1. Field of the Invention:
The present invention is directed to a light source device capable of creating secondary higher harmonic waves and in turn transforming the waves into parallel beams of light. The secondary higher harmonic waves are generated using laser beams passed through a secondary higher harmonic wave generating element.
2. Description of the Related Art:
In a secondary higher harmonic wave generating element of the photo waveguide path type, however, the secondary higher harmonic waves radiate from the photo waveguide unit having a given width towards the substrate, so that there are no desirable wave surface characteristics are exhibited. Namely, the secondary higher harmonic waves are composed of groups of parallel beams of light showing a surface symmetry, and hence there is such a defect that the beams of light can not be converged at a small spot. As a result, it has been difficult, until now, to apply the secondary higher harmonic waves to writing to an optical storage medium such as a photo disk having minute pits and reading from the optical storage medium.
In contrast, the secondary higher harmonic wave generating element of the optical fiber type exhibits an axial symmetry, and therefore these secondary higher harmonic waves are expanded in a ring-like configuration. It is expected that favorable convergence characteristics are provided.
To be specific, the secondary higher harmonic waves emerging from the secondary higher harmonic wave generating element of the optical fiber type have equi-phase surfaces each assuming a conical shape. FIG. 8 depicts this feature. The secondary higher harmonic waves expand to form a conical beam B via a clad 42 of an optical fiber 4. For the purpose of converting beam B into parallel beams of light, as illustrated in FIG. 9, a conical collimator lens 50 can be employed.
Since the conical collimator lens 50 has a considerable thickness, it is difficult to apply to a small-sized light source device and the handling and adjustment thereof are inconvenient and cumbersome. An additional problem is that the light source device can not satisfactorily be miniaturized.