Semiconductor optical device

A semiconductor optical device includes a stem; a semiconductor optical element mounted on the stem; a resin cap including a cylindrical body portion, a plate portion, and an edge portion; and a lens attached integrally to the plate portion of the cap. The edge portion of the cap is bonded to the stem so that the cap covers the semiconductor optical element. The cylindrical body portion of the cap has at least one first portion and second portions which are spaced apart from each other in the circumferential direction of the cylindrical body portion and which project inwardly relative to the at least one first portion. The stem has projections, and each projection vertically underlies and engages or contacts a surface of a respective one of the second portions of the cap.

FIELD OF THE INVENTION

The present invention relates to a semiconductor optical device.

BACKGROUND ART

Semiconductor optical devices in which a lens is attached integrally to its mounting member by molding have been known, as disclosed, e.g., in Japanese Laid-Open Patent Publication No. H07-218773. (In the case of the semiconductor optical device disclosed in this publication, the mounting member is a pipe.) Traditionally, in the manufacture of semiconductor optical devices, the circumference of the lens is metalized, and the lens is secured to a mounting member of metal by soldering, etc. The technique disclosed in the above publication has an advantage over this conventional technique in that a reduced number of parts and a reduced number of joins are required and hence higher mass productivity can be attained since the lens is attached integrally to the mounting member by molding.

In the case of CAN packages, the lens is mounted to a cylindrical mounting member called a cap. The cap may be formed of a resin, and the lens may be attached integrally to this cap by molding to achieve the same advantages as described in connection with the technique of the above publication. However, unlike metal caps, which are traditionally used, a resin cap cannot be secured to the stem by welding. Therefore, the cap may be bonded to the stem by an adhesive.

In semiconductor optical devices configured as CAN packages, the semiconductor optical element is mounted inside the cap. The semiconductor optical element is either a semiconductor laser diode or a photodiode. The accuracy of the alignment of the lens with the optical axis of the semiconductor optical element is an important factor in determining the performance of the semiconductor optical device. In the alignment process, the lens is positioned relative to the semiconductor optical element so that the lens is spaced a predetermined distance from the semiconductor optical element in the direction of the optical axis of the semiconductor optical element (i.e., Z direction in, e.g.,FIG. 1) and oriented perpendicular to the optical axis of the semiconductor optical element (i.e., oriented parallel to X-Y plane inFIG. 1). That is, the cap with the lens integrally attached thereto must be accurately aligned with and secured to the stem.

In order to accomplish this, Japanese Laid-Open Patent Publication No. H07-218773 noted above and Japanese Laid-Open Patent Publication No. 2003-035855 disclose techniques in which a mounting member (cap) with a lens integrally attached thereto and a stem are provided with steps and/or recesses, thereby making it possible to accurately align the mounting member with the stem using these steps and recesses.

Other prior art include Japanese Laid-Open Patent Publication Nos. 2010-183002 and H03-030581.

CAN packages are configured by mounting various components (including optical elements, such as a semiconductor optical element, and electrical parts) in a closely spaced relationship on a stem and then covering and sealing these components with a cap. Since the cap is mounted on the top surface of the stem, the area available on the top surface for mounting components is limited. Further, providing the cap and the stem with steps or recesses for positioning the cap on the stem (as described in connected with the above conventional techniques) requires the use of some area on the stem, thus reducing the area available on the top surface of the stem for mounting components.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems. It is, therefore, an object of the present invention to provide a semiconductor optical device including a cap and a stem and configured such that the cap can be accurately aligned with and secured to the stem while maximizing the interior space of the cap.

