A semiconductor laser consisting of III-V nitride semiconductor material (AlxGayIn1-x-yN (herein, 0≦x≦1, and 0≦y≦1)) such as gallium nitride is a key device for realizing ultra-high density recording on an optical disc and is a blue violet semiconductor laser which is at a level closest to a practical use. Increasing an output of such a blue violet semiconductor laser allows not only rapid writing on optical discs but also application to laser displays. This is an essential technology for developing a new technical field.
In optical disc systems of a recording and reproduction type, a semiconductor laser with a high output is desirable. As an effective way to increase an output, a method to render reflectances of end surfaces of a resonator asymmetrical is known (see, for example, “Handotai reza (semiconductor laser)”; Kenichi Iga Ed.; First edition; Ohmsha Ltd.; Oct. 25, 1994; p. 238). It is a general method for semiconductor lasers used for writing on optical discs. In this method, end surfaces forming a resonator are coated with dielectric films so that the end surfaces have asymmetrical reflectances. Among the end surfaces forming the resonator, a front end surface from which a laser light is emitted has a low reflectance, and a rear end surface on the opposite side has a high reflectance (for example, 10% for the front end surface and 90% for the rear end surface). A reflectance of a dielectric multilayer film can be controlled based on a refractive index, a film thickness and the number of layers laminated of a used dielectric member.
A semiconductor laser is mounted (assembled) to a can package as shown in FIG. 11. The package consists of a base 803 and a cap 804. A semiconductor laser 801 and a submount 802 which is a heat radiator for the semiconductor laser 801 are mounted to the base 803. A space inside the cap is sealed with nitrogen (N2) gas or the like.
The cap consists of glass 806 for taking out light and a metal base (can 805). The cap is adhered with a fusible glass 807 (can be fixed at several hundreds degree) in order to keep air tightness.
Such a semiconductor laser suffers from a problem in that dust and mold may adhere to a surface of the laser package and affect an output property. In order to solve this problem, a method of forming a film having a photocatalytic function on a surface of a package of a laser has been proposed (see Japanese Laid-Open Publication No. 2003-59087).
A solid-state laser has also been developed as a coherent light source with a high output. A wavelength conversion element is inserted into a resonator of the solid-state laser. This enables generating visible light with a high output. In such a solid-state laser, dust attached to laser end surfaces causes deterioration of an outputting property and shortens the life of the laser. In order to solve this problem, a method of providing a film having a photocatalytic effect on a surface of an optical component has been proposed (see Japanese Laid-Open Publication No. 2001-70787). A structure in which a film having a photocatalytic function is formed on a solid-state laser resonator mirror is also shown.
In conventional light sources, it is intended that light from the coherent light source is used to activate a catalytic function of a photocatalyst. However, photocatalyst depends on wavelengths. For activating the photocatalytic functions, wavelengths of the coherent light sources which can be used are limited. Specifically, for activating a photocatalyst efficiently, light sources with a wavelength of 390 nm or shorter are required. Thus, there is a problem in that coherent light sources which can utilize a photocatalyst are limited to light sources with short wavelengths of 390 nm or shorter.
An object of the present invention is to solve the above described conventional problem and provide a coherent light source with eased limitations on wavelengths at emission. Another object of the present invention is to provide an optical system with eased limitations on wavelengths at emission.
USPTO Backgrounds
USPTO Backgrounds