OPTICAL SEMICONDUCTOR DEVICE

Abstract: An optical semiconductor device comprises an optical semiconductor element (6) which may be a light emitting element or a light receiving element, enclosed within a lensed-cap comprising a cap (40) with a lens (41) attached to it. A thread (42) is formed in the outer side surface of the lensed-cap so that the lensed-cap can be screw-fitted into a housing provided with a corresponding thread in its inner wall. The optical semiconductor device (44) is screwed into the housing so as to form a module.

Description: The present invention relates to an optical semiconductor device comprising a light receiving element such as a photodiode or a light emitting element such as a light emitting diode enclosed in a cap with a lens attached to it. More particularly, according to the present invention, provided is such an optical semiconductor device including a cap having a thread in its outer surface which is screwed into a threaded inside surface of a housing in which the device is to be housed, whereby positional adjustment of the optical semiconductor device for controlling its sensitivity is facilitated. A conventional optical semiconductor device is formed into a module by telescopically inserting it into a housing. Therefore, in order to adjust the axial position of the optical semiconductor device within the housing, washer-like spacers must be placed in the housing. This adjustment of the axial position of the semiconductor device is necessary in order to adjust the sensitivity of the optical semiconductor device module. For that purpose, the number of the spacers inserted between the housing inner surface and the optical semiconductor device is adjusted to change the axial position of the semiconductor device, while monitoring its sensitivity, during the fabrication of an optical semiconductor device module. Accordingly, fabrication of optical semiconductor modules has been a troublesome work. Japanese Unexamined Patent Publication No. SHO 60-216315 discloses an invention in which optical elements including an optical-fiber holder, a columnar rod-lens and a reflector mirror are housed in a cylindrical container, and these optical elements are fixed in position in the container by means of a threaded lid that is screwed into an open end of the container with a corresponding thread formed in its inside surface. The invention of this Japanese unexamined patent publication provides means for pressing the optical elements into the container for! fixing them in position, but it is not to adjust the axial position of the elements. Japanese Unexamined Patent Publication No. SHO 63-169604 discloses an invention according to which an optical fiber is connected to an optical link by engaging a thread on the clad of the optical fiber with a thread formed in the inner surface of a connector-terminal element provided in the optical link. The object of the invention of this publication, however, is to provide means for connecting the optical fiber with a light emitting or light receiving element, keeping them in mechanical, intimate contact with each other, and is not to provide means for adjusting the distance of the light emitting or light receiving element from the optical fiber. Optical semiconductor devices typically include a lens for focussing light emitted from an optical semiconductor element, such as a photodiode, for onward transmission for example along a fibre optic cable. An example of such a device is shown in an article in RTP REGELUNGSTECHNISCHE PRAXIS, vol. 23, No. 4 April 1981 pages 135-139 by K. FIEBELKORN entitled "Electronica 80" Lichtleiter-Ubertragungssysterne". It has also been proposed to position the optical semiconductor element in a cylindrical cap having a lens at one end. An example of such an arrangement is shown in US-A-4186995. This patent discloses an assembly of an optical semiconductor device comprising a semiconductor element in a cap as described above, an optical fibre and a housing for securing one with respect to the other. The housing includes shoulder means against which the cap abuts and the optical fibre is held with its end just short of the shoulder means. The position of the optical fibre with respect to the cap is fixed. It would be advantageous if the position of the optical semiconductor device with respect to the optical fibre could be readily adjusted to ensure optimum sensitivity of the device. According to the present invention, an optical semiconductor device includes a cylindrical cap with a lens attached to it. A thread is formed in the outer side surface of the cap, which thread can mate with a thread formed in the inside surface of a housing that houses the optical semiconductor device. (Hereinafter, such an optical semiconductor device is referred to as "lens-capped" optical semiconductor device, and such a cap is referred to as "lensed cap".) In order to form such a lens-capped optical semiconductor device into a module by housing it in a housing, an electrically conductive bonding agent, for example, may be first applied over the threaded outer side surface of the lensed-cap, screwing it into the housing, while monitoring the sensitivity of the optical semiconductor device, and stopping the screwing of the cap at a position where an optimum sensitivity is attained, so that the lens-capped optical semiconductor device is secured in position by means of the bonding agent. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a partially broken, side view of an example of conventional optical semiconductor devices; Figure 2 is a side view illustrating how the conventional optical semiconductor element is assembled together with a housing into a module; Figure 3 is a partially cross-sectional, side view of the module comprising the conventional optical semiconductor element housed in the housing; Figure 4 is a partially cross-sectional, side view showing the structure of an optical semiconductor device according to a first embodiment of the present invention; Figure 5 is a partially cross-sectional, side view of a module comprising the optical semiconductor device of Figure 4 screwed into a housing; Figure 6 is a partially cross-sectional, side view for use in exemplifying various dimensions of the optical semiconductor device module of Figure 5; Figure 7 shows another embodiment of the present invention; and Figure 8 schematically illustrates how an optical semiconductor device module in general, such as the ones shown in Figure 3 or 5, is coupled to an optical fiber via a receptacle. Before explaining an optical semiconductor device according to the present invention, structures and problems of conventional devices are first described with reference to the accompanying drawings. In Figure 1, there is illustrated a conventional lens-capped optical semiconductor device with a portion of its cap shown cut away. Referring to Figure 1, a glass-ball lens 4 is fixed in an end wall closing one end of a cylindrical cap 2 which has no irregularities in its side surface. The cap 2 is formed, for example, of Kovar plated with nickel (Ni) as an underlying layer which, in turn, is plated with gold (Au). The glass-ball lens 4 is formed, for example, of Kovar glass having an index of refraction n of 1.487. An optical semiconductor element 6 such as, for example, a photodiode, is coupled via a mount 8 to a stem 10 which is secured to the cap 2. Usually, the stem 10 and the cap 2 are hermetically sealed by welding in a nitrogen stream. The purpose of carrying out the welding in a nitrogen stream is to prevent characteristic degradation of the optical semiconductor device during its operation. One of three leads 12, 14 and 16 mounted on the stem 10 is electrically connected to the stem 10 and the cap 2 for grounding them, and the other two leads are connected to respective electrodes of the photodiode 6. For example, as the photodiode 6, an InGaAs pin photodiode may be used, which is suitable for receiving light in a range of wavelengths of from 1000 nm to 1600 nm and has a diameter of an effective light receiving area of about 80 µm. Figure 2 illustrates how the conventional lens-capped optical semiconductor device is fixed in position in a housing to form a module, and Figure 3 shows a completed optical semiconductor device module. A lens-capped optical semiconductor device 18 of Figure 2 is of the structure shown in Figure 1 and is assembled with a housing 22 into a module, with a number of position adjusting spacers 20 disposed between the inner wall of the housing and the optical semiconductor device 18. Each of the spacers 20 may be of, for example, a washer-like shape having a thickness of about 0.125 mm. When assembling into a module, an electrically conductive adhesive, for example, is applied over a side surface of the cap 2. Then, monitoring the sensitivity of the optical semiconductor device 18, the number of the spacers 20 is changed to adjust the position of the device 18 in the direction indicated by an arrow Z so that an optimum sensitivity is obtained. Thus, an optical semiconductor device module 36 having a structure as shown in Figure 3 results. As is understood from Figure 3, the optical semiconductor device 18 and the housing 22 are bonded by the conductive adhesive 24 filling the space between the device 18 and the housing 22. The optical semiconductor device module 36 shown in Figure 3 is used in a manner as illustrated in Figures 8(a) and 8(b). Specifically, a receptacle 28 is welded to the housing 22 of the optical semiconductor device module 26, and a coupling 30 of the receptacle 28 and a coupling 34 provided at the tip end of the optical fiber 32 are brought into screw-engagement with each other. Thus, the optical semiconductor device module 26 and the optical fiber 32 are optically coupled as shown in Figure 8(b). When the above-stated conventional lens-capped optical semiconductor device 18 is inserted into the housing 22, it is necessary to put or remove spacers 20 into or from the housing 22 in order to adjust the sensitivity, which makes the