According to a first aspect of the present invention, a semiconductor optical device includes: a stem, a semiconductor optical element secured to the stem, a resin cap, and a lens. The resin cap includes a cylindrical body portion having an inside surface and an outside surface which extend along an entire length of the cylindrical body portion. The resin cap further includes a plate portion disposed at one end of the cylindrical body portion and an edge portion disposed at the other end of the cylindrical body portion. The edge portion has a lower surface bonded to the stem so that the resin cap covers the semiconductor optical element. The lens is attached integrally to the plate portion of the cap. Wherein, the cylindrical body portion has at least one first portion and a plurality of second portions which are spaced apart from each other in a circumferential direction of the cylindrical body portion and which project inwardly relative to the at least one first portion, and wherein each of the second portions has a first engagement feature, and the stem has a plurality of second engagement features, each vertically underlying and engaging or contacting a respective one of the first engagement features of the second portions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Configuration of Device of First Embodiment

FIG. 1is a perspective view of a semiconductor optical device20in accordance with a first embodiment of the present invention. In this embodiment, the semiconductor optical device20has a CAN package structure. Referring toFIG. 1, the semiconductor optical device20includes a stem32and a cap (or lid)28which is mounted on and covers the stem32. The stem32and the cap28are bonded together by an adhesive. The space enclosed by the cap28and the stem32is sealed, and filled with a filler gas such as air, dry gas, or nitrogen gas.

FIG. 2is a perspective view of the cap28of the semiconductor optical device20of the first embodiment. The cap28is made of a resin. The cap28has a cylindrical body portion28a. The cylindrical body portion28ahas an outside surface and an inside surface28dwhich extend along the entire length of the cylindrical body portion28a. The cap28has a plate portion28bat one end of the cylindrical body portion28aand an edge portion28cat the other end of the cylindrical body portion28a. The edge portion28cis bonded to the stem32by an adhesive140so that the cap28covers a semiconductor optical element100. It should be noted that the adhesive140is applied to the entire circumference of the edge portion28c.

A lens27is secured to the plate portion28bin such a manner that the lens27is integrated with the cap28. Specifically, the lens27is attached integrally to the cap28by molding.

The cap28has three recesses29, which may be hereinafter referred to as the recesses29a,29b, and29c, respectively, for convenience.

FIGS. 3A and 3Bshow bottom views of the cap28of the semiconductor optical device20of the first embodiment.FIGS. 3A and 3Bare substantially the same, except that the parts numbered inFIG. 3Aare not numbered inFIG. 3B, and vice versa. As shown inFIG. 3B, the cylindrical body portion28ahas three first portions P1 and three second portions P2. The second portions P2 are spaced apart from each other in the circumferential direction of the cylindrical body portion28aand project inwardly relative to the first portions P1. The first portions P1 have an inner curvature radius r1, and the second portions P2 have an inner curvature radius r2 which is smaller than the inner curvature radius r1. The first portions P1 of the cap28have a relatively small thickness, and the second portions P2 have a relatively large thickness. It should be noted that the first portions P1 and the second portions P2 of the subsequently described variations of the first embodiment and the subsequently described second and third embodiments have the same configurations as the first portions P1 and the second portions P2 of the first embodiment.

FIG. 4is a perspective view showing the internal configuration of the semiconductor optical device20of the first embodiment. Referring toFIG. 4, lead pins36configured as bar terminals are bonded to the stem32. Although in this example the semiconductor optical device20has four lead pins36, it is to be understood that it may have five or more lead pins36.

The stem32is made of a metal and may be, e.g., a circular ion plate having a diameter of approximately 3-10 mm. The stem32has four through-holes40therein, each receiving a respective one of the four lead pins36therethrough. The lead pins36are bonded to the stem32by glass hermetic material44. This hermetic material also seals the gaps between the through-holes40and the lead pins36. A metal block14is bonded by solder to the top surface32aof the stem32, which surface serves as the main surface of the stem32. Further, a submount13is bonded onto the metal block14by solder, and the semiconductor optical element100is bonded to the submount13by solder. In this example, the semiconductor optical element100is a semiconductor laser element. It should be noted, however, that the semiconductor optical device20may be configured as a photodetector device having a photodiode as its semiconductor optical element.

The semiconductor optical element100is connected to each lead pin36on the top surface32aside of the stem32by a gold wire15serving as a signal line.

The cap28covers components on the top surface32aside of the stem32, such as the upper projecting portions of the lead pins36, the gold wires15, the metal block14, the submount13, and the semiconductor optical element100. The cap28is bonded to the top surface of the stem32by the adhesive140so that the space within the cap28is hermetically sealed. The lens27is integrally attached to and forms a part of the top of the cap28, and laser light exits the semiconductor optical device through this lens27.

