This nonprovisional application claims priority under 35 U.S.C. ยง119(a) on Patent Application No. 2005-176679 filed in Japan on Jun. 16, 2005, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor laser device including a light-receiving element for receiving monitor light.
2. Description of Related Art
Even when a semiconductor laser device is fed with a constant drive current, the laser light output of the semiconductor laser device varies greatly with temperature. To drive a semiconductor laser device on an APC (automatic power control) basis, that is, to keep the laser light output thereof constant, of the laser light emitted from both ends of the semiconductor laser device, the part emitted from one end is received, as monitor light, with a light-receiving element such as a photodiode so that, based on the current produced as a result, the drive current fed to the semiconductor laser device is controlled.
For the sake of productivity and work efficiency, a frame-type semiconductor laser device is generally so structured that the optical axis of the laser, including the monitor light, is parallel to the light-receiving surface of the light-receiving element. In this structure, however, of the monitor light, only the part traveling off the optical axis and thus having low intensity is detected on the light-receiving surface of the light-receiving element. Thus, the portion of monitor light received by the light-receiving surface of the light-receiving element is small, and the light-receiving element yields an accordingly low output. This makes it difficult to control the drive current, and may cause the semiconductor laser device to break down when too much drive current is passed through it.
With the above described disadvantage in mind, the semiconductor laser device 110 proposed in JP-A-2003-31885 is built, as shown in
In the semiconductor laser device proposed in JP-A-2003-31885, however, the high-intensity part of the monitor light that travels on the optical axis does not strike the light-receiving surface 115a of the light-receiving element 115, and thus the portion of the monitor light that actually strikes the light-receiving surface 115a is not remarkably larger than in a case where no reflective surface 117 is provided.
An object of the present invention is to provide a semiconductor laser device having a structure that permits part of monitor light emitted by a semiconductor laser device and traveling on the optical axis to be received by a light-receiving surface of a light-receiving element, thereby increasing the amount of light received by the light-receiving surface so as to increase the output of the light-receiving element, based on which a drive current is appropriately controlled.
To achieve the above object, according to the present invention, a semiconductor laser device provided with a semiconductor laser element, a light-receiving element that receives monitor light emitted from the semiconductor laser element, and a leadframe on which the semiconductor laser element and the light-receiving element are mounted is further provided with a first reflective surface that is disposed on the optical axis of the monitor light and a second reflective surface that is disposed on the optical axis of first reflected light that results from the monitor light being reflected from the first reflective surface. Here, second reflected light resulting from the first reflected light being reflected from the second reflective surface strikes the light-receiving surface of the light-receiving element.
According to the present invention, preferably, the above structured semiconductor laser device is further provided with a base portion arranged on the leadframe and a lid portion arranged on the base portion so as to cover the semiconductor laser element and the light-receiving element. Here, the first reflective surface is located on the base portion and the second reflective surface is located on the interior surface of the lid portion.
According to the present invention, preferably, in the above structured semiconductor laser device, the semiconductor laser element is mounted on the leadframe with a submount interposed in between, and the height from the leadframe to the semiconductor laser element is greater than the height from the leadframe to the light-receiving surface of the light-receiving element.
According to the present invention, preferably, in the above configured semiconductor laser device, the light-receiving element is mounted on the submount.
Thus, according to the present invention, the monitor light traveling on the optical axis and thus having higher intensity than the monitor light traveling off the optical axis is reflected on the first reflective surface and then on the second reflective surface so as to strike the light-receiving surface of the light-receiving element. This helps increase the amount of light striking the light-receiving surface, and thus helps increase the output of the light-receiving element. Based on this output, a semiconductor laser device according to the present invention can properly control the drive current thereof.
Moreover, according to the present invention, the semiconductor laser element is mounted on the leadframe with a submount interposed in between, and the height from the leadframe to the semiconductor laser element is greater than the height from the leadframe to the light-receiving surface of the light-receiving element. This helps increase the portion of the monitor light that strikes the light-receiving surface of the light-receiving element directly from the semiconductor laser element. Thus, the drive current can be controlled more properly.
