1. Field of the Invention
The present invention relates to a light source including a semiconductor laser.
2. Description of the Background Art
As light sources for lighting devices and display devices, replacing short-lived lamps, semiconductor light-emitting elements such as semiconductor laser diodes (LD) or light-emitting diodes (LED) have come to be used. As for this kind of applications, light-emitting elements corresponding to the three colors of red, green and blue, which are so-called the three primary colors of light, are used.
There is a limit to increasing illumination with the light of a conventionally-used lamp, and the illumination on a screen becomes darker as the screen becomes larger. However, a laser light beam has such properties as high directivity, coherence and energy density, and therefore, a higher illumination may be obtained by adding a plurality of laser light beams. However, when coherent light such as a laser light beam is illuminated on a screen, a pattern including glaringly shiny spots called speckle noise is observed, and gives discomfort to those who are looking at the screen. The speckle noise appears due to an interference effect, which is a property of a laser light beam, and is a factor to lower the quality of lighting and displayed images.
Therefore, specifically when a light source includes a semiconductor laser, a request for a higher power output and reducing the speckle noise becomes stronger.
In order to emit a high power output laser light beam and reduce the speckle noise, a conventional semiconductor laser light source includes two semiconductor diode arrays each of which has a plurality of active regions, which are laser light beam emission points, and each of the semiconductor diode arrays is determined to be a multi-beam laser diode array configured to emit a plurality of laser beams (laser light beams) of different properties. It is considered that increasing the active regions enables to emit a plurality of laser light beams, and adding these laser light beams together enables to obtain higher power output and multi-wavelengths (see, for example, Japanese Patent Application Laid-Open No. 07-211991 (1995)).
In addition, another semiconductor laser light source emits a laser light beam with high brightness and high power output by using a fiber-coupling method used to optically couple light beams from a plurality of semiconductor lasers to an optical fiber (see, for example, Japanese Patent Application Laid-Open No. 2011-243717).
Furthermore, another semiconductor laser light source reduces the speckle noise by emitting lasers of different wavelengths from a semiconductor laser array having a plurality of light emission points (see, for example, Japanese Patent Application Laid-Open No. 2009-111230).
However, according to a technology described in Japanese Patent Application Laid-Open No. 07-211991 (1995), a semiconductor laser chip including active regions, which are laser light beam emission points, is required to be mounted on a semiconductor laser block because thermal resistance should be considered, and the width of the semiconductor laser chip has to be increased so as to increase the active regions and emit a plurality of laser light beams. If the semiconductor laser block is specified to a certain size, there is a limit to the number of active regions that can be mounted on the semiconductor laser block. If the size of the semiconductor laser block is made large, the number of mountable active regions is increased, but there has been a problem that the overall structure of the semiconductor laser light source becomes large.
In addition, according to a technology described in Japanese Patent Application Laid-Open No. 2011-243717, by using a fiber coupling, laser light beams from a plurality of semiconductor laser arrays are condensed and a laser light beam with high power output is emitted. However, one semiconductor laser array having radiation emitters configured to emit laser light beams is mounted on one semiconductor laser block, and therefore, the number of semiconductor laser blocks is required to be increased so as to emit a laser light beam with higher power output. With the increase of the number of the semiconductor laser blocks, emitting a laser light beam with high power output is made possible, but there has been a problem that the semiconductor laser light source becomes large.
Furthermore, according to a technology described in Japanese Patent Application Laid-Open No. 2009-111230, one semiconductor laser array having a plurality of light emission points is mounted on one heat sink (semiconductor laser block), and therefore, the number of semiconductor laser blocks is required to be increased so as to emit a laser light beam with higher power output. With the increase of the number of the semiconductor laser blocks, emitting a laser light beam with high power output is made possible, but there has been a problem that the semiconductor laser light source becomes large.