Photoelectric device with optical fiber and laser emitting chip

What is claimed is:

1. A photoelectric device comprising:

a package including a wall;

a laser light emitting chip disposed within the package and capable of emitting laser light along an optical axis;

an optical fiber having a tip at one end which faces said chip, said tip being positioned to receive said laser light and spaced from said chip;

a first fixing means for securing the optical fiber to the wall of said package;

a second fixing means disposed between the optical fiber tip and the first fixing means for fixing the position of the optical fiber tip within said package; and

said first fixing means being positioned to have an offset relation from the optical axis of the light emitting chip.

2. A photoelectric device as recited in claim 1, wherein said first fixing means is biased to one side of a prolongation of the optical axis.

3. A photoelectric device as recited in claim 1, wherein said optical fiber is formed of quartz glass.

4. A photoelectric device as recited in claim 1, wherein said optical fiber is held fixedly by metallic holding members.

5. A photoelectric device as recited in claim 4, wherein said optical fiber is soldered to said second fixing means.

6. A photoelectric device as defined in claim 1 wherein said second fixing means includes a tubular positioning member formed of a deformable thin walled material having first and second end portions through which the optical fiber extends;

said first end portion being secured to a rigid support and said second end portion being spaced from the rigid support so as to be movable relative to said support; and

means engaging only the second end portion of the tubular member for holding the optical fiber in a position within said tubular member whereby displacement of the second end portion of the tubular member in a direction lying in a plane that is perpendicular to the optical axis positionally moves the optical fiber tip relative to the optical axis of the emitted laser light.

7. A photoelectric device comprising: a package, a laser light emitting chip disposed within said package, an optical fiber having a free end which receives the laser light emitted from said laser light emitting chip and transmits the laser light, and a light receiving element which receives the laser light emitted from said laser light emitting chip, characterized in that said laser light emitting chip, said light receiving element and a free end of said optical fiber located opposite to said laser light emitting chip are fixed to a heat sink fixedly provided on the bottom wall of said package; and

said laser light emitting chip is biased to one side of the center axis of said package so that the electrodes thereof can be electrically connected to corresponding leads by short wires.

8. A photoelectric device as recited in claim 7, wherein a thermistor for detecting the temperature of said heat sink is attached to said heat sink.

9. A photoelectric device as recited in claim 7, wherein a Peltier element for cooling said heat sink is provided contiguously with the bottom surface of said heat sink.

10. A photoelectric device as recited in claim 7, wherein said package has a fixing point, said heat sink supports a positioning and fixing member which in turn supports said optical fiber at a fixing point and said optical fiber extends in a nonlinear shape between the fixing point on said positioning and fixing member and a fixing point on said package.

11. A photoelectric device as recited in claim 7, wherein said optical fiber is passed through and fixed to a tubular positioning and fixing member capable of plastic deformation, fixedly penetrating a holding part formed in said heat sink.

12. A photoelectric device comprising: a heat sink having a center axis, a holding part and a supporting part formed in the main surface thereof; a laser light emitting chip mounted on said holding part and biased to one side of the center axis of said heat sink; a tubular positioning and fixing member fixed to said supporting part to fixedly hold an optical fiber which receives the laser light emitted from said laser light emitting chip; and a chip carrier mounted with a light receiving element which receives the laser light emitted from said laser light emitting chip on one surface thereof and fixed to the main surface of said heat sink.

13. A photoelectric device as recited in claim 12, wherein a thermistor for detecting the temperature of said heat sink is attached to said heat sink.

14. A photoelectric device as recited in claim 12, wherein said positioning and fixing member is capable of deforming plastically within a plane perpendicular to the axis of said optical fiber.

15. A photoelectric device as recited in claim 12, wherein a recess for use as a fulcrum for leverage in deforming said positioning and fixing member is formed in said heat sink.

16. A photoelectric device as recited in claim 12, wherein said positioning and fixing member is biased to one side of the center axis of said heat sink, and the axis of said positioning and fixing member is inclined at a predetermined angle to the center axis of said heat sink.

17. A photoelectric device as recited in claim 12, wherein solder is attached in an annular shape to the free end of said positioning and fixing member.