In accordance with the first embodiment, the mount to which the semiconductor optical element100is mounted has a multilayer structure including the submount13and the metal block14. That is, the submount13and the metal block14form a mount of thermally conductive material. This mount is used for dissipating heat from the semiconductor optical element100. That is, the mount has a heat dissipation function. The semiconductor optical element100is mounted on the submount13, with its junctions facing downward. The submount13serves to reduce the thermal stress between the semiconductor optical element100and the metal block14and dissipate heat from the semiconductor optical element100. The material of the submount13is aluminum nitride (AlN). The material of the metal block14is copper (Cu). The solder used to bond the submount13to the metal block14is low melting solder of AuSn. The submount13may be formed of silicon carbide (SiC).

FIG. 5is a top view of the stem32of the semiconductor optical device20of the first embodiment. InFIG. 5, the dashed lines indicate where the cap28is mounted on the top surface of the stem32. The stem32has three projections33. As can be seen by comparison betweenFIGS. 3A,3B, and5, each projection33vertically underlies a respective one of the second portions P2 of the cap28. Thus, in the semiconductor optical device20of the first embodiment, the stem32has the projections33, which are disposed in such a manner that each projection33vertically underlies and engages or contacts a respective one of the second portions P2 of the cap28.

Further, as can be seen by comparison betweenFIGS. 3 and 5, the recesses29of the cap28have a greater cross-sectional area than the projections33of the stem32and disposed such that each projection33fits into a respective one of the recesses29. Further, the depth D of the recesses29is less than the height H of the projections33, as described later in detail.

Each of the three projection33of the stem32vertically underlies a respective one of the three second portions P2 of the cap28and extends around a portion of the circumference of the stem32. That is, these three projections33are located at the vertices of an acute triangle on the top surface of the stem32, and each second portion P2 of the cap28vertically overlies a respective one of the projections33of the stem32. As a result, the cap28is stably supported by the three projections33, which are located at different points on the stem32.

The adhesive140is applied to the entire circumference of the edge portion28cof the cap28so that the entire edge portion28cis bonded to the top surface32aof the stem32by the adhesive140. That is, the first portions P1 and the second portions P2, which form the edge portion28c, are bonded to the top surface32aof the stem32by the adhesive140so that the recesses29of the cap28are bonded to the projections33of the stem32.

In the present embodiment, the second portions P2 of the cap28, which are brought into contact with the stem projections33for positioning the cap28at a predetermined vertical position, are configured to extend around different portions of the circumference of the cylindrical body portion28aof the cap28. It should be noted that the vertical or height direction corresponds to the Z direction as illustrated inFIG. 1and coincides with the direction of the optical axis of the semiconductor optical element100. It should be noted that although the second portions P2 of the cap28have a relatively large thickness and hence a relatively small inner curvature radius r2, they extend around only a portion of the circumference of the cylindrical body portion28a, as described above. This means that the first portions P1 of the cap28, which are not brought into contact with the projections33of the stem32and hence have a relatively small thickness and a relatively large inner curvature radius r1, extend around the rest of the circumference of the cylindrical body portion28a. Therefore, the space enclosed and defined by the cap28and the top surface32aof the stem32is larger than would be the case if the second portions P2 of the cap28together extended around the entire circumference of the cylindrical body portion28a. In this way the cap28can be accurately positioned at a predetermined vertical position while maximizing the interior space of the cap28.

FIG. 25is a diagram showing the top surface of a stem1232, presented as a comparative example for the present embodiment. The stem1232has a cylindrical projection1233. This projection1233has the same function as the projections33of the stem32of the first embodiment and is bonded to the edge portion28cof the cap28. In the example shown inFIG. 25, the space enclosed by the cap28, the top surface of the stem1232, and the inner surface of the projection1233(which space is available for mounting electronic components) is smaller than the space enclosed by the cap28and the top surface of the stem32of the first embodiment shown inFIG. 5, since in the first embodiment the projections33of the stem32extend around only a portion of the circumference of the stem32and furthermore the second portions P2 of the cap28extend around only a portion of the circumference of the cylindrical body portion28aof the cap28. Thus, the configurations of the cap28and the stem32of the first embodiment results in increased space between them, as compared to the example ofFIG. 25.

