Lens holding block for semiconductor laser

Abstract: A flat portion (22) has a flat top surface, on which a chip carrier (14) is provided. A light-emitting element (13) (e.g. a laser) is mounted on the chip carrier. A vertical portion (23) is integral with the flat portion and extends vertically, i.e., perpendicularly to the flat top surface of the flat portion. A metal plate (25) made of a metal having good welding performance is silver-brazed onto the vertical portion. A lens barrel (16) containing a lens (15) for focusing a light beam from the light-emitting element is inserted in a through-hole of the vertical portion and the metal plate, and welded to the metal plate so that the optical axes of the light-emitting element and the lens coincide with each other.

Description: BACKGROUND OF THE INVENTION The present invention relates to a lens holding block to be used in light-emitting modules for the optical communication etc. In the optical communication technology, an electrooptical conversion element such as a laser diode or LED is used as a signal source or light-emitting source. The positioning in an optical system needs to be performed with micron-order accuracy to efficiently introduce light from the above light-emitting element to an optical fiber. Referring to Figs. 5 and 6, a description is made of coupling between a lens and a light-emitting element mounted on a chip carrier. As shown in Fig 5, a light-emitting element 13 is mounted on a recess 12 of a chip carrier 14, which is provided on the top surface of a block 11. Also provided on the top surface of the block 11 is a metal lens-barrel 16 containing a lens 15 for focusing light emitted from the light-emitting element 13. The positioning between the light-emitting element 13 and the lens 15 is performed such that the lens-barrel 16 is first positioned with respect to the light-emitting element 13 and then fixed using wedge-shaped parts 17. However, the insertion of the wedge-shaped parts 17 may break the once optimized positional relationship between the light-emitting element 13 and the lens 15. Therefore, this type of positioning is deficient in accuracy. In the case of Fig. 6, instead of using the wedge-shaped parts 17, a lens-barrel 16 containing a lens 15 is pressed against and fixed to the end face of a block 11 on which a chip carrier 14 having a light-emitting element 13 is mounted. While this type of positioning can provide sufficient accuracy within plane perpendicular to the optical axis, it is also deficient in accuracy in the optical-axis direction because the distance between the lens 15 and the light-emitting element 13 is adjusted visually using a microscope or is dependent on the accuracy of machining. Document JP-A-2 308 209 discloses an optical module having a flat lens block with a vertical portion accommodating a lens holder. The lens holder is welded to the vertical portion of the lens block. After the fixation of the lens holder, an adjustment movement of the lens with respect to the light-emitting element is achieved by bending the lens holder. Document EP-A-0 356 331 describes an optical module including a lens holder which supports the optical lens in a fixed condition wherein a lens holder guide is fixed to a substrate for supporting the lens holder. The adjustment of this optical module is achieved by moving the lens holder within the lens holder guide. SUMMARY OF THE INVENTION An object of the present invention is to provide a lens holding block which enables accurate positioning between a light-emitting element and a lens. This object is solved by a lens holding block with the features contained in claim 1. Advantageous embodiments of the lens holding block are defined in the dependent claims. According to an embodiment of the invention, a lens holding block for holding a chip carrier on which a light-emitting eiement is mounted and a lens-barrel containing a lens for focusing a light beam emitted from the light-emitting element, comprises: a flat portion having a flat top surface on which the chip carrier is to be provided; and a vertical portion being perpendicular to the flat top surface and integral with the flat portion and having an opening into which the lens-barrel is to be inserted, for holding the lens-barrel so that optical axes of the light-emitting element and the lens coincide with each other. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a lens holding block according to a first embodiment of the present invention; Fig. 2 is a sectional view of the lens holding block of Fig. 1; Fig. 3 is a perspective view of a lens holding block according to a second embodiment of the invention; Fig. 4 is a perspective view of a lens holding block according to a third embodiment of the invention; Fig. 5 is a perspective view of a conventional lens holding block; and Fig. 6 is a perspective view of another conventional lens holding block. DESCRIPTION OF THE PREFERRED EMBODIMENTS Lens holding blocks according to preferred embodiments of the present invention are hereinafter described with reference to the accompanying drawings. Embodiment 1 Figs. 1 and 2 are a perspective view and a sectional view of a lens holding block according to a first embodiment of the invention. In this lens holding block, a block flat portion 22 of a block main body 21 has a flat surface, on which a chip carrier 14 is provided. A light-emitting element 13 is mounted on a recess 12 of the chip carrier 14. The block main body 21 further has a block vertical portion 23 extending upward, i.e., perpendicularly to the flat surface of the block flat portion 22. The block flat portion 22 and the block vertical portion 23 are integral with each other. A through-hole 24 is formed in the block vertical portion 23, and serves to fixedly hold a lens-barrel 16 (containing a lens 15) so that its axis coincides with the optical axis of the light-emitting element 13. That is, the diameter of the through-hole 24 is larger than the outer diameter of the lens-barrel 16 so that the central axis of the lens 15 can be made coincident with the optical axis of the light-emitting element 13 and that the distance therebetween can be adjusted. It is preferred that the block main body 21 be made of a metal having a large heat conductivity to efficiently conduct the heat generated by the light-emitting element 13. Further, to enable welding with high fixing accuracy, a metal plate 25 having good welding performance (e.g., a Fe-Ni-Cr alloy and a Fe-Ni alloy) is silver-brazed onto the block vertical portion 23 on its side opposite to the side where the chip carrier 14 is provided. A though hole 24' for holding the lens-barrel 16 is also formed in the metal plate 25 in the same manner as the through-hole 24 in the block vertical portion 23. With the above constitution, the relative positioning between the lens 15 and the light-emitting element 13 is performed in the following manner. First, the block main body 21 is fixed in, for instance, a transmission module. Then, while output light of an optical fiber 26 (that is located on the side of the lens-barrel 16 opposite to the side where the light-emitting element 13 is provided) is monitored, the lens-barrel 16 (containing the lens 15) is moved along and rotated about the optical axis and two axes perpendicular to the optical axis. The relative positioning is performed with accuracy of about 0.1 µm. As a result, highly accurate positioning can be performed without relying on the machining accuracy or visual recognition using a microscope or the like. As for the fixing by welding, since the welding portion (indicated by marks "×" in Fig. 2) for fixing the lens barrel 16 is located on a circle having the optical axis as its center, the welding (e.g., YAG laser welding) can be performed simultaneously at a plurality of points. Therefore, a deviation between the axes can be minimized, in contrast to the case of using the wedge-shaped parts. Embodiment 2 Fig. 3 shows a lens holding block according to a second embodiment of the invention. Like the block main body 21 of the first embodiment (Fig. 1), a block main body 121 of this embodiment has a block flat portion 122 and a block vertical portion 123, which are perpendicular to and integral with each other. A metal plate 125 is silver-brazed onto the block vertical portion 123. As a specific feature of this embodiment, the block vertical portion 123 and the metal plate 125 has respective cut portions 27 and 27' for holding the lens barrel 16. According to this embodiment, since the approximate position of the lens barrel 16 containing the lens 15 can be recognized with a microscope, the time required for the lens positioning can be reduced. Embodiment 3 Fig. 4 shows a lens holding block according to a third embodiment of the invention. A block main body 221 of this embodiment consisting of a block flat portion 222 and a block vertical portion 223 has the same structure as the block main body 21 of the first embodiment (Fig. 1). As a specific feature of this embodiment, the block main body 221 is made of a Fe-Ni-Cr alloy. Therefore, the metal plate 25 for YAG laser welding of the Fig. 1 lens holding block is not required in this embodiment. The lend holding block of this embodiment may be suitable for the case where quantity of the heat generated by the light-emitting element 13 is small or the temperature of the light-emitting element 13 need not be controlled with high accuracy. As described above, according to the invention, the relative positioning between the lens and the light-emitting element can be performed with high accuracy, and the lens holding block of the invention can be effectively used in transmission modules for the optical communication etc.