18. A photoelectric device comprising:

a heat sink having a holding part and a supporting part formed in the main surface thereof;

a laser light emitting chip mounted on said holding part;

a tubular positioning and fixing member fixed to said supporting part to fixedly hold an optical fiber which receives the laser light emitted from said laser light emitting chip; and

a chip carrier mounted with a light receiving element which receives the laser light emitted from said laser light emitting chip on one surface thereof and fixed to the main surface of said heat sink wherein the light receiving surface of said light receiving element is inclined to the optical axis of the laser light.

19. A photoelectric device comprising:

a laser light emitting chip capable of emitting light along an optical axis;

an optical system which receives light from said chip and which includes an optical fiber having a tip spaced from said chip and adapted to receive said emitted light; and

means mounting said optical fiber so that said tip is capable of positional movement in any direction in a plane that is perpendicular to the optical axis without subjecting the optical fiber to tensile stress thereby to precisely align the optical fiber tip with said optical axis including a tubular positioning member having deformable, thin walls, the tubular member being rigidly supported at one end and engaging the optical fiber only at its other end whereby displacement of said second end portion of the tubular member positionally moves the optical fiber tip.

20. A photoelectric device comprising:

laser light emitting chip capable of emitting light along an optical axis;

an optical fiber having a tip spaced from said chip and adapted to receive said emitted light;

means mounting said optical fiber so that the tip is capable of positional movement in any direction in a plane that is perpendicular to the optical axis without subjecting the optical fiber to stress along the length of the fiber, said mounting means including a tubular positioning member formed of deformable, thin walls and having first and second end portions;

means mounting said first end portion to a rigid support;

means securing a portion of the optical fiber at said second tubular member end portion whereby displacement of the second end portion of the tubular member positionally moves the optical fiber tip.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates to a photoelectric device and, more specifically, to a photoelectric device having a package containing a laser chip which emits laser light, and an optical fiber cable which guides the laser light emitted from the laser chip outside the package.

A semiconductor laser device is used as a light source for the optical communication system. An exemplary laser module, namely, a semiconductor laser device, for the optical communication system is published in "Hitachi Hyoron", Hitachi Hyoron Sha, No. 10, pp. 39-44, Oct., 1983. This semiconductor laser device is of a so-called direct disposition system, in which the free end of the optical fiber is disposed opposite to the resonant end face of the semiconductor laser element, and is formed in a flat module having a box-shaped package. This semiconductor laser device has a metallic stem with the central portion of the main plane thereof sealed by a cap formed of a metallic plate and is provided internally with a semiconductor laser element (laser diode chip) and a light receiving element which detects the optical output of laser light emitted from the resonant end face of the laser diode chip. Further, this semiconductor laser device employs a laser diode chip which emits a laser light of a 1.3 .mu.m band, and a single-mode optical fiber for long-distance large-capacity communication. In this semiconductor laser device, the free end of the optical fiber facing the light emitting surface of the laser diode chip are supported on a positioning shaft, which is bent to adjust the position of the free ends of the optical fiber for optical axis alignment.

The applicant of this patent application has proposed a technique to improve the efficiency of the optical connection of the laser diode chip and the optical fiber of a semiconductor laser device in Japanese Patent Application No. 58-151560. According to this technique, the free end of the optical fiber is held by a flexible holder, and an external force is applied to the head of the flexible holder after fixing the optical fiber and the laser diode chip to adjust the position of the free ends of the optical fiber so that the respective optical axis of the optical fiber and the laser diode chip are aligned with each other.

A light emitting module for optical communication is published in "NEC Giho", Vol. 38, No. 2, pp. 84-89, 1985. This light emitting module comprises, in a package, a laser element which emits a laser light, a Ge-PD (light receiving element) for monitoring the back radiation of the laser element, a thermistor for monitoring the temperature of the laser element, and a Peltier element functioning as a temperature regulating cooler; an optical fiber cable for transmitting the laser light outside the package is connected to the package. The light emitting module is a dual in line package. The laser element and the thermistor are mounted on a block fixed on the Peltier element, while the optical fiber is secured to the block. The light receiving element is fixed to the block.

In either foregoing semiconductor laser device, the optical fiber is disposed with the free end thereof opposite the laser diode chip and are held fixedly at a position near the wall of the package and at a position near the laser diode so as to extend linearly between the two positions.