The cap28can be accurately positioned relative to the stem32simply by grinding or shortening the tip of each projection33. Specifically, if the distance between the lens27and the semiconductor optical device100is greater than the desired distance, then the tips of the three projections33may be equally shortened to move the cap28toward the stem32. It should be noted that technical difficulties in manufacture prevent the top surface32aof the stem32from being a completely flat surface; therefore the top surface32ais bound to have spatial variations in height within a certain tolerance, resulting in inclination of the cap28. In order to prevent such inclination of the cap28, the projections33may be adjusted to different heights by grinding their tips, so as to compensate for the height variations of the top surface32a. It should be noted that it is easy to grind down the projections33since they extend around only a portion of the circumference of the stem32.

Further, the recesses29of the cap28are rectangular in cross-section; that is, these recesses29have four sides. Therefore, it is possible to prevent misalignment between the cap28and the stem32in directions parallel to the top surface32aof the stem32(i.e., X-Y plane inFIG. 1) by fitting the recesses29of the cap28onto the projections33of the stem32. In this way, the cap28can also be accurately positioned at the desired X-Y position.

FIG. 6is a cross-sectional side view of the semiconductor optical device20of the first embodiment taken along line A-A′ ofFIG. 1. As shown inFIG. 6, the cap is secured to the stem so that the center C of the lens is on the optical axis AX of the semiconductor optical element100. Thus, the cap is accurately positioned and oriented relative to the stem32(or the semiconductor optical element100). This may be accomplished by grinding or shortening the tips of the projections33of the stem32so that the projections33have suitable different heights.

FIG. 7is an enlarged cross-sectional view of the portion shown in dashed line X ofFIG. 6.FIG. 7illustrates only the projection33bfor convenience; however, the other projections33(i.e., the projections33aand33c) have the same configuration as the projection33b. As shown inFIG. 7, the projection33bhas a height H. Further, the recess29bhas a depth D. The depth D is less than the height H. Further, the projection33bhas an upper edge133band side surfaces133a. Further, the recess29bhas a bottom surface129aand side surfaces129b. The width W2 of the bottom surface129aof the recess29bis greater than the width W1 of the upper edge133bof the projection33b.

FIG. 7shows a cross-sectional view of the recess29band the projection33btaken along only one plane. It should be noted, however, that the cross-sectional view of the recess29band the projection33btaken along a plane perpendicular to that plane (i.e., perpendicular to the plane of the paper inFIG. 7) is identical to the cross-sectional view ofFIG. 7. That is, the recesses29have lateral dimensions slightly greater than those of projections33so that each projection33fits into a respective one of the recesses29. In the present embodiment, the difference between the width W2 of the bottom surface129aof the recess29band the width W1 of the upper edge133bof the projection33bis relatively large so that the adhesive140can be applied in a substantial amount between the recess29band the projection33b. However, the difference between the width W2 and the width W1 may be just large enough that the projection33bwill fit into the recess29beven if these widths vary within a tolerance range.

The adhesive140is applied between the recess29band the projection33bso that the upper edge133b(facing in the Z direction) and the side surfaces133a(perpendicular to X-Y plane) of the projection33bare bonded to the recess29b, making it possible to firmly secure the cap28to the stem32and thereby achieve enhanced transverse load resistance.

FIG. 8is a diagram showing the way in which the cap28is positioned at a predetermined vertical position by the projections33of the stem32, demonstrating advantages of the semiconductor optical device20of the first embodiment. Specifically, in this example, the projections33band33chave different heights H1 and H2. The reason for this is that there is a difference G in height between the portions of the stem top surface32aunderlying the recess29band underlying the recess29c, as shown inFIG. 8. The height H1 of the projection33bis greater than the height H2 of the projection33cto compensate for this height difference G. It should be noted that the recesses29band29chave the same depth D.