module assembling work troublesome. Furthermore, it may occur that when an adhesive is applied over the side surface of the cap 2 and the capped device 18 is inserted into the housing 20 after the positional adjustment has been made for an optimum sensitivity, the adhesive may enter into spaces between adjacent spacers or into the space between the end wall of the cap 2 and the spacer, so that the position in the direction Z of the optical semiconductor device 18 and, hence, its sensitivity may change. According to the present invention, which is defined in present claims 1 and 8, the above-stated problems present in the conventional devices are eliminated, so that when a lens-capped optical semiconductor device is to be assembled into a module, its positional adjustment for adjusting its sensitivity can be done very easily. Figure 4 shows a lens-capped optical semiconductor device 44 according to one embodiment of the present invention. A lensed-cap 40 is shown partially cut away. A thread 42 is formed in the outer side surface of the cap 40 with a glass-ball lens 4 mounted on the closing end wall. The thread 42 is formed to mate with a thread formed in the inside surface of a housing which is described later. Like the cap 2 of the conventional optical semiconductor device shown in Figure 1, the cap 40 may be formed of Kovar plated with nickel to form an underlying layer which is in turn plated with gold. Similarly, Kovar glass having an index of refraction n of of 1.487 may be used as the material of the glass- ball lens 4. An optical semiconductor element 6, such as, for example, photodiode, is mounted on a stem 10 via a mount 8 disposed therebetween is coupled to the cap 40, and the stem 10 is bonded to the cap 40. In order to prevent the characteristics of the optical semiconductor device 18 from degrading during operation, the cap 40 and the stem 10 are joined by welding in a stream of nitrogen. One of three leads mounted to the stem 10 is electrically connected to the stem 10 and the cap 40, and the remaining two leads are electrically connected to respective electrodes of the photodiode 6. As the photodiode 6, an InGaAs pin photodiode, for example, may be used, which is suitable for receiving light having a wavelength in a range of from 1000 nm to 1600 nm and which has a diameter of an effective light receiving area of about 80 µm. Needless to say, in place of a light receiving element such as a photodiode, a light emitting element such as a light emitting diode can be used as the optical semiconductor element 6. Figure 5 shows a module 50 formed by incorporating the lens-capped optical semiconductor device 44 shown in Figure 4 with a housing 46. The inner wall surface of the housing 46 is provided with a thread 48 which mates with the thread 42 of the cap 40. The housing 46 is formed of, for example, gold, stainless steel or aluminum. Prior to screwing the lens-capped optical semiconductor device 44 into the housing 46, a screw securing agent such as, for example, an adhesive, preferably an electrically conductive adhesive, is applied over the surface of the thread groove of the cap 40. While monitoring the sensitivity of the lens-capped optical semiconductor device 44, the device 44 is screwed into the housing 46, and when an optimum sensitivity is attained the screwing of the device 44 is stopped so that it is secured to the housing 46 by means of the adhesive applied over the thread groove of the cap 40. Thus, the module 50 shown in Figure 5 is completed. A receptacle 28 like the one shown in Figure 8 is welded to the housing 46. A coupling 30 provided on the receptacle 28 is brought into screw-engagement with a coupling 34 of an optical fiber 32. Thus, the optical semiconductor device module 50 is coupled to the optical fiber 32. Figure 6 is for use in exemplifying dimensions of various sections of the optical semiconductor device module shown in Figure 5, in which A is the outer diameter of the cap 40; B is the outer diameter of the lower end portion of the cap 40 (i.e. the diameter of the stem 10); C is the height of the cap 40; D is the length of the leads 12, 14 and 16; E is the thickness of the leads; F is the outer diameter of the housing 46; G is the height of the housing 46; H is the diameter of the glass-ball lens 4; and I is the height of the lens 4 above the end wall surface of the cap 40. Examples of the respective dimensions are as follows. A: 4.7 ± 0.2 mm B: 5.4 ± 0.2 mm C: 3.8 ± 0.3 mm D: 15 ± 1 mm E: 0.45 mm F: about 7.8 mm G: about 6.9 mm H: 1.5 ± 0.1 mm I: 0.7 ± 0.15 mm The leads 12, 14 and 16 are arranged on a circle having a diameter of about 2.54 mm with an angular spacing of 90° from each other. Figure 7 shows another embodiment of the present invention. The lens-capped optical semiconductor device according to this embodiment comprises an optical semiconductor device having a conventional structure shown in Figure 1 and a threaded cylindrical member 52 fitted over the cap 2 of the optical semiconductor device. The cylindrical member 52 may