SUMMARY OF THE INVENTION

As is described in the cited papers, to enable a semiconductor laser device to function fully and stably as a component of an optical communication equipment, it is essential to align the respective optical axes of the laser diode chip and the optical fiber at a high accuracy and to maintain the configuration of the parts, which are positioned at a high accuracy, for an extended period of time.

In the conventional semiconductor laser device, the optical fiber is held fixedly at a position near the laser diode chip and at a position near the wall of the package so that the optical fiber will extend linearly between the two positions. Since the optical fiber is formed of quartz having a coefficient of thermal expansion which is far smaller than that of metals forming holding members holding the optical fiber at the two positions, the optical fiber linearly extended between the two position is unable to follow the variation of the distance between the two positions attributable to temperature variation when the distance between the two positions is as small as several millimeters to several tens millimeters. It has been found by the inventors of the present invention that, since the optical fiber is unable to follow the variation of the distance between the two holding positions, the optical fiber or the solder fixing the optical fiber is subjected to repeated stress and thereby the solder is caused to fracture and the optical fiber is caused to break by buckling. Since the fatigue fracture of the solder make the solder unable to hold the optical fiber securely, the free end of the optical fiber is dislocated to deteriorate the optical connection of the optical fiber and the laser diode chip making optical communication impossible. Optical communication is obliged to be interrupted also by the buckling of the optical fiber.

Furthermore, the disposition of the light receiving element for monitoring the laser light, and the thermistor for temperature detection also is important to enable all the parts to exhibit their full functions. Moreover, since those parts which need to be assembled at a high accuracy are very small, a technique for integrally assembling those very small parts in a module is important in respect of the improvement of the reliability of the semiconductor laser device, productivity of the production line and yield, and the reduction of the manufacturing cost of the semiconductor laser device.

On the other hand, as is described in the cited papers, a technique for aligning the optical axes to enable the optical fiber to efficiently receive the laser light emitted from the light emitting surface of the laser diode chip is very important to improve the reliability of the semiconductor laser device and the yield of the manufacturing process.

As is further described in the cited papers, leads of 0.45 mm in diameter are arranged on the bottom wall of the package to construct a dual in line package. In such a semiconductor laser device, the leads penetrate the bottom wall of the package and hence the length of each lead extending from the bottom wall is large. The inventors of the present invention have found that such a lead vibrates in connecting a wire to the upper end of the lead through ultrasonic bonding to the upper end of the lead, and thereby the wire is unable to be connected to the upper end of the lead satisfactorily. The inventors found a further disadvantage of such a long lead that an increased parasitic inductance of the long lead deteriorates the high-frequency band characteristics.

As is described in the cited paper, Hitachi Hyoron, also important is a technique for aligning the respective optical axes of the laser diode chip and the optical fiber to secure the satisfactory optical connection of the laser diode chip and the optical fiber. To maintain the optical connection as assembled, the optical fiber needs to be fixed near the free end thereof. Generally, solder, which does not produce any gas, is used as a bonding material for fixing the optical fiber, to enhance the reliability of the semiconductor laser device.

The inventors of the present invention have found that, in some cases, the optical fiber correctly positioned relative to the laser diode chip is dislocated in fixing the optical fiber to a holding member by soldering. Generally, the holding members holding the optical fiber and the laser diode chip, and a base supporting those holding members are formed of metals, respectively. Accordingly, in soldering the optical fiber to the holding member, the holding member is heated locally and the heat is transferred from the holding member to the base making the holding member unable to be heated to a temperature necessary for soldering. Furthermore, since the soldering heat is transferred to the base to heat the peripheral parts causing the thermal expansion and deformation of those peripheral parts, so that the disposition of the laser diode and the optical fiber is varied causing the deterioration of the alignment of the respective optical axes of the laser diode chip and the optical fiber, which has been adjusted previous to soldering. If the optical fiber is thus fixed with their optical axes in misalignment with the optical axis of the laser diode chip, the efficiency of the optical connection of the laser diode and the optical fiber is reduced, and hence the semiconductor device cannot be used, and reassembling the faultily assembled semiconductor laser device requires troublesome work.

It is therefore a first object of the present invention to provide a photoelectric device the efficiency of the optical connection of which is not affected by temperature variation.