As described above, the depth D of the recesses29is less than the height H of the projections33. Therefore, each recess29is held by a respective one of the projections33(serving as a stopper), so that the recess29is vertically spaced apart from the top surface32aof the stem32by an amount equal to the difference between the depth of the recess29and the height of the projection33. This means that since the height H1 of the projection33bis greater than the height H2 of the projection33c, the recess29bis held higher than the recess29crelative to the top surface32aof the stem32, thereby compensating for the height difference G described above. Thus, the vertical position and orientation of the cap28can be adjusted by grinding and thence shortening the projections33. In this way, the lens27can be accurately positioned relative to the semiconductor optical element100, as shown inFIG. 6.

Variations of Device of First Embodiment

FIGS. 9A to 13Bare diagrams showing variations of the semiconductor optical device20of the first embodiment wherein the cap28and/or the stem32are replaced by a different cap and/or stem.

The variation shown inFIGS. 9A and 9Bincludes a cap228instead of the cap28. The cap228is similar to the cap28, except that the second portions P2 have a different configuration. Specifically, the recesses229of the second portions P2 of the cap228have a different shape than the recesses29of the second portions P2 of the cap28.FIG. 9Ais a bottom view of the cap228, andFIG. 9Bis a cross-sectional view of the stem32and the cap228mounted thereon, taken along line B-B′ ofFIG. 9A.

As shown inFIG. 9A, in this variation, the recess229of each second portion P2 is a groove extending from the inner surface to the outer surface of the edge portion of the cap228. That is, each recess229is a groove extending from the inside surface228dto the outside surface of the cap228. As shown inFIG. 9B, each projection33of the stem32fits into a respective one of the recesses (or grooves)229and is bonded to that recess by an adhesive140. It should be noted that the first portions P1 of the cap228(or the edge portion of the cap228) are also bonded to the top surface32aof the stem32by the adhesive140during the bonding of the projections33to the recesses229.

The variation shown inFIGS. 10A and 10Bincludes a cap328instead of the cap28. The cap328is similar to the cap28, except that the second portions P2 have a different configuration. Specifically, each second portion P2 of the cap328has a step portion329.

FIG. 10Ais a bottom view of the cap328, andFIG. 10Bis a cross-sectional view of the stem32and the cap328mounted thereon, taken along line C-C′ ofFIG. 10A. In this variation, each step portion329(of the second portions P2) extends from the inner surface of the edge portion328cof the cap328. That is, each step portion329projects inwardly from the inside surface328dof the cap328.

As can be seen from the cross-section ofFIG. 10B, the edge portion328cprojects downward relative to the plane of the bottom surface of each step portion329. That is, the bottom surface of the edge portion328cis lower than that of the step portions329. The upper edge of each projection33of the stem32is brought into contact with the bottom surface of a respective one of the step portions329. Thus, each projection33fits into a respective one of the step portion329and is bonded to that step portion by an adhesive140. It should be noted that the first portions P1 of the cap328(or the edge portion of the cap328) are also bonded to the top surface32aof the stem32by the adhesive140during the bonding of the projections33to the step portions329.

The variation shown inFIGS. 11A and 11Bincludes the cap328(described above in connection with the variation shown inFIGS. 10A and 1-B) and a stem432(described below) instead of the cap28and the stem32of the first embodiment. The stem432is similar to the stem32, except that the projections33are replaced by projections433having a different configuration.FIG. 11Ais a top view of the stem432, andFIG. 11Bis a cross-sectional view of the stem432and the cap328mounted thereon, taken along line D-D′ ofFIG. 11A. The projections433of the stem432of this variation have a dimension in the radial direction of the stem432greater than the dimension of the projections33of the stem32of the first embodiment in the radial direction of the stem32. As a result, the upper edge of each projection433can be brought into contact with the entire bottom surface of a respective one of the step portions329of the cap328. This variation has the same advantages as described above in connection with the first embodiment. Further, the three projections33of the stem32of the first embodiment may be replaced by a single large circular projection. In this case, the cross-section of each second portion12and the adjacent portion of the stem32taken along a line corresponding to line D-D′ ofFIG. 11Ais the same as that shown inFIG. 11B. However, the central portion of the stem32on which various components such as the metal block14are mounted is higher than the edge portion of the stem32; that is, the components are mounted on the circular projection. This configuration also has the same advantages as described above in connection with the first embodiment. Thus, since the three projections33of the stem32are replaced by a single large circular projection, the stem has a simpler configuration, making it possible to reduce manufacturing costs without degrading the positioning accuracy of the cap relative to the stem.