be shrink-fitted over the cap 2, or it may be bonded by an adhesive, such as an electrically conductive adhesive, to the cap 2. The lens-capped optical semiconductor device with the threaded cylindrical member 52 fitted thereover is screwed into a housing to form a module, as in the case of the first embodiment. As stated above, according to the present invention, when a lens-capped optical semiconductor device is assembled into a module, no troublesome working of placing or removing spacers into or from a housing as done in conventional techniques, is required for adjusting the sensitivity of the optical semiconductor device. According to the present invention, the assemblage of a module can be done in a simple manner by applying a bonding agent, such as an adhesive, over the outer surface of the cap of the device and, while monitoring the sensitivity of the device, screwing the device into a housing until an optimum sensitivity is attained, and, then, the semiconductor device is held in that position so that it is fixed to the housing by the adhesive which has been applied over the cap. Thus, the assemblage of modules can be done in a very simple manner, and, further, it never occurs that the sensitivity of the device changes after the module is completed. Furthermore, the lens-capped optical semiconductor device and the housing assembled into a module will never be separated from each other even if a mechanical shock is applied to the module, because they are joined not only by an adhesive but also by the screw-engagement.

Claims: An optical semiconductor device comprising an optical semiconductor element (6) enclosed in a lensedcap comprising a cap (40) with a lens (4) attached thereto; characterised in that said cap (40) is provided with a thread (42) on its outer side surface so that said lensedcap can be screw-fitted into a housing (46) provided with a corresponding thread (48) on its inner surface. An optical semiconductor device according to claim 1, wherein said lensedcap (40) is provided with a thread (42) directly formed on its outer side surface. An optical semiconductor device according to claim 1, wherein said lensed-cap (40) is provided with a cylindrical member (52) fitted over and secured to said lensedcap (40) said cylindrical member being provided with a thread (42) formed on its outer peripheral surface. An optical semiconductor device according to claim 1, wherein said optical semiconductor element (6) is a light receiving element. An optical semiconductor device according to claim 4, wherein said light receiving element is a photodiode. An optical semiconductor device according to claim 1, wherein said optical semiconductor element (6) is a light emitting element. An optical semiconductor device according to claim 6, wherein said light emitting element is a light emitting diode. An optical semiconductor device module, comprising a lensedcap (40) in which an optical semiconductor element (6) is enclosed and a housing (46), characterised in that the cap (40) has a thread (42) formed in its outer surface, the housing has a corresponding thread (48) formed in its inner surface, and the cap is screwed into the housing. An optical semiconductor device module according to claim 8, wherein said lensedcap (40) is provided with a thread (42) directly formed on its outer side surface. An optical semiconductor device module according to claim 8, wherein said lensedcap (40) is provided with a cylindrical member (52) fitted over and secured to said lensed-cap (40), said cylindrical member (52) being provided with a thread (42) formed on its outer peripheral surface. An optical semiconductor device module according to claim 8, wherein said optical semiconductor element (6) is a light receiving element. An optical semiconductor device module according to claim 11, wherein said light receiving element is a photodiode. An optical semiconductor device module according to claim 8, wherein said optical semiconductor element (6) is a light emitting element. An optical semiconductor device module according to claim 13, wherein said light emitting element is a light emitting diode. An optical semiconductor device module according to claim 8, wherein said lensedcap (40) is screwed into said housing, with an adhesive applied over the outer side surface of said lensed-cap (40). An optical semiconductor device module according to claim 15, wherein said adhesive is an electrically conductive adhesive. An optical semiconductor device module according to claim 8, wherein said lensedcap (40) is screwed into said housing, with the position of said lensed-cap being adjusted so as to provide an optimum sensitivity of said optical semiconductor element (6) enclosed in said lensed cap (40). An optical semiconductor device module according to claim 8, wherein said housing is adapted to have a receptacle (28) attached thereto for coupling with an optical fiber (32).

Inventors: TADA, KATSUHISA C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: G02B6
IPC codes: G02B6, H01L33, H01L31