It is a second object of the present invention to provide a photoelectric device having an optical fiber and optical fiber fastening parts which are not damaged even when subjected to temperature variation.

It is a third object of the present invention to provide a technique for aligning optical axes at high accuracy.

It is a fourth object of the present invention to provide a photoelectric device having high reliability.

It is a fifth object of the present invention to provide a highly productive technique for manufacturing a photoelectric device.

It is a sixth object of the present invention to provide a technique for manufacturing a photoelectric device at a reduced manufacturing cost.

It is a seventh object of the present invention to provide electronic parts of constructions which enable reliable ultrasonic bonding.

It is an eighth object of the present invention to provide electronic parts of constructions reducing the parasitic inductances of the leads and the like.

It is a ninth object of the present invention to provide electronic parts capable of functioning in high-frequency bands.

It is a tenth object of the present invention to provide electronic parts of constructions permitting efficient local heating in a short time.

It is an eleventh object of the present invention to provide a semiconductor laser device of a construction capable of being assembled without spoiling the efficiency of optical connection secured in a preparatory assembling process.

The above and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing the essential portion of a photoelectric device, in a first embodiment, according to the present invention;

FIG. 2 is a perspective view of the photoelectric device of FIG. 1;

FIG. 3 is a sectional view of the photoelectric device of FIG. 1;

FIG. 4 is a sectional side elevation of the photoelectric device of FIG. 1;

FIG. 5 is a perspective view of the subcarrier of the photoelectric device of FIG. 1;

FIG. 6 is a plan view of a heat sink provided on the subcarrier of FIG. 5;

FIG. 7 is a fragmentary sectional view of an optical fiber positioning and fastening member provided on the subcarrier of FIG. 5;

FIG. 8 is a perspective view of assistance in explaining a mode of mounting a laser diode chip on the subcarrier;

FIG. 9 is a perspective view of a package body;

FIG. 10 is an enlarged fragmentary sectional view showing leads and lead reinforcing members;

FIG. 11 is a sectional view showing a Peltier element and a subcarrier mounted on the package body of FIG. 9;

FIG. 12 is a sectional view showing an optical fiber fastened to the subcarrier;

FIG. 13 is a diagrammatic view showing a manner of fastening an optical fiber;

FIG. 14 is a perspective view of assistance in explaining a manner of aligning the optical axes of a laser diode chip and an optical fiber;

FIG. 15 is a perspective view of assistance in explaining directions of movement of the optical fiber positioning and fastening member;

FIG. 16 is a sectional view showing the essential portion of a photoelectric device, in a second embodiment, according to the present invention;

FIG. 17 is a perspective view showing the essential portion of a photoelectric device, in a third embodiment, according to the present invention;

FIG. 18 is a perspective view showing the essential portion of a photoelectric device, in a fourth embodiment, according to the present invention;

FIG. 19 is a schematic illustration of assistance in explaining a manner of fastening the leads of a photoelectric device, in a fifth embodiment, according to the present invention;

FIG. 20 is a perspective view showing the essential portion of the photoelectric device of FIG. 19;

FIG. 21 is a sectional view showing the essential portion of a photoelectric device, in a sixth embodiment, according to the present invention;

FIG. 22 is a sectional view showing the essential portion of a semiconductor laser device, in a seventh embodiment, according to the present invention;

FIG. 23 is a general perspective view of the semiconductor laser device of FIG. 22; and

FIG. 24 is a sectional view showing the positioning pin for positioning and fixing the optical fiber of a modification of the semiconductor laser device of FIG. 22 according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A photoelectric device, in a first embodiment, according to the present invention will be described with reference to FIGS. 1 through 15 as applied to an originating device incorporating a laser diode chip which emits a laser light of 1.3 or 1.5 .mu.m in wavelength, for use in optical communication systems.