The variation shown inFIG. 12includes a cap528instead of the cap28. The cap528is similar to the cap28, except that the second portions P2 have a different configuration.FIG. 12is a bottom view of the cap528. Referring toFIG. 12, the second portions P2 of the cap528have a relatively small thickness, as compared to the second portions P2 of the cap28of the first embodiment. Specifically, in the case of the cylindrical body portion of the cap528, the first portions P1 and the second portions P2 have substantially the same thickness. Instead, the three second portions P2 are displaced toward the center axis of the cylindrical body portion of the cap528relative to the first portions P1 and have recesses529a,529b, and529c, respectively, formed therein. (It should be noted that the first portions P1 and the second portions P2 are formed on the edge portion528cof the cylindrical body portion.) Each projection33of the stem32fits into and is in contact with a respective one of the recesses529(i.e., recesses529a,529b, and529c) in the same manner as shown inFIG. 9B.

The variation shown inFIGS. 13A and 13Bincludes a cap628and a stem632instead of the cap28and the stem32.FIG. 13Ais a bottom view of the cap628, andFIG. 13Bis a top view of the stem632. In the first embodiment and the variations thereof described above, the cylindrical body portion28ahas three second portions P2 having a recess, and the stem has three projections, each of which fits into a respective one of the recesses of the second portions P2. In the variation shown inFIGS. 13A and 13B, on the other hand, the cylindrical body portion of the cap628has two second portions P2 having a recess629, and the stem632has two projections633. Specifically, in the variation shown inFIGS. 13A and 13B, the two second portions P2 are disposed at diagonally opposite positions on the edge portion of the cylindrical body portion of the cap628and have a relatively large length along the circumference of the cylindrical body portion (and are larger in area than the second portions P2 of the first embodiment). Further, the two projections633of the stem632are also disposed at diagonally opposite positions on the top surface of the stem632and have a relative large length along the circumference of the stem632(and hence are larger in area than the projections33of the first embodiment). As a result, although the stem632has only two projections (namely, the two projections633), the cap628is stably supported by and secured to these projections. Further, it is possible to maximize the interior space of the cap628, as in the first embodiment.

Returning now to the variation shown inFIGS. 11A and 11B,FIG. 14shows the way in which the cap328is bonded to the stem432by an adhesive140. As a result of the configurations of, e.g., the step portion329aof the cap328and the projection433aof the stem432, the adhesive140is trapped on the bottom surface of the step portion329a(i.e., tapped on the left side of the cap328as viewed inFIG. 14), thus preventing the adhesive from flowing onto the inside surface328dof the cap328(i.e., preventing the adhesive from flowing toward the right side of the cap as viewed inFIG. 14). Returning now to the semiconductor optical device20of the first embodiment,FIG. 15shows the way in which, e.g., the recess29bof the cap28is bonded to the projection33bof the stem32by an adhesive140. As a result of the configurations of the recesses29of the cap28and the projections33of the stem32, the adhesive140is trapped at the central portion of each recess29, thus preventing the adhesive140from flowing onto the outside of the edge portion28cof the cap28. Thus, in the first embodiment and the variations thereof described above, the configurations of the cap and the stem together have the effect of controlling the flow of the adhesive140and thereby controlling the amount and location of adhesive trapped.

FIG. 16is a diagram showing another variation of the semiconductor optical device20of the first embodiment. The variation shown inFIG. 16includes a cap1028and a stem1032instead of the cap28and the stem32. The cap1028is similar to the cap28, except that the recesses29are replaced by recesses1029. The stem1032is similar to the stem32, except that the projections33are replaced by projections1033.