Claims: A lens holding block on which a light-emitting element (13) and in which a lens-barrel (16) containing a lens (15) for focusing a light beam emitted from the light-emitting element (13) are mounted, said block comprising: a block main body (21, 121, 221) having a flat top surface on which the light-emitting element is mounted; a lens holding portion (23) extending perpendicularly to the flat top surface and integral with the block main body (21, 121, 221), said lens holding portion having a lens-barrel accommodating opening (24, 27, 224) through which the lens-barrel (16) passes thereby accommodating the lens-barrel (16) so that the optical axes of the light-emitting element (13) and the lens (15) coincide with each other, wherein the block main body is formed of a metal having a large heat conductivity, and wherein the transverse dimension(s) of the lens-barrel accommodating opening (24, 27, 224) is greater than the outer diameter of the lens-barrel (16), and a a tubular welding portion (X) in which the lens barrel (16) is snugly fit, said welding portion having an outwardly projecting flange at one end characterized by a flat metal plate (25) made of a material having good welding properties which is attached to said lens holding portion (23) and provided with an accommodating opening conforming with said lens barrel accommodating opening in the lens holding portion, the flange of the welding portion being welded to the plate so that the lens barrel can extend through the openings. The lens holding block of claim 1 being arranged as a part of a light source unit, said light source unit further comprising: a chip carrier on which the light-emitting element (13) is mounted. The lens holding block of claim 1 or 2 wherein the metal plate is fixed to the lens holding portion (23) on a side opposite to a side where the light-emitting element (13) is provided. The lens holding block of claim 3, wherein the metal plate is silver-brazed onto the lens holding portion (23). The lens holding block of claim 3, wherein the opening of the metal plate and the lens-barrel accomodating opening (24, 27, 224) of the lens holding portion (23) constitute a through-hole. The lens holding block of claim 3, wherein the opening of the metal plate and of the lens holding portion (23) are in the form of a U-shaped recess. The lens holding block of claim 3, wherein the metal plate is made of a Fe-Ni-Cr alloy.

Inventors: TANIDA KAZUHIRO, TANIDA, KAZUHIRO, Tanida, Kazuhiro, c/o Yokohama Works Of
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1993
Main classification: G02B6
IPC codes: G02B6, H01S5, H01L33, G02B7