Referring to FIGS. 1 to 4, the photoelectric device has a box-shaped package 1. The package 1 has one end provided with a flange 3 having through holes 2 for receiving fastening members for fastening the package 1 and the other end provided with a fiber guide 4 for guiding an optical cable 5. The photoelectric device is of a dual in line construction having leads 6 arranged in two rows and penetrating the bottom wall of the package 1. The package 1 consists of a box-shaped package body 7 having an upper opening and a lid 8 hermetically covering the upper opening of the package body 7. A base plate 9 is fixed to the upper surface of the bottom wall of the package body 7; a Peltier element 10 is mounted fixedly on the base plate 9; a subcarrier 11 is mounted fixedly on the Peltier element 10. The subcarrier 11 comprises a heat sink 14 having a holding part 12 and a supporting part 13 rising from the main surface thereof, a laser diode chip 15 held on the holding part 12, a tubular positioning and fixing member 17 for positioning and fixing a optical fiber 16 which receives the laser light emitted from the laser diode chip 15, a light receiving element 18 for monitoring the laser light, and a thermistor 19 for monitoring the temperature of the heat sink 14. In the package 1, the jacket of the optical fiber cable 5 is removed to expose the optical fiber 16 each having a core and a cladding enclosing the core. The free end of the exposed optical fibers 16 is held by the positioning and fixing member 17 so as to be disposed opposite to one of the light emitting faces of the laser diode chip 15. The respective electrodes of the elements are connected to the corresponding leads 6 by conductive wires 20, respectively. In this photoelectric device, neither a resin nor a soldering flux is filled in the package 1 to obviate the deterioration of the characteristics of the photoelectric device attributable to a resin or a soldering flux.

The laser light emitted from the laser diode chip 15 is transmitted to a desired place through the optical fiber cable 5 for optical communication. The output of the laser diode chip 15 is controlled on the basis of the output of the light receiving element 18 monitoring the laser light for stable optical communication. The Peltier element 10 is controlled on the basis of the output of the thermistor 19 monitoring the temperature of the heat sink 14 so that the laser diode chip 15 is maintained at a fixed temperature for stable optical communication.

Incidentally, the photoelectric device is characterized in that the optical fiber 16 is extended slack in a moderate curve between the fiber guide 4 attached to one end of the package body 7 and the positioning and fixing member 17 of the subcarrier 11 as illustrated in FIGS. 1 and 13. Fixing members fixing the optical fiber 16 to the subcarrier 11 and to the fiber guide 4 are formed of a metal such as, for example, covar, and the optical fiber 16 is formed of a quartz glass having a coefficient of thermal expansion which is far smaller than those of metals. Therefore, the optical fiber 16 is unable to follow the variation of the distance between the fixing positions attributable to the variation of temperature if the optical fiber 16 is taut between the subcarrier 11 and the fiber guide 4. Consequently, the optical fiber 16 and the solder fixing the optical fiber 16 are subjected to repeated stress, and thereby the optical fiber 16 is buckled and the solder is caused to fracture by fatigue making stable light transmission impossible. When the optical fiber 16 is extended slack in a moderate curve between the fixing positions, the optical fiber 16 is allowed to bend as indicated by an alternate long and short dash line or by an alternate long and two short dashes line in FIG. 13 when one of the fixing positions is shifted toward the fiber guide 4 from a point A to a point C or away from the fiber guide 4 from the point A to a point B, so that the optical fiber 16 is not exposed to an excessive stress and are not damaged. Accordingly, the optical fiber 16 is not subjected to repeated stress and hence the solder fixing the optical fiber 16 is not caused to fracture by fatigue.

The components of the photoelectric device will be described hereinafter. The photoelectric device is assembled by integrating several subassemblies. For example, principal subassemblies are the package body 7 and the subcarrier 11. The subassemblies will be described prior to the description of the general construction of the photoelectric device and a manner of assembling the same.

As mentioned above, the package 1 consists of the box-shaped package body 7 and the flat lid 8, which are formed of Kovar, namely, an iron/nickel/cobalt (Fe/Ni/Co) alloy.

Referring to FIG. 9, the package body subassembly comprises the package body 7 as a principal component, the flange 3, the fiber guide 4, the leads 6 and the base plate 9. The flange 3 having through holes 2 is attached to one end of the package body 7. The leads 6 are arranged in two rows, for example, seven leads 6 in each row, on the bottom wall of the package body 7 as illustrated in FIG. 10. Each lead 6 penetrates the bottom wall of the package body 7 and is secured to and insulated from the bottom wall of the package body 7 by an insulating fixing material 21 such as, for example, a borosilicate glass. As shown in FIGS. 1 and 2, for example, the respective left end leads 6 of the front and back rows are the external terminals of the light receiving element 18, leads 6 second and third from the left of the front row are the external terminals of the laser diode chip 15, the leads fourth and fifth from the left of the front row are the external terminals of the thermistor 19, the respective right end leads 6 of the front and back row are the external terminals of the Peltier element 10, and the rest of the leads 6 are idle leads which are not used in this embodiment.