Each projection1033of the stem1032has an upper edge1033c, a first side surface1033ahaving a width W4, and a second side surface having a width W3, where W3<W4, and decreases stepwise in width toward the upper edge1033c(i.e., decreases stepwise in width with increasing distance from the top surface of the stem1032). The recesses1029of the cap1028have a plurality of steps. Each recess1029has a bottom surface1029a, a first side surface1029bhaving a width W6, and a second side surface1029chaving a width W5, where W5>W6, and decreases stepwise in width toward the bottom surface1029a. As a result of the configurations of the cap1028and the stem1032as described above, adhesive is trapped primarily on the central portion of the inner surface of each recess1029, thus preventing adhesive from flowing onto the outside surface of the cap. Further, the configurations of the cap1028and the stem1032result in an increased adhesion area of adhesive, thus increasing adhesion between the cap1028and the stem1032.

FIG. 16shows a cross-sectional view of a recess1029and a projection1033which fits into the recess1029, taken along only one plane. It should be noted, however, that the cross-sectional view of the recess1029and the projection1033taken along a plane perpendicular to that plane (i.e., perpendicular to the plane of the paper inFIG. 16) is identical to the cross-sectional view ofFIG. 16. That is, the recesses1029of the cap1028have lateral dimensions slightly greater than those of the projections1033of the stem1032so that each projection1033will fit into a respective one of the recesses1029.

Although in the first embodiment the stem32has projections, it is to be understood that the present invention is not limited to this particular type of stem. Each second portion P2 of the cap28may have a projection, and the stem32may have recesses in the place of and instead of the projections33. Further, the cap may be accurately positioned by adjusting the depth D of the recesses29of the cap instead of or in addition to adjusting the height H of the projections33of the stem.

It should be noted that the projections33of the stem32may be produced by machining, or by securing separate metal block pieces to the top surface32aof the stem32such as by welding.

In the first embodiment, the cylindrical body portion28aof the cap28has three second portions P2 which are spaced apart from each other and extend around different portions of the circumference of the cylindrical body portion28a. It should be noted, however, that in other embodiments the cylindrical body portion28amay have a different number of second portions P2 (i.e., two, or four or more second portions P2) which are spaced apart from each other and extend around different portions of the circumference of the cylindrical body portion28a. In such cases, the stem32may have projections33vertically underlying two or more of these second portions P2 of the cylindrical body portion28a.

It should be noted that although in the first embodiment the projections33of the stem32are rectangular as viewed in plan, in other embodiments they may have a different shape. The projections33may be triangular, trapezoidal, pentagonal, or any other polygonal shape, as viewed in plan. Further, they may be circular or elliptical as viewed in plan. Further, the projections33of the stem32need not have a shape analogous to that of the recesses29of the cap28. The present embodiment requires only that each projection33fit into a respective one of the recesses29.

Second Embodiment

FIG. 17is a diagram illustrating a configuration of a semiconductor optical device in accordance with a second embodiment of the present invention. The semiconductor optical device of the second embodiment is similar to the semiconductor optical device20of the first embodiment, except that the second portions P2 of the cap have a different configuration.

FIG. 17shows an enlarged cross-sectional view of a portion of the cap728of the semiconductor optical device of the second embodiment, which portion corresponds to the portion shown in dashed line X ofFIG. 6. That is, the cross-section shown inFIG. 17corresponds to the cross-sections shown inFIGS. 7 and 9Ato11B, and also corresponds to the cross-section shown inFIG. 14. The cap728is similar to the cap328described above with reference toFIGS. 10A and 10B, and the three second portions P2 of the cap728have the step portions329a,329b, and329c, respectively. However, the cap728differs from the cap328in that the cap728has a through-hole700for at least one of the step portions329a,329b, or329c.

In the example shown inFIG. 17, when the cap728and the stem432are assembled, a first opening of the through-hole700for the step portion329bfaces a side surface of the projection433bof the stem432of the semiconductor optical device, and a second opening of the through-hole700is located outside the step portion329b, specifically, at the outside surface of the cap728. This through-hole700serves as a spill port for the adhesive140. The provision of the through-hole700for the step portion329ballows the step portion329bto be bonded to the projection433bof the stem432by a substantially predetermined amount of adhesive.

