1. Field of the Invention
The present invention relates to a laser apparatus capable of coupling light, which is outputted from a laser light source, to an optical fiber, and then outputting the light.
2. Description of the Background Art
Display devices can be categorized into: a light emitting display device which emits light, such as an organic light emitting display device, a plasma display device or the like; and a light receiving display device which is not capable of emitting light and which requires a light source, such as a liquid crystal display device or the like. A general liquid crystal display device includes: two display boards provided with electric field generating electrodes; and a liquid crystal layer having dielectric constant anisotropy, which is provided between the two display boards. An electric field is generated in the liquid crystal layer by applying a voltage to the electric field generating electrodes; a light valve is formed by adjusting an intensity of the electric field by varying the voltage; and a desired image is obtained by adjusting a transmission factor of light passing through the liquid crystal layer. For this light, generally, a separately provided artificial backlight source is used.
A cold cathode fluorescent lamp (CCFL), which is provided at the rear of a liquid crystal panel and which uniformly irradiates the entire liquid crystal panel with light, is often used as a backlight source of a liquid crystal display device. Generally, the CCFL is used such that the light of the CCFL, which is incident on the side of a light guide plate, is substantially evenly outputted from the front of the light guide plate so as to be radiated on the back of the liquid crystal panel, i.e., edge light type, or such that multiple CCFLs are arranged at the back of the liquid crystal panel, and the CCFLs directly radiate the light on the liquid crystal panel through a diffuser panel, i.e., direct light type.
In recent years, in consideration of the environment and power saving, development of an image display device is advanced, in which a light-emitting diode (LED) or a laser, which does not use mercury and which consumes less power, is used as a light source. In particular, a laser is the most appropriate to be used as a light source of an image display device, not only because of its low power consumption but also from the viewpoint of image quality such as a color reproduction range or the like.
Meanwhile, in order to simplify a structure of an LCD television and to slim an LCD television, a lightbox or a light guide plate is usually used. Structures as disclosed in Japanese Laid-Open Patent Publications No. 2002-169480 (Patent Document 1) and No. 2006-202703 (Patent Document 2) are proposed as backlight devices using a lightbox or a light guide plate.
For example, Patent Document 1 proposes a system in which monochromaticity, polarized nature, and straightforwardness of laser light are used so as to cause the laser light to be: linearly reflected on a hologram mirror; incident on a lightbox; and then planarly radiated via a half mirror array.
Patent Document 2 proposes a system in which light sources are arranged in an array-like manner at the right and left to a light guide plate, and triangular-shaped portions provided at a bottom surface of the light guide plate cause light to be planarly radiated. In the case where laser lights whose polarization directions are uniform are used in these systems, an advantage is obtained in which by maintaining the polarization, a more efficient backlight can be realized as compared to a case where the laser lights are non-polarized lights.
However, in the system disclosed in Patent Document 1 in which the hologram mirror is used to reflect laser light, if the three primary colors RGB are used for laser light sources, reflection directions, at the hologram mirror, of laser lights of the respective colors are different from each other. This may cause color unevenness in distribution of light finally outputted from a light guide plate. Further, profiles of the laser lights are reflected in light intensity distribution of the laser lights having been reflected by a plane hologram mirror. Therefore, if the laser lights are, for example, Gaussian-shaped, brightness at a central portion of the light guide plate increases, and this causes unevenness in brightness, which is unfavorable.
In general, reflectivity of a hologram mirror is low since diffraction efficiency is low for a particular wavelength. This inevitably causes loss of light intensity. Furthermore, since half mirrors are used in the structure for causing laser light to rise two-dimensionally, reflectivity differences among the half mirrors are reflected in brightness distribution. Moreover, light intensity distribution of a light source is reflected in distribution of laser light having been reflected by the half mirrors. Accordingly, brightness unevenness due to a light source profile occurs in accordance with a pitch among the half mirrors. Still further, in the case of radiating light for a large area and for a short distance, it is necessary to provide a substantial number of half mirrors whose transmission properties are slightly different from each other. This is extremely unrealistic because a number of problems are caused, for example, considerable difficulty and a cost increase in manufacturing.
Also in the system disclosed in Patent Document 2 in which light sources are arranged in an array-like manner at the sides of a light guide plate, light source profiles are reflected in lights rising within the light guide plate, and brightness unevenness due to a combination of multiple light source profiles is caused. Further, in the case of using lasers as the light sources of Patent Document 2, laser lights entering the light guide plate arrive, due to straightforwardness of the laser lights, at an opposite side of the light guide plate to a side thereof which the laser lights have entered. Then, the laser lights are transmitted through the light guide plate and lost. Even if the laser lights are reflected using a reflective member or the like, the laser lights, which horizontally travel, keep traveling for a long distance while reflecting on the reflective member or the like, and then are absorbed by the light guide plate. This results in loss of light intensity. Meanwhile, in the case where the laser lights are widely incident near an entrance of the light guide plate, brightness increases near the entrance and this causes brightness unevenness. Thus, this system also has a number of problems.