Moreover, according to the present invention, the light-receiving element is mounted on the submount. This makes it possible, when the semiconductor laser device is fabricated, to properly arrange the semiconductor laser element and the light-receiving element simply by arranging the submount on the leadframe. This helps eliminate the step of positioning the light-receiving element on the leadframe in such a way that monitor light strikes the light-receiving element, and thus helps reduce fabrication cost.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in
The semiconductor laser element 14 is in the form of a chip produced by joining together and then cleaving a p-type semiconductor and an n-type semiconductor. When a voltage is applied between the p-type and n-type semiconductors so as to pass a drive current, their junction, namely a p-n junction layer, emits light. This light is then amplified by resonance between two mutually parallel mirror surfaces that are formed at opposite cleavage surfaces with different reflectivities, so that, through the mirror surface having the lower reflectivity, main laser light 21 emerges. Also through the mirror surface having the higher reflectivity, laser light having lower intensity than the main laser light 21 leaks out, and this light is used as monitor light 22.
The semiconductor laser element 14 is arranged in such a manner that the optical axis 20 of the main laser light 21 and the monitor light 22 is parallel to the leadframe 11. The light-receiving element 15, such as a photodiode, is arranged in such a manner that the height from the leadframe 11 to the light-receiving surface 15a thereof is approximately equal to the thickness of the submount 13 and that the light-receiving element 15 is parallel to the optical axis of the monitor light 22. Thus, the monitor light 22 traveling off the optical axis 20 directly strikes the light receiving element 15. The lid portion 18 has an opening at the right in
As shown in the block diagram
In this embodiment, on the surface of the base portion 12 that is struck by the monitor light 22, a plating is formed to form a first reflective surface 16. The first reflective surface 16 is so inclined that the monitor light 22 traveling on the optical axis 20 is reflected toward the lid portion 18. Moreover, on and around the part of the inner surface of the lid portion 18 that is struck by first reflected light 23 resulting from the monitor light 22 traveling on the optical axis 20 being reflected from the first reflective surface 16, a plating is formed to form a second reflective surface 17. The inclination angle of the first reflective surface 16 is so set that second reflected light 24 resulting from the first reflected light 23 being reflected from the second reflective surface 17 strikes the light-receiving surface 15a of the light-receiving element 15.
With this structure, part of the monitor light 22 that travels off the optical axis 20 strikes the light-receiving surface 15a of the light-receiving element 15; also, part of the monitor light 22 that travels on the optical axis and that has stronger intensity than the part traveling off the optical axis is reflected by the first and second reflective surfaces 16 and 17, and then strikes the light-receiving surface 15a of the light-receiving element 15. This increases the portion of the monitor light 22 that strikes the light-receiving surface 15a of the light-receiving element 15, and thus increases the output of the light-receiving element 15. Thus, based on the current produced by the light-receiving element 15 receiving the monitor light 22, it is possible to control the drive current properly.
Moreover, in this embodiment, as shown in
Moreover, in this embodiment, as shown in
Moreover, in this embodiment, materials having different reflectivities may be used to form the platings forming the first and second reflective surfaces 16 and 17. By giving the platings different reflectivities, it is possible to adjust the portion of the monitor light striking the light-receiving element 15 to suit the sensitivity thereof, and this makes it possible to control the drive current with high precision. A plurality of lid portions 18 having different platings formed as the second reflective surface 17 may be prepared. This makes it possible to adjust the portion of the monitor light striking the light-receiving element 15 to suit the sensitivity thereof simply by selecting an appropriate one of the lid portions 18 and hence without changing the structure of, for example, the leadframe 11 or the submount 13.
In this embodiment, the first and second reflective surfaces 16 and 17 may be formed otherwise than by plating; for example, they may be formed by vapor-depositing metal such as aluminum, or by laying a mirror-surfaced metal sheet, or by any other manner, so long as they reflect light.
Semiconductor laser devices according to the present invention can be used as high-precision light source for reading signals from optical discs such as CDs, CD-Rs, DVDs, and DVD-Rs.
Number | Date | Country | Kind |
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2005-176679 | Jun 2005 | JP | national |