FIG. 18Ais a bottom view of the cap728of the semiconductor optical device of the second embodiment. As shown inFIG. 18A, each of the three second portions P2 of the cap728may have a through-hole700. Further, each of the second portions P2 may have a plurality of through-holes700.FIG. 18Bis a diagram showing the way in which the cap728and the stem432are bonded together.

FIGS. 19 and 20are diagrams showing a variation of the semiconductor optical device of the second embodiment (or first embodiment). Specifically,FIG. 19is a bottom view of the cap28of this variation (or semiconductor optical device) wherein the cap has through-holes702.FIG. 20is a cross-sectional view showing the way in which the cap28is mounted on the stem32. This variation differs from the semiconductor optical device of the first embodiment in that each second portion P2 of the cap28has a through-hole702which is similar to the through-holes700of the second embodiment.

It should be noted that all three second portions P2 need not be provided with a through-hole702; only one or two of them may have a through-hole702.

Third Embodiment

FIG. 21is a diagram showing a configuration of a semiconductor optical device in accordance with a third embodiment of the present invention. Specifically,FIG. 21shows the configuration of the cap828of the semiconductor optical device of the third embodiment. The cap828is similar in basic configuration to the cap328described above with reference toFIGS. 10A and 10B, and the three second portions P2 of the cap828have a step portion329. However, the cap828differs from the cap328in that each step portion329(which constitutes a portion of the edge portion328cof the cap828) has a slit structure800formed in its surface. Except for this feature, the semiconductor optical device of the third embodiment is similar in configuration to the semiconductor optical device of the first embodiment.

Each slit structure800includes a plurality of parallel slits. Thus, in the third embodiment, the bottom surface of the edge portion328cof the cap828, which surface is bonded to the stem32, has slit structures800which are spaced apart from each other in the circumferential direction of the cylindrical body portion328aof the cap828. It should be noted that the edge portion328cof the cap828may have a plurality of concentric slits extending around the entire circumference of the cylindrical body portion328a.

FIG. 22is a cross-sectional view showing a configuration of the semiconductor optical device of the third embodiment. Specifically,FIG. 22is a cross-sectional view of one of the step portions329having a slit structure800and the adjacent portion of the edge portion328c. As a result of this configuration, adhesive140is trapped in the slits of the step portion329, resulting in an increased adhesion area.

FIGS. 23 and 24are diagrams showing variations of the semiconductor optical device of the third embodiment. In the variation shown inFIG. 23, the bottom surface of the edge portion328cof the cap828has slit structures801adjacent to, but not in, the step portions329. Each slit structure801is oriented perpendicular to a respective one of the step portions329. In the variation shown inFIG. 24, the bottom surface of the edge portion328cof the cap828has three slit structures802, each parallel to a respective one of the step portions329. (It should be noted that the bottom surface of the edge portion328cmay be provided with slit structures that are at any angle with respect to the step portions.) The cross-sectional structure of the slit structures801and802described above may be identical to that of the slit structures800of the third embodiment. Further, the number and width of slits of the slit structures801and802may be equal to those of the slit structures800.

Though not shown, the recesses29of the cap28of the first embodiment may have a slit structure formed in an inner surface thereof (i.e., in the bottom surface129aor a side surface129b). The features and advantages of the present invention may be summarized as follows. Thus, in the semiconductor optical device of the present invention, the cylindrical body portion of the cap has a plurality of second portions, each extending around only a portion of the circumference of the cylindrical body portion and having a first engagement feature (e.g., a recess or projection). Further, the stem of the semiconductor optical device has a plurality of second engagement features (e.g., projections or recesses), each underlying and engaging or contacting a respective one of the first engagement features of the second portions of the cap. This configuration allows the cap to be accurately positioned at a predetermined vertical position relative to the stem while maximizing the interior space of the cap.

The entire disclosure of Japanese Patent Application No. 2013-016560, filed on Jan. 31, 2013, including specification, claims, drawings, and summary, on which the Convention priority of the present application is based, is incorporated herein by reference in its entirety.