Wires 20 are connected to the Peltier element 10 by welding or the like without using a resin or a flux, while the rest of the wires 20 are connected to the leads 6 by ultrasonic bonding. In an ultrasonic bonding process, the wires 20 are bonded to the leads 6 by means of ultrasonic vibrations. Therefore, in connecting the wires 20 to the respective upper end of the long leads 6. The leads 6 are liable to be vibrated making satisfactory bonding impossible. Accordingly, in this embodiment, the leads 6 which are subjected to wire bonding are interconnected by a reinforcing plate 22 to restrict the vibration of the leads 6 during the ultrasonic bonding process.

The reinforcing plate 22 is formed so as to stabilize the performance of the photoelectric device in operation in a high-frequency band. The reinforcing plate 22 is a partly metallized insulating ceramic plate. That is, nickel films 23 are formed by plating over the surface of areas where the reinforcing plate 22 contacts the leads 6, respectively. The leads 6 are fixed firmly to the nickel films 23 by silver solder 24. Accordingly, the leads 6 are restrained from vibration during the ultrasonic bonding process. Furthermore, since the nickel films 23 are formed in a fixed width, area through which electric current flows is increased, so that the parasitic inductance of the leads 6 is reduced to enable stable optical communication in a high-frequency band as high as 565 Mbit/sec. For example, the parasitic inductance on the order of 6 nH of a lead of 0.45 mm in diameter and 7 mm in length is reduced to 3 nH by providing gold films 23 of a fixed width over the areas where the reinforcing plate 22 contacts the leads 6.

The fiber guide 4 is attached to the wall of the package body 7 opposite the wall to which the flange 3 is attached. The fiber guide 4 comprises a tubular outer guide member 25 and an inner guide member 26 fitted in the inner portion of the outer guide member 25. The inner portion of the outer guide member 25 penetrates the wall of the package body 7 and the outer guide member 25 is fixed hermetically to the package body 7 by brazing. The outer portion of the outer guide member 25 has a thin wall which can be easily squeezed by caulking. The outer portion of the inner guide member 26 is inserted in the inner portion of the outer guide member 25, the inner portion of the inner guide member 26 is reduced in diameter and the free end of the inner portion of the inner guide member 26 is cut obliquely to form an inclined surface. Prior to passing the free end of the optical fiber cable 5 through the fiber guide 4, the jacket of the optical fiber cable 5 covering the free end of the optical fiber cable 5 is removed to expose the optical fiber 16 along a fixed length so that the exposed optical fiber 16 extends through the entire length of the inner guide member 26 and part of the outer guide member 25, while the jacketed portion of the optical fiber cable 5 extends through the outer portion of the outer guide member 25.

The base plate 9 is fixed to the inner surface of the bottom wall of the package body 7 at a position near the wall to which the flange 3 is attached with a brazing filler material. The Peltier element 10 is fixed to the upper surface of the base plate 9, and hence it is desirable to form the base plate 9 of a material having a high thermal conductivity. The upper and lower electrode plates 27 of the Peltier element 10 are formed of an alumina ceramic having a coefficient of thermal expansion on the order of 6.7.times.10.sup.-6 /.degree.C. Therefore, if the base plate 9 is formed of copper having a high thermal conductivity and a coefficient of thermal expansion of 17.0.times.10.sup.-6 /.degree.C., the solder joining the electrode plate 27 to the base plate 9 will be caused to break by fatigue due to the difference between the electrode plate 27 and the base plate 9 in thermal expansion. Accordingly, to avoid the breakage of the solder, the base plate 9 is formed, for example, of a copper/tungsten (Cu/W) alloy having a coefficient of thermal expansion in the range of 6.0 to 7.0.times.10.sup.-6 /.degree.C. and a thermal conductivity in the range of 0.5 to 0.67 cal/cm.sec..degree.C. One side of the base plate 9 is in contact with the wall of the package body 7 to transfer heat from the base plate 9 through the wall of the package body 7 to the flange 3. The coefficient of thermal expansion of covar forming the bottom wall of the package body 7 is 5.3.times.10.sup.-6 /.degree.C. The base plate 9 may be formed of SiC or the like.

