid conductor, 34 is a light receiving element, 35 is a chip coil, 36 is a thermistor, 37 is a lead auxiliary member, 38 is a soldering portion, 39a to 39f are bonding wires, 40 is a CAN case, 41 Indicates a lens.

  As shown in FIGS. 1 and 2, an optical transmission module 20 according to the present invention includes a thermoelectric module 25 (hereinafter referred to as TEC) mounted on a circular stem 21 in which a plurality of lead terminals 22 are disposed. A light emitting element 24 (hereinafter referred to as an LD) such as a laser diode is mounted on the module so that the temperature can be controlled. Then, in order to accommodate these mounted components, the light emitted from the LD 24 is sealed with a cylindrical CAN case 40 provided with a lens 41 for condensing the light emitted from the LD 24 onto an optical fiber (not shown). Configured as a transmission module.

  The stem 21 is formed of a thermally conductive and conductive metal in a disc shape, and among the plurality of lead terminals 22, the signal transmission lead terminal is electrically insulated by a glass seal, and is connected to a ground lead. The terminal is directly connected to the stem and fixed. A pedestal 23 is provided in the central region of the stem 21 so as to protrude perpendicularly from the reference surface 21a in the optical axis direction. The TEC 25 is disposed so that one surface of the pedestal 23 is in contact with the other surface. It arrange | positions so that the carrier 32 may touch. The TEC 25 has a structure in which a plurality of thermoelectric conversion elements 28 are arranged between the heat absorption side ceramic substrate 26 and the exhaust heat side ceramic substrate 27, and the exhaust heat side ceramic substrate 27 is arranged so as to be in contact with the pedestal 23.

  As shown in the enlarged schematic diagram of FIG. 3, the TEC 25 has electrodes formed in a predetermined pattern on opposing surfaces of the heat absorption side ceramic substrate 26 and the exhaust heat side ceramic substrate 27, and a plurality of thermoelectric conversion elements 28 are (P A type and an N type element are alternately connected in series, and the electrodes at both ends are connected to the feed conductor. In the present invention, the width of the exhaust heat side ceramic substrate 27 is made larger than the width of the heat absorption side ceramic substrate 26, and wiring posts 29 are provided at portions of the exhaust heat side ceramic substrate 27 protruding from both sides of the heat absorption side ceramic substrate 26. Suppose that it is a terminal for power feeding.

  Further, one end of the heat absorption side ceramic substrate 26 is formed with a length protruding from the end of the exhaust heat side ceramic substrate 27, and a columnar portion 30 extending toward the exhaust heat side ceramic substrate 27 is provided in this portion. A light emitting element as a heat generating member is mounted on the top portion 30a of the columnar portion 30 as described later. The columnar portion 30 is formed of a material having a high thermal conductivity (metal or ceramic) and may be integrally formed from the same material as the heat absorption side ceramic substrate 26, but is formed separately and integrated. It may be. Further, a solid conductor 33c (see FIG. 2) can be formed on the back surface 30b of the heat absorption side ceramic substrate 26 as a ground conductor.

  Returning to FIGS. 1 and 2, the entire assembly structure will be described. The LD 24 is mounted on the columnar portion 30 of the heat absorption side ceramic substrate 26 of the TEC 25 via an LD carrier 31 having good thermal conductivity. In the wiring carrier 32 arranged on the other surface of the pedestal 23, wiring conductors 33a and 33b for supplying a driving current to the LD 24 are formed as differential lines, and a bonding wire 39a (hereinafter simply referred to as a wire) is formed on the LD 24. Connected. It is desirable to use a wire 39a having a small parasitic inductance such as a ribbon wire. Further, by arranging the wiring conductors 33a and 33b and the wire 39a in parallel with each other, the parasitic inductance due to the influence of the mutual inductance can be reduced.

  The wiring conductors 33a and 33b on the wiring carrier 32 are connected to the LD driving lead terminals 22a and 22b. In this connection, it is desirable that the end portions of the wiring conductors 33a and 33b are abutted against the tops of the lead terminals 22a and 22b to form a soldering portion 38 and are directly connected by solder. Further, a chip coil 35 for LD power supply is mounted on the wiring conductors 33a and 33b, and is connected to the lead terminal 22c by a wire 39c. Moreover, a thin film resistor (not shown) can be inserted in the middle of the wiring conductors 33a and 33b for impedance matching.

  The wiring carrier 32 can be mounted with a photodiode 34 (hereinafter referred to as PD) that detects the light emitted backward from the LD 24 and monitors the light output of the LD. The PD 34 is disposed at a position where the light emitted from the LD 24 can be received, and one of the two PD electrodes is connected to the monitoring lead terminal 22d by a wire 39b. The other electrode is connected to the stem 21 by providing a via or metallized wiring provided on the wiring carrier, or connected to the stem 21 using a grounding post or the like and connected to the ground.

  As described above, in order to efficiently dissipate the heat generated by the LD 24 as much as possible, the heat absorption side ceramic substrate 26 can effectively operate the TEC by not mounting a heat generating member other than the LD 24 or a member having a large heat capacity. Therefore, low power consumption can be realized. However, in order to accurately detect the operating temperature of the LD 24 and perform appropriate drive control, the temperature detection thermistor 36 needs to be arranged as close to the LD 24 as possible to perform accurate temperature measurement. For this reason, the thermistor 36 is mounted on the heat absorption side ceramic substrate 26 on which the LD 24 is mounted.