Referring to FIGS. 5 and 6, the heat sink 14 is the principal component of the subcarrier 11. The heat sink 14 is a rectangular plate having the holding part 12 and the supporting part 13 rising from the main surface thereof. The holding part 12 extends across the central portion of the main surface of the heat sink 14 while the supporting part 13 extends in parallel to the holding part 12 on one side of the heat sink 14. The holding part 12 and the supporting part 13 are perpendicular to an inclined axis inclined at an angle .theta. to the center axis of the heat sink 14. The tubular positioning and fixing member 17 penetrates and is fixed to the supporting part 13. The positioning and fixing member 17 is an adjustable tube for guiding the optical fiber 16 and for adjusting the position of the free ends of the optical fiber 16. Accordingly, the positioning and fixing member 17 is formed of a material capable of plastic deformation such as, for example, a nickel alloy. As illustrated in FIG. 3, the positioning and fixing member 17 has a deformable, thin, tubular adjusting section 28 passed through the supporting part 13 and a thick, tubular guide section 29 having a shoulder in abutment with the side surface of the supporting part 13. A taper hole is formed in the guide section 29 to facilitate passing the optical fiber 16 through the positioning and fixing member 17. The inside diameter of the positioning and fixing member 17 is slightly greater than the diameter of 125 .mu.m of the optical fiber 16. The free end of the adjusting section 28 is cut aslant, as will be described hereinafter, to form an inclined surface having an increased area for soldering the optical fiber 16 to the adjusting section 28. A drop of solder 30 not having any flux is attached beforehand to the inclined surface of the adjusting section 28 as shown in FIG. 7. The drop of solder 30 is attached to the inclined surface through steps of passing a dummy wire 31 having a diameter slightly greater than the diameter of 125 .mu.m of the optical fiber 16 such as, for example, a piano wire of 150 .mu.m in diameter, through the positioning and fixing member 17, attaching a drop of solder to the free end of the adjusting section 28, drawing out the dummy wire 31, i.e., the piano wire, from the positioning and fixing member 17 as shown in FIG. 7, and removing the flux adhering to the drop of solder 30 through ultrasonic washing.

A submount 32 is attached fixedly by a fluxless low temperature melting-solder such as, for example, a Pb/Sn/In solder, to the holding part 12 at a position on the prolongation of the adjusting section 28 of the positioning and fixing member 17. The submount 32 is formed of an insulating SiC having a high thermal conductivity and a coefficient .alpha. of thermal expansion of 3.7.times.10.sup.-6 /.degree.C. which is approximate to those of Si and a compound semiconductor. As shown in FIG. 8, the main surface of the submount 32 is metallized to form a metal layer 33. Au/Sn eutectic layers 34 and 35 are formed on the metal layer 33, and the laser diode chip 15 and a gold pedestal 36 are attached fixedly to the upper Au/Sn eutectic layers 34 and 35, respectively. The eutectic layers 34 and 35 may be substituted by a Pb layers or Pb/Sn layers. Thus, the lower electrode of the laser diode chip 15 is connected electrically through the metal layer 33 to the pedestal 36 and as shown in FIG. 8, is fixed to the submount 32 with the resonator 38 which emits a laser light 37 positioned apart from the submount 32, namely, with the P-surface of the pn laser diode facing up. The upper electrode of the laser diode chip 15 is connected electrically to the holding part 12 by two wires 20, while the pedestal 36 is connected electrically to the leads 6 by two wires 20 as shown in FIGS. 1 and 2. Such a manner of electrical connection of the laser diode chip 15 and the holding part 12 and that of the pedestal 36 and the leads 6 are necessary to change the polarity to use the driving side of the laser diode chip 15 in driving the same by a fast transistor. The laser diode chip 15 is mounted on the submount 32, and then the submount 32 is fixed to the holding part 12.

In this embodiment, the laser diode chip 1