  The thermistor 36 is mounted on, for example, the base portion of the columnar portion 30 on which the LD 24 is mounted. One terminal of the thermistor 36 is connected to the lead auxiliary member 37 using a wire 39d, and the other terminal is formed on the back side of the heat absorption side ceramic substrate 26 via a via or the like provided in the mounting portion. It is electrically connected to the solid conductor 33c. When a via is not provided in the mounting portion of the thermistor 36, the side surface of the heat absorption side ceramic substrate 26 may be metalized to be grounded to the solid conductor 33c.

  The heat absorption side ceramic substrate 26 is arranged in a state of being lifted from the reference surface 21 a of the stem 21 and is thermally separated from the stem 21. For this reason, the solid conductor 33c formed on the entire back surface of the heat absorption side ceramic substrate 26 is also separated from the reference surface 21a of the stem 21 and is not electrically connected. Accordingly, the solid conductor 33c is grounded by being electrically connected to the ground post 22 'provided on the stem 21 and electrically conducting by the wire 39f.

  The lead auxiliary member 37 that is wire-connected to the thermistor 36 is formed in a J shape, for example. The end opposite to the end connected to the wire is directly connected to the lead terminal 22g by solder or the like and supported and fixed. Instead of using the lead auxiliary member 37, a wiring path for the thermistor 36 may be provided on the heat absorption side ceramic substrate 26 by metallization or the like and electrically connected to the lead terminal 22g by wire connection. Further, the wiring posts 29 provided on both sides of the exhaust heat side ceramic substrate 27 are electrically connected to the lead terminals 22e and 22f for supplying power to the TEC 25 using the wires 39e.

  FIG. 4 is a circuit diagram of the optical transmission module 20 described above, and shows a connection state between each mounted component and the lead terminal. The LD 24 is connected to the lead terminals 22a and 22b through impedance matching thin film resistors R to the wiring conductors 33a and 33b of the differential line, and a modulation current signal is supplied to the LD 24 from the signal control circuit IC through the capacitor C. The LD 24 is connected to the lead terminal 22c via a coil L (chip coil 35) and supplied with a bias current and the like. The PD 34 connects the anode electrode to the lead terminal 22d and connects the cathode electrode to the ground (stem) to monitor the light emission output of the LD 24.

  The TEC 25 is connected to the lead terminals 22e and 22f from the wiring post provided on the above-described heat-exhaust-side ceramic substrate, and supplied with a feeding current for cooling control. The shape of the wiring post may be L-shaped to facilitate wiring. The thermistor 36 for detecting the temperature of the LD 24 has one terminal connected to the lead terminal 22g and the other terminal connected to the wire 39f, the ground post 22 ', and the stem 21 via the solid conductor 33c.

The optical transmission module configured as described above can be configured as a coaxial module in which the LD 24 is mounted on the stem 21 and sealed with the CAN case 40. In the TEC 25 that controls the temperature of the LD 24 that is a light emitting element, a thermistor 36 is mounted on the heat absorption side ceramic substrate 26, but only the LD 24 is mounted as a heating element. Further, the heat absorption side ceramic substrate 26 is floated from the stem 21 and has a small heat capacity. As a result, the TEC 25 can significantly reduce power consumption for cooling.
The wiring of the LD 24 is connected to the wiring conductors 33a. In 33b, it is possible to reduce the parasitic impedance by shortening the wire length, reduce the noise, and make the impedance matching possible.

It is a figure explaining the outline of the optical transmission module by this invention. It is the figure seen from the opposite side of FIG. It is a figure which shows the outline of the thermoelectric module by this invention. It is a figure which shows the circuit diagram of the optical transmission module 20 by this invention. It is a figure explaining the prior art. It is a figure which shows the state of the conventional transmission signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Optical transmission module, 21 ... Stem, 21a ... Reference plane, 22, 22a-22g ... Lead terminal, 22 '... Ground post, 23 ... Base, 24 ... Light emitting element (LD), 25 ... Thermoelectric module (TEC), 26 ... heat absorption side ceramic substrate, 27 ... waste heat side ceramic substrate, 28 ... thermoelectric conversion element, 29 ... wiring post, 30 ... columnar portion, 30a ... top portion, 30b ... back surface, 31 ... LD carrier, 32 ... wiring carrier, 33a , 33b ... wiring conductor, 33c ... solid conductor, 34 ... light receiving element (LD), 35 ... chip coil, 36 ... thermistor, 37 ... lead auxiliary member, 38 ... soldering part, 39a-39f ... bonding wire, 40 ... CAN Case, 41 ... lens.

Claims (5)

A thermoelectric module for an optical transmission module having a mounting portion for a light emitting element, and comprising a thermoelectric element, a heat exhaust side ceramic substrate, and a heat absorption side ceramic substrate,
The exhaust heat side ceramic substrate is wider than the heat absorption side ceramic substrate, and has power supply wiring posts on both sides,
The heat absorption-side ceramic substrate has a columnar portion on which the light-emitting element that protrudes from one end portion of the exhaust heat-side ceramic substrate and extends toward the exhaust heat-side ceramic substrate is mounted. Thermoelectric module for transmission module.   The exhaust heat-side ceramic substrate of the thermoelectric module is in contact with one surface of a pedestal that protrudes in the optical axis direction from the reference surface of the stem on which the light emitting element is mounted and the lead terminal is disposed. An optical transmission module, wherein a wiring carrier is disposed on the other surface of the pedestal and sealed with a CAN case having a lens.   The optical transmission module according to claim 2, wherein a light receiving element for monitoring the light emitting element is mounted on the wiring carrier.   The wiring conductor of the wiring carrier is connected to the light emitting element by a plurality of wires parallel to each other, and is directly connected to the lead terminal to be impedance-matched. Optical transmission module.   The thermistor is mounted in the heat absorption side ceramic substrate of the said thermoelectric module, The optical transmission module of any one of Claims 2-4 characterized by the above-